Class 7th Science EM (Full Book)

 Class 7th  EM Science (Full Book)

Seven Science NCERT CBSE

Nutrition in Plants

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Introduction

Food is the most important and basic thing for life. Carbohydrates, proteins, fats, vitamins and minerals are the components of food. These components are necessary for all living beings. All plants and animals require food for their growth and getting energy. The process of utilization of food by an animal to obtain energy for growth and development is known as nutrition. Plants make their food themselves but animals cannot. Hence, animals depend directly or indirectly on the plant.

Review Questions:-

Question - 1. What are the components of food?

Answer – Carbohydrates, proteins, fats, vitamins and minerals are the components of food.

Question - 2. What is nutrition?

Answer – The process of utilization of food by a living organism to obtain energy is called nutrition.

Question - 3. Why is need of nutrition?

Answer – Animals do not make their food themselves which plants do. Animals eat plants or plant eating animals. Hence, animals are directly or indirectly depend on plants.

Mode of nutrition in plant

Autotrophic Nutrition

Auto means self and trophos means nourishment. Plants are called autotrophs because they make their food themselves. The making of food for themselves is called the Autotrophic nutrition. Autotrophic nutrition is found in green plants.

Heterotrophic Nutrition

The word Heterotrophic is the combination of two words i.e. Hetero + Trophos. Hetero means ‘others’ and ‘trophos’ means nourishment. If organisms depend on others for their food, it is called the Hetetrophic Nutrition.

Animals cannot make their food themselves. They depend for food upon plants. Therefore, nutrition in animals is called Hetetrophic Nutrition. Animals are known as Heterotrophs.

Saprotrophic Nutrition

The taking of nutrients by organism from dead and decaying matter in the form of solution is called the saprotrophic nutrition. The organisms which use saprotrophic mode of nutrition are called saprotrophs. For example: fungi.

Questions – 1: What is autotroph?

Answer- Organisms that make their food themselves are called autotrophs.

Question-2: What is autotrophic mode of nutrition?

Answer: The mode of nutrition in which the organism makes its own food is called autotrophic mode of nutrition.

Question -3: Give some example of autotrophs.

Answer: All green plants, such as grass, mango, bougainvillea, etc. are the examples of autotrophs.

Question-4: What is heterotrophic mode of nutrition?

Answer: The mode of nutrition in which an organism takes food from another organism is called heterotrophic mode of nutrition. The nutrition in animals and non-green plants is the example of heterotrophic mode of nutrition.

Question-5: Give examples of Heterotrophs.

Answer: Animals and non green plants are the examples of heterotrophs.

Question-6: What is saprotrophs?

Answer: Plants which get their nutrition from dead or decaying plants in liquid form are called saprotrophs.

Photosynthesis - Food Making Process in Plants

The process of making of food by green plants in the presence of sunlight and chlorophyll is known as photosynthesis.

Photosynthesis is the combination of two words- Photo + Synthesis. ‘Photo’ means light and ‘Synthesis’ means to make.

Process of food making in green plants:

Green plants make their food themselves. Green leaves make food from Carbon dioxide and water in the presence of sunlight and chlorophyll.

Hence, for taking place of photosynthesis carbon dioxide, water and sunlight must be reached at the green leaves in addition to presence of chlorophyll.

Leaves have several tiny pores like structure on its lower surface. This is called stomata through which leaves absorb carbon dioxide from air. Water is transported to the leaves through hair like pipelines from the roots. These pipelines are present throughout the plant, i.e. from roots to branches and leaves. These pipe-lines are known as Xylem. Xylem is a type of tissues. Chlorophyll, a green pigment, is found in green leaves. Chlorophyll absorbs sunlight and gives energy. Chlorophyll absorbs sunlight, carbon dioxide and water and convert them to carbohydrate and oxygen. Carbohydrate is used as food and oxygen is emitted out to atmosphrere.This whole process of making food by plants is called photosynthesis.

The reaction takes place in the process of photosynthesis can be written as:

Carbondioxide + Water  Carbohydrate + Oxygen

Carbohydrate which is produced in the process of photosynthesis is ultimately converted into starch and stored into leaves. From leaves it is transported to the parts of plants. Starch is a type of carbohydrate. The oxygen so produced is released into atmosphere through the stomata.

Leaves are known as the kitchen or food factories of the plants because photosynthesis takes place in leaves. Leaves look green because of the presence of chlorophyll.

Besides leaves, photosynthesis takes place in other green parts of the plant also, such as in green stems. Chlorophyll is necessary for photosynthesis; hence photosynthesis takes place only in green plants.

The leaves of plants that grow in desert areas are modified in spine like structure or scales to reduce the loss of water in the course of transpiration. In such plants photosynthesis takes place in green stems.

The photosynthesis helps to maintain a balance between oxygen and carbon dioxide in the atmosphere as it absorbs carbon dioxide and release oxygen.

Sunlight is necessary for photosynthesis. Thus sun is the ultimate source of energy for all living organism.

Our earth is the only unique planet, where photosynthesis takes place. In the absence of photosynthesis life would not be possible on earth.

Following are necessary for photosynthesis to be taken place:

• Presence of sunlight

• Presence of Chlorophyll

• Presence of Water

• Presence of carbon-dioxide

Photosynthesis in Algae

Green patches in ponds or near the stagnant water can be seen easily. These green patches are living organism called algae. Algae are plants. Often algae grow near the shallow waterlogged areas such as near tube-wells, taps, etc. One may slip over it. Algae look green because of presence of Chlorophyll. Algae prepare their own food by the process of photosynthesis.

Questions- 1 - What is photosynthesis?

Answer- The process of making food in green plants in the presence of sunlight is known as photosynthesis.

Questions- 2 - What are the essentials factors for the photosynthesis?

Answer - Carbon dioxide, water, chlorophyll and sunlight are essentials factors for the photosynthesis to take place.

Question – 3 - What is chlorophyll?

Answer- Chlorophyll is the green pigment present in green leaves.

Question – 4 – Why do leaves look green?

Answer – Leaves look green because of the presence of chlorophyll, which is a green pigment.

Questions- 5: What is the function of chlorophyll?

Answer - Chlorophyll absorbs the sunlight for photosynthesis.

Question – 6: What are the final products made after photosynthesis?

Answer- Glucose and oxygen are the final products after photosynthesis.

Questions – 7: What are stomata?

Answer- The small pores present on the lower surface of leaf, are called stomata.

Questions- 8: What is function of stomata?

Answer - Stomata absorb carbon dioxide from air for photosynthesis.

Question - 9: What is the ultimate source of energy?

Answer – Sun is the ultimate source of energy.

Question – 10: How water is transported to the leaves?

Answer: Water is transported to the leaves through pipe like structures from the roots of plant. These pipe-like structures are present from root to leaves through branches throughout.

Synthesis of plant food other than carbohydrate

Plants need proteins and fats besides the carbohydrate. Proteins are nitrogenous substances which contain nitrogen. Although nitrogen is present in abundance in atmosphere, but plant cannot absorb atmospheric nitrogen. Plant gets nitrogen from soil. Certain types of bacteria called rhizobium, are present in soil. They convert gaseous nitrogen into usable form and release it into the soil. Plants absorb these soluble forms of nitrogen along with water and other minerals through their roots.

Sometimes farmers add nitrogenous fertilizer to their field to fulfill the need of nitrogen. In this way plants gets fulfillment of nitrogen along with other nutrients. After the fulfillment of all nutrients plants synthesise proteins and fats.

Question: 1 – What are the nutrients other than carbohydrates which are required by plants?

Answer: Proteins and fats are the nutrients; other than carbohydrates; which are required by plants.

Question: 2 – In which form do plants absorb nitrogen?

Answer: Plants absorb soluble form of nitrogen.

Question: 3 – Why do farmers add nitrogenous fertilizers to the soil?

Answer: Farmers add nitrogenous fertilizers to the soil to fulfill the requirement of nitrogen of the plants. Nitrogen is necessary to synthesise proteins.

Question: 4 – Which microorganism help to provide nitrogen to the plants?

Answer: A certain type of bacteria called rhizobium help to provide nitrogen to the plants.

Question: 5 – How do plants absorb nutrients other than carbohydrates from the soil?

Answer: Other nutrients are available in the soil in the form of minerals. Plants absorb these minerals from the soil; along with water.

Modes of Nutrition in non-green plants

Heterotrophic Mode of Nutrition in Plants

Some plants do not have the chlorophyll. Hence, they cannot synthesise their food by themselves. Such plants are known as non green plants. They depend on other organisms for food. Such plants use the heterotrophic mode of nutrition. Some of them are called parasite. A parasite is an organism which lives on or inside the body of another organism and takes shelter and food from that organism. The host; in this case; is always at loss.

Plants that do not have chlorophyll are called non-green plants. Plants, which live on other plants for food, are called parasitic plants.

Parasite (Parasitic Plant):

Plants that get their food from other plants by living on them are called parasite. Example; Cuscuta, mistletoe.

Cuscuta is a vine like plant with yellowish stem. It twines around big trees, like banyan tree. Cuscuta gets nutrition from the tree on which it lives. The tree upon which it climbs and lives is called the host. Here, banyan is the host and cuscuta is the parasite.

Some plants are total parasite while some are partial parasite.

A total parasite fully depends on other plants for their nutrition. For example - cuscuta.

Partial parasite

Partial parasite is a parasite that receives a part of its nutrients from host. For example; mistletoe bears green leaves. It synthesises its own food, but receives water and mineral from host plant.

Question: 1 – What do you understand by parasitic plants?

Answer: A plant which lives on another plant and takes nutrients is called a parasitic plant.

Question: 2 – Give some example of parasitic plants.

Answer: Cuscuta and mistletoe

Question: 3 – Why some plants are called parasites?

Answer: Some plants are unable to prepare their own food and need to take food from another plant. Hence, they are called parasites.

Question: 4 – What is the mode of nutrition in non-green plants?

Answer: Non-green plants show heterotrophic mode of nutrition.

Question: 5 – What do you understand by non-green plants?

Answer: A plant which lacks chlorophyll is called non-green plant.

Question: 6 – What do you understand by host?

Answer: An organism which provides shelter and nutrition to another organism is called a host.

Question: 7 – What is partial parasite?

Answer: A parasite which depends for some of the nutrients; on another organism; is called a partial parasite.

Question: 8 – Give example of partial parasitic plants?

Answer: Misteltoe

Insectivorous plant

Some plants eat insects. Such plants are called insectivorous plants. They trap and digest the insects. Pitcher plant is the example of an insectivorous plant. In pitcher plant the leaf is modified to form a pitcher like structure. The bright colour of the pitcher makes it very attractive to insects. Inside the pitcher; there are several hair-like structures. These hairs direct the trapped insects downwards. When an insect sits on the pitcher of the plant, the lid closes and the insects get trapped inside the pitcher. The insect is then digested by the enzymes secreted by the cells of the plants.

Cause of eating of insects by plants:

The soil of marshy land is deficient in nitrogen. Plants living in marshy areas do not get nitrogen from the soil. Their nitrogen need is fulfilled by sucking the juice of insects. Venus flytrap, utricularia, drosera and Rafflesia are the other examples of insectivorous plants.

Question: 1 – What is an insectivorous plant?

Answer: A plant which fulfills its nitrogenous needs by eating insects is called an insectivorous plant.

Question: 2 – Give an example of insectivores plant?

Answer: Pitcher plant, Venus Fly trap, Bladderwort, Drosera, Rafflesia

Question: 4 – Why does a plant eat insects?

Answer: Plants living in marshy areas do not get nitrogen from the soil. To fulfill their nitrogenous need, they need to eat insects.

Question: 5 – Write a brief note on pitcher plants?

Answer: In a pitcher plant, the leaf is modified into a pitcher like structure. The pitcher is complete with a lid. The inside of pitcher is full of hair-like structures. The pitcher is used to trap insects which may fall in it.

Saprotrophs –

Saprtrophs are non-green plants e.g. Agaricus (Mushroom) fungi, yeasts and bacteria. Saprotrophs get their food from dead or decaying organic matters. They grow on decaying organic matters such as cow-dung, wood, bread, etc.

Saprotrophs secrete digestive juice over the decaying materials and absorb nutrients from them. This is called Saprotrophic Mode of Nutrition. Such plants are called saprotophs.

Question: 1 – What do you understand by saprotrophs?

Answer: An organism which feed on dead and decaying material is called a saprotroph. In this mode of nutrition, digestive enzymes are secreted on the food. The digested food is then absorbed by the organism. In saprotrophs digestion takes place outside the body of the organism.

Question: 2 – Saprophytes grow in which type of places?

Answer: Saprophytes grow in humid and hot conditions.

Question: 3 – Give some example of saptrotrophs.

Answer: Mushroom, yeast, toadstool, etc.

Symbiosis or mutualism –

Symbiosis is the combination of two Greek words ‘Sym’ menas ‘with’ and ‘biosis’ means ‘living’, which means living together. In symbiosis or mutualism two different types of organisms live and work together for their mutual benefit from each other. They share shelter and nutrients, e.g. Lichens. Lichens are composite organisms composed of fungus and alga. Fungus is a saprophyte and alga is an autotroph. The Fungus supplies water and minerals to the cells of the alga while the alga supplies food; prepared by photosynthesis.

A bird sitting on the back of a rhino is an example of symbiosis. The bird gets worms to eat, while the rhino gets rid of those worms.

Replenishment of Nutrients in Soil

Some fungus live in the roots of the plans. Roots of the plants provide shelter and food to the fungus while fungus provides important nutrients to the plants.

Because of continuous farming nutrients keep declining in the soil. Hence, to replenish those nutrients fertilizers are added to the soil.

Plants require a lot of nitrogen to grow and to be healthy. Although, a lot of nitrogen is available in the atmosphere, but plants cannot absorb nitrogen in gaseous form. There is a bacterium called Rhizobium, which lives in the root nodules of legumes, such as gram, moong, etc. These bacteria can absorb nitrogen from the atmosphere and make it available for the plants. Rhizobium cannot make its food, hence, it provides nitrogen to the legumes and in return legumes provide them food and shelter. This is an example of symbiotic relationship. This has great importance for farmers. Fields in which leguminous plants are grown from time to time, do not need addition of nitrogenous fertilizers.

Question: 1 – What is the meaning of word ‘Symbiosis’?

Answer: It is a relationship between two organisms in which both the organisms benefit each other.

Question: 2 – What is Lichen?

Answer: The lichen is a composite organism formed because of symbiosis of algae and fungi.

Question: 3 – Give an example of symbiotic relationship.

Answer: A small bird; called plover; cleans the crocodile’s teeth. The crocodile keeps its mouth open and the bird takes out meat fibres stuck between the teeth. The bird gets food in lieu of providing dentist’s services to the crocodile.

Question: 4 – How do nutrients get replenished in the soil?

Answer: There are two main means through which nutrients get replenished in the soil. One of them is the nitrogen fixation in soil. Nitrogen fixation replenishes nitrogenous nutrients in the soil. Another mean is decomposition of dead remains of plants and animals (or farm waste). Decomposition of dead remains replenishes various other nutrients in the soil.

Question: 5 – What is Rhizobium?

Answer: Rhizobium is a bacterium.

Question: 6 – What is the function of Rhizobium?

Answer: Rhizobium helps leguminous plants in nitrogen fixation in soil.

Question: 7 – How does Rhizobium help farmers?

Answer: By helping in nitrogen fixation, rhizobium increases soil fertility and thus helps farmers.

Question: 8 – Why do farmers prefer to sow leguminous plants?

Answer: Leguminous plants carry out nitrogen fixation in soil and thus improve soil fertility.

Question: 9 – In which form do plants absorb nitrogen?

Answer: Plants absorb nitrogen in the form of nitrates.

NCERT Solution (Part-1)

1. Why do organisms need to take food?

Answer: Organisms need to take food so that they can get raw material for growth and repair and can get energy for carrying out various activities.

2. Distinguish between a parasite and a saprotroph.

Answer: A parasite lives on or inside the body of another organism; to get shelter and food. A parasite lives on a live host. On the other hand, a saprotroph feeds on dead and decaying remains of animals and plants.

3. How would you test the presence of starch in leaves?

Answer: Steps to test the presence of starch in leaves:

• Boil the leaf in water for about 10 minutes.

• After that, boil the leaf in alcohol; over water bath.

• Wash the boiled leaf with cold water and spread on a flat surface.

• Pour a few drops of iodine on the leaf.

• If the iodine turns into dark blue colour, it shows the presence of starch in the leaf.

4. Give a brief description of the process of synthesis of food in green plants.

Answer: Photosynthesis is the process by which green plants make food. Green plants trap solar energy with the help of chlorophyll. Water and carbon dioxide are the raw materials, which are converted into carbohydrates; during the process. Oxygen is the byproduct of photosynthesis. This can be shown by the following equation:

 

5. Show with the help of a sketch that the plants are the ultimate source of food.

Answer: The following figure shows a food chain, which shows that the plants are the ultimate source of food.

6. Fill in the blanks:

(a) Green plants are called ___________since they synthesise their own food.

Answer: Autotrophs

(b) The food synthesised by the plants is stored as _________________.

Answer: Starch

(c) In photosynthesis solar energy is captured by the pigment called ___________.

Answer: Chlorophyll

(d) During photosynthesis plants take in ______________________ and release __________________.

Answer: Carbon dioxide, oxygen

7. Name the following:

(a) A parasitic plant with yellow, slender and tubular stem.

Answer: Amarbel (Cuscuta)

(b) A plant that has both autotrophic and heterotrophic mode of nutrition.

Answer: Pitcher plant

(c) The pores through which leaves exchange gases.

Answer: Stomata

8. Tick the correct answer:

(a) Amarbel is an example of:

(i) Autotroph

(ii) Parasite

(iii) Saprotroph

(iv) Host

Answer: (ii) Parasite

(b) The plant which traps and feeds on insects is:

(i) Cuscuta

(ii) China rose

(iii) Pitcher plant

(iv) Rose

Answer: (iii) Pitcher plant

9. Match the items given in Column I with those in Column II:

10. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) Carbon dioxide is released during photosynthesis. (F)

(ii) Plants which synthesise their food themselves are called saprotrophs. (F)

(iii) The product of photosynthesis is not a protein. (T)

(iv) Solar energy is converted into chemical energy during photosynthesis. (T)

11. Choose the correct option from the following:

(a) Which part of the plant gets carbon dioxide from the air for photosynthesis?

(i) Root hair

(ii) Stomata

(iii) Leaf veins

(iv) Sepals

Answer: (ii) Stomata

(b) Plants take carbon dioxide from the atmosphere mainly through their:

(i) Roots

(ii) Stem

(iii) Flowers

(iv) Leaves

Answer: (iv) Leaves

2. Nutrition in Animal

Plants make their food by the process of photosynthesis, but animals cannot make their food themselves. Animals get their food from plants. Some animals eat plants directly while some animals eat plant eating animals. Thus, animals get their food from plants either directly or indirectly.

All organisms require food for survival and growth. Requirement of nutrients, mode of intake of food and its utilization in body are collectively known as nutrition.

Nutrition in complex animals involves following steps:

• Ingestion
• Digestion.
• Absorption.
• Assimilation
• Egestion.

Ingestion- The intake of food is called ingestion. Method of ingestion, i.e. taking of food, varies from one animal to another.

Digestion - The process of breaking down of complex component of food into simpler substances is called digestion.

The process of digestion is different in human, grass eating animals, amoeba, etc.

Absorption – The process of passing of digested food into blood vessels in the intestine is called the absorption.

Assimilation – The conversion of absorbed food in complex substances such as proteins and vitamins required by body is called assimilation.

In other words, assimilation is the conversion of absorbed food (nutrients) into living tissues. Through the process of assimilation our cells are supplied with oxygen and nutrients.

Egestion – Removal of waste materials from the body is called egestion. The faecal matter is removed through the anus from time-to-time.

Since the waste of food left after digestion is also called faeces, hence the process of egestion is also known as defecation.

Different Ways of Tajubg Food: Ingestion

Different organism takes food in different ways.

• A humming bird sucks nectar of plants.
• Human beings use their hands to put food into their mouth and swallow the food after chewing.
• Infants of human and many other animals feed upon their mother’s milk by sucking them.
• A snake swallows the animals they prey upon without chewing them.
• A frog captures prey with its sticky tongue.
• An earthworm uses its muscular pharynx to swallow its food.
• Spiders weave sticky web in which small insects get stuck.
• Some aquatic animals filter tiny particles floating nearby and feed upon them.
• Amoeba, a unicellular animal, engulfs tiny particles of food by using pseudopodia. Amoeba surrounds the food by pseudopodia and then makes a food vacuole to engulf the food.
• In multicellular organisms; like hydra there are numerous tentacles around their mouth. Hydra uses tentacles to surround its prey and kill them with its stinging cells. Then the food is pushed inside the body cavity.

Digestion

After taking of food, food is digested and then it is passed to the different parts of body for the growth, repair and other vital functioning of body.

The food we take is primarily in the form of complex substances. Food in such complex form is not used as such by animals. Hence, they need to be first broken down into simpler soluble forms so that they can be absorbed by the cells of the body.

The process of breaking down of complex component of food into simpler substances is called digestion. The process of digestion is different in human, grass eating animals, amoeba, hydra, etc.

Enzymes help in the breakdown of complex molecules like carbohydrates, protein, fats, etc. into simple molecules.

Digestion in unicellular animals; like Amoeba; is intracellular. The digestive enzymes are secreted in the food vacuoles.

Question – 1 – What is ingestion?

Answer- The intake of food is called ingestion.

Questions - 2 - What is digestion?

Answer- The breaking down of solid and complex food into simple and soluble forms is called digestion.

Question – 3 – What is absorption?

Answer- The process of passing of digested food into blood vessels in the intestine is called the absorption.

Question – 4 – What do you understand by assimilation?

Answer - The conversion of absorbed food in complex substances such as proteins and vitamins required by body is called assimilation.

Question – 5 – What do you understand by egestion?

Answer- Removal of waste materials from the body, time to time from anus is called egestion.

Questions – 6 - What are the steps of nutrition involved in animals?

Answer- There is five steps of nutrition involved in animals. These are Ingestion, Digestion, Absorption, Assimilation and Egestion.

Questions – 3 - What are Pseudopodia?

Answer- The false feet of amoeba are called pseudopodia.

(The word pseudopodia is the combination of pseudo and podus. Pseudo means false and podus means feet. Singular of pseudoposida is pseudopodium)

Digestion in Human

The digestive system of humans is well developed. It consists of the gut or alimentary canal, along with many associated digestive glands. The alimentary canal is divided into mouth, oesophagus, stomach, small intestine, large intestine and rectum.

Mouth: The food is ingested through the mouth. The mouth contains tongue, teeth and salivary glands. Teeth break the food into smaller particles. This process is called mastication. The chewed food is mixed with saliva. Saliva is a watery fluid secreted by the salivary glands. Saliva contains a type of enzyme called the salivary amylase, which converts starch into sugar.

Teeth: Our teeth cut, tear and grind the food before we swallow it. There are four types of teeth in our mouth.

Incisors: These are flat and chisel-shaped teeth. They lie in the front of the mouth. There are eight incisor teeth; four in the upper jaw and four in the lower jaw. The incisor teeth are well adapted for cutting and biting of food items.

Canines: These are round shaped, sharp and pointed teeth. Canines are well adapted to hold and tear the food. There are four canine teeth found in human.

Premolars: There are two premolars on each side of each jaw. Premolars help in crushing and grinding the food. There are total 8 premolar teeth in an adult human.

Molars: There are two molars on both sides in both the jaws. They have almost a flat surface with small projections. These teeth are meant for fine grinding of food.

There are total 12 molar teeth including the wisdom teeth in an adult human. The 4 molar teeth are also called wisdom teeth. Wisdom teeth usually grow between the ages of 18 to 21.

The tooth is covered with a white substance called enamel. It is the hardest substance in the human body.

Milk teeth and Permanent teeth

Humans get two sets of teeth in their lifetime. The first set erupts when we are babies, are called milk teeth. Milk teeth last until we are about 8 years old. Milk teeth are replaced by the second set of teeth and are called permanent teeth.

An adult human has 32 teeth in all; 16 in each jaw.

Question-1- How many types of teeth are found in human beings?

Answer- There are four types of teeth in human beings. These are called incisors, canines, premolars and molars.

Question – 2 – How many incisors are found in an adult human?

Answer – There are 8 incisors, 4 in lower and 4 in upper jaw, found in an adult human.

Question – 3 – What is the function of incisors?

Answer – Incisors are used to cut and bite the food.

Question – 4 – How many canines are found in an adult human?

Answer – There are four canine found in an adult human.

Questions - 4 - What is the functions of Canines?

Answer - Canines are the type of teeth, which help to hold and tear the food.

Question – 5 – How many premolars are found in an adult human?

Answer – There are 8 premolars found in an adult human.

Question – 6 – What is the function of premolars?

Answer - Premolars help in crushing and grinding the food.

Question – 7 – How many molars are found in an adult human?

Answer – There are total 12 molars are found in an adult human.

Question – 8 – What is wisdom tooth?

Answer – Wisdom teeth are molar teeth that grow usually between the age of 18 to 21 in an human.

Question- 9 - How many teeth does a human adult have?

Answer- A human adult has 32 teeth in all; 16 teeth in each jaw.

Question – 10 – What do you understand by milk and permanent teeth?

Answer – Human has two sets of teeth. These are called milk teeth and permanent teeth. Milk teeth start growing at the baby stage and are replaced gradually by permanent teeth from the age of 8 year.

Question- 11 - What is Enamel?

Answer - The white substance that covers our teeth is called enamel. It is the hardest substances in the human body.

Tongue – The tongue is a muscular organ. Tongue helps to mix saliva in the food. It also helps to push the food down the food-pipe or oesophagus. Taste receptors are present in tongue and give us the sense of taste.

Oesophagus – It is a tube-like structure connecting the mouth and the stomach. It is about 30 cm. long. Oesophagus has powerful muscles which gently push the food down to the stomach. The oseophagus contracts and relaxes in a rhythmic fashion to facilitate the forward movement of food. This movement happens in other parts of the alimentary canal as well and is called peristalsis. There is no digestion takes place in oesophagus.

Stomach –It is a muscular J- shaped thick walled bag. Stomach is the widest part of alimentary canal. It receives food at one end from food pipe and open into the small intestine from other end.

Stomach churns the food to mix digestive juices. The food in the stomach is churned into semi solid. The churned semi-solid food is called chime. Gastric juice is secreted from the wall of stomach and mixed with food. Gastric juice contains some enzymes and hydrochloric acid. The enzymes present in the gastric juices break down protein from food. The hydrochloric acid kills the harmful bacteria present if any in the food and helps the gastric enzymes to work.

Small intestine – The food leaves the stomach at certain intervals of time and enters into the small intestine.

The small intestine is the longest part of the digestive system. It is about 20 feet or seven meters long in an adult human. Small intestine is a highly coiled tube. It consists of three parts: duodenum, jejunum and Ileum.

In the duodenum, the liver and pancreas pour their secretions. Liver secretes bile juice and pancreas secretes the pancreatic juice. The bile juice contains the bile which carries out emulsification of fat. In this process, the fat is broken into tiny droplets. The pancreatic juice contains several enzymes. The enzymes of the pancreatic juice break down starch into simple sugars and proteins into amino acids.

Minerals and vitamins do not need to be changed because cells are able to absorb them easily.

From duodenum the food goes to the lower part of the intestine. There are numerous finger-like projections on the wall of the small intestine. These projections are called villi. They have fine blood capillaries to absorb the food. After absorption; food mixes in the blood stream and is carried to all the cells of the body. The cells utilize this food to release energy.

Large intestine: The digested food enters into large intestine after small intestine. The large intestine is wider and shorter than small intestine. It is about 1.5 metre in length.

In large intestine excess of water from the materials is absorbed. The semi solid residue is stored in the last part of the large intestine called rectum and finally throw out of the body through the anus time to time. The throwing out of waste of digested food from rectum is called egestion.

Egestion is also known as defecation.

Digestion in Grass Eating Animals -

Ruminants: None of the animal can digest cellulose which is a major component of the food eaten by herbivores. The plant eating animals digest their food in two steps. Their stomach is divided into four chamber the rumen, reticulum, omasum and abomasum.

First of all, half chewed food is swallowed and it then goes from mouth to the rumen, the first chamber of the stomach. Here, it is acted upon by bacteria. These microorganisms digest the cellulose. This half digested food goes to the second muscular chamber; the reticulum. From the reticulum the food is sent back to the mouth; as cud; to be chewed again. Chewing of the cud is called rumination and such animals are called ruminating animals or ruminants. Cow, goat, buffaloes, sheep, bison, etc. are good example of ruminating animals. The re-chewed food is swallowed for the second time. After passing the first two chambers it enters the third chamber; the omasum. Here the food is further broken down into smaller pieces and finally enters the fourth chamber, the abomasum. Here, all enzymes act upon the food and the digestion is completed.

After digestion and absorption, nutrients from food are taken to the cells in all parts of the body. The cells oxidize the food to release energy.

Very short answer type question:

Question- 1.What is a carnivorous animal? Give two examples.

Answer- Animals, which eat the flesh of other animals, are called carnivorous, e.g. lion, tiger.

Question – 1 - What is the function of the digestive juice secreted by the liver?

Answer- The digestive juice from the liver breaks up fat into tiny particle.

Question – 2 - Name the organs that make up the alimentary canal.

Answer-Mouth, oesophagus, stomach, small intestine, large intestine and rectum are the parts of the alimentary canal.

Question- 3 - Name the four types of teeth.

Answer: The four types of teeth are: Incisors, Canines, Premolars and Molars.

Question – 4 - Name the four compartments in a ruminant’s stomach.

Answer: Four compartments in a ruminant’s stomach: Rumen, reticulum, omasum and abomasums.

Choose the correct answer:

Questions -1 - Movement of food through alimentary canal is called by which of these terms?

(a) Locomotion

(b) Peristalsis

(c) Pumping

(d) Sliding.

Answer-(b) Peritalsis

Question – 2 - The liver produces which of these enzymes?

(a) Amylase

(b) Trypsin

(c) Lipase

(d) None of these

Answer-(d) None of these.

Question – 3 - Which of these is not a part of nutrition?

(a) Digestion

(b) Excretion

(c) Assimilation

(d) Egestion

Answer-(b) Excretion.

Question – 4 - Digestive juice is not secreted by which of these organs?

(a) Small intestine

(b) Liver

(c) Stomach

(d) Oesophagus

Answer- (b) liver

Question – 5 - The walls of the large intestine absorb which of these?

(a) Cellulose

(b) Digested food

(c) Oxygen

(d) Water

Answer-(d) Water.

Question – 6 - Which of the following is not a part of ruminant stomach?

(a) Reticulum

(b) Anus

(c) Omasum

(d) Abomasum.

Answer-(b) Anus.

Question – 7 - Bile is produced by which organ?

(a) Pancreas

(b) Gall bladder

(c) Liver

(d) Stomach.

Answer- (c ) Liver

Match the following

Answer- 1-E, 2-D, 3- B, 4- A, 5- C

Fill in the blanks.

1- Most of the enzymes in the small intestine comes from ______

2-The __________ present on our tongue help us to taste food.

3-Saliva is secreted in the mouth by _______________

4-Living organism that cannot make their own food are called__________

Anwser-

1- stomach

2- Taste receptor

3- salivary gland

4- Hetrotrophic

Write true and false

1- Absorption and assimilation are similar processes.

Answer - F

2- Some plants are heterotrophic and depend on others for food.

Answer - T

3- Hydrochloric acid is present in the stomach.

Answer - T

4- Pitcher plant is an example of insectivorous plant.

Answer - T

5- Saprophytes are green in colour.

Answer - F

6- Ruminants have a three-chambered stomach.

Answer - F

7- An adult human has 32 teeth in all – 16 in each row.

Answer - T

8- Tongue gives the sense of smell.

Answer - F

Test Your Knowledge                      NCERT Exercise Solution-Nutrition In Animals

 

 

Nutrition in Animals

NCERT Exercise and Solution

Q -1 Fill in the blanks.

(a) The main steps of digestion in humans are _____ ____ _____ _____ ______

Answer - The main steps of digestion in humans are Ingestion digestion absorption assimilation egestion

b. The largest gland in human body is _______

Answer- The largest gland in human body is liver.

c. The stomach releases hydrochloric acid and _____ juices which act on food.

Answer- The stomach releases hydrochloric acid and digestive juices which act on food.

d. The inner wall of the small intestine has many finger like structure called _______.

Answer- The inner wall of the small intestine has many finger like structure called villi.

e. Amoeba digest its food in the ________

Answer – Amoeba digest its food in the vacuoles.

Q - 2 - Mark T if the statement is true and F if it is false.

a. Digestion of starch starts in the stomach.

Answer - F

b. The tongue helps in mixing food with sliva.

Answer - T

c. The gall bladder temporarily stores bile.

Answer - T

d. The ruminants bring back swallowed grass into their mouth and chew it for some time .

Answer - T

Q - 3 - Tick (√) mark the correct answer in each of the following.

a. Fat is completely digested in the

(a) Stomach

(b) Mouth

(c) Small intestine

(d) Large intestine

Answer - (c)Small intestine

b. Water from the undigested food is absorbed mainly in the

(a) stomach

(b) food pipe

(c) Small intestine

(d) Large intestine

Answer - (d)Large intestine

Q - 4 - Match the column

Q - 5 - What are villi? What is their location and function.

Answer - Villi is the finger like projections. These are found in the inner walls of small intestine. It helps in absorption of the digested food.

Q- 6 -Where is the bile produced? Which component of the food does it digest?

Answer - Bile is produced in the liver. Bile helps in digestion of fats.

Q -7- Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.

Answer - Cellulose is the type of carbohydrates which is digested in ruminants but not in humans. Ruminants have a large sac –like structure between the small intestine and large intestine, in which cellulose of the food is digested by the action of certain bacteria. Such structure is not present in human. Hence human cannot digest cellulose while ruminants can.

Q- 8 - Why do we get instant energy from glucose?

Answer - Glucose is simple sugar so there is no need of digestion. It directly reaches the cells where it gives energy after respiration.

Q -9 - Which part of the digestive canal is involved in:

(a) Absorption of food ________

(b) Chewing of food ________

(c) Killing of bacteria ________

(d) Complete digestion of food _______

(e) Formation of faeces _________

Answer -

(a) Small Intestine

(b) Mouth

(c) Stomach

(d) Small Intestine

(e) Large Intestine

Q - 10 - Match the following column

Answer- A -3,   B - 4,   C- 1,   D- 5,   E - 2,   F- 6

Q - 11 - Lable the diagram of the digestive system.

Answer

Test Your Knowledge                       Nutrition in Plants - class Note 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fiber To Fabric.

Clothe is one of our basic needs. Clothe protects us from heat, cold, rain, dust, insects, etc. Clothes also make one civilized and smart. Clothes are made of cloth. Cloth is also known as fabric. Fabric is made of fiber.

Fibers are two types – Natural and Manmade.

Natural fibers- Natural fibers are obtained from plants and animals; such as jute, cotton, wool, silk, etc.

Manmade fibers- Fibers that are synthesized in laboratory are called manmade fiber, such as terylene, terry-cotton, acrylic, etc.

Natural fiber: Natural fibers can be classified into two types – Plant fiber and Animal fiber.

Plant Fiber: Fiber obtained from plants is called plant fiber. For example – cotton, jute, flex, etc.

Animal Fiber: Fiber obtained from animals is called animal fiber. For example – wool and silk.

WOOL

There are many animals that bear a thick coat of hair on their body. Such animals generally live in cold climates. Thick coat of hair over the body of such animals traps lot of air and keep them warm as air is a bad conductor of heat. It prevents the warmth of the body from escaping and also prevents the coldness of the surroundings from entering. Thus, thick layer of hair over their body protects them from harsh cold. For example: Sheep, Goat, Camel, Yak, etc.

Fleece and Wool bearing animals: Sheep, goat, Camel, Yak, etc. bear two types of hair – coarse hair and fine-soft under hair. Fine soft hair is found close to the skin in such animals. The fine soft under hair is called fleece. Fiber for wool is obtained from the fleece (hair) of such animals and hence such animals are called wool bearing animals.

Many breeds of sheep are found in India. Sheep gives milk and meat; in addition to wool, but are reared mainly to obtain wool in different parts of the world.

Angora wool is obtained from Angora Goats. Angora Goats are found in hilly regions, such as Jammu and Kashmir. Pashmina wool is obtained from Pashmina Goats. Yak wool is obtained commonly in Tibet and Laddakh. Alpaca and Llama are other animals that give wool.

Selective breeding and rearing of sheep: Some breeds of sheep bear only a coat of fine hair. Such animals are reared by selective breeding. Selective breeding is the process to obtain animals or plants having special characteristics.

In India, sheep are reared generally in the sates of Jammu and Kashmir, Himachal Pradesh, Uttaranchal, Arunachal Pradesh and Sikkim, or the plains of Haryana, Punjab, Rajasthan and Gujarat.

Food of sheep: Sheep are herbivores and feed generally on grass and leaves. Apart from grass and leaves they also feed on corn and oil cakes. Oil cakes are materials left after obtaining of oil from oil seeds.

Process to obtain wool from sheep: Steps given below are followed to obtain wool from sheep or other wool bearing animals:

Step 1 – Shearing - The fleece (hair) of sheep is shaved off along with a thin layer of skin. In olden days this was done using pair of metal blades. But now-a-days machine is used to cut off the fleece. This is similar to shaving of beards or hair. This process is called shearing.

Shearing is done generally in summer so that sheep could get new hair by winter to get protection against cold.

Step -2 – Scouring – Fleece, after shearing, is washed properly to remove dirt and grease. The washing of fleece; after shearing; is called scouring.

Step- 3 – Sorting – After scouring, fleece are sorted according to texture. This process is called sorting.

Step – 4 – After sorting, fluffy fibers; called burr; are picked out from hair. Burr is the fiber that gives wool.

Step 5 – Dying – After sorting and picking out of burrs, these are dyed in desired colors.

Step 6 – Spinning – The fibers are then straightened, combed and rolled into yarns.

Wool yarn is used in knitting sweaters and woolen cloths, i.e. fabric.

SILK

Silk is another important animal fiber. Silk worm spins silk. Silkworm is reared to obtain silk.

History of Silk:

Silk was discovered in China; around 3500 BC. Silk became a prized possession because of its fine quality and luster. Originally, it was used by emperors only. It was through trade that silk spread to other parts of the world over a period of time. Silk was a staple item of trade during ancient times. Due to this, the ancient trade routes which linked China to other parts of the world are called ‘Silk Route’.

As per historians, silk was produces in India also. Proof of use of silk in during the Indus Valley Civilization has also been found.

Types of Silk: Different types of silk worm produce different types of silk; in terms of luster and texture. For example; tassar silk, mooga silk, kosa silk, etc. are produced by different types of silk moth. Mulberry silk is the most common silk moth.

Rearing of silkworm: Rearing of silkworm is known as SERICULTURE. Silkworms are reared on mulberry leaves as they feed on mulberry leaves.

Life cycle of silkworm:

Female silk moth → Lays eggs → After about 14 days eggs are hatched into larva → Grown into Pupa →Weave a net and enclosed itself → Produce liquid protein from its salivary glands moving it’s head in the shape of ‘8’ forming cocoon→ Live in the cocoon for some time → After coming out of cocoon grows into silk moth.

Silk moth to silk:

After they are laid by the silk moth; eggs are stored over a clean cloth or paper strips. When larvae are hatched from eggs, they are kept in clean bamboo trays with fresh leaves of mulberry. Larvae feed on mulberry leaves for about 20 to 25 days. After that, larvae move into tiny chambers of bamboo in which they start spinning cocoon. They do it by secreting liquid protein from their salivary glands. Finally they enclose themselves in cocoon. Cocoons get hardened because of exposure to air.

Obtaining of silk from cocoon:

First of all, cocoons are boiled and then silk fiber is separated out; using machines. Machine unwinds the silk thread from cocoons. The process by which silk fiber is obtained is called REELING THE SILK.

Silk thread so obtained is woven into different types of cloths, i.e. fiber.

 Fibre to Fabric

NCERT Question and Answer

Question: 1 - You must be familiar with the following nursery rhymes

a. ‘Baa baa black sheep have you any wool’.

b. ‘Mary had a little lamb. whose fleece was white as snow’.

Answer the following question.

(a) Which parts of the black sheep have wool?

Answer - The skin of black sheep have wool.

(b) What is meant by the fleece of the lamb?

Answer: Fleece means hair of the lamb.

Question:2 - The silkworm is (a) caterpillar (b) a larva choose the correct option.

(i) a (ii) b (iii) both ‘a’ and ‘b’ (iv) neither ‘a’ nor ‘b’

Answer: (b) both 'a' and 'b'

Question: 3 - Which of the following does not yield wool?

(a)Yak

(b) Camel

(c) Goat

(d) Woolly dog

Answer: (d) Woolly dog

Question: 4 - What is meant by the following terms?

(a) Rearing

(b) Shearing

(c) Sericulture

Answer:

(a) Rearing: Taking care of animals including feeding, grazing, breeding, etc. for meat, and other useful products.

(b) Shearing –The removal of wool from the sheep is called shearing.

(c) Sericulture - The rearing of silkworm for obtaining silk is known as sericulture.

Questions: 5 - Give below is sequence of steps in the processing of steps in the processing of wool which are the missing steps? Add them.

Shearing _________ Sorting _________ _______________.

Answer: Shearing   Scouring  Sorting  Colouring   Spinning

Question: 6 - Make sketches of the two stages in the life history of the silk moth which are directly related to the production of silk.

Answer-

Question:7 - Out of the following which are the two terms related to silk production.silk production.

a. Sericulture

b. Floriculture

c. Moriculture

d. Apiculture and

e. Silviculture

Answer: (a) Sericulture and (b) Moriculture are related to silk production.

Question: 8 - Match the following

Answer: 1 – (e),   2 – (c),    3 – (b),    4 – (a)

Question: 9 - Given below is a crossword puzzle based on this lesson. Use hints to fill in the blank spaces with letters that complete the words.

Answer:

 

1 (D) - SCOUR

2 (D) - SILK

3 (D) - FIBRE

1 (A) - WOOL

2 (A) - MULBERRY

3 (A) - CATERPILLAR

 

 

 

 

 

 

 

 

 

Heat

Class - Seven Science; CBSE NCERT

Heat is the transfer of energy from a hot body. The sense of touch can be used to understand the degree of hotness or coldness of something. But the sense of touch is not reliable and cannot be always used to say how much hot anything is. Moreover, using the sense of touch can be risky in case of something very hot. Thus, hotness of anything is measured in terms of TEMPERATURE in reliable way. To measure temperature a device called THERMOMETER is used.

Unit of heat:

There are three units which are used to measure the temperature: Degree Celsius, Fahrenheit and Kelvin.

Degree Celsius: Degree Celsius is written as °C and read as degree Celsius or simply Celsius. For example 20°C; it is read as twenty degree Celsius.

Fahrenheit: Fahrenheit is written as °F and read as degree Fahrenheit. For example 25°F; it is read as twenty five degree Fahrenheit.

Kelvin: Kelvin is written as K. For example 100K; it is read as hundred Kelvin.

Thermometer:

Thermometer is a device which is used to measure temperature.

Thermometer is made of a long narrow glass tube; with a bulb at one end. The narrow tube appears as a continuous silver line; because it is filled with mercury. Mercury is a metal which is in liquid state at room temperature and it readily expands or contracts at the slightest change in temperature. Hence, mercury is used in thermometer.

Types of thermometer:

Laboratory Thermometer: Laboratory thermometer is used to measure the temperature. The scale of temperature is graduated generally from –10°C to 110°C over the glass tube. Each division of temperature scale is further divided into 10 parts to read fraction of temperature.

Clinical Thermometer: Clinical thermometer is used to measure the body temperature. The scale of temperature is graduated from 35°C to 42°C and or from 94°F to 108°F. The temperature of human body always remains within this range and this is the range on the clinical thermometer. There is a kink make near the bulb of clinical thermometer which prevents the automatic fall of mercury level.

Digital Thermometer: In digital thermometer, reading of temperature is displayed digitally as in digital watches. This is safer because no mercury is used in this. It is important to note that mercury is a highly toxic substance.

Maximum-Minimum Thermometer: Maximum – minimum thermometer is used to measure the daily temperature to prepare weather reports.

Reading of thermometer and measuring of temperature:

• Take a clinical thermometer and hold it horizontally with reading scale towards your eye.
• Do not hold the thermometer from the bulb.
• Rotate the thermometer slightly clockwise and anticlockwise. By doing this you will see a shiny thin silvery thread.
• The end of the silvery thread shows the reading of temperature. If mercury lining ends at 37, the reading is 37°C.
• Wash the bulb end of thermometer with an antiseptic solution.
• Give two or three jerks slightly. By doing this the mercury level would fall. When it falls to 35°C or below, put it below the tongue and wait for one minute.
• Take out the thermometer and read the temperature. Temperature would be near 37°C.
• The normal body temperature is 37°C. This can differ from person to person.

Use of Laboratory Thermometer:

• Take some water in a beaker.
• Take a laboratory thermometer and immerse its bulb end in water; holding it vertically. Ensure to dip whole portion of bulb end. The bulb end should not touch the bottom or side of the beaker.
• Observe the movement of rise of mercury. When it becomes stable, take the reading of the thermometer.
• Repeat this with hot water and take the reading.

Difference between clinical and laboratory thermometer:

Transfer of heat:

Heat is transferred by conduction, convection and radiation.

Conduction:

Transfer of heat from one particle to the adjacent particle is known as conduction of heat. In solids, heat is transferred by the process of conduction. In this process, the transfer of heat takes place through adjacent molecules.

Example: When one end of an iron rod is put over flame then part which is nearer to the flame is heated first and heat is gradually transferred to the other end of the rod. This happens because particles of iron rod which are nearer to the flame receive the heat and transfers this to the adjacent particles. Subsequently, the adjacent particles transfer the heat to the next adjacent particles. This process continues and heat reaches to the other end of the rod. Thus, heat transfer in solid takes place through conduction.

Conductor and Insulator:

Materials which allow heat to pass through it are called conductor or good conductor of heat, such as iron, copper, aluminium, etc. All metals are good conductors of heat. Since, mercury is a metal and found in liquid state at room temperature, that’s why it is used in thermometer.

Since metals are the good conductor of heat that’s why kitchen utensils are made of metals or alloys of metals.

Materials which do not allow heat to pass through them are called bad conductor or poor conductor of heat. They are also called insulators. Example: rubber, wood, plastic, etc. This is the cause that handles of frying pan or other kitchen utensils are made of plastic.

Convection:

The transfer of heat because of movement of the molecules of the medium; via mass transfer; is called convection or convection of heat.

Water and air are bad conductors of heat. But they do become hot, in spite of being bad conductors. Heat transfer in fluids takes place through convection.

Convection in water: When water is heated in a pan, the particles of water which are near the source of heat; get heated first. Because of heating, they become light; and rise in water. The gap which is created because of rise of hot particles is filled cold particles of water from the surrounding area. Thus a cyclical movement of particles begins and ends up heating the whole water of the pan. The cyclical movement in fluids because of heating is called convection current.

Convection in air: Air gets heated because of convection; the way water gets heated. Air near the source of heat gets heated and rises above. This leaves a gap; which is filled by the colder air from the surrounding. The convection current thus starts in air which results in heating up of air.

When you place your palm above a flame you will feel the hotness of the flame. But when you will place your palm below the flame the area will be colder. This shows how the colder air from below moves up; due to convection current.

Land and Sea Breeze:

Sea Breeze: In coastal areas, the breeze that moves from sea surface to the land is called sea breeze. This happens because, during daytime, land gets heated more quickly than water. As a result, warm air from land rises up; leaving a gap. To fill that gap, colder air from the ocean surface rushes towards the land. This phenomenon continues and a continuous flow of cold air keeps coming towards the land. This gives rise to the phenomenon which is called the sea breeze. Because of this, people living in coastal areas prefer to live in a sea facing house.

Land Breeze: In coastal areas, the breeze which moves from land towards the sea is called land breeze. In the night, the land cools down more quickly than the ocean surface. This makes the air over the water surface warmer than air over the land surface. Warmer air over the water surface rises in the air and air from the land rushes towards the water surface to fill the gap. This phenomenon continues which creates a flow of air from land to the sea. This phenomenon is called land breeze.

Radiation:

All hot bodies emit heat by the process of radiation. Radiation of heat does not require a medium. Sunlight comes to the earth because of radiation as there is no medium present between the atmosphere of the earth and the sun.

One can feel the heat of bonfire by standing around it. We get warmth from the room heater because of radiation.

Reflection and absorption of heat: When heat falls over an object some of the heat is absorbed by the body and some of the heat is reflected. The temperature of an object increases because of absorption of heat.

In conventional room heater you can see the reflector attached with it. The reflector of the room heater reflects the heat towards the person sitting or standing near the room heater.

Reflection is the cause that umbrella is used to protect from heat of the sun in summer. Dark color absorbs more heat while light color reflects most of the heat. That’s why wearing light colored clothes is preferred in summer, dark colored clothes are preferred in winter.

Dark clothes absorb more heat and keep one comfortable in winter. On the other hand, light clothes reflect most of the heat and keep one comfortable in summer.

Now-a-days many kitchen utensils come in black color, since utensils of black color absorb more heat and thus cooking becomes faster.

Woolen Cloth: Woolen clothes are used in winter season. Wool is a poor conductor of heat. In addition to it; air gets trapped in woolen fiber to further increase the poor conductivity of wool. This prevents the radiation of heat of our body to the surrounding and prevents the cold from surrounding to affect our body. Thus, wearing woolen cloth makes one comfortable in winter season.

Important Terms:

• Temperature: The reliable measure of hotness or coldness of anything.
• Thermometer: A device to measure the temperature.
• Degree Celsius: Unit of measurement of temperature.
• Clinical Thermometer: A device to measure the temperature of human body.
• Laboratory Thermometer: Used to measure the temperature in laboratory.
• Maximum-Minimum Thermometer: Use to measure the temperature of climate.
• Conduction: Mode of transfer of heat in solids.
• Convection: Mode of transfer of heat in liquids and air.
• Radiation: Mode of transfer of heat without medium.
• Conductor: Materials that allow the flow of heat through them.
• Insulator: Materials that do not allow the flow of heat through them.
• Land breeze: Breeze that flows from land surface to sea surface in summer nights.
• Sea breeze: Breeze that flows from sea surface to water surface in summer days.

 Class seven science Heat NECRT Exercise Solution

Question: 1 - State similarities and differences between the laboratory thermometer and the clinical thermometer.

Answer:

Question: 2 - Give two examples each of conductors and insulators of heat.

Answer:

Examples of conductor: Iron, copper

Examples of insulator: Rubber, plastic

Question: 3 - Fill in the blanks:

(a) The hotness of an object is determined by its __________.

Answer: Temperature.

(b) Temperature of boiling water cannot be measured by a _____________ thermometer.

Answer: Clinical Thermometer

(c) Temperature is measured in degree ______________.

Answer: Celsius

(d) No medium is required for transfer of heat by the process of __________.

Answer: Radiation

(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ______________.

Answer: Conduction.

(f ) Clothes of ______________ colours absorb heat better than clothes of light colours.

Answer: Dark

Question: 4 - Match the following :

Question: 5 - Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing?

Answer: By wearing more layers of clothing, air gets trapped between different layers. This makes different layers of insulation and thus provides better protection against cold. On the other hand, wearing just one piece of clothing creates just one insulator layer and hence is less effective in beating the cold.

Question: 6 - Look at Fig. 4.13 (in NCERT Text Book). Mark where the heat is being transferred by conduction, by convection and by radiation.

Answer: 

Question: 7 - In places of hot climate it is advised that the outer walls of houses be painted white. Explain.

Answer: White colour reflects most of the heat falling on it. This makes the house colder. Thus, in places of hot climate it is advised that the outer walls of house be painted white.

Question: 8 - One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be

(a) 80°C

(b) more than 50°C but less than 80°C

(c) 20°C

(d) between 30°C and 50°C

Answer: (d) between 30°C and 50°C

Question: 9 - An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will

(a) flow from iron ball to water.

(b) not flow from iron ball to water or from water to iron ball.

(c) flow from water to iron ball.

(d) increase the temperature of both.

Answer: (b) not flow from iron ball to water or from water to iron ball.

Question: 10 - A wooden spoon is dipped in a cup of ice cream. Its other end

(a) becomes cold by the process of conduction.

(b) becomes cold by the process of convection.

(c) becomes cold by the process of radiation.

(d) does not become cold.

Answer: (d) does not become cold.

Question : 11 - Stainless steel pans are usually provided with copper bottoms. The reason for this could be that

(a) copper bottom makes the pan more durable.

(b) such pans appear colourful.

(c) copper is a better conductor of heat than the stainless steel.

(d) copper is easier to clean than the stainless steel.

Answer: (c) Copper is a better conductor of heat than the stainless steel.

  

 

 

 

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Acid, Base and Salt

• Acid
• Base
• Salt
• Indicator
• Neutralization or Neutralization Reaction
• Use of neutralization

Substances can be divided into three types – Acid, Base and Salt.

ACID: Taste of acid is sour. There are many substances that contain acid and so taste sour. For example – lemon, curd, pickles, orange juice, vinegar, etc.

Substances that taste sour are called acidic. The chemical nature of such substance is known as ACIDIC.

The word acid comes from Latin ‘ACERE’ which means sour.

BASE: Taste of base is bitter. Substances that contain base taste bitter. For example; soap or soap solution, baking soda, washing soda, etc.

The chemical nature of substances that contain base is known as BASIC.

INDICATOR: It is not always possible to know the acidic or basic nature of substances by tasting them. Tasting a substance in laboratory is not also advisable because it may be harmful. Thus, to test the chemical nature (acidic or basic nature) of substance a special kind of substance is used. This special kind of substance which is used to test the acidic or basic nature of anything is known as INDICATOR.

Indicator is a substance that shows the acidic or basic nature of a substance by change in its colour.

Types of Indicator: Indicators can be divided into two types.

Natural Indicator: Indicators that are obtained from naturally occurring substance are called NATURAL INDICATORS. For example; litmus, turmeric, china rose, etc.

Synthetic Indicator: Indicators that are made in laboratory are called SYNTHETIC INDICATORS. For example; phenolphthalein, methyl orange, etc.

NATURAL INDICATORS:

Litmus: Litmus is extracted from Lichens. Lichen is a composite organism. Lichens consist of fungi and algae living in symbiotic relationship.

Litmus is a purple coloured liquid in distilled water. Litmus comes in the form of strips of two colours. One is called blue litmus paper and another is called red litmus paper.

Litmus liquid and litmus paper are used to detect the acidic or basic nature of a substance.

Colour of litmus paper in acid: Blue litmus paper turns into red when dipped in acidic solution.

Colour of litmus paper in base: Red litmus paper turns into blue when dipped in basic solution.

Turmeric: Turmeric is used as another natural indicator. Turmeric is of yellow colour. Turmeric paper turns into red when it is dipped into basic solution. Turmeric paper does not change its colour with acid.

China Rose: China rose is another natural indicator. China rose solution gives dark pink (magenta) colour with acid and green colour with base.

Acid Rain: Carbon dioxide, sulphur dioxide and nitrogen dioxide which are released from vehicles and chimneys mix with droplets of rain and turn the rain water acidic. When this acidic rain water falls over earth, it is known as acid rain. Acid rain damages the buildings and is harmful for plants and animals.

Taj Mahal; which is made of marble is in threat because of acid rain. Many parts of Taj Mahal and other many historical buildings and monuments have got damaged due to acid rain.

Characteristics of Acid:

• Sour in taste.
• Turns blue litmus paper red.
• Turns the solution of China rose to dark pink colour (magenta).

Characteristics of Base:

• Bitter in taste.
• Turns red litmus paper blue.
• Turns solution of China rose to green.
• Turns turmeric paper to red.

Neutralisation:

When solution of acid is mixed with the solution of base, both of them neutralize each other and a third substance; called salt; is formed. Such phenomenon is called neutralization or neutralization reaction. The solution formed because of mixing of solution of acid and base is neither acidic nor basic in nature. Such solution is known as neutral solution.

Salt formed because of neutralization reaction may be acidic or basic in nature. Acidic or Basic nature of salt depends upon the strength of acid and base. In neutralization reaction heat is evolved. Reactions in which heat is evolved are known as exothermic reactions. Thus, neutralization reaction is an exothermic reaction.

Sodium hydroxide is a base and hydrochloric acid is an acid. When solution of sodium hydroxide is mixed with the solution of hydrochloric acid, both neutralize each other and common salt (Sodium chloride) is formed. Since, it is an exothermic reaction, so reaction mixture becomes slightly hot. The reaction involved in this can be written as follows:

Sodium chloride is the chemical name of common salt which is used in household.

Neutralization Reaction in Everyday Life:

There are many uses of neutralization reaction in everyday life.

Indigestion: Our stomach releases hydrochloric acid to kill bacteria; if any; present in food. Hydrochloric acid released in our stomach also helps in the digestion of food. Sometime our stomach produces more hydrochloric acid than required. Production of more hydrochloric acid in the stomach manifests as indigestion. This condition can be painful and causes pain in the stomach.

To get rid of such symptoms, a medicine made of milk of magnesia (a base) is taken orally. Milk of magnesia, being a base neutralizes the hydrochloric acid and gives relief from pain because of indigestion.

Ant sting: Ant sting or bee sting contains methanoic acid. Methanoic acid is also known as formic acid. Bee or ant injects formic acid into our skin, while biting. Injection of acid by ant or bee results in pain at the place of bite.

Rubbing baking soda over the skin gives relief from pain due to ant or bee sting. Baking soda, which is a base, neutralizes the effect of acid injected by bee or ant. Another base, such as zinc carbonate (Calamite solution) is also used in the case of ant or bee sting.

Soil Treatment: Sometimes soil becomes acidic or basic due to excess use of fertilizers or wrong method of harvesting. Acidic or basic nature of soil affects the yield as plants do not grow properly on such soil.

Acidic soil is treated with slaked lime or quick lime. Slaked lime (Calcium hydroxide) and quick lime (Calcium oxide) are bases. Use of slaked lime or quick lime neutralizes the acidic nature of soil.

Basic soil is treated with organic matter. Organic matter releases acid and neutralizes the basic nature of soil.

Factory Waste: Wastes of most of the factories are acidic. If such acidic wastes are flushed into rivers, acid present in them kills the aquatic organisms and pollutes the water. Thus, factory wastes are treated with basic substances to neutralize the acid present in them before being flushed in the river.

Important Points:

• Acid is sour in taste.
• Acid turns blue litmus paper to red.
• Acid turns China rose solution to dark pink.
• Base is bitter in taste.
• Base turns red litmus paper to blue.
• Base turns turmeric paper or solution to red.
• Base turns China rose solution into green.
• Indicator is a special substance which shows the acidic or basic character of a substance by change in colour.
• Litmus, turmeric and solution of China rose are natural indicators.
• Litmus is obtained from lichens.
• Solutions of acid and base neutralize each other when mixed in proper ratio. This is called neutralization or neutralization reaction.
• In neutralization reaction between the solutions of acid and base, a new substance called salt is formed.
• Salt formed because of neutralization reaction may be acidic or basic in nature. The acidic or basic nature of salt depends upon the strength of acid and base used for neutralization reaction.

 NCERT Book Exercise Solution

Question: 1. State differences between acids and bases.

Answer:

Question: 2. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

Answer:Since window cleaner turns red litmus paper to blue, it is basic in nature.

Question:3. Name the source from which litmus solution is obtained. What is the use of this solution?

Answer:

Litmus solution is obtained from lichens. Litmus solution is used to detect the acidic and basic characteristic of a substance.

Question: 4. Is the distilled water acidic/basic/neutral? How would you verify it?

Answer:Distilled water is neutral in character, i.e. it is neither acidic nor basic.

Neutral nature of distilled water can be verified by the use of blue and red litmus paper.

Distilled water does not change the colour of either blue or red litmus paper.

Question: 5. Describe the process of neutralization with the help of an example.

Answer:When the solution of acid is mixed with the solution of base in proper ratio, both of them neutralize the effect of each other and a new substance; called salt; is formed; along with water. This is called neutralization or neutralization reaction.

Example: When the solution of sodium hydroxide (a base) is mixed with the solution of hydrochloric acid (an acid) in proper ratio, both neutralize each other and the reaction mixture so obtained is neutral in character. In this reaction, a new substance sodium chloride (common salt) is formed.

The reaction involved in this can be written as follows:

Question: 6. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) Nitric acid turns red litmus blue. (T/F)

Answer:F

(ii) Sodium hydroxide turns blue litmus red. (T/F)

Answer:F

(iii) Sodium hydroxide and hydrochloric acid neutralize each other and form salt and water. (T/F)

Answer:T

(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)

Answer:F

(v) Tooth decay is caused by the presence of a base. (T/F)

Answer:F

Question: 7. Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labeled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?

Answer:

Dorji would dip blue and red litmus paper in the sample of each of the bottles.

Sample of solution of bottle which turns blue litmus paper red is acidic.

Sample of solution of bottle which turns red litmus paper blue is basic.

Sample of solution of bottle which does not change the colour of either blue or red litmus paper is neutral in nature.

After detecting the acidic, basic and neutral nature of soft drink, Dorji would serve the drink to the customers according to their requirement.

Question: 8. Explain why:

(a) An antacid tablet is taken when you suffer from acidity.

Answer:

Antacid means substance that works against acid. Antacid tablet is taken in the case of acidity to neutralize the excess acid produced in the stomach.

Antacid tablets neutralize the acid produced in the stomach and give relief from acidity.

(b) Calamine solution is applied on the skin when an ant bites.

Answer:Calamine solution, which is zinc carbonate, is a base. In the case of ant bites, ant injects an acid; called formic acid; in the skin which causes pain and irritation. By applying calamine solution, it neutralizes the effect of acid inject in the course of ant bite and gives relief from pain.

(c) Factory waste is neutralized before disposing it into the water bodies.

Answer:

Most of the factory wastes contain acid. It they are flushed into water as they are, then acid present in them would kill the aquatic organisms; along with creating pollution. Thus, it is necessary to neutralize the factory waste before disposing it into the water bodies.

Question: 9. Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.

Answer:

Label the test tubes as A, B and C.

Dip the turmeric indicator in test tube A. If the turmeric paper changes to red then the liquid in the test tube is sodium hydroxide; which is a base. Otherwise, it is either hydrochloric acid or sugar solution; which is neutral.

If the liquid in the test tube A is not sodium hydroxide then keep it aside and repeat above procedure with the test tube B. If it is not sodium hydroxide then the liquid in test tube C must be sodium hydroxide.

Take aside the test tube with sodium hydroxide and pour sodium hydroxide in remaining two test tubes. The test tube which becomes warm contains acid. When acid and base neutralize each other, heat is released in the process.

Question: 10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

Answer:If blue litmus paper is dipped in a solution and it would remain blue then the solution may be basic or neutral in character.

Blue litmus paper does not change its colour with basic solution and neutral solution.

Question: 11. Consider the following statements:

(a) Both acids and bases change colour of all indicators.

(b) If an indicator gives a colour change with an acid, it does not give a change with a base.

(c) If an indicator changes colour with a base, it does not change colour with an acid.

(d) Change of colour in an acid and a base depends on the type of the indicator.

Which of these statements are correct?

(i) All four (ii) a and d (iii) b and c (iv) only d

Answer:(iv) only d

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Physical and Chemical Changes

We see different types of changes; everyday in our surrounding. Growth of tree, rising of sun, setting of sun, different shape and size of moon, burning of coal, paper, wood, etc. are the examples of changes around us.

Before knowing the scientific meaning of changes; it is necessary to understand some terms, i.e. physical properties, chemical properties, reversible and irreversible.

Physical Properties: Shape, Size and State of substance are known as physical properties. For example; when a sheet of paper is folded, its shape changes and this is an example of change in physical property.

Chemical Properties: The internal properties of a substance are known as chemical properties. For example curd is the product of milk but the internal properties of milk and curd are completely different.

Reversible: Things or processes which can be reversed are called: Things or processes which can be reversed are called reversible. For example, a folded sheet of paper can be unfolded and hence folding a sheet of paper is reversible.

Irreversible: Things or processes which cannot be reversed are called irreversible. For example, when milk turns into curd; it cannot be changed back to milk and hence is an irreversible change.

Types of Changes: - Physical Change and Chemical Change.

Physical Change:

Change in which only physical properties of a substance change and no new substance is formed is called Physical Change.

Most of the physical changes are reversible, this means we can get the substance back even after the change.

Examples:

Folding of a paper sheet: A paper can be folded or unfolded and hence it is an example of physical change. Moreover, no new substance is formed in this process, so it is a physical change.

Tearing of paper sheet: Even after being torn in very small pieces; each piece is a piece of paper. Since no new substance is formed in this process, so it is a physical change.

Melting of wax: In melting, only the state of the wax changes; from solid to liquid. Solid wax can be obtained from molten wax. This i: In melting, only the state of the wax changes; from solid to liquid. Solid wax can be obtained from molten wax. This is an example of physical and reversible change.

Melting of ice into water: In melting, only the state of water changes. Water can be changed to ice and vice-versa. This is an example of physical and reversible change.

Freezing of water:After freezing, water changes into ice. In this change; there is only the change in the state of water. Water can be obtained back from ice; by melting.

Change of water into vapour (Vaporisation): Vapour is another state of water. Water can be obtained after condensation of vapour. This is a physical and reversible change.

Change of vapour into water (Condensation): This is also a physical and reversible change as water can be changed into vapour again by the process of vaporization.

Stretching of a rubber band: In this change, only the size of the rubber band changes. The rubber band comes back in its original shape and size, once it is released. This is a physical and reversible change.

Chemical Changes:

Changes in which chemical properties of substance change and a new substance is formed are called chemical changes. Some of the chemical changes are irreversible. Even in case of reversible chemicalChanges in which chemical properties of substance change and a new substance is formed are called chemical changes. Some of the chemical changes are irreversible. Even in case of reversible chemical change, the change cannot be reversed by simple physical processes.

Examples:

Burning of paper, wood, fuel or anything:

When something is burnt, many new substances are formed; especially carbon dioxide is formed in most of the cases. Once something is burnt, the ash or carbon dioxide cannot be turned into the original substance. Hence, burning oWhen something is burnt, many new substances are formed; especially carbon dioxide is formed in most of the cases. Once something is burnt, the ash or carbon dioxide cannot be turned into the original substance. Hence, burning of anything is chemical and irreversible change.

Melting of wax and burning of wax are different kinds of change. Burning of wax is chemical change while melting of wax is a physical change. Burning of wax is irreversible while melting of wax is reversible.sed back.

Reaction between vinegar and Baking Soda:

Vinegar is an acid (Acetic acid). The chemical name of baking soda is sodium hydrogen carbonate or sodium bicarbonate.

When vinegar reacts with acetic acid, it gives carbon dioxide. A hissing sound is produced when baking soda is added to vinegar. This happens because of production of carbon dioxide. When carbon dioxide is passed through lime water (calcium hydroxide), it turns the lime water milky. This happens because of formation of calcium carbonate. Water is also formed; along with calcium carbonate. The reaction involved in this can be written as follows:

These are the examples of chemical changes. In the first case, a new substance; carbon dioxide is formed. In the second case, a new substance; calcium carbonate is formed. The lime water turns milky because of formation of calcium carbonate.

These reactions are irreversible, as original substance cannot be retrieved from these by simple physical processes.

Burning of magnesium ribbon:

Magnesium ribbon burns with dazzling light in air and forms magnesium oxide. The ash of magnesium oxide gives magnesium hydroxide when mixed with water. Solution of magnesium hydroxide turns blue litmus paper red; this shows its basic characteristic. Reaction involved in it can be written as follows:

These are chemical changes as new substances are formed after change. Original substances cannot be retrieved by simple physical processes.

Reaction between solution of copper sulphate and iron: Copper sulphate solution is blue in colour. Copper sulphate is also known as blue vitriol. When an iron nail or shaving blade is left in copper sulphate solution; for some time; the colour of solution changes from blue to pale green. This happens because of the formation of iron sulphate. Additionally, a layer of brown copper gets deposited over the iron nail or blade. The reaction can be written as follows:

Rusting of Iron: Deposition of a brown layer on iron is called rusting. In rusting, a new substance is formed. The chemical structures of iron and rust are completely different. Rust is iron oxide. Iron is a grey-black material while rust is reddish brown

Thus, this is a chemical and irreversible change. Reaction in rusting can be written as follows:

When articles made of iron come in contact with moisture present in air, they get rusted. Iron is converted into iron oxide, i.e. rust. The iron article becomes weak in due course as all the iron slowly turns into rust. This is corrosion of iron. Rusting gives a huge monetary loss to the people and nation.

Prevention of rusting: For rusting, both water and oxygen should come in contact with iron. If anyone of these is prevented to come in contact with iron, rusting can be prevented. So, rusting is prevented using following methods:

Painting: articles such as; iron gates, grills, etc. are painted at regular intervals of time.

Applying of layer of grease: Applying a layer of grease prevents the iron articles from coming in contact with moist air. This prevents rusting. That is why grease is applied over the chain of bicycle and also over many machine parts.

Galvanisation: In the process of galvanization; a layer of non-reactive metal, such as zinc is deposited over iron articles. The layer of non-reactive metal prevents the iron articles from coming in contact with moisture. Thus it prevents rusting. Water p

Crystallisation: Common salt is obtained by the vapourisation of sea water, but crystals of common salt are very small. When a small crystal of common salt is left dipped in the saturated solut In the process of galvanization; a layer of non-reactive metal, such as zinc is deposited over iron articles. The layer of non-reactive metal prevents the iron articles from coming in contact with moisture. Thus it prevents rusting. Water pipes, which are made of iron, are galvanized to prevent rusting.

Crystallisation:Common salt is obtained by the vapourisation of sea water, but crystals of common salt are very small. When a small crystal of common salt is left dipped in the saturated solution of common salt for some time, big crystal of common salt is obtained. Formation of big and pure crystal of a substance from the saturated solution is called CRYSTALLISATION.

Characteristics of Physical change:

• Only physical properties of substance change.
• No new substance is formed in this change.
• Most of the Physical changes are reversible.

Characteristics of Chemical change:

• Chemical properties of substance change.
• New substance is formed.
• Some of the Chemical changes are irreversible.
• Chemical change cannot be reversed by simple physical means.

Signs of Chemical Change:

• Evolution of heat.
• Production of sound.
• Change in colour.
• Change in smell.
• Evolution of gas.

Physical And Chemical Changes

NCERT Book Exercise Class VII science Question and Answer

1. Classify the changes involved in the following processes as physical or chemical changes:

(a) Photosynthesis

(b) Dissolving sugar in water

(c) Burning of coal

(d) Melting of wax

(e) Beating aluminium to make aluminium foil

(f ) Digestion of food

Answer:

(a) Chemical change.

(b) Physical change.

(c) Chemical change

(d) Physical change

(e) Physical change

(f) Chemical change

2. State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.

(a) Cutting a log of wood into pieces is a chemical change. (True/False)

(b) Formation of manure from leaves is a physical change. (True/False)

(c) Iron pipes coated with zinc do not get rusted easily. (True/False)

(d) Iron and rust are the same substances. (True/False)

(e) Condensation of steam is not a chemical change. (True/False)

Answer:

(a) False (b) False (c) True (d) False (e) True

3. Fill in the blanks in the following statements:

(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of _________.

Answer: Calcium carbonate.

(b) The chemical name of baking soda is _________.

Answer: Sodium hydrogen carbonate.

(c) Two methods by which rusting of iron can be prevented are _________ and _________.

Answer: Polishing, Glavanisation.

(d) Changes in which only _________ properties of a substance change are called physical changes.

Answer: Physical

(e) Changes in which new substances are formed are called _________ changes.

Answer: Chemical

4. When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.

Answer: When baking soda is mixed with lemon juice, bubbles formed because of evolution of carbon dioxide gas. This is a chemical change, because in this reaction new substances are formed.

5. When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.

Answer: In burning of candle some of the wax melts, which is physical change, while most of the wax burnt, which is a chemical change.

In the burning of wood, water present in wood changes into vapour, this is physical change, while burning of wood is a chemical change.

6. How would you show that setting of curd is a chemical change?

Answer: In the setting of curd, milk changes into new substance, curd. This is an irreversible process that means milk cannot get back from curd. Formation of new substance and irreversible process shows that setting of curd is a chemical change.

7. Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.

Answer: In burning of wood, new substances are formed and hence is a chemical change. While cutting the wood into small pieces no new substance is formed, thus it is a physical change.

Hence, burning of wood and cutting it into small pieces are considered as two different types of changes.

8. Describe how crystals of copper sulphate are prepared.

Answer:

Process:

• Water is taken in a beaker.
• Few drops of sulphuric acid is added to the water.
• Water is let to boil.
• When water starts boiling, copper sulphate powder is added to the water with continuous stirring the solution.
• When copper sulphate starts deposited into bottom of the beaker, then solution is filtered and left for cooling.
• After cooling, the crystals of copper sulphate is prepared.

9. Explain how painting of an iron gate prevents it from rusting.

Answer: Iron get rusted because of reaction with oxygen present in moist air. By painting iron gate, iron is prevented to come into contact with oxygen present in moist air, which prevent it be getting rusted.

10. Explain why rusting of iron objects is faster in coastal areas than in deserts.

Answer: Iron get rusted because of reaction with oxygen present in moist air. In coastal areas, air contains more moisture because of sea or ocean, while in deserts air is dry and hot. Thus because of getting more moist air iron objects getting rusted faster in coastal areas than in deserts.

11. The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exist as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (Change – B). The following statements pertain to these changes. Choose the correct one.

(i) Process – A is a chemical change.

(ii) Process – B is a chemical change.

(iii) Both processes A and B are chemical changes.

(iv) None of these processes is a chemical change.

Answer: (ii) Process – B is a chemical change.

12. Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one.

(i) Process – A is a chemical change.

(ii) Process – B is a chemical change.

(iii) Both processes A and B are chemical changes.

(iv) None of these processes is a chemical change.

Answer: (iii) Both processes A and B are chemical changes.

 

 

 

 

Weather, Climate and Adaptation of Animals to Climate

Weather: The day to day condition of atmosphere at a particular place is called weather. The weather can be comfortable, or can be too hot or cold.

Weather Report: The daily report about weather; usually released by the meteorological department is called weather report. Weather report is often shown along with the news on television.

Elements of weather: The various elements of weather are: temperature, humidity, rainfall, wind-speed, etc.

Temperature: Temperature depends upon the duration of sunshine. During the summer season, the duration of the sunshine is longer. Due to this, the temperature is high in summer. The day temperature is minimum in the morning and maximum at noon.

Humidity: Humidity is the amount of moisture present in air. Humidity is generally measured in percentage. Humidity is generally at the highest level; during the rainy season.

Rainfall: Amount of rainfall is measured in terms of mm. For this, an apparatus; called rain gauge is used.

Wind-speed: Speed of wind also affects the condition of weather.

Department of Meteorology: This is a Government Department. The Meteorological Department measures the elements of weather and keeps their record. Meteorologists use data from satellites and analyse the data to forecast about the weather.

Climate: Climate is the average weather condition of at least 25 years; in a given geographical part.

The climate of India is said to be hot and humid, because the temperature is usually high and so is the humidity for most parts of the year. The climate of Rajasthan is said to be hot and dry because temperature is very high but humidity is very low. On the other hand, the climate of Kashmir is said to be cold because temperature is low.

Rainforest: Rainforest is found generally near the equator. Places near the equator receive more sunshine and hence more rainfall. This makes the place hot and humid. Temperatures vary from 15⁰C to 40⁰C generally near the equator. Rainforests are also present in some tropical areas.

Desert: Temperature in desert is generally higher and it receives less or little rain fall. So deserts are hot and dry.

Polar Region: Polar Region is at high latitude and hence do not receive adequate sunshine. Due to this, temperature is very low in the Polar Regions. The Polar Region is covered with snow, because of the low temperature.

Climate and Adaptation:

At several places, such as desert, polar region, etc. climate is very harsh. Many organisms live and thrive at these places, in spite of the harsh climate. Animals and plants; living in such places; develop certain features which help them survive the harsh climate. To develop certain features in order to survive the given climate is called adaptation.

Adaptation in Polar Region:

In Polar Regions, the sun does not set for about six months and it does not appear for another six months of the year. These regions are covered with snow for most part of the years. In winter, temperature may down to -37°C. Hence, the climate of Polar Regions becomes extreme and harsh. In spite of such condition, many animals live at those places, for example: Polar Bear, Penguin, Snow Leopard, etc. These animals show various adaptations which help them in surviving in the harsh climate of the Polar Region.

Polar Bear: Polar bear has two thick layers of fur over its body. In addition to this, they have thick layer of fat under the skin; called blubber. These layers act as insulator and prevent the bear from extreme cold. Because of the white fur, the Polar Bear can easily mix with its snowy background and can hide from its prey and predator. Getting hide with surrounding because of special colour and pattern is known as camouflage.

Polar bears have wide paws with long curved nails, called claws. This helps them to move on the snow. r swimming to keep them cool. Wide paws work as a rudder, while swimming. They are very good swimmers.

Polar bear has a highly developed sense of smell. It helps the Polar bear in finding a fish even from under a thick layer of snow.

These adaptations help Polar RThese adaptations help Polar Region to survive in the extreme condition of the Polar Region.

Penguin: Penguins also live in the Polar Region. Penguins are of white colour with black back. They have thick layer of fat under their skin. This protects them from extreme cold.

They usually remain huddled together. This helps in keeping them warm. nd curved claws which help them to walk in snow and to swim in water.

These adaptations help the penguin to survive in the extreme condition of the Polar Region.

Birds: There are many types of birds found in Polar Regions. They fly to the warm regions during winter to survive. Long distance travel; in search of favourable climate; is called migration.

Some migratory birds are known to travel as long as 15000 km to keep them survive in opposite climatic conditions. Arctic tern is known to be the longest traveler among the migratory birds.

Apart from birds, many fish and mammals also migrate to other places in such opposite climatic conditions.

Tropical Rain Forest:

In India, Tropical Rainforests are found in the Western Ghats and in Assam. Rainforests are also found in Southeast Asia, Central America and Central Africa.

Rainforests have plenty of food which supports variety of life. Many animals are found in the rainforests, e.g. leopard, elephant, snakes, tigers, monkey, buffaloes, frogs, apes, lizards, many types of birds, insects, etc.

In spite of plenty of food, there is a high level of competition for survival among animals in the rainforest.

Adaptive features of animals found in rain forest:

Lion: The colour of lion helps it in blending in its background. Lion has a highly developed sense of smell and night vision. All of these help a lion in catching the prey.

Elephant: Elephants have well developed sense of smell. It helps the elephant in finding the food. The trunk has powerful muscles which help the elephant in uprooting even a big tree. Elephants have good sense of hearing which help the elephant in sensing danger way in advance. An elephant uses its trunk to sprinkle water all over its body so that it can cool down its body temperature.

Monkeys: Monkeys are highly adapted to live in the rainforests. Monkey uses its palms and soles to grip a branch and thus can hang and swing from a branch. It can also use its tail to hold a branch. Monkeys can climb to the topmost branch of a tree and thus can see very far in the jungle. This helps them in sensing the danger and also in finding the food.

Frogs: Frogs are adapted to live both on land and in water. The greenish colour of the frog helps it in mixing with the green foliage. Frog has a long and sticky tongue with which it catches its prey. The tree-frog has developed sticky pads in its claws. This helps the tree-frog in climbing a tree and in holding on to a branch.

Important Points:

• Weather: Day to day atmospheric condition.
• Climate: Average atmospheric condition for at least 25 years.
• Elements of weather: Temperature, Humidity, Rainfall, Wind-speed, etc.
• Rainforest: Dense forest near equator and tropical regions.
• Desert: A region with little rainfall, high temperature and full of sand.
• Polar Regions: Regions near poles, having very low temperature, area is covered with snow most of the parts of year.
• Adaptation: Special habits of animals which enable them to survive in particular climatic conditions.

Camouflage: Special colour of animals because of which they can resemble with background of surrounding which hide themselves from predators. Wind, Strom And Cyclone

NCERT Questions And Answer:

Question: 1. Fill the missing word in the blank spaces in the following statements:

(a) Wind is——————air.

Answer: Moving

(b) Winds are generated due to——————heating on the earth.

Answer: Uneven

(c) Near the earth’s surface __________air rises up whereas ___________ air comes down.

Answer: Warm, cold

(d) Air moves from a region of ——— pressure to a region of——— pressure.

Answer: High, Low

Question: 2. Suggest two methods to find out wind direction at a given place.

Answer: Two methods to find the direction of wind:

(a) Take a handful of sand or dust. Release it slowly from a height and observe the direction in which the falling sand is moving. This will show the direction of wind.

(b) Tie a thin plastic sheet or cloth with a stick. Keep the stick at a place which is as high as possible. The direction in which the cloth sways shows the direction of wind.

Qeustion: 3. State two experiences that made you think that air exerts pressure (other than those given in the text).

Answer: I have seen paratroopers jumping from aeroplanes. The parachute helps them in reaching the ground safely. The air pressure reduces the speed of the parachute and the paratrooper lands without getting injured.

Question: 4. You want to buy a house. Would you like to buy a house having windows but no ventilators? Explain your answer.

Answer: A house should have ventilators along with windows. The warm air would rise up and exit from the ventilators. The cooler air would rush in through the windows. This will help in making the rooms comfortable. A room without ventilators shall not be cooled as efficiently as one with ventilators.

Question: 5. Explain why holes are made in hanging banners and hoardings.

Answer: Banners and hoardings are usually very large. The air pressure; because of the moving air; can blow away the banners. Holes are made in banners and hoardings so that the wind can move through them. This helps in reducing the impact of air pressure on the hoardings and thus they are not get blown away.

Question: 6. How will you help your neighbours in case cyclone approaches your village/town?

Answer: I will take following steps to help my neighbours in case of cyclone:

• I will help people to reach to a safer place.
• I will organize a community kitchen during the stress period.
• I will provide first aid to injured people.
• I will also arrange for safe drinking water for the people.

Question: 7. What planning is required in advance to deal with the situation created by a cyclone?

Answer: Following planning is required to deal with the situation created by a cyclone:

• Proper shelters should be built by the government agencies so that people can be accommodated in them.
• Alternate arrangements of seamless communication among rescue agencies should be made.
• Proper stock of emergency medicines should be kept.
• Proper arrangements of safe drinking water should be made.
• Government should chalk out a rehabilitation plan for those affected by cyclone.

Question: 8. Which one of the following place is unlikely to be affected by a cyclone.

(i) Chennai (ii) Mangaluru (Mangalore) (iii) Amritsar (iv) Puri

Answer: (iv) Puri

Question: 9. Which of the statements given below is correct?

1. In winter the winds flow from the land to the ocean.
2. In summer the winds flow from the land towards the ocean.
3. A cyclone is formed by a very high-pressure system with very high-speed winds revolving around it.
4. The coastline of India is not vulnerable to cyclones.

Answer: (i) In winter the winds flow from the land to the ocean

 

Wind, Storm and Cyclone

Air: Air is a mixture of gases.

Wind: Moving air is called wind.

Air exerts pressure: The fact that Air exerts pressure can be understood by many examples.

Tube of bicycle gets inflated when air is filled in it. This happens because air exerts pressure.

It is difficult to move the bicycle against the direction of wind. Similarly, a sailor feels it difficult to sail his boat against the direction of wind. This happens because air exerts pressure.

When boiled water is filled in a tin can and its mouth is closed with the lid; followed by cold water being poured over it, the can gets distorted. This happens because air inside the can gets condensed and creates low pressure. The higher pressure from outside distorts the shape of the can.

You can fly a kite because air exerts pressure from the rear portion of the kite.

Aeroplane can fly because air exerts pressure.

Birds can fly because air exerts pressure.

High speed wind creates area of low air pressure:

Thatched roof is blown off because of high speed wind. This happens because high speed wind creates an area of low pressure. Due to this, the thatched roof is sucked up and finally gets blown away. Thus, increase in wind speed is associated by decrease in air pressure.

Movement of air:

Air moves from high pressure zone to low pressure zone of air. Air; from high pressure zone; rushes towards the low pressure zone; to fill the gap. Thus, greater is the pressure difference greater will be the speed of wind and vice-versa.

Cause of Wind Movement:

Pressure difference in the air is cause by differential heating. Warm air rises up because it becomes lighter. This creates an area of low pressure below the rising air. The area of low pressure is quickly filled in by cooler air from around. That is how the wind movement is created on the earth. Thus differential heating of air creates pressure difference; which makes the wind movement.

Movement of Air Because of Uneven Heating on Earth:

Movement of Air in Equatorial Region: The Equatorial region gets the highest amount of sunshine throughout the year. Due to this, the air near the equatorial region gets heated. The warm air rises up and creates an area of low pressure. The cooler air; from the higher latitudes; rushes towards the equator to fill the gap. This results in the wind movement from tropical zones towards the equator. Similarly, wind movement is caused in other parts of earth.

Movement of Air Because of Uneven Heating of Land and Water:

Sea Breeze: In coastal areas, the land warms up faster than the ocean surface. Warm air from the land rises up and creates an area of low pressure near the ground. The low pressure zone is filled in by cooler air from the ocean surface. This gives rise to the sea breeze.

Land Breeze: During night, the land cools down faster than the ocean surface. The warmer air from the ocean surface rises up and creates an area of low pressure near the surface. This is filled in by cooler air from the land. This gives rise to the land breeze.

Monsoon: The flow of moist air from ocean towards land in summer is called Monsoon or Monsoon wind. The word Monsoon came from Arabic word ‘mausim’, which means weather. The term ‘Monsoon’ had traditionally been used to describe the typical climate of the Indian Peninsula during the rainy season. Now-a-days, the term ‘Monsoon’ is being also used to describe the similar climate in other parts of the world.

Monsoon winds carry water vapour which falls over the land in the form of rain after cooling down. In India, the harvest depends on the monsoon wind because it is the major factor towards bringing rainfall in India.

Thunderstorm: Many a times, rain is associated with lightning. Rain with lightning is called thunderstorm. This happens mostly in the summer. Thunderstorm occurs frequently in hot and humid tropical areas, such as India.

In summer, the air rises up along with lot of moisture. After rising up to a certain height water vapour cools down and starts coming down in the form of water droplets. The swift drifting of water droplets creates electricity among clouds. This manifests in the form of lighting and sound. This is known as thunderstorm.

CYCLONE: Fast moving air towards a centre; usually with heavy rain; is known as cyclone. Wind direction, wind speed, humidity and temperature together create cyclone.

When water vapour in the clouds cools down it releases heat. This heat warms the air around the clouds. The warm air rises up and creates a low pressure zone. This low pressure zone is quickly filled in by cooler air from the surrounding. This creates a system in which the centre is having very low pressure and is surrounded by wind moving around it. The wind from the surroundings moves in a circular fashion towards the centre and gives rise to cyclone.

The centre of the cyclone is called ‘eye’. A cyclone may be 10 to 15 km high. It is a rotating mass of air. The diameter of eye may be vary from 10 to 30 km. Eye of a cyclone is a calm area, but around the eye air may move with high speed such as 150 to 250 km/h.

Destruction caused by Cyclone: A strong cyclone can be very destructive.

Since cyclone is accompanied with high speed wind, it can damage houses, telephone poles, electric poles and uproot trees.

Strong wind of the cyclone may push the sea water towards the sea shore in the form of high wave. These high waves may damage houses and push water to low land which may be accompanied with loss of life and properties.

Being the area of very low pressure, eye of cyclone lifts water in the centre. This may cause the rise of water up to 3 to 15 metre high. This appears like a water wall. This water wall; when pushed towards seashore; can inundate a large area, which can cause the loss of live and property.

In India, the eastern coastal region is more vulnerable to cyclones; in terms of intensity and frequency of cyclones, compared to the western coast.

Cyclone is known by different names in different countries. Cyclone is known as HURRICANE in the American continent. It is known as TYPHOON in Philippines and Japan.

TORNADOES: Tornadoes are the very fast moving dark cloud in the shape of a funnel. The speed of violent tornadoes may be up to 300km. Tornadoes are as destructive as cyclone. Tornadoes may form within cyclones.

ANEMOMETER: An instrument which measures the speed of wind.

Effective Safety Measures:

(1) Safety services towards cyclone and other disaster by Government and other agencies:

• Cyclone forecast and warning services: With the advances in technology, cyclone can be forecast in about 24 to 48 hours in advance. This becomes possible because of satellites and computers. When a cyclone is nearer to the coastline, the cyclone warning is forecasted almost at every half an hour.
• Rapid communication to the Government and concerned people: Communication about the cyclone is given quickly to the Government and the people so that proper safety measures and rescue operations can be carried out.
• Construction of cyclone shelters in the cyclone prone area.
• Shifting the people quickly to a safer place.

(2) Action on the part of people:

• Pay attention towards warning broadcasts from time to time.
• In case of a cyclone warning, stock necessary food items and medicines.
• If possible, move to a safer place.
• Fishermen should not venture into the sea during a cyclone warning.
• Cooperate with others in the community.
• Help the rescue team.

Important Points:

• Wind: Moving air is called wind.
• Air exerts pressure.
• Air expands on heating.
• Warm air is lighter and rises up.
• Air moves from high pressure to low pressure.
• Air Current: Movement of air from high pressure zone to low pressure zone creates air current.
• Uneven heating on land creates air current.
• Air moves from 0-30⁰ north and from 0-30⁰ south towards equator.
• Land gets heated as well as loses heat faster than water.
• Monsoon: The flow of air from ocean towards land in summer is called Monsoon or Monsoon wind.
• Monsoon winds carry vapour which falls over the land in the form of rain after cooling down.
• In India harvest is depend on monsoon wind, which brings rain.
• Thunderstorm: Rain with lightning is called thunderstorm. This happens mostly in the summer.
• Thunderstorm occurs frequently in hot and humid tropical areas, such as India.
• Cyclone: Fast moving air towards a circle usually with heavy rain is known as cyclone.
• Wind direction, wind speed, humidity and temperature together creates cyclone.
• Eye: Centre of cyclone is known as eye.
• Tornadoes: Tornadoes are the very fast moving dark cloud in the shape of funnel. Tornadoes may form within cyclones.
• The speed of violent tornadoes may be up to 300km.
• Tornadoes are as destructive as cyclone.
• Anemometer: An instrument which measures the speed of wind.

 

 

Wind, Storm and Cyclone

Air: Air is a mixture of gases.

Wind: Moving air is called wind.

Air exerts pressure: The fact that Air exerts pressure can be understood by many examples.

Tube of bicycle gets inflated when air is filled in it. This happens because air exerts pressure.

It is difficult to move the bicycle against the direction of wind. Similarly, a sailor feels it difficult to sail his boat against the direction of wind. This happens because air exerts pressure.

When boiled water is filled in a tin can and its mouth is closed with the lid; followed by cold water being poured over it, the can gets distorted. This happens because air inside the can gets condensed and creates low pressure. The higher pressure from outside distorts the shape of the can.

You can fly a kite because air exerts pressure from the rear portion of the kite.

Aeroplane can fly because air exerts pressure.

Birds can fly because air exerts pressure.

High speed wind creates area of low air pressure:

Thatched roof is blown off because of high speed wind. This happens because high speed wind creates an area of low pressure. Due to this, the thatched roof is sucked up and finally gets blown away. Thus, increase in wind speed is associated by decrease in air pressure.

Movement of air:

Air moves from high pressure zone to low pressure zone of air. Air; from high pressure zone; rushes towards the low pressure zone; to fill the gap. Thus, greater is the pressure difference greater will be the speed of wind and vice-versa.

Cause of Wind Movement:

Pressure difference in the air is cause by differential heating. Warm air rises up because it becomes lighter. This creates an area of low pressure below the rising air. The area of low pressure is quickly filled in by cooler air from around. That is how the wind movement is created on the earth. Thus differential heating of air creates pressure difference; which makes the wind movement.

Movement of Air Because of Uneven Heating on Earth:

Movement of Air in Equatorial Region: The Equatorial region gets the highest amount of sunshine throughout the year. Due to this, the air near the equatorial region gets heated. The warm air rises up and creates an area of low pressure. The cooler air; from the higher latitudes; rushes towards the equator to fill the gap. This results in the wind movement from tropical zones towards the equator. Similarly, wind movement is caused in other parts of earth.

Movement of Air Because of Uneven Heating of Land and Water:

Sea Breeze: In coastal areas, the land warms up faster than the ocean surface. Warm air from the land rises up and creates an area of low pressure near the ground. The low pressure zone is filled in by cooler air from the ocean surface. This gives rise to the sea breeze.

Land Breeze: During night, the land cools down faster than the ocean surface. The warmer air from the ocean surface rises up and creates an area of low pressure near the surface. This is filled in by cooler air from the land. This gives rise to the land breeze.

Monsoon: The flow of moist air from ocean towards land in summer is called Monsoon or Monsoon wind. The word Monsoon came from Arabic word ‘mausim’, which means weather. The term ‘Monsoon’ had traditionally been used to describe the typical climate of the Indian Peninsula during the rainy season. Now-a-days, the term ‘Monsoon’ is being also used to describe the similar climate in other parts of the world.

Monsoon winds carry water vapour which falls over the land in the form of rain after cooling down. In India, the harvest depends on the monsoon wind because it is the major factor towards bringing rainfall in India.

Thunderstorm: Many a times, rain is associated with lightning. Rain with lightning is called thunderstorm. This happens mostly in the summer. Thunderstorm occurs frequently in hot and humid tropical areas, such as India.

In summer, the air rises up along with lot of moisture. After rising up to a certain height water vapour cools down and starts coming down in the form of water droplets. The swift drifting of water droplets creates electricity among clouds. This manifests in the form of lighting and sound. This is known as thunderstorm.

CYCLONE: Fast moving air towards a centre; usually with heavy rain; is known as cyclone. Wind direction, wind speed, humidity and temperature together create cyclone.

When water vapour in the clouds cools down it releases heat. This heat warms the air around the clouds. The warm air rises up and creates a low pressure zone. This low pressure zone is quickly filled in by cooler air from the surrounding. This creates a system in which the centre is having very low pressure and is surrounded by wind moving around it. The wind from the surroundings moves in a circular fashion towards the centre and gives rise to cyclone.

The centre of the cyclone is called ‘eye’. A cyclone may be 10 to 15 km high. It is a rotating mass of air. The diameter of eye may be vary from 10 to 30 km. Eye of a cyclone is a calm area, but around the eye air may move with high speed such as 150 to 250 km/h.

Destruction caused by Cyclone: A strong cyclone can be very destructive.

Since cyclone is accompanied with high speed wind, it can damage houses, telephone poles, electric poles and uproot trees.

Strong wind of the cyclone may push the sea water towards the sea shore in the form of high wave. These high waves may damage houses and push water to low land which may be accompanied with loss of life and properties.

Being the area of very low pressure, eye of cyclone lifts water in the centre. This may cause the rise of water up to 3 to 15 metre high. This appears like a water wall. This water wall; when pushed towards seashore; can inundate a large area, which can cause the loss of live and property.

In India, the eastern coastal region is more vulnerable to cyclones; in terms of intensity and frequency of cyclones, compared to the western coast.

Cyclone is known by different names in different countries. Cyclone is known as HURRICANE in the American continent. It is known as TYPHOON in Philippines and Japan.

TORNADOES: Tornadoes are the very fast moving dark cloud in the shape of a funnel. The speed of violent tornadoes may be up to 300km. Tornadoes are as destructive as cyclone. Tornadoes may form within cyclones.

ANEMOMETER: An instrument which measures the speed of wind.

Effective Safety Measures:

(1) Safety services towards cyclone and other disaster by Government and other agencies:

• Cyclone forecast and warning services: With the advances in technology, cyclone can be forecast in about 24 to 48 hours in advance. This becomes possible because of satellites and computers. When a cyclone is nearer to the coastline, the cyclone warning is forecasted almost at every half an hour.
• Rapid communication to the Government and concerned people: Communication about the cyclone is given quickly to the Government and the people so that proper safety measures and rescue operations can be carried out.
• Construction of cyclone shelters in the cyclone prone area.
• Shifting the people quickly to a safer place.

(2) Action on the part of people:

• Pay attention towards warning broadcasts from time to time.
• In case of a cyclone warning, stock necessary food items and medicines.
• If possible, move to a safer place.
• Fishermen should not venture into the sea during a cyclone warning.
• Cooperate with others in the community.
• Help the rescue team.

Important Points:

• Wind: Moving air is called wind.
• Air exerts pressure.
• Air expands on heating.
• Warm air is lighter and rises up.
• Air moves from high pressure to low pressure.
• Air Current: Movement of air from high pressure zone to low pressure zone creates air current.
• Uneven heating on land creates air current.
• Air moves from 0-30⁰ north and from 0-30⁰ south towards equator.
• Land gets heated as well as loses heat faster than water.
• Monsoon: The flow of air from ocean towards land in summer is called Monsoon or Monsoon wind.
• Monsoon winds carry vapour which falls over the land in the form of rain after cooling down.
• In India harvest is depend on monsoon wind, which brings rain.
• Thunderstorm: Rain with lightning is called thunderstorm. This happens mostly in the summer.
• Thunderstorm occurs frequently in hot and humid tropical areas, such as India.
• Cyclone: Fast moving air towards a circle usually with heavy rain is known as cyclone.
• Wind direction, wind speed, humidity and temperature together creates cyclone.
• Eye: Centre of cyclone is known as eye.
• Tornadoes: Tornadoes are the very fast moving dark cloud in the shape of funnel. Tornadoes may form within cyclones.
• The speed of violent tornadoes may be up to 300km.
• Tornadoes are as destructive as cyclone.
• Anemometer: An instrument which measures the speed of wind.

Wind, Strom And Cyclone

NCERT Questions And Answer:

Question: 1. Fill the missing word in the blank spaces in the following statements:

(a) Wind is——————air.

Answer: Moving

(b) Winds are generated due to——————heating on the earth.

Answer: Uneven

(c) Near the earth’s surface __________air rises up whereas ___________ air comes down.

Answer: Warm, cold

(d) Air moves from a region of ——— pressure to a region of——— pressure.

Answer: High, Low

Question: 2. Suggest two methods to find out wind direction at a given place.

Answer: Two methods to find the direction of wind:

(a) Take a handful of sand or dust. Release it slowly from a height and observe the direction in which the falling sand is moving. This will show the direction of wind.

(b) Tie a thin plastic sheet or cloth with a stick. Keep the stick at a place which is as high as possible. The direction in which the cloth sways shows the direction of wind.

Qeustion: 3. State two experiences that made you think that air exerts pressure (other than those given in the text).

Answer: I have seen paratroopers jumping from aeroplanes. The parachute helps them in reaching the ground safely. The air pressure reduces the speed of the parachute and the paratrooper lands without getting injured.

Question: 4. You want to buy a house. Would you like to buy a house having windows but no ventilators? Explain your answer.

Answer: A house should have ventilators along with windows. The warm air would rise up and exit from the ventilators. The cooler air would rush in through the windows. This will help in making the rooms comfortable. A room without ventilators shall not be cooled as efficiently as one with ventilators.

Question: 5. Explain why holes are made in hanging banners and hoardings.

Answer: Banners and hoardings are usually very large. The air pressure; because of the moving air; can blow away the banners. Holes are made in banners and hoardings so that the wind can move through them. This helps in reducing the impact of air pressure on the hoardings and thus they are not get blown away.

Question: 6. How will you help your neighbours in case cyclone approaches your village/town?

Answer: I will take following steps to help my neighbours in case of cyclone:

• I will help people to reach to a safer place.
• I will organize a community kitchen during the stress period.
• I will provide first aid to injured people.
• I will also arrange for safe drinking water for the people.

Question: 7. What planning is required in advance to deal with the situation created by a cyclone?

Answer: Following planning is required to deal with the situation created by a cyclone:

• Proper shelters should be built by the government agencies so that people can be accommodated in them.
• Alternate arrangements of seamless communication among rescue agencies should be made.
• Proper stock of emergency medicines should be kept.
• Proper arrangements of safe drinking water should be made.
• Government should chalk out a rehabilitation plan for those affected by cyclone.

Question: 8. Which one of the following place is unlikely to be affected by a cyclone.

(i) Chennai (ii) Mangaluru (Mangalore) (iii) Amritsar (iv) Puri

Answer: (iv) Puri

Question: 9. Which of the statements given below is correct?

1. In winter the winds flow from the land to the ocean.
2. In summer the winds flow from the land towards the ocean.
3. A cyclone is formed by a very high-pressure system with very high-speed winds revolving around it.
4. The coastline of India is not vulnerable to cyclones.

Answer: (i) In winter the winds flow from the land to the ocean

 

 

 

 

Soil

Soil – Mixture of rocks particles, sand and humus is known as soil. Soil supports the growth of plants by holding their roots and supplying water to them.

Formation of soil – Soil is formed by weathering. Weathering is the process of breaking down of rocks by the action of wind, water and climate. Formation of even one inch of soil takes many years.

Composition of Soil: Soil contains humus, water, clay, sand and gravel.

Humus: The decaying dead matters in soil are called humus. Humus makes the soil fertile and provides nutrients to the plants.

Soil Profile: Different vertical layers of soil are known as soil profile. The feel (texture), colour and chemical compositions of soil are different in each layer.

                          

Horizons: Layers of soil are referred as horizons. Horizons of soil are categorized into four types: A-horizon, B-horizon, C-horizon and Bedrock.

A horizon: Top layer of soil is called A-horizon. It is also called top-soil. A-horizon is generally dark in colour. It is rich in humus. A horizon is generally soft and porous. It retains more water.

Roots of small plants are entirely embedded in topsoil. Topsoil also provides shelter to many living organism, such as worm, insect, moles, rats, snakes, etc.

B-horizon: The next layer of the soil from top is known as B-horizon. This layer is harder and more compact than the top soil. This is generally known as the middle layer of soil. This is less rich in humus but contains most of the minerals present in the soil.

C-horizon: The third layer of soil is known as C-horizon. C-horizon is made of small lumps of rocks with cracks and crevices.

Bedrock: The layer below the C-horizon is known as bedrock. Bedrock is composed of rocks and is hard to dig with spades.

Type of Soil: Size of particles of soil is very important for the properties of soil. So, soils are categorized mainly in three types based on the proportion of size of particles. These are Sandy Soil, Clayey Soil and Loamy Soil.

Sandy Soil: Particles of sandy soil are larger in size. Because of larger in size, sand particles cannot fit close together and hence there is enough space among them. These spaces are filled with air. Water drains quickly through sandy soil. So, sandy soil is called well aerated, light and dry.

Sandy soil is not fit for vegetation as it does not retain water. However, millets can be grown on sandy soil.

Clayey Sol: Particles of clayey soil are very small in size. This makes the particles of clayey soil packed tightly. There is very little space among the particles. Water does not drain quickly through clayey soil because of less space among particles. So, clayey soil is not well aerated and retains more water.

Clayey soil is used in making of toys. Clayey soil is good for growing paddy.

Loamy Soil: Particles of loamy soil are smaller than sand and larger than clay. Loamy soil is the mixture of sandy soil, clayey soil and silt. Silt is the deposit in river beds.

Loamy soil has right water holding capacity and is well aerated. This is considered as the best soil for the growth of plants.

Properties of Soil:

Percolation Rate of Water: Amount of water drained through water in unit time is known as percolation rate of water in soil. Percolation rate of water can be calculated using the formula given here.

The percolation rate of water in sandy soil is fastest and in clayey soil is slowest.

Moisture present in soil: Amount of water present in soil is called moisture present in soil. The amount of moisture present in clayey soil is highest and that in sandy soil is lowest.

Absorption of water: Different soil absorbs different amount of water. Clayey soil absorbs the highest amount of water because of its higher water retention capacity. On the other hand, sandy soil absorbs the least amount of water because of its lower water retention capacity.

Soil and Crop: Different types of soil are found are found at different places. A particular soil type may not be suitable for certain types of crop. That’s why different types of crop are grown in different parts of the world.

Sandy soil: Sandy soil is not fit for any crop as it does not retain water. However, some thorns and bushes do grow on sandy soil. Millets can be grown on sandy soil.

Clayey Soil: Clayey soil is best suited for paddy, as it can retain water for a longer time. This is also suitable for wheat and grams.

Loamy Soil: Loamy soil is considered the best for almost all types of crops. It is suitable for lentils and other pulses.

Sandy Loam: Sandy loam soil is suitable for the growth of cotton plants as it can easily drain water and is well aerated.

Soil Erosion: Removal of topsoil by weathering agents; such as wind, water and ice is known as soil erosion. Soil erosion affects the fertility of soil, as humus present in the soil is eroded along with soil. It is important to prevent the soil erosion.

Preventive measures for soil erosion:

Deforestation should be prevented at all cost to prevent soil erosion.

Shelter belt plantation of trees is good for preventing soil erosion.

Terrace farming in hilly areas is effective in preventing soil erosion.

 Soil - NCERT Question And Answer

Tick the most suitable answer in questions 1 and 2.

Question: 1. In addition to the rock particles, the soil contains

(i) air and water

(ii) water and plants

(iii) minerals, organic matter, air and water

(iv) water, air and plants

Answer: (iii) minerals organic matter, air and water

Question: 2. The water holding capacity is the highest in

(i) sandy soil

(ii) clayey soil

(iii) loamy soil

(iv) mixture of sand and loam

Answer: (ii) Clayey soil

Question: 3. Match the items in Column I with those in Column II:

Question: 4. Explain how soil is formed.

Answer: Soil is formed by the process of weathering. The breaking down of rocks because of the action of wind, rain, ice, etc. is called weathering.

Question: 5. How is clayey soil useful for crops?

Answer: Clayey soil can retain much water and consequently contains lot of moisture even in summer. That’s why it is most useful for crops like paddy which requires lot of water. Clayey soil is useful for wheat also.

Question: 6. List the differences between clayey soil and sandy soil.

Answer:

Question: 7. Sketch the cross section of soil and label the various layers.

Answer:

Question: 8. Razia conducted an experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.

Answer:

Given, Time = 40 minute

VolumeVolume of water = 200 ml

Question: 9. Explain how soil pollution and soil erosion could be prevented.

Answer: Soil pollution and soil erosion could be prevented using following:

Plantation

Better farming method, like crop rotation and mixed farming

Use of manure instead of synthetic fertilization.

Use of natural pesticides.

Avoid dumping non-biodegradable items in soil.

Terrace farming in hilly areas.

Question: 10. Solve the following crossword puzzle with the clues given:

Across

2. Plantation prevents it.

5. Use should be banned to avoid soil pollution.

6. Type of soil used for making pottery.

7. Living organism in the soil.

Down

1. In desert soil erosion occurs through.

3. Clay and loam are suitable for cereals like.

4. This type of soil can hold very little water.

5. Collective name for layers of soil.

Answer:

 

Respiration in Organism

RESPIRATION: The biological process in which food is utilized to produce energy is called respiration. Respiration is necessary for survival for the living beings. A living being cannot survive even for a few seconds, without respiration. During respiration, it is mainly the carbohydrate which is oxidized to produce energy. This can be shown by following equation:

SITE OF RESPIRATION: Respiration happens inside the cells. As respiration happens inside the cell, it is also called cellular respiration. A cell organelle; called mitochondria; is the site of cellular respiration.

TYPES OF RESPIRATION:

• AEROBIC RESPIRATION: Aerobic respiration takes place in the presence of oxygen. Carbon dioxide and water are the end products of aerobic respiration. Aerobic respiration happens in most of the organisms.

• ANAEROBIC RESPIRATION: Anaerobic respiration takes place in the absence of oxygen. Anaerobic respiration usually happens in most of the microbes. Alcohol and carbon dioxide are formed at the end of anaerobic respiration. In some cases, lactic acid is formed at the end of anaerobic respiration.

• Anaerobic respiration also happens in our muscle cells. When someone runs or walks too fast, one may feel a throbbing pain in calf muscles. This happens because of deposition of lactic acid; produced by anaerobic respiration. Once the person takes rest for some time, the pain goes away.

Review Questions

1. What is respiration?

Answer: Respiration is a biological process in which food is utilized to produce energy.
 

2. What is the end product of respiration in most of the organisms?

Answer: Carbon dioxide and water 

3. What is the end product of anaerobic respiration in muscle cells?

Answer: Lactic Acid

BREATHING: The process of taking in and giving out air; for respiration; is called breathing. Breathing involves two man steps, viz. inhalation and exhalation. During inhalation, we breathe in air which is rich in oxygen. During exhalation, we breathe out air which is rich in carbon dioxide.

RATE OF BREATHING: When we are doing normal activities, the rate of breathing is normal. The rate of breathing increases when we do strenuous physical works; such as running, swimming, jogging, etc. the rate of breathing decreases when we take rest or when we are sleeping.

PROCESS OF BREATHING: The breathing is controlled by the movement of diaphragm. Diaphragm is a membrane which is between the chest and abdomen. The movement of diaphragm is controlled by a group of muscles; called intecostalis muscles.

When the diaphragm moves down, the ribcage expands. This leads to the expansion inside the lungs. As a result, the air moves into the lungs. This process is called inspiration or inhalation.

           

When the diaphragm moves up, the ribcage contracts. This leads to contraction of the lungs. As a result, the air moves out of the lungs. This process is called expiration or exhalation.

To show that carbon dioxide is released during exhalation:

Carbon dioxide reacts with limewater to make calcium carbonate. This property is utilized to show the evolution of carbon dioxide during respiration. For this, take a test tube and pour some limewater in it. Dip a drinking straw in the test tube. Blow air in the limewater through the drinking straw. It is observed that the limewater turns milky. This shows that carbon dioxide is released during exhalation.

Review Questions:

1. What is breathing?

Answer: The process of taking in and giving out air; for respiration; is called breathing.

2. What is the respiratory organ in humans?

Answer: Lungs 

3. Which membrane controls the movement of lungs?

Answer: Diaphragm

BREATHING IN OTHER ANIMALS

Animals, which belong to amphibia, reptilian, aves and mammalia, use the lungs for breathing. Amphibians breathe through their skin, when they are in water. Smaller animals have different organs for breathing.

BREATHING IN FISH: Fish have a pair of gills. The breathe air; dissolved in water; through gills.

BREATHING IN COCKROACH: Cockroach and other insects breathe through spiracles and tracheae. There is a network of hollow tubes running through the body of an insect. These hollow tubes are called trachea. Each trachea opens on the body surface in the form of very small pore. These pores are called spiracles.

BREATHING IN EARTHWORM: Earthworms breathe through their skin. The skin of earthworm always remains moist, which helps in breathing.

Breathing in Unicellular Animals: Unicellular animals breathe through the cell membrane.

BREATHING IN PLANTS: Plants can be of various sizes. Developing respiratory organs could not be a fruitful solution for plants; because of their unlimited growth. Each plant part breathes through its external layer of cells. Roots breathe through root hairs. Stems breathe through epidermis. Leaves have numerous small pores; called stomata; for breathing.

Review Questions:

1. What is the respiratory organ in fish? 
   Answer: Gills 
2. What is the respiratory organ in cockroach?

Answer: Spiracles and tracheae 

3. Which organ is used by a frog for breathing under water?

Answer: Skin

Respiration in Organism

Question: 1 - Why does an athlete breathe faster and deeper than usual after finishing the race?

Answer: When the athlete runs in the race, his body needs more oxygen. His rate of breathing increases so that more oxygen can be supplied to the body. This is the reason, an athlete needs to breathe faster and deeper than usual; after finishing the race.

Question: 2 - List the similarities and differences between aerobic and anaerobic respiration.

Answer: The similarities and differences between aerobic and anaerobic respiration are as follows:

Similarities: Food is oxidized in both cases and energy is released.

Differences: Carbon dioxide and water are the end products of aerobic respiration, while alcohol or lactic acid is the end product of anaerobic respiration. Aerobic respiration is more efficient than anaerobic respiration.

Question: 3 - Why do we often sneeze when we inhale a lot of dust-laden air?

Answer: When dust particles enter our nostril, it triggers a message to the brain. The brain instructs the nasal chamber to initiate sneezing. This is a method to remove the unwanted dust particles from the nostrils. Sneezing is a type of defense mechanism used by our body.

Question: 4 - Take three test-tubes. Fill each of them with water. Label them A, B and C. Keep a snail in test-tube A, a water plant in test-tube B and in C, keep snail and plant both. Which test-tube would have the highest concentration of CO2?

Answer: The test tube A will have the highest concentration of carbon dioxide. The carbon dioxide comes because of respiration by the snail. In test tubes B and C; a part of the carbon dioxide is utilized by the plant for photosynthesis and hence there is less concentration of carbon dioxide.

Question: 5 - Tick the correct answer:

  (a) In cockroaches, air enters the body through

1.  lungs
2.  gills
3.  spiracles
4.  skin

Answer: (iii) Spiracles

  (b) During heavy exercise, we get cramps in the legs due to the accumulation of

1. carbon dioxide
2.  lactic acid
3.  alcohol
4.  water

Answer: (ii) Lactic acid

  (c)  Normal range of breathing rate per minute in an average adult person at rest is

1. 9–12
2.  15–18
3. 21–24
4. 30–33

Answer: (ii) 15 – 18

   (d) During exhalation, the ribs

1. move outwards
2. move downwards
3.  move upwards
4. do not move at all

Answer: (ii) Move downwards

Question: 6 - Match the items in Column I with those in Column II:

Question: 7 - Mark ‘T’ if the statement is true and ‘F’ if it is false:

1. During heavy exercise the breathing rate of a person slows down. (F)
2.  Plants carry out photosynthesis only during the day and respiration only at night. (F)
3.  Frogs breathe through their skins as well as their lungs. (T)
4.  The fishes have lungs for respiration. (F)
5. The size of the chest cavity increases during inhalation. (T)

Question: 8 - Given below is a square of letters in which are hidden different words related to respiration in organisms. These words may be present in any direction— upwards, downwards, or along the diagonals. Find the words for your respiratory system. Clues about those words are given below the square.

Answer:

1. The air tubes of insects
2.  Skeletal structures surrounding chest cavity
3. Muscular floor of chest cavity
4. Tiny pores on the surface of leaf
5. Small openings on the sides of the body of an insect
6. The respiratory organs of human beings
7. The openings through which we inhale
8. An anaerobic organism
9. An organism with tracheal system

Question: 9 - The mountaineers carry oxygen with them because:

1. At an altitude of more than 5 km there is no air.
2. The amount of air available to a person is less than that available on the ground.
3. The temperature of air is higher than that on the ground.
4. The pressure of air is higher than that on the ground.

Answer: (b) The amount of air available to a person is less than that available on the ground

Transportation in Animals and Plants

Transportation in Unicellular Organisms: In unicellular organisms, transportation of substances happens through diffusion and osmosis. Gases move in and out of the cell by diffusion. Other substances move by osmosis.

DIFFUSION: Random motion of particles in order to attain equilibrium of concentration is called diffusion. Diffusion can be observed in many aspects of day to day life. The aroma of food comes from the kitchen because of diffusion. A pleasant smell of flowers comes because of diffusion. Bad odour of garbage comes because of diffusion.

OSMOSIS: Movement of water through a semi-permeable membrane from high water concentration to low water concentration is called osmosis. Osmosis is a type of diffusion. Cell membrane is a semi-permeable membrane. Substances move across the cell membrane because of osmosis. Seeds swell up; when soaked in water; because of osmosis.

Review Questions

1. What is diffusion? 
   Answer: Random movement of particles in order to attain equilibrium of concentration is called diffusion. 
2. What is osmosis? 
   Answer: Movement of water through semi-permeable membrane from high water concentration to low water concentration is called osmosis.

CIRCULATORY SYSTEM IN HUMANS

Diffusion and osmosis can result in transportation of substances to short distances only. For bigger and complex organisms, there is a need of a more complex system for transportation of substances.

The circulatory system in humans is composed of three main components, viz. heart, blood vessels and blood.

BLOOD

Blood is a type of tissue which is responsible for transportation of substances. Blood works as the carrier of various substances. Following are the main components of blood.

Blood Cells, Platelets and Plasma

PLASMA: Plasma makes the liquid part of the blood. It makes the largest part of the blood. Plasma is pale in colour.

BLOOD CELLS: There are two main kinds of blood cells in the human blood, viz. Red Blood Cells and White Blood Cells.

1. Red Blood Cells or Red Blood Corpuscles (RBC): These are in the shape of discs. They contain a pigment; called haemoglobin. Haemobglobin binds with oxygen and thus is mainly responsible for transportation of oxygen in the body. Haemoglobin also transports some amount of carbon dioxide. 
2. White Blood Cells or White Blood Corpuscles (WBC): These are present in various shapes. WBCs engulf foreign particles and harmful microbes. Thus, WBCs help in fighting the diseases. WBCs make the immune system of the body.

PLATELETS: Platelets are responsible for clotting or coagulation of blood. In case of an injury, the blood clots after some time. This prevents excess loss of blood. Clotting of blood is a defense mechanism in the body.

BLOOD VESSELS:

Blood vessels are of three main types, viz. arteries, veins and capillaries.

ARTERIES: Arteries are made of thicker walls. Arteries carry oxygenated blood from the heart to different organs. Pulmonary artery is an exception, because it carries deoxygenated blood from the heart to the lungs.

VEINS: Veins are made of thinner walls. Veins carry deoxygenated blood from different organs to the heart. Pulmonary vein is an exception, because it carries oxygenated blood from the lungs to the heart.

CAPILLARIES: These fine branches of arteries and veins.

Review Questions

1. What is blood? 
   Answer: Blood is a type of tissue which is responsible for transportation of substances. 
2. What is the role of RBCs? 
   Answer: Transportation of oxygen.

HEART

: 

The heart is a small muscular organ which is responsible for pumping the blood. The human heart has four chambers, viz. the right auricle, the right ventricle, the left auricle and the left ventricle. The upper chambers are called auricle or atrium. The lower chambers are called ventricle. The following flow chart shows the movement of blood through the heart (the blue colour shows deoxygenated blood and the red colour shows oxygenated blood):

From the body → Right Auricle → Right Ventricle → Pulmonary Artery → Lungs → Pulmonary Vein → Left Auricle → Left Ventricle → To the body

HEART BEAT: While pumping the blood, different chambers of the heart contract and relax in turns. The contraction and relaxation of different chambers produces a thumping sound. This sound can be heard as heart beat. One heart beat indicates one cycle of pumping action by all the four chambers. The heart of a normal human beats for 72 times in a minute. The heart pumps about 70 mL blood in one beat. This means that heart pumps a whopping 5 liter blood in a minute.

PULSE: A certain locations in the body, a pulse; similar to heart beat; can be felt. This happens because of blood rushing in with every heart beat. The pulse rate is same as the heart rate. Pulse can be felt near the wrist, neck, ankle, etc.

STETHOSCOPE: This is a device which is used by doctors to listen to the heart beat and pulse. Stethoscope is composed of a long rubber tube, two ear pieces and a diaphragm.

Review Questions

1. Which organ in the human body is responsible for pumping of blood? 
   Answer: heart 
2.  Which type of blood is carried by arteries? 
   Answer: Oxygenated Blood

EXCRETION

Various activities always go on inside the body of a living being. These activities are collectively called metabolism. Many harmful substances are created during metabolic activities. These substances can prove lethal if not removed from the body in time. Removal of waste from the body is called excretion.

Excretory System

The human excretory system is composed of a pair of kidneys, two tubes; called ureter and a urinary bladder.

KIDNEY: Kidneys are bean-shaped. They work like filters. Blood; laden with waste materials enters the kidney. The waste is filtered from the blood and the purified blood is sent to the normal circulation. The waste; along with water; is transferred to the urinary bladder through the ureters. The content of the ureter is called urine. Urine contains 95% water, 2.5% urea and 2.5% other wastes. Urine is expelled out from time to time.

Type of waste and mode of excretion: Protein is made up of nitrogen. Metabolism of protein creates nitrogenous wastes in the body. The nitrogenous waste is the main waste in animals. The nitrogenous waste takes different forms in different animals. These are; ammonia, urea and uric acid. Based on the type of nitrogenous waste, animals can be divided into following categories:

AMMONOTELIC: Ammonia is the main nitrogenous waste in these animals. Lot of water is required for removal of ammonia. Ammonotelism is present in aquatic animals, e.g. fish, frogs, etc.

UREOTELISM: Urea is the main nitrogenous waste in these animals. Less water is required for removal of urea. Ureotelism is present in mammals.

URECOTELISM: Uric acid is the main nitrogenous waste in these animals. Removal of uric acid requires negligible amount of water. Urecotelism is present in reptiles and aves.

Note: Some of the wastes are removed along with sweat. Carbon dioxide is an important waste which is removed through the lungs.

Review Questions

1. Which is the main excretory organ in humans? 
   Answer: Kidneys 
2. Which is the main excretory product in humans? 
   Answer: Urea

TRANSPORTATION IN PLANTS:

For transportation in plants, there are two main tissues, viz. xylem and phloem. These are composed of narrow tube-like structures. Xylem is responsible for transport of water, while phloem is responsible for transport of food.

Transport of Water: Plants take water from soil. Following are the main steps in transport of water in plants.

In Roots: From soil, the water enters the root hairs because of osmosis. From root hairs water enters further because of root pressure.

IN STEM: Various factors are at play during transportation of water through xylem in stems. The transport of water through xylem is also called ‘Ascent of Sap’.

1. Root pressure is responsible for the rise of water to some height.
2. Capillary action pushes the water further up. The rise of liquid in a very narrow tube is called capillary action. Capillary action happens because of very small diameter of the tube. 
3. Adhesion Cohesion: Water molecules stick to each other and make a continuous column inside the xylem tubes. 
4.  Transpiration pull: There are numerous small pores on the surface of leaves. These pores are called stomata. Water vapour is continuously removed through stomata during daytime. Removal of water vapour in plants is called transpiration. This creates a pull in the underlying xylem tissues. The pull is called transpiration pull. Transpiration pull creates a suction effect on the water column inside the xylem.

TRANSPORT OF FOOD: Food is prepared in leaves and needs to be transported to different plant parts for use and for storage. The transport of food takes place through phloem. Some biological force is used in transport of food in plants.

Review Questions

1. Transport of water and minerals in plants happens through which tissues? 
   Answer: Xylem 
2.  Transport of food in plants happens through which tissues? 
   Answer: Phloem

Transportation in Animals and Plants

Question: 1 - Match structures given in Column I with functions given in Column II.

2 - Fill in the blanks.

(i) The blood from the heart is transported to all parts of the body by the ………….

Answer: Heart

(ii) Haemoglobin is present in ………….cells.

Answer: Red Blood

(iii) Arteries and veins are joined by a network of …………

Answer: Capillaries

(iv) The rhythmic expansion and contraction of the heart is called…………..

Answer: Heart Beat

(v) The main excretory product in human beings is ………………

Answer: Urea

(vi) Sweat contains water and …………….

Answer: Waste products

(vii) Kidneys eliminate the waste materials in the liquid form called …………..

Answer: Urine

(viii) Water reaches great heights in the trees because of suction pull caused by ………..

Answer: Transpiration

Question: 3 - Choose the correct options:

(a) In plants, water is transported through

(i) Xylem

(ii) Phloem

(iii) Stomata

(iv) Root hair

Answer: (i) Xylem

(b) Water absorption through roots can be increased by keeping the plants

(i) in the shade

(ii) in dim light

(iii) under the fan

(iv) covered with a polythene bag

Answer: (iii) Under the fan

Question: 4 - Why is transport of materials necessary in a plant or in an animal? Explain.

Answer: The cells of plants and animals need various substances to carry out important metabolic activities. Further, many waste products are created during these metabolic activities. Transport of materials is necessary to supply the various substances and to remove the waste products.

Question: 5 - What will happen if there are no platelets in the blood?

Answer: Platelets are responsible for clotting of blood. If there are no platelets, the blood would not clot in case of an injury. This will lead to excess blood loss and finally in death of the person.

Question: 6 - What are stomata? Give two functions of stomata.

Answer: The numerous pores on the surface of leaf are called stomata. Transpiration and exchange of gases (carbon dioxide and oxygen) are some of the functions of stomata.

Question: 7 - Does transpiration serve any useful function in the plants? Explain.

Answer: Transpiration serves important functions in plants. Transpiration creates the transpiration pull; which is responsible for the rise of water to great heights in tall plants and other trees.

Question: 8 - What are the components of blood?

Answer: The main components of blood are: Plasma, Blood Cells and Platelets.

Question: 9 - Why is blood needed by all the parts of a body?

Answer: Blood acts as a carrier of various substances. Every part of the body needs certain substances to perform its functions. Additionally, every part creates some waste products. Blood is needed by all parts of the body so that various substances can be supplied to them and waste can be removed from them.

Question: 10 - What makes the blood look red?

Answer: Blood is red because of the presence of a pigment; called haemoglobin.

Question: 11 - Describe the function of the heart.

Answer: The heart is a pumping organ which pumps the blood. The heart pumps the deoxygenated blood to the lungs; for oxygenation. Moreover, the heart pumps the oxygenated blood to different parts of the body.

Question: 12 - Why is it necessary to excrete waste products?

Answer: Waste products can prove lethal if not removed in time. Hence, it is necessary to excrete the waste products.

Question: 13 - Draw a diagram of the human excretory system and label the various parts

Answer

 

Reproduction In Plants

Reproduction: The process by which a living being produces its offspring is called reproduction.

Types of Reproduction:

1 - Asexual Reproduction: When a single parent is involved in the process, it is called asexual reproduction. Following means of asexual reproduction are used by plants:

(a) Budding: This method is used by unicellular plants; like yeast. Yeast is a fungus and fungi are also known as non-green plants. The yeast cell produces a bud which gets its own nucleus. The bud develops to certain size and detaches from the mother cell to produce the new yeast.

(b)Fragmentation: In some simple plants, the plant body is divided into smaller fragments. Each fragment then develops into a new plant. Example: Spirogyra.

(c) Spore Formation: Special spore-bearing organs are present in some plants; especially in fungi and algae. These are called sporangiophores. The sporangiophore bears spores. The spores germinate to develop a new plant.

(d) Vegetative Propagation: When a new plant is developed by a vegetative part; such as root, stem or leaf; it is known as vegetative propagation. For example: when the tuber of potato is cut into several pieces and each piece bears an ‘eye’; each piece produces a new plant. The stems of moneyplant, rose, mango, etc. can produce new plants when they are inserted in soil. The leaf of bryophyllum produces new plants through its notches.

Review Questions:

(A) Give an example of an organism which reproduces by budding.

Answer: Yeast

(B)How many parents are involved in asexual reproduction?

Answer: Only one

2 - Sexual Reproduction: When two parents are involved in the process, it is called sexual reproduction. Two gametes, viz. male and female gametes, are formed. The fusion of male and female gametes is called fertilization. Zygote is formed after fertilization. The zygote develops into an embryo and finally into a new individual.

Flower: Flower is a special organ of flowering plants (angiosperms) which works as the reproductive system. A flower is composed of four distinct whorls.

(1) The outermost whorl is called calyx. It is composed of green leaf-like structures; called sepals.

(2) The second whorl is called corolla. It is composed of colourful structures; called petals. Petals are colourful so that insects and other animals can be attracted towards them. This is necessary for pollination.

(3) Androecium: The third whorl is called androecium. It is composed of stamens. Stamen has two main parts. The tube-like portion is called filament. The capsule like structure at the top is called anther. The anther produces pollen grains; which are the male gametes.

(4) Gynoecium: The whorl at the center is called gynoecium. It has a swollen base; called ovary and a tube-like structure; called style. The top of the tube is somewhat flattened and is called stigma. Ovary produces the eggs or female gametes.

Review Questions

A -What is the benefit of colourful petals for plants?

Answer: Colourful petals attract insects, birds and other animals. It helps in cross pollination.

B - What is the name of the male gamete in a flowering plant?

Answer: Pollen grain

Pollination: The transfer of pollen grains from anthers to stigma is called pollination. Pollination is of two types, viz. self pollination and cross pollination.

Self Pollination: When anthers of the same flower are transferred to the stigma; it is called self pollination.

Cross Pollination: When anthers from a different flower are transferred to the stigma; it is called cross pollination. The flowers can be on the same plant or on different plants. Cross pollination is the norm in most of the plants. Plants need help from various agents of pollination to carry out cross pollination. Wind, insects, birds and other animals play the role of agent of pollination.

Fertilization: The fusion of the male gamete and the female gamete is called fertilization. When pollen settles on top of the stigma, it germinates to produce a pollen tube. The pollen tube enters the ovary through the style. Male nuclei are transferred to the ovary, through the pollen tube. The cell formed, just after fertilization, is called zygote. Zygote develops into embryo. Each embryo develops into a seed. The seed is an embryo which is enclosed in a protective coat. The ovary gets transformed into fruit.

Dispersal of Seeds: If all the seeds were to germinate near the mother plant, the new plants shall not get adequate resources; like sunlight, air and nutrients. For proper growth of the new plants, it is necessary that they develop away from the mother plant. For this, it is necessary that seeds are spread far and wide. The process of spreading seeds to different places is called dispersal of seeds. Many agents of seed dispersal assist the plants in this process.

Dispersal by Wind: Seeds of some plants are light-weight and some hair-like or wing-like structures are present on them. Such seeds float on air and are thus dispersed by wind. Example: Dandelion, maple, drumstick, etc.

Dispersal by Water: Dispersal by water takes place in some aquatic plants and in some which grow near a water body. Seeds of water lily float and thus dispersed by water. The coconut seed has a tough fibrous covering which has plenty of air inside. This helps the coconut seeds in floating on water.

Dispersal by Animals: Some seeds have spine like structures on them. They get stuck to the fur of animals and thus get spread to different places. Examples; Beggar tick, Xanthium, Urena, etc. Some seeds are swallowed by birds and animals along with fruits. These seeds get dispersed with bird or animal droppings.

Dispersal by Bursting: Some fruits burst open when they mature. The force of bursting is enough to spread the seeds. Examples; Ladyfinger, castor, balsam, etc.

Dispersal by Humans: Human beings also help in dispersal of seeds, especially during farming.

Review Questions:

1- What is pollination?

Answer: Transfer of pollen grains from anther to stigma is called pollination.

2 - Give two examples of seeds which are dispersed by wind.

Answer: Dandelion, maple

Class 7 Plant Reproduction

NCERT Solution

Fill in the blanks:

1.                    Production of new individuals from the vegetative part of parent is called_____________.
Answer: Vegetative propagation

2.        A flower may have either male or female reproductive parts. Such a flower is called_____________.
Answer: Unisexual flower

3.        The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as _____________.
Answer: Pollination

4.        The fusion of male and female gametes is termed as _____________.
Answer: Fertilisation

5.        Seed dispersal takes place by means of _____________, _____________ and _____________.
Answer: Wind, Water, Animal

Answer the following question:

1.                    Describe the different methods of asexual reproduction. Give examples.
Answer: There are following methods of asexual reproduction:

Vegetative Propagation: In this method, the vegetative part of a flowering plant produces a new individual. Example: growth of potato plant from ‘eye’ of potato, growth of new plants from leaf of bryophyllum, etc.

Budding: This method is seen in yeast. Yeast is a unicellular plant. It produces a small bud. The bud grows to a certain size and gets detached from the mother cell. The daughter cell then develops into a new individual.

Fragmentation: This method is seen in spirogyra. A filament of spirogyra divides into many fragments. Each fragment then develops into a new individual.

2.                    Explain what you understand by sexual reproduction.
Answer: When two parents are involved in reproduction, this method is called sexual reproduction. Formation of male and female gametes is the first step of sexual reproduction. The male and female gametes fuse during fertilization to produce zygote. The zygote subsequently develops into an embryo which further develops into a new individual.

3.        State the main difference between asexual and sexual reproduction.
Answer: Some difference between asexual and sexual reproduction are as follows:

1.        A single parent is involved in asexual reproduction, while two parents are involved in sexual reproduction.

2.        Gamete formation is an important part of sexual reproduction, but this does not take place during asexual reproduction.

4.        Sketch the reproductive parts of a flower.
Answer:

5.                    Explain the difference between self-pollination and cross-pollination.
Answer: Following are the main differences between self pollination and cross pollination:

0.        In self pollination; pollen grains are transferred to the stigma of the same flower, while in cross pollination; pollen grains are transferred to the stigma of different flower.

1.        In self pollination; flowers do not need assistance from external agents, but such assistance is required in case of cross pollination.

6.        How does the process of fertilisation take place in flowers?
Answer: Once pollen grain lands on the stigma, it produces a pollen tube. This process is called germination of pollen grain. The pollen tube penetrates the style and reaches the ovary. Male nucleus is transferred through this pollen tube. Finally, fusion of male and female nuclei takes place inside the ovary. This step is called fertilization.

7.        Describe the various ways by which seeds are dispersed.
Answer: Following are the various methods of seed dispersal:

Dispersal by Wind: Seeds of some plants are light-weight and some hair-like or wing-like structures are present on them. Such seeds float on air and are thus dispersed by wind. Example: Dandelion, maple, drumstick, etc.

Dispersal by Water: Dispersal by water takes place in some aquatic plants and in some which grow near a water body. Seeds of water lily float and thus dispersed by water. The coconut seed has a tough fibrous covering which has plenty of air inside. This helps the coconut seeds in floating on water.

Dispersal by Animals: Some seeds have spine like structures on them. They get stuck to the fur of animals and thus get spread to different places. Examples; Beggar tick, Xanthium, Urena, etc. Some seeds are swallowed by birds and animals along with fruits. These seeds get dispersed with bird or animal droppings.

Dispersal by Bursting: Some fruits burst open when they mature. The force of bursting is enough to spread the seeds. Examples; Ladyfinger, castor, balsam, etc.

Dispersal by Humans: Human beings also help in dispersal of seeds, especially during farming.

• Plant Nutrition

• Animal Nutrition

• Fibre Fabric

• Heat

• Acid Base

• Changes

• Climate

• Storm Cyclone

• Soil

• Respiration

• Transportation

• Reproduction

• Motion

• Electricity

• Light

• Water

• Forest

• Wastewater

Plant Nutrition Animal Nutrition Fibre Heat Acid Base Changes Climate Storm Soil Respiration Transportation Reproduction MotionElec

Time And Motion

Motion: When an object changes its position with elapse of time in respect to a stationary object, such as a building, electric pole, etc., the object is said to be in motion.

Slow and Fast Motion: If an object ‘A’ covers a distance in less time and another object covers the same distance in more time, the object A is called a faster moving object and object B is called a slower moving object. In other words, object A has faster motion and object B has slower motion.

Rectilinear Motion: Motion along a straight line is known as RECTILINEAR MOTION OR MOTION ALONG A STRAIGHT LINE. For example: Motion of a car along a straight line

Curvilinear Motion: Motion along a curve line is known as CURVILINEAR MOTION. For example: Motion of car or any moving object along a curve line

Circular Motion: Motion along a circle is known as CIRCULAR MOTION. For example: Motion of cyclist along a circular park.

Speed: Distance covered by an object in unit time is called speed.

Speed may be divided into three types: Uniform speed, Non-Uniform Speed and Average Speed

Uniform Speed: If an object covers a fixed distance in each unit of time the motion is known as UNIFORM MOTION or UNIFORM SPEED.

Non-uniform Speed: If an object does not cover a fixed distance in each unit of time the motion is known as NON-UNIFORM MOTION or NON-UNIFORM SPEED.

Average Speed: Total distance covered divided by total time taken is known as AVERAGE SPEED.

Speed is also known as VELOCITY.

Review Question:

Question: 1 – A car covers a distance of 100 km in 5 hour, calculate its speed.

Solution:

Given, Total distance = 100 km

Total time taken = 5 hour

We know that

Question: 2 – A car covers 20 km in the first hour and cover 30 km in the last 4 hours. Find its average speed.

Solution:

Given,

Total distance covered = 20 km + 30 km = 50 km

Total time taken = 1 hour + 4 hour = 5 hour

We know that,

Periodic Motion or Oscillatory Motion: When an object repeats its motion after every fixed interval of time, the motion of the object is called PERIODIC MOTION OR OSCILLATORY MOTION.

In many wall clocks pendulum is used even today. A device having a string suspended with a fixed point with a bob at bottom is called pendulum.

The motion of pendulum starting from one extreme end to another extreme end and back to the first extreme end is called one oscillation. Similarly, the motion of a simple pendulum from its mean position to extreme left and extreme right and back to the mean position is called one oscillation.

Time Period: Time taken to complete one oscillation by the pendulum is called time period.

Review Question:

Question: 1 – A pendulum takes 20 second to complete 10 oscillations, calculate its time period.

Solution:

Given, Number of oscillations = 10

Time taken = 20 second

We know that,

Unit of Time: Time is measured in second. Thus, unit of time is second. Second is denoted by ‘s’.

60 second = 1 minute

60 minute = 1 hour

24 hour = 1 day

7 day = 1 week

365 days = 1 year

Unit of speed: Unit of speed is meter/second (m/s), or metre/minute (m/min) or kilometer/hour (km/h).

1000 metre (m) = 1 kilometer (km)

Speedometer: A device used to measure the speed of a vehicle is called SPEEDOMETER.

Odometer: A device used to measure the distance covered by a vehicle.

Distance Time Graph: When distance covered by an object and time taken to cover the distance is represented on a graph, the graph is called distance time graph.

If a vehicle cover a distance of 5 km every hour and travels for 5 hours, the time distance time graph for the given vehicle can be plotted as follows using the table given below:

Distance time graph of a moving vehicle with a constant speed is a straight slanting line.

Speed-time graph for the same vehicle will be a straight line parallel to x-axis.

Important Points:

Motion: When an object changes its position with elapse of time in respect to a stationary object, such as a building, electric pole, etc., the object is said to be in motion.

Slow and Fast Motion: If an object A covers more distance and object B covers less distance in same time, then object A is called in Fast Motion and object B is called in Slow Motion.

Rectilinear Motion: Motion along a straight line is known as RECTILINEAR MOTION OR MOTION ALONG A STRAIGHT LINE.

Curvilinear Motion: Motion along a curve line is known as CURVILINEAR MOTION.

Circular Motion: Motion along a circle is known as CIRCULAR MOTION.

Speed: Distance covered by an object in unit time is called speed. This means Speed is equal to Distance upon Time.

Uniform Speed: If an object covers a fixed distance in each unit of time the motion is known as UNIFORM MOTION or UNIFORM SPEED.

Non-uniform Speed: If an object does not cover a fixed distance in each unit of time the motion is known as NON-UNIFORM MOTION or NON-UNIFORM SPEED.

Average Speed: Total distance covered divided by total time taken is known as AVERAGE SPEED.

Periodic Motion or Oscillatory Motion: When an object repeats its motion after every fixed interval of time, the motion of the object is called PERIODIC MOTION OR OSCILLATORY MOTION.

Oscillation: The motion of pendulum starting from one extreme end to another extreme end and back to the first extreme end is called one oscillation.

Time Period: Time taken to complete one oscillation by the pendulum is called time period.

Unit of Time: Time is measured in second.

Unit of speed: Unit of speed is meter/second (m/s).

Speedometer: A device used to measure the speed of a vehicle is called SPEEDOMETER.

Odometer: A device used to measure the distance covered by a vehicle.

Distance time graph of a moving vehicle with a constant speed is a straight slanting line.

Speed-time graph for the same vehicle will be a straight line parallel to x-axis.

 

Motion and Time

NCERT Book Exercise Questions and Answer

Question: 1. Classify the following as motion along a straight line, circular or oscillatory motion:

(i) Motion of your hands while running.

(ii) Motion of a horse pulling a cart on a straight road.

(iii) Motion of a child in a merry-go-round.

(iv) Motion of a child on a see-saw.

(v) Motion of the hammer of an electric bell.

(vi) Motion of a train on a straight bridge.

Answer: (i) Periodic motion or Oscillatory motion

(ii) Along a straight line (Linear motion)

(iii) Circular motion

(iv) Periodic motion or oscillatory motion

(v) Periodic motion or oscillatory motion

(vi) Linear motion

Question: 2. Which of the following are not correct?

(i) The basic unit of time is second.

(ii) Every object moves with a constant speed.

(iii) Distances between two cities are measured in kilometres.

(iv) The time period of a given pendulum is not constant.

(v) The speed of a train is expressed in m/h.

Answer: (ii), (iv) and (v)

Question: 3. A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?

Answer:

Given, Number of oscillation = 20

Time taken = 32 second

We know that,

Question: 4. The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.

Answer: Given, distance = 240 km

Time taken = 4 hour

We know that,

Question: 5. The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.

Answer:

Given,

Initial reading of odometer = 57321.0 km

Final reading of odometer = 57336.0 km

Initial time = 08:30 AM

Final time = 08:50 AM

Thus,

Distance covered = Final reading of odometer – Initial reading of odometer

  = 57336.0 km – 57321.0 km = 15 km

Total time taken = Final time – Initial time = 08:50 AM – 08:30 AM = 20 minute

So, speed = 0.75 km/minute or 45km/hour

Question: 6. Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s, calculate the distance between her house and the school.

Answer:

Given, Speed = 5 m/s

Time taken = 15 minute

Distance =?

We know that,

Question: 7. Show the shape of the distance-time graph for the motion in the following cases:

(i) A car moving with a constant speed.

(ii) A car parked on a side road.

Answer:

Question: 8. Which of the following relations is correct?

Question: 9. The basic unit of speed is:

(i) km/min (ii) m/min (iii) km/h (iv) m/s

Answer: (iv) m/s

Question: 10. A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:

(i) 100 km (ii) 25 km (iii) 15 km (iv) 10 km

Answer:

Given,

Speed for first 15 minute = 40km/h

Speed for next 15 minute = 60 km/h

We know that,

Distance = Speed X Time

Therefore, Distance covered in first 15 minute i.e. 0.25 hour = 40 km/h X 0.24 hour = 10 km

Distance covered in next 15 minute = 60 km/h X 0.25 hour = 15 km

Thus, total distance covered = 10 km + 15 km = 25 km

Hence, Answer (ii) is correct

Question: 11. Suppose the two photographs, shown in Fig. 13.1 and Fig. 13.2 had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs, calculate the speed of the blue car.

Answer:

Figure in question is given from text book.

Do the following steps to calculate the speed:

Measure the distance cover by blue car.

Multiply the distance measured in cm by 100 to get the distance covered by car in meter.

Divide th distance in meter by 10 second (time given in question).

Result will be the speed of car in meter/second.

Suppose the distance of car is 3.5 cm.

Thus, Distance covered by car = 3.5 x 100 = 350 meter.

Time (given in question) = 10 second

Question: 12. Figure given here shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Answer: Vehicle A is moving faster which is evident from higher slope for distance time graph of this vehicle; compared to that of the other vehicle.

Question: 13. Which of the following distance-time graphs shows a truck moving with speed which is not constant?

Answer: (iii) The slope of the graph in this option is not a straight line and hence it does not show a uniform motion.

Electric Current and Its Effects

Electric Current: The flow of electric charge is called electric current. In an electric circuit, the charge is often carries by moving electrons. The SI unit of electric current is Ampere (A). The SI unit of electric charge is Coulomb.

Electric Circuit: The path through which electric charge moves is called electric circuit.

Symbols in Electric Circuit: Different components of electric circuit are shown by certain symbols. Use of symbol makes it easy to represent an electric circuit. Use of standard symbol makes it easy to understand by anybody. For example; a TV mechanic can identify different components of a TV by looking at its circuit diagram.

Electric Cell: It is a device which produces electric charge because of some chemical reactions. The cell which is used in a torch is called dry cell. The wet cells are used in car batteries. A normal dry cell gives an output of 1.5 Volt (V).

Battery: A group of cells is called battery. More than one cell is used in most of the devices; because the device needs more than 1.5 V of power.

Closed Circuit: When the circuit is complete, it is called closed circuit. Current flows only in a closed circuit.

Open Circuit: When the circuit is incomplete, it is called open circuit. Current does not flow in an open circuit.

Review Questions:

1. What is the SI unit of electric current?

Answer: Ampere

2. What is an electric cell?

Answer: It is device which produces electric charge because of some chemical reaction.

Heating Effect of Electric Current: When electric current flows through a conducting wire, the temperature of wire increases. This is called heating effect of electric current.

Devices Which Work on Heating Effect of Electric Current: Incandescent bulb is an example of a device which works because of the heating effect of electric current. The filament of bulb is made of tungsten. Tungsten has very high melting point and that is the reason it is used in electric bulb. Moreover, argon gas is filled inside the bulb. Argon prevents the filament from catching fire. Electric iron, water heater, geyser, toaster, etc. are some other devices which work on heating effect of electric current.

Elements of Heating Appliances: A heating appliance has a highly coiled wire or a metallic rod. The highly coiled structure increases the surface area and thus provides more heat. The elements are usually made of constantan which is a metal with very high melting point.

Electric Fuse: Electric fuse is a safety device which is used in household wirings and in many appliances. Electric fuse has body made of ceramic and two points for attaching the fuse wire. The fuse wire melts whenever there is overload in the wiring. This breaks the circuit and helps in preventing damage to costly appliances and to the wiring. In electrical devices a glass fuse is often used. This is a small glass tube, in which lies the fuse wire.

MCBs (Miniature Circuit Breaker): MCBs have been replacing electric fuse from wirings at most of the places. The electric fuse has a big practical problem. Whenever the wire fuses, one needs to replace the wire to resume electric supply. More often than not, this proves to be a cumbersome task. Miniature circuit breakers break the circuit automatically. One just needs to switch it on to resume the electric supply. Many models of MCBs have a built in mechanism by which the electric supply is automatically resumed.

Review Questions

1. The electric bulb works on which property of electric current?

Answer: Heating effect of electric current.

2. What is the full form of MCB?

Answer: Miniature Circuit Breaker

Magnetic Effect of Electric Current: Hans Christian Oersted (1777 – 1851) was the first to show that electric current also produces magnetic effect. He kept a magnetic compass near a current carrying conductor. It was observed that the magnetic compass shows deflection, when the current passes through the conductor.

Electromagnet: Magnetic effect of electric current has been used in making powerful electromagnets. For this, wire is wrapped around an iron rod in many turns and electric current is supplied to the wire. As long as the current is supplied the iron rod behaves like a magnet. More number of turns makes more powerful magnet. Electromagnet is used in electric bells and also in powerful cranes.

Electric Bell: Electric Bell is composed of two rods of cast iron. Coil is made around the iron rods. A metallic strip is placed parallel to the coils. The metallic strip is fitted with a hammer at one end. Another end of the strip is connected to the circuit. A gong is placed in a position so that it can be hit by the hammer. When current flows in the circuit, the cast iron rods become electromagnet and attract the metallic strip. The metallic hammer hits the gong because of that. Once the metallic strip is pulled towards the electromagnet, it gets disconnected from the point and there is a break in the circuit. A spring pulls the metallic strip back because no magnetism is left in the electromagnet. This cycle continues and the electric bell produces a ringing sound.

Electric Current and Its Effects NCERT Exercise Solution

1. Draw in your notebook the symbols to represent the following components of electrical circuits: connecting wires, switch in the ‘OFF’ position, bulb, cell, switch in the ‘ON’ position, and battery.

Answer:

2. Draw the circuit diagram to represent the circuit shown in Fig.14.21. (See textbook for question figure)

Answer:

3. Fig.14.22 shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.

Answer:

4. The bulb in the circuit shown in Fig.14.23 does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.

Answer: The positive terminals of both the cells are together and that is why the bulb is not glowing. The cells should be kept in a way that the positive terminal of one cell is near the negative terminal of another cell; to make the bulb glow.

5. Name any two effects of electric current.

Answer: The two effects of electric current are; heating effect and magnetic effect.

6. When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.

Answer: This happens because when electric current passes through a conducting wire, a magnetic field is created around the wire. The magnetic field causes deflection in the magnetic compass.

7. Will the compass needle show deflection when the switch in the circuit shown by Fig.14.24 is closed?

Answer: Yes

8. Fill in the blanks:

(a) Longer line in the symbol for a cell represents its …………..terminal.

Answer: Positive

(b) The combination of two or more cells is called a ……………

Answer: Battery

(c) When current is switched ‘on’ in a room heater, it ……………….

Answer: heats up

(d) The safety device based on the heating effect of electric current is called a ……………

Answer: Electric fuse

9. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (F)

(b) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T)

(c) An electromagnet does not attract a piece of iron. (F)

(d) An electric bell has an electromagnet. (T)

10. Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.

Answer: Since plastic is a non-magnetic material, so electromagnet cannot be used to separate plastic bags from a garbage heap.

11. An electrician is carrying out some repairs in your house. He wants to replace a fuse by a piece of wire. Would you agree? Give reasons for your response.

Answer: A special wire with low melting point should be used for the fuse wire and any other wire would not serve the purpose. Hence, I would not agree with the electrician.

12. Zubeda made an electric circuit using a cell holder shown in Fig. 14.4, a switch and a bulb. When she put the switch in the ‘ON’ position, the bulb did not glow. Help Zubeda in identifying the possible defects in the circuit.

Answer: There can following possibilities:

• The terminals of cells are not in correct position.
• The connections are loose.
• The bulb may have fused.

13. In the circuit shown in Fig. 14.25

(a) Would any of the bulb glow when the switch is in the ‘OFF’ position?

Answer: None of the bulbs would glow.

(b) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?

Answer: All the bulbs would glow at once.

Light: Light is a form of energy. We are able to see the world around us because of light.

Propagation of Light:

Light always travels in a straight line. The following experiment proves that light always travels in a straight line. When the candle is viewed through a straight tube, its flame can be seen. In case of a bent tube, the flame cannot be seen.

Reflection: When light falls on a shiny surface, it bounces back. This phenomenon is called reflection. We are able to see images in mirrors or in water, because of reflection.

Laws of Reflection: There are two laws of reflection.

1. The incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.
2. Angle of incident and angle of reflection are equal.

Whenever an image is formed by a mirror or by any reflecting surface; the laws of reflection are obeyed.

Real Image: When the image can be obtained on a screen, it is called real image. Real image is formed in front of mirror. Images formed on the retina are real images. Images formed on the film of a camera are real images.

Virtual Image: When the image cannot be obtained on a screen, it is called virtual image. Virtual image is formed behind the mirror.

Image formation in Plane Mirror: Image is of the same size as object. The distance of image and object from the plane mirror is same. Image is erect and virtual.

Lateral Inversion in Plane Mirror: A plane mirror makes laterally inverted image. This is the reason, your right hand looks like the left hand of your image. The word ‘AMBULANCE’ is written in laterally inverted form on the front of the ambulance. This is deliberately done so that the driver in a vehicle ahead can easily spot the ambulance and can give way.

Review Questions

1. What is light? 
   
   Answer: Light is a form of energy which helps us in getting the vision. 
2. What is normal to the point of incidence? 
   
   Answer: The perpendicular to the surface at the point at which the incidence ray falls is called normal.

Spherical Mirror:

When the mirror is a part of a sphere, it is called spherical mirror. Spherical mirrors are of two types. In concave mirror, the reflective surface is inside the sphere, i.e. is depressed. In convex mirror, the reflective surface is outside the sphere, i.e. is bulged or protruded.

Image formation in Concave Mirror: In case of concave mirror, the image is usually inverted, real and smaller than the object. When the object is kept too close to the concave mirror, the image is erect, virtual and larger than the object.

Uses of Concave Mirror:

• Concave mirror is used by dentists and ENT specialists to focus a beam of light to see inside a patient’s mouth or ears. 
• Concave mirror is used in solar furnace, because rays of sunlight converge at a point once they reflect from the concave mirror. 
• Concave mirror is used as barber’s mirror, because it shows a larger image when object is too close.

Image formation in Convex Mirror: In case of convex mirror, the image is erect, virtual and smaller than the object.

Uses of Convex Mirror:

• Convex mirror is used in rear view mirrors, as it shows smaller images from a bigger field of view. 
• Convex mirror is used on hairpin bends, to see the vehicles coming from other side of the bend.

Review Questions:

1. Which type of image is usually formed in case of concave mirror? 
   
   Answer: Inverted, real and smaller
2. Which type of image is formed in case of convex mirror? 
   
   Answer: Erect, virtual and larger

Lens

Lens is made of two transparent surfaces in which at least one surface is curved. Convex and concave lenses in which both surfaces are either convex or concave are the most common types.

Image formation in Convex Lens: In case of convex lens, the image is usually inverted, real and smaller than the object. When the object is kept too close to the convex lens, the image is erect, virtual and larger than the object.

Image formation Concave Lens: In case of concave lens, the image is erect, virtual and smaller than the object.

Uses of Lens: Convex lens is used in microscope, telescope and camera. Convex lens is also used in reading glasses. Concave lens is used in spectacles.

Components of White Light: The white light, or visible spectrum, is composed of seven colours. These colours are VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange and Red). When white light passes through a prism, it breaks down into its component colours. This is the reason rainbows show all the colours of the visible spectrum.

Newton’s Disc: Since Newton was the first to make this; it is called Newton’s Disc. It is a circular disc on which seven colours of the rainbow are painted on seven different sectors. When the disc is rotated at certain speeds, it appears to be white. This shows, how the seven colours make the white light.

Review Questions

1. How many colours are there in the visible spectrum? 
   
   Answer: Seven 
2. Which type of lens is used in a camera? 
   
   Answer: Convex

NEXT 
Light - Class Seven Science - Chapter Note 
Light - Class Seven Science - NCERT Solution 
Light - Class Seven Science - MCQs 

  Solution of NCERT Exercise

Question: 1 - Fill in the blanks:

1. An image that cannot be obtained on a screen is called ____________. 
   
   Answer: Virtual
2. Image formed by a convex __________ is always virtual and smaller in size. 
   
   Answer: Mirror
3. An image formed by a __________ mirror is always of the same size as that of the object.
   
   Answer: Plane
4. An image which can be obtained on a screen is called a _________ image.
   
   Answer: Real
5. An image formed by a concave ___________ cannot be obtained on a screen.
   
   Answer: Lens

Question: 2 -Mark ‘T’ if the statement is true and ‘F’ if it is false:

1. We can obtain an enlarged and erect image by a convex mirror. 
   (F)
2. A concave lens always form a virtual image. 
   (T)
3. We can obtain a real, enlarged and inverted image by a concave mirror. 
   (F)
4. A real image cannot be obtained on a screen. 
   (F)
5. A concave mirror always form a real image. 
   (F)

Question: 3 -Match the items given in Column I with one or more items of Column II.

Question: 4 -State the characteristics of the image formed by a plane mirror.

Answer: In case of plane mirror, the image is erect, virtual and of same size as the object.

Question: 5 -Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.

Answer: Some examples: A, H, I, M, O, T, U, V, W and X

Question: 6 -What is a virtual image? Give one situation where a virtual image is formed.

Answer: The image which cannot be obtained on a screen is called virtual image. For example, virtual image is always formed in case of plane mirror and convex mirror.

Question: 7 -State two differences between a convex and a concave lens.

Answer: A convex lens can make enlarged image, while a concave lens would always make smaller image. A convex lens usually makes real image, while a concave lens always makes a virtual image.

Question: 8 -Give one use each of a concave and a convex mirror.

Answer: (a) Concave mirror is used in solar furnace. (b) Convex mirror is used in rear view mirrors.

Question: 9 -Which type of mirror can form a real image?

Answer: Concave mirror

Question: 10 - Which type of lens forms always a virtual image?

Answer: Concave lens

Choose the correct option in questions 11–13

Question: 11 - A virtual image larger than the object can be produced by a

1. Concave lens
2. Concave mirror
3. Convex mirror
4. Plane mirror

Answer: (c) Concave mirror

David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be

1. 3 m
2. 5 m
3. 6 m
4. 8 m

Answer: (a) 3 m

Question: 13 -The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be

1. 1 m/s
2. 2 m/s
3. 4 m/s
4. 8 m/s

Answer: (b) 2 m/s

Water: A Precious Resource

Availability of Water on Earth:

About 71% of the earth’s surface is filled with water. But out of this, a very small amount is available for the human use.

If a bucketful of water shows the total water on the earth, then a mug of water shows the total freshwater available on the earth. Out of this, a glass of water shows the water which is available as groundwater. About one-fourth spoonful of water shows all the water available in lakes and rivers of the world.

Water Cycle: Water is available in all the three states of matter. Ice is the solid state, water is the liquid state and vapour is the gaseous state; in which water is available. The water on the earth keeps on changing in all the three states in a cycle. This is known as water cycle. The water cycle helps in keeping the amount of water on the earth as constant.

Following are the main steps of water cycle in nature:

Evaporation: Water from the surface of the earth keeps on evaporating and turns into vapour. The water vapour also comes from green plants through transpiration.

Condensation: The water vapour condenses to from clouds.

Precipitation: Water from the clouds falls on the land; in the form of precipitation. At higher altitudes, the condensed water from the clouds also falls in the form of ice.

Collection: The rainwater falls on the ground and runs off to the nearest water bodies. Some of this water seeps down the ground to recharge the groundwater. Rest of the water goes to the ocean via rivers.

Review Questions:

1. How much of the earth’s surface is covered by water?

Answer: 71% 

2. How much of the total water on the earth is available for human use?

Answer: About 1% 

Groundwater

Groundwater is the most important source of water for us. The water is stored under the ground; between layers of rocks. The upper limit of groundwater at a place is called the water table at that place. Water table is usually higher in the plains but is very low in the plateaus. This is the reason it is easier to install a hand-pump in the northern plains. On the other hand, it takes a heavy drilling machine to install a tube-well in the plateaus.

Depletion of water table: Due to growing human population, there is an increased demand for potable water. There is more need for drinking water and also for water for other purposes; like irrigation, economic activities and recreation. The supply of water either remains the same or has decreased, but demand has been continuously increasing. The mismatch in supply and demand is resulting in depletion of water table and most of the places are facing acute shortage of water.

Growing population means, there is more demand for foodgrains and hence farming is being done on a larger scale. More farming means more consumption of water for irrigation.

Growing population also means more construction of houses and pucca roads. This has created an impervious layer of concrete above the ground at most of the places. This has adversely affected the natural recharge of underground aquifers.

Forests have been cut to clear land for meeting the demand of a growing population. Trees make the rocks pervious to water and thus facilitate recharge of underground aquifers. Reduced forest cover has also hampered the natural recharge of underground aquifers.

Uneven Rainfall: India is a large country. Some parts of the country get excess rainfall, while some other parts get deficient rainfall. As a result, while some parts of the country are flooded during the rainy season, many other parts suffer from draught like conditions. Uneven rainfall also adds to the problem of water shortage.

Tackling of Water Shortage

Rain Water Harvesting:

Collection of rainwater for future use is called rainwater harvesting. India has a long history of different rainwater harvesting structures; especially in rain deficient areas. For example; tankas and bawris had been in use in the northwestern part of India; especially in Rajasthan. Tanka is an underground tank to collect rainwater. Bawri is an open tank in which water used to be collected. Steps were made around the bawri so that one can easily access the water.

Rainwater harvesting can also be done in modern homes. The runoff rainwater from the rooftop should be collected in an underground reservoir. Such reservoirs are usually filled with sand and gravel to filter out impurities from water. The water can either be used directly or can be channelized to recharge the underground water.

Drip Irrigation: Drip irrigation is a method through which maximum number of plants can be irrigated with minimum use of water. For this, pipelines are laid throughout the rows of plants. Pipes are pierced at strategic points to release water in droplets. This helps in saving the water which is an important but scarce resource.

Review Questions:

1. Which is the main source of water for us?

Answer: Groundwater 

2. Which is the main culprit of shortage of potable water?

Answer: Growing human population 

Steps one can take to conserve water:

• Immediately repair any leaking tap in the household.
• Don’t let the tap remain open while brushing your teeth.
• Water left after washing or bathing can be used for mopping and for watering the plants.
• Avoid using a shower and use a bucketful of water instead.

Test Your Knowledge             NCERT Questions And Solutions

 

Water: A Precious Resource

NCERT Exercise Solution:

Question: 1 - Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. (T)

(b) Water shortage is a problem faced only by people living in rural areas. (F)

(c) Water from rivers is the only source for irrigation in the fields. (F)

(d) Rain is the ultimate source of water. (T)

Question: 2 - Explain how groundwater is recharged?

Answer: The surface water seeps down the ground through the porous layers of the soil. This process is called infiltration and is responsible for recharging the groundwater.

Question: 3 - There are ten tubewells in a lane of fifty houses. What could be the long term impact on the water table?

Answer: Ten tube-wells in a lane of fifty houses can lead people to mindlessly exploit the groundwater. This can lead to depletion of the water table in the long run.

Question: 4 - You have been asked to maintain a garden. How will you minimise the use of water?

Answer: Drip irrigation can be used in the garden to minimize the use of water.

Question: 5 - Explain the factors responsible for the depletion of water table.

Answer: Following factors are responsible for depletion of water table:

There is more demand of water due to increasing population. Increasing population means there is ever increasing demand of water for various human activities.

Deforestation has removed a large portion of forest cover. This has disturbed the natural process of recharging the groundwater.

While demand for water has increased, the supply has reduced. The mismatch between demand and supply is mainly responsible for depletion of water table.

Question: 6 - Fill in the blanks with the appropriate answers:

(a) People obtain groundwater through________ and ________.

Answer: Wells and tube-wells

(b) Three forms of water are ________, ________ and ________.

Answer: Ice, water and vapour

(c) The water bearing layer of the earth is ________.

Answer: Aquifer

(d) The process of water seepage into the ground is called ________.

Answer: Infiltration

Question: 7 - Which one of the following is not responsible for water shortage?

(i) Rapid growth of industries

(ii) Increasing population

(iii) Heavy rainfall

(iv) Mismanagement of water resources

Answer: (iii) Heavy rainfall

Question: 8 - Choose the correct option. The total water

(i) In the lakes and rivers of the world remains constant.

(ii) Under the ground remains constant.

(iii) In the seas and oceans of the world remains constant.

(iv) Of the world remains constant.

Answer: (iv) Of the world remains constant

Test Your Knowledge                         Class Note: Water:A Precious Resource

 

Forests: Our Lifeline

Forest: An area with high density of trees is called a forest. A forest is a system which is composed of plants, animals and microorganisms.

Forest as Habitat: Forest is the habitat for a variety of living beings. Many plants, animals and microbes live in the forest.

A typical tree forest is composed of two distinct layers, viz. overstory ( or canopy) and understory. A tree can be divided into two parts: trunk and branches. The branches of a tree make its crown. Crowns of several trees; in the forest; make the canopy. In dense forests, the canopy looks like the roof of the forest. There are many animals and creatures which live only on the canopy, e.g. monkeys.

Crowns of trees come in various shapes. Some common examples are shown in the given figure.

The lower layer of the forest is called understory. It is composed of herbs and shrubs. The understory is a different world in itself. The understory may not get proper sunlight in dense forests.

There are many animals and creatures which live only in the understory of a forest.

Review Questions

Question: 1 - What is forest?

Answer: An area with dense cover of trees is called forest.

Question: 2 - What is overstory in a forest?

Answer: The upper leafy portion of a forest is called overstory.

Important Forest Produce: Many important forest produce are useful for us. Some examples are given below:

• Firewood and dry leaves are used as kitchen fuel in villages which are close to a forest.
• Timber is an important raw material; for construction activities and for making furniture and artifacts.
• Wood pulp is used in manufacturing paper.
• Honey, kendu leaves, catechu, lac, raisin, etc. are important forest produce.
• Many medicinal plants and herbs are found in forests.

Forest as a System:

Every part of the forest contributes in making a self-sustaining system. The green plants prepare food through photosynthesis. The herbivores directly take food from the green plants. The carnivores take food from the herbivores. This makes a food chain, which can be shown by following example:

Grass → Deer → Lion

When an animal or a plant dies, its dead remains rot in due course of time and turn into soil-like thing. The process is called decomposition and microorganisms carry out this process. Decomposition is the process by which all the raw materials are returned to the nature. The soil-like thing made after decomposition is called humus. It makes the soil highly fertile. The topsoil of forest is fertile because of presence of humus.

Role of Forest in Preserving the Environment: Forest plays an important role in preserving the environment. Green plants take solar energy and convert it into chemical energy while making food. Thus, solar energy is transferred to other living beings through the green plants. Green plants utilize carbon dioxide during photosynthesis and release oxygen. That is how the green plants maintain the balance of carbon dioxide and oxygen in the environment.

Role of Forest in Water Cycle: The roots of the trees make the soil porous. Rainwater seeps through these pores and recharge groundwater. Forests prevent wastage of rainwater in the form of runoff. Forests also prevent flash floods by slowing down the movement of water.

Role of Forest in Soil Conservation: The roots of the trees hold the topsoil in place. This prevents soil erosion by wind or by running water.

Deforestation and its Effect: Large scale cutting of trees to clear land for human use is called deforestation. Due to growing human population, vast tracts of forest have been removed. This has created many problems. Some of them are given below:

• Reduced forest cover has led to soil erosion and loss of soil fertility at many places.
• Reduced forest cover has disturbed the natural process of recharging of groundwater. This has resulted in shortage of drinking water at many places.
• Reduced forest cover means there is loss of habitat for many animals. Existence of most of the animals is in danger because of this.
• Reduced forest cover means there is higher percentage of carbon dioxide in the atmosphere. This is leading to global warming. The average temperature of the earth is on the rise.

Review Questions:

Question: 1 - What do you understand by deforestation?

Answer: Large scale cutting of trees to clear land for human use is called deforestation.

Question: 2 - What is humus?

Answer: The part of the topsoil which is composed of decomposed remains of plants and animals is called humus.

Wastewater

Wastewater: The water which gets contaminated after various works; like washing, bathing, mopping, etc. is called wastewater.

World Water Day: 22nd March

International Decade for Action on Water for Life: 2005 – 2015: It was declared by the General Assembly of the United Nations. Its main goal was to reduce the number of people who do not have access to safe drinking water; by half.

Sewage Treatment: The process of removing impurities from waste water before it can be reused or sent to the water bodies is called sewage treatment or cleaning of water.

Sewage: The liquid waste which has water as its largest component; along with various types of impurities; is called sewage.

Sewers: The pipes which carry wastewater.

Sewerage: The network of sewers.

Manhole: These are the holes made in sewers at frequent intervals, so that timely inspections and cleaning of sewers can be done through them. The manhole is covered with a hard lid so that people and traffic can easily move over it.

Review Questions:

1. What is sewer?

Answer: The pipe which carries the wastewater is called sewer.

2. What is sewerage?

Answer: The network of sewers is called sewerage.

Wastewater Treatment Plant or Sewage Treatment Plant:

These are large plants where wastewater is cleaned before being sent to the nearest water bodies or being reused. The sewage treatment involves physical, chemical and biological processes to remove impurities from the wastewater.

Physical Process:

1. Filtration: The wastewater is passed through bar screen. Large objects; like rags, sticks, plastic bags, cans, etc. are removed in this process.

2. Grit and Sand Removal: The wastewater is slowly passed through the sedimentation tank. Grit, sand and pebbles settle down at the bottom.

3. Sedimentation: Water is then sent to the sedimentation tank. Solids; like faeces settle at the bottom. Floatable impurities; like oil and grease float on the surface. A scraper removes the faeces from the water. The impurity thus collected is called sludge; which is sent to the sludge tank. The sludge can be used to produce biogas or to produce manure. A skimmer removes the floatable impurities. Now, the water is called clarified water.

Biological Process

4. Aeration: Air is pumped into clarified water so that bacteria can proliferate. Bacteria consume the human waste. It leaves food waste, soap and other unwanted materials in the water. The microbes settle down at the bottom after several hours. Water is then removed from the top. This water is fit for irrigation and can be used for that purpose.

Chemical Process

5. Chlorination: Water purified through aeration is not fit for human consumption. It needs to be treated with chlorine. For this, bleaching powder is added to the water. The chlorine kills whatever germs may be left in the water. After chlorination, the water is fit for drinking.

Review Questions

1. Which process during the wastewater treatment results in proliferation of bacteria?

Answer: Aeration

2. Which process during the wastewater treatment kills the germs?

Answer: Chlorination

Better Housekeeping Practices to Maintain Sanitation:

Do not throw cooking oil and fat in the drain. This can block the drain. The fat and oil clogs the pores in the soil; in open drains. This reduces the filtering capacity of soil.

Do not throw chemicals; like paint, insecticides, medicines, etc. into the drain. They kill the bacteria which otherwise help in cleaning the water.

Do not throw used tea leaves, solid food, soft toys or napkins in the drain. They can clog the drain and do not allow oxygen to enter the sewage water. Oxygen is important for the natural process of decomposition.

Sanitation and Disease

Maintaining overall cleanliness in the home and in surroundings is called sanitation. Sanitation is important for the health of a person and that of the community.

Many people have the habit of defecating in the open. Uncovered human excreta attract flies and other insects. These insects carry the germs of many dangerous diseases; like cholera, typhoid and jaundice. With constant public awareness campaign, the practice of open defecation can be stopped.

Poor sanitary condition also contaminated the groundwater because contaminants percolate down the ground.

Stagnant water is a perfect breeding ground for mosquitoes. Mosquitoes are the carriers of several diseases; like malaria, dengue, chikungunya and filaria.

Alternative Arrangements for Sewage Disposal

In the absence of a sewerage system, arrangements for onsite sewage disposal can be made. For example; septic tanks are built in which human excreta are collected. In due course of time, the human excreta get decomposed into compost.

Composting pits can be made to dump waste and to make manure from them. Sewage can be collected into biogas plants to produce useful biogas.

Chemical toilets are new discoveries. They do not require much water for the disposal of human excreta and are environment friendly. Such toilets are ideal for the trains.

Sanitation at Public Places

Maintaining sanitation at public places is also important. In a heavily populated country; like India; any public place is always teeming with people. More footfall at public places results in more filth. Sanitation workers often work continuously to maintain cleanliness at public places. But it is our responsibility also to maintain sanitation at public places. We should follow some simple rules to help the sanitation workers. For example; always throw the trash in a dustbin and avoid littering. Don’t spit at public places and use the dustbin or special bins marked for the purpose.

Test Your Knowledge                        NCERT Exercise And Solution

 

Wastewater - NCERT Book Exercise - Solution

1. Fill in the blanks:

(a) Cleaning of water is a process of removing ……………….

Answer: Contaminants

(b) Wastewater released by houses is called ……………

Answer: Sewage

(c) Dried ……………. is used as manure.

Answer: Sludge

(d) Drains get blocked by …………….. and …………………

Answer: Oil and fat

2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.

Answer: The liquid waste which has water as its largest component; along with various types of impurities; is called sewage. Discharging untreated sewage into rivers or seas contaminates the water of these water bodies. Contaminated water is dangerous for aquatic plants and animals. So, it is harmful to discharge untreated sewage into rivers or seas.

3. Why should oils and fats be not released in the drain? Explain.

Answer: Oil and fats can clog the drains. In open drains, they block the pores in the soil and thus hamper the filtration by soil. Hence, oil and fats should not be released in the drain.

4. Describe the steps involved in getting clarified water from wastewater.

Answer: The following steps are involved in clarifying wastewater:

• Insoluble waste is removed by filtration and sedimentation processes.

• Bacteria are allowed to grow through the process of aeration. Bacteria eat away human waste from the wastewater.

• Chlorination is used to kill the germs in clarified water. After this step, the water becomes fit even for human consumption.

5. What is sludge? Explain how it is treated.

Answer: The solid waste which settles at the bottom of the sedimentation tank is called sludge. The sludge is further treated by the process of aeration. This helps in growth of bacteria which eat away the human waste.

6. Untreated human excreta is a health hazard. Explain.

Answer: Untreated human excreta contains many microbes which can cause deadly diseases; like cholera, diarrhea, jaundice and typhoid. The germs of these diseases can easily reach human population through insects and through contaminated food and water. Thus, untreated human excreta are a health hazard.

7. Name two chemicals used to disinfect water.

Answer: Bleaching Powder and Chlorine Tablets

8. Explain the function of bar screens in a wastewater treatment plant.

Answer: Bar screens are large filters which are placed in the form of vertical screens. Large solid wastes; like sticks, pebbles, sand, cans, plastic bottles, plastic bags, etc. are filtered out when the wastewater moves through the bar screen.

9. Explain the relationship between sanitation and disease.

Answer: Sanitation and disease are closely related. Lack of sanitation leads to unhygienic conditions; which creates many communicable diseases. Maintenance of sanitation removes the chances of such diseases.

10. Outline your role as an active citizen in relation to sanitation.

Answer: My role as an active citizen can be in maintaining sanitation in the neighbourhood and at public places. For this, I shall follow these steps:

• Throwing garbage at designated places and in garbage bins.

• Preventing clogging of drains by not releasing oil and fat and solid waste into the drain.

• Using a dustbin to throw trash at public places.

• By not spitting at public places.

11. Study the following statements about ozone:

(a) It is essential for breathing of living organisms.

(b) It is used to disinfect water.

(c) It absorbs ultraviolet rays.

(d) Its proportion in air is about 3%.

Which of these statements are correct?

(i) (a), (b) and (c)

(ii) (b) and (c)

(iii) (a) and (d)

(iv) All four

Answer: (ii) b and c

12. Here is a crossword puzzle. Good Luck!

Across

3. Liquid waste products: SEWAGE

4. Solid waste extracted in sewage treatment: SLUDGE

6. A word related to hygiene: SANITATION

8. Waste matter discharged from human body: EXCRETA

Down

1. Used water: WASTE

2. A pipe carrying sewage: SEWER

5. Micro-organisms which causes cholera: BACTERIA

7. A chemical to disinfect water: OZONE

Answer: