CBSE Class 7

These NCERT Solutions for Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals of Climate Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Weather, Climate and Adaptations of Animals of Climate NCERT Solutions for Class 7 Science Chapter 7

Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals of Climate Textbook Exercise Questions and Answers

Question 1.
Name the elements that determine the weather of a place.
Answer:
Temperature, humidity, rainfall and wind speed are the elements that determine the weather of a place.

Question 2.
When are the maximum and minimum temperatures likely to occur during the day?
Answer:
The temperature is minimum in the morning and maximum at the noon.

Question 3.
Fill in the blanks:
(a) The average weather taken over a long time is called …………………
(b) A place receives very little rainfall and the temperature is high throughout the year. The climate of that place will be ………………… and …………………
(c) The two regions of the earth with extreme climatic conditions are …………………and …………………
Answer:
(a) climate,
(b) hot and dry,
(c) polar region and desert

Question 4.
Indicate the type of climate of the following areas:
(a) Jammu and Kashmir: ___________
(b) Kerala: ___________
(c) Rajasthan: ___________
(d) North-east India: ___________
Answer:
(a) Moderately hot and wet
(b) Hot and wet
(c) Hot and dry
(d) Hot and wet

Question 5.
Which of the two changes frequently, weather or climate?
Answer:
Weather

Question 6.
Following are some of the characteristics of animals:
(i) Diets heavy on fruits
(ii) White fur
(iii) Need to migrate
(iv) Loud voice
(v) Sticky pads on feet
(vi) Layer of fat under skin
(vii) Wide and large paws
(viii) Bright colours
(ix) Strong tails
(x) Long and large beak
For each characteristic indicate whether it is adaptation for tropical rainforests or polar regions. Do you think that some of these characteristics can be adapted for both regions?
Answer:

Yes, some adaptations like loud voice, wide and large paws, strong tails, long and large beak, etc., can be adapted for both regions.

Question 7.
The tropical rainforest has a large population of animals. Explain why it is so.
Answer:
Dense forest provides large amount and variety of food as well as large shelter. This supports a large population to survive in the rainforest.

Question 8.
Explain, with examples, why we find animals of certain kind living in particular climatic conditions.
Answer:
Animals of certain kinds have adaptations for a particular climate because they possess some special features which help them to survive in that climate. Such special features are called adaptations. For examples:

• Polar bear is able to survive in polar regions because of special adaptations like white fur, strong sense of smell, a layer of fat under the skin, wide and large paws for swimming and walking.
• Monkeys are adapted to live in tropical rainforests. To help them live on trees, they have long tails for grasping branches. Their hands and feet are such that they can easily hold on to the branches.

Hence, if polar bear comes to tropical region, it will feel extreme heat and if monkey comes to polar region, it may die due to extreme cold. Therefore, certain animals live only in particular climatic conditions.

Question 9.
How does the elephant living in the tropical rainforest adapt itself?
Answer:
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 helps 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.

Question 10.
A carnivore with stripes on its body moves very fast while catching its prey. It is likely to be found in
(a) polar regions
(b) deserts
(c) oceans
(d) tropical rainforests
Answer:
(d) tropical rainforests

Question 11.
Which features adapt polar bears to live in extremely cold climate?
(a) A white fur, fat below skin, keen sense of smell.
(b) Thin skin, large eyes, a white fur.
(c) A long tail, strong claws, white large paws.
(d) White body, paws for swimming, gills for respiration.
Answer:
(a) A white fur, fat below skin, keen sense of smell.

Question 12.
Which option best describes a tropical region?
(a) Hot and humid
(b) Moderate temperature, heavy rainfall
(c) Cold and humid
(d) Hot and dry
Answer:
(a) Hot and humid

Ncert Extended Learning Activities and Projects

Question 1.
Collect weather reports of seven successive days in the winter months (preferably December). Collect similar reports for the summer months (preferably June). Now prepare a table for sunrise and sunset times as shown:

Try to answer the following questions:
a. Is there any difference in the time of sunrise during summer and winter?
b. When do you find that the sun rises earlier?
c. Do you also find any difference in the time of sunset during the month of June and December?
d. When are the days longer?
e. When are the nights longer?
f. When are the days sometimes longer and sometimes shorter?
g. Plot the length of the day against the days chosen in June and December.
(Instructions for plotting graphs are given in chapter 13)
Hint:
a. Yes, there is a difference in the time of sunrise during summer and winter as the days get longer in summer and shorter in winter.
b. The sun rises earlier in summer than in winter.
c. Yes, there is a difference in the time of sunset during summer and winter as the days get longer in summer and shorter in winter while the and night is longer in winter than in summer. So there is a difference in the time of sunset during the month of June and December.
d. Days are longer in summer (in the month of June).
e. Nights are longer in winter (in the month of December).
f. Days are longer in summer and shorter in winter because the earth spins on an axis that is tilted. The axis changes the position of the sun in the sky, making it appear for more or fewer hours, depending on the season and the latitude or distance from the equator.
g. Do it yourself.

Question 2.
Collect information about the Indian Meteorological Department. If possible, visit its website:
http//www.imd.gov.in.
Write a brief report about the things this department does.
Answer:
Meteorology focuses on the lower parts of the atmosphere, primarily the troposphere, where most weather conditions take place. Meteorologists use scientific principles to observe, explain and forecast our weather. The Indian Meteorological Department (IMD), also referred to as the Met Department, is an agency of the Ministry of Earth Sciences of the Government of India.

Functions of Meteorological department: It performs the study and observation of:

• increase or decrease of air pressure in defined regions.
• formation of clouds.
• seismic changes that may cause earthquakes.
• changes in the atmosphere that may cause storms, hurricanes, etc.
• variation of the atmospheric temperature, humidity, wind velocity, etc.
• time of sunrise and sunset, maximum and minimum temperature of the previous day.

On the basis of the study and the observations, they predict about things such as what would be the weather tomorrow, when monsoon is expected or when cyclone, hurricane, tornado, etc., are expected.

Activity 1

Objective: To locate polar regions and tropical rainforests on the world map.
Materials Required: A outline map of word and different colours.
Procedure: Mark polar regions and rainforest with different colours on the map.
Observations:

Adaptations of some animals of tropical rainforests are describe below:
i. Red-eyed frog: It has sticky pads on its feet to help it climb on trees on which it lives.
ii. Monkeys: They have long tails, for grasping the branches of trees on which they live. Their hands and feet help them in holding branches.
iii. Toucan: It possesses a long, large beak that helps to reach the fruits on branches that are too weak to bear its weight.

iv. Lions and Tigers: They have thick skin, sensitive hearing, sharp eyesight and a skin colour to camouflage in the environment and protect them from predators.

v. Lion-tailed Macaque (Beared Ape): It lives in western ghats. It has a silver-white mane which surrounds the head from the cheeks down to its chin. It is a good climber and lives on trees. It feeds of fruits, seeds, leaves, stems, flowers and buds. It also feeds on insects under tree bark and rarely comes down on the ground as it finds sufficient food on trees.
vi. Elephant: It uses its trunk as nose and hence, it has a strong sense of smell. Its tusks are modified teeth with which it can tear the bark of trees to eat. It has large ears that helps it to hear ever the softest sounds and keep cool in hot weather.

• Desert: Deserts have an extreme climate. These regions receive less rainfall and large amount of sunlight. Days are extremely hot and nights are cold.
• Hibernation: Period of time when an animal goes into a deep sleep. They eat extra food and find great shelter in order to do this. During hibernation, breathing rate and heartbeat rate falls. This helps them in overcoming the harsh weather conditions.

Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals of Climate Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Define weather.
Answer:
It is the day-to-day condition of the atmosphere at a particular time and place.

Question 2.
Define climate.
Answer:
The average weather condition of a place over a long period of time is called the climate of that place.

Question 3.
What is adaptation?
Answer:
The presence of specific body features or certain habits which enable an animal or a plant to live and survive in a particular habitat is called adaptation.

Question 4.
What is humidity?
Answer:
Humidity is a measure of the moisture content in the air.

Question 5.
Why do penguins huddle together?
Answer:
Penguins huddle together to keep warm.

Question 6.
What is the climate of Jammu and Kashmir?
Answer:
The climate of Jammu and Kashmir is moderately hot and wet.

Question 7.
How does the ability to camouflage help an animal?
Answer:
Ability to camouflage helps an animal to protect it from the predators. As the animal gets blended with the background, it is not easily visible to its predators and prey.

Question 8.
What type of place experiences hot and dry climate?
Answer:
The region that receives very little rainfall experiences hot and dry climate, such as desert.

Question 9.
Name some animals found in rainforests.
Answer:
Animals found in rainforests are monkeys, apes, gorillas, tigers, elephants, leopards, lizards, snakes, birds, insects, etc.

Question 10.
Name some animals that migrate.
Answer:
Birds, mammals, many types of fish, insects, etc., migrate seasonally in search of more hospitable climates.

Question 11.
Name some animals found in polar regions.
Answer:
Polar bears, penguins, fishes, musk, oxen, reindeers, foxes, seals, whales and birds are found in polar region.

Question 12.
Name the elements that determine the weather of a place.
Answer:
Temperature, humidity, rainfall, wind speed, etc., are the elements that determine the weather of a place.

Question 13.
What are maximum and minimum thermometers?
Answer:
Special thermometers used to record the maximum and minimum temperatures of the day are called maximum and minimum thermometers.

Question 14.
Write the names of two animals which live in Indian tropical rainforests.
Answer:
Bears and elephants.

Question 15.
Name the instrument used to measure humidity.
Answer:
Hygrometer.

Short Answer Type Questions

Question 1.
What is rain gauge?
Answer:
Rainfall is measured by an instrument called the rain gauge. It is basically a measuring cylinder with a funnel on top to collect rainwater.

Question 2.
What are the characteristics of the polar regions?
Answer:
The polar regions are present in an extreme climate. These regions are covered with snow and it is very cold for most part of the year. The sun does not set for six months and does not rise for other six months. In winter, the temperature can be as low as -37°C.

Question 3.
Name some countries where the tropical rainforests are found.
Answer:
Examples of some countries where the tropical rainforests are found are India, Malaysia, Indonesia, Brazil, Republic of Congo, Kenya, Uganda and Nigeria.

Question 4.
Write some of the adaptations of animals found in tropical rainforests.
Answer:
Some adaptations of animals living in the tropical rainforests include living on the trees, development of strong tails, long and large beaks, bright colours, loud voice, diet of fruits, sensitive hearing, sharp eyesight, thick skin, ability to camouflage in order to protect themselves from predators, etc.

Question 5.
How do migratory birds find their way?
Answer:
It seems that these birds have a built-in sense of direction and know in which direction to travel. Some birds probably use landmarks to guide them. Many birds may be guided by the sun during the day and stars at night. There is some evidence that birds may use the magnetic field of the earth to find directions.

Question 6.
How is weather a complex phenomenon?
Answer:
The weather is a complex phenomenon as it can vary over very short periods of time. It can happen sometimes that it is sunny in the morning, but suddenly clouds appear from nowhere and it starts raining heavily. Or, a heavy rain may vanish in a matter of minutes and give way to bright sunshine. Since weather is such a complex phenomenon, it is not easy to predict.

Question 7.
What are the various body features which make penguin a good swimmer?
Answer:
Their body is streamlined and their wings have become modified into flippers. They have webbed feet. These features help penguins in swimming.

Question 8.
Differentiate between weather and climate.
Answer:

Question 9.
What is migration?
Answer:
Migration refers to the movement of organisms from one place to another to escape the harsh, climatic conditions. 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.

Question 10.
How does the sun cause the changes in the weather?
Answer:
Sun is a huge sphere of hot gases burning at a very high temperature. The distance of the sun from us is very large. Even then, the energy sent out by the sun is very large in amount. Hence, sun is the primary source of energy that causes changes in weather. Energy absorbed and reflected by the earth’s surface oceans and atmosphere play important roles in determining the weather at any place.

Question 11.
Why is it cooler farther away from the equator?
Answer:
As we move forward towards the poles, the sun rays fall in a slanting angle on the land and have more and more areas to heat up. So, the heat is spread out over a larger area and it becomes colder and colder with increasing latitude. Hence, it is cooler farther away from the equator.

Question 12.
How animals living in the cold places protect themselves from cold?
Answer:
The animals which live in the cold places like whales, seals and penguins have thick skin which protects them from cold. They also have thick fur. They also have a deposit of fat layer called blubber under their skin which insulates their body from severe cold.

Long Answer Type Questions

Question 1.
Explain weather and its elements.
Answer:
The day-to-day conditions of atmosphere at a particular place is called weather. The weather can be comfortable or can be too hot too or cold. The various elements of weather are: temperature, humidity, rainfall, wind speed, etc.

a. 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.
b. Humidity: Humidity is the amount of moisture present in the air. It is generally measured in percentage. Humidity is generally at the highest level during the rainy season.
c. Rainfall: Amount of rainfall is measured in terms of mm. For this, an apparatus called rain gauge is used.
d. Wind-speed: Speed of wind also affects the condition of weather.

Question 2.
Explain the adaptations of polar bear to live in polar regions. Also construct a how chart for the same.
Answer:
The adaptations of polar bear are:

• It has a thick white fur which is not easily visible in the snowy white background. Hence, its predators and prey are unable to see it.
• It has two thick layers of fur. These keep it warm in cold weather.
• It has a layer of fat under the skin. The fat insulates its body from cold and keeps it warm.
• It has long, curved and sharp claws that help it to walk on ice.
• It has a very strong sense of smell that helps the bear to locate and catch its prey.
• It has wide and large paws that helps it in swimming. Polar bears are good swimmers. It helps them in keeping warm.

Question 3.
How is a penguin adapted to live in the polar region?
Answer:
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. They have curved claws which help them to walk in snow. They have streamlined body and webbed feed to help them swim in water. These adaptations help the penguin to survive in the extreme condition of the polar region.

Question 4.
Write adaptations shown by lion¬tailed Macaque (or bearded ape) of Indian tropical forests.
Answer:
A lion-tailed macaque has the following adaptations:

• It lives in the rainforests of Western Ghats.
• Its most outstanding feature is the silver-white mane, which surrounds the head from the cheeks down to its chin.
• It is a good climber and spends a major part of its life on the trees.
• It feeds mainly on fruits. It also eats seeds, young leaves, stems, flowers and buds.
• This bearded ape also searches for insects under the bark of the trees.
• Since it is able to get sufficient food on the trees, it rarely comes down on the ground.

Picture-Based Questions

Question 1.
Observe the following picture and answer the following questions:

a. Identify the animals shown in the picture.
b. What does this picture show?
c. What is the need of condition illustrated?
Answer:
a. The given picture is of penguins.
b. This picture shows penguins huddling together.
c. Penguins huddle together to keep them warm.

Question 2.
Observe the following picture and answer the questions that follow:

a. Identify the animal in the given picture.
b. Name the habitat of this animal.
c. Write the features of this animal.
Answer:
a. The given picture is lion-tailed macaque.
b. It lives in tropical rainforests and in western ghats in India.
c. The hand and feet of lion-tailed macaque have very good grip which helps it in leaping between the branches. It feeds mainly on fruits on the trees. It also eats seeds, leaves, stems, flowers and buds.

NCERT Solutions for Class 7 Science

• Class 7 Science Chapter 1 Nutrition in Plants
• Class 7 Science Chapter 2 Nutrition in Animals
• Class 7 Science Chapter 3 Fibre to Fabric
• Class 7 Science Chapter 4 Heat
• Class 7 Science Chapter 5 Acids, Bases and Salts
• Class 7 Science Chapter 6 Physical and Chemical Changes
• Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals of Climate
• Class 7 Science Chapter 8 Winds, Storms and Cyclones
• Class 7 Science Chapter 9 Soil
• Class 7 Science Chapter 10 Respiration in Organisms
• Class 7 Science Chapter 11 Transportation in Animals and Plants
• Class 7 Science Chapter 12 Reproduction in Plants
• Class 7 Science Chapter 13 Motion and Time
• Class 7 Science Chapter 14 Electric Current and its Effects
• Class 7 Science Chapter 15 Light
• Class 7 Science Chapter 16 Water: A Precious Resource
• Class 7 Science Chapter 17 Forests: Our Lifeline
• Class 7 Science Chapter 18 Wastewater Story

These NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Physical and Chemical Changes NCERT Solutions for Class 7 Science Chapter 6

Class 7 Science Chapter 6 Physical and Chemical Changes Textbook Exercise Questions and Answers

Question 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

Question 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.
b. Formation of manure from leaves is a physical change.
c. Iron pipes coated with zinc do not get rusted easily.
d. Iron and rust are the same substance.
e. Condensation of steam is not a chemical change.
Answer:
a. False, it is physical change.
b. False, it is chemical change.
c. True.
d. False, they are different substances.
e. True

Question 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 …………………
b. The chemical name of baking soda is …………………
c. Two methods by which rusting of iron can be prevented are ………………… and …………………
d. Changes in which only ………………… properties of a substance change are called physical changes.
e. Changes in which new substances are formed are called ………………… changes.
Answer:
a. calcium carbonate
b. sodium hydrogen carbonate
c. painting or greasing, galvanisation
d. physical
e. chemical

Question 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 (Sodium hydrogen-carbonate) is mixed with lemon juice (citric acid), bubbles are formed. These bubbles are formed due to the evolution of carbon dioxide gas. This is a chemical change. In this change, citric acid contained in lemon juice reacts with sodium hydrogen carbonate which results in the evolution of carbon dioxide gas. The reaction can be represented as follows:
Lemon juice + Baking soda → Carbon dioxide + Other substances

Question 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:
When a candle bums, both physical and chemical changes occur:

• Physical changes: On heating, melting candle is a physical change since it again turns into solid wax on cooling.
• Chemical changes: The wax vapours bum to give new substances like carbon dioxide, carbon soot, water vapour, heat and light. This is a chemical change.

LPG is another example in which the physical change occurs when LPG comes out of the cylinder and is converted from liquid to gaseous state and the chemical change occurs when gas burns in air.

Question 6.
How would you show that setting of curd is a chemical change?
Answer:
The curd is formed from milk. Both the curd and the milk have different properties. Also, once the curd is formed, it cannot be reversed back into milk. So, there is a formation of new substance with different properties and also it is an irreversible process. Hence, setting of curd is a chemical change.

Question 7.
Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.
Answer:
Burning of wood is a chemical change because in burning, new substances are formed and heat and light are produced. Wood + Oxygen → Carbon dioxide + Charcoal + Heat + Light
But cutting it into small pieces is a physical change because no new substance is formed in this. We can only reduce the size of wood by cutting which is a physical property.

Question 8.
Describe how crystals of copper sulphate are prepared.
Answer:
Crystals of copper sulphate are prepared by the method of crystallisation. A cup of water is taken in a beaker. Few drops of dilute sulphuric acid are added to this. The water is then heated and when it starts boiling, copper sulphate powder is added. Copper sulphate powder should be added on till the solution becomes saturated, i.e., no more powder can be dissolved. It is then filtered into a china dish and allowed to cool. The solution should be kept undisturbed. Slowly, the crystals of copper sulphate separate out.

Question 9.
Explain how painting of an iron gate prevents it from rusting?
Answer:
Painting of an iron gate prevents it from rusting because it cuts the direct contact of iron from the air and therefore there is no further exposure of iron to oxygen and moisture in the air which can cause rusting. Hence, rusting is prevented.

Question 10.
Explain why rusting of iron objects is faster in coastal areas than in deserts.
Answer:
Both the air and the moisture are required for rusting to take place. In coastal areas, the quantity of moisture present in the air is more than in deserts. In desert areas, the amount of moisture in the air is very low. Therefore, rusting of iron objects is faster in coastal areas than in deserts.

Question 11.
The gas we use in the kitchen is called liquefied petroleum gas (LPG). In the cylinder it exists 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.
a. Process-A is a chemical change.
b. Process-B is a chemical change.
c. Both processes A and B are chemical changes.
d. None of these processes is a chemical change.
Answer:
b. Process-B is a chemical change.

Question 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.
a. Process-A is a chemical change.
b. Process-B is a chemical change.
c. Both processes A and B are chemical changes.
d. None of these processes is a chemical change.
Answer:
c. Both processes A and B are chemical changes.

NCERT Extended Learning Activities and Projects

Question 1.
Describe two changes that are harmful. Explain why you consider them harmful. How can you prevent them?
Hint:
Two changes which are harmful are:
a. Rusting of iron: When iron is left exposed to air it reacts with oxygen and water in the air to form a powdery substance called rust.
Rusting of iron is harmful as rust slowly eats away the iron leading to its considerable loss. Rusting can be prevented by oiling, polishing and painting.

b. Spoilage of food grains: Food grains get spoiled over a period of time. This causes a loss to us. It can prevented in the following ways:

• Drying food grains before storage.
• Keeping the food grains in safe, cool and dry place.
• Spraying insecticides in godowns.
• Cleaning and packaging of food grains before storage.

Question 2.
Take three glass bottles with wide mouths. Label them A, B, C. Fill about half of bottle A with ordinary tap water. Fill bottle B with water which has been boiled for several minutes, to the same level as in A. In bottle C, take the same boiled water and of the same amount as in other bottles. In each bottle put a few similar iron nails so that they are completely underwater. Add a teaspoonful of cooking oil to the water in bottle C so that it forms a film on its surface. Put the bottles away for a few days. Take out nails from each bottle and observe them. Explain your observations.

Hint:
In test tube B: Formation of rust will take place since air from the atmosphere will dissolve in boiled water as it is uncovered.
In test tube C: No rust formation will occur since only water is present. No air is present in it as oil cuts off supply of air.
By the above observations we conclude that both air and water are essential for rusting. If out of these one is missing, rusting will not take place.

Question 3.
Prepare crystals of alum.
Hint:
Prepare a supersaturated solution of alum in a beaker by dissolving the powdered alum in water. For this, take a beaker half filled with water on a stand and heat it till it starts boiling. Add alum slowly to this solution. Keep on adding alum until no more alum can be dissolved. Filter the warm solution into another beaker. Now keep the filtered solution in a water bath containing ice. Do not disturb the solution. Large crystals of solid alum will be formed at the base of beaker when solution cools down.

Question 4.
Collect information about the type of fuels used for cooking in your area. Discuss with your teacher/parents/ others which fuels are less polluting and why.
Hint:
The following types of fuels are used in our area:
a. Solid fuels: coal, dung cake, wood, etc.
b. Liquid fuel: Kerosene oil.
c. Gaseous fuel: LPG. LPG is a less polluting fuel.

Activity 1

Objective: To study the change in state of ice.
Materials Required: A piece of ice, glass/ plastic tumbler.
Procedure:

• Take some ice in a glass or plastic tumbler.
• Melt some portion of ice by placing the tumbler in the sun.
• Now we have a mixture of ice and water.
• Now place the tumbler in a freezing mixture.
• The mixture becomes solid ice once again.

Observations: On heating the ice, it is converted into water and on freezing, it again changes into ice.
Conclusion: In this activity, solid changes into liquid and liquid changes back into solid. Thus, there is no change in the properties of water.

Activity 2

Objective: To study the change in state of water. Materials required: Water, beaker, Bunsen burner and a pan with handle.
Procedure:

• Take some water and boil it in a beaker.
• Water vapour rises from the surface of water.
• Hold an inverted pan by its handle over the steam at some distance from the boiling water. You can also keep some ice cubes over the pan.
• Observe the inner surface of the pan.

Observations: When the water heated, it is converted into steam. On cooling down, the steam it converted into water again.
Conclusion: In this activity, there is no change in the properties of water. No new substance is formed. So, the boiling of water to form steam is a physical change.

Chemical Properties: The internal properties of a substance which are not directly observable from outside are known as its chemical properties. For example, curd is a product of milk but the internal properties of milk and curd are completely different.

Chemical Change: These changes are the changes in which the composition and chemical properties of a substance get changed. In chemical changes, new substances are produced. These changes are permanent and irreversible. For example, burning of a candle, formation of curd from milk, ripening of fruits, rusting of iron and silver jewellery getting tarnished or copper articles getting covered by green layer are all chemical changes.

Characteristics of Chemical Change:

• A chemical change is a permanent change. It usually cannot be reversed by simple physical processes.
• A lot of energy in the form of heat, light, etc., is either absorbed or given out in a chemical change.
• A permanent change in colour may take place in a chemical change.
• A change in smell or odour may take place or a new smell may be given off in a chemical change.
• A gas may evolve in a chemical change.
• A sound may also be produced in a chemical change.

Some examples of chemical changes are:
i. Burning: Burning of any substance such as coal, wood, etc., is always a chemical change and is accompanied by production of heat. When magnesium ribbon is burnt in air, it produces a dazzling white flame leaving behind ashes of magnesium oxide. When these ashes are dissolved in water, magnesium hydroxide (a base) is produced. Both these are chemical changes and can be represented as follows:
Magnesium (Mg) + Oxygen (O₂) → Magnesium oxide (MgO)
Magnesium oxide (MgO) + Water (H₂O) → Magnesium hydroxide [Mg(OH)₂]

Activity 3

Objective: To study burning of magnesium ribbon in air.
Materials Required: A magnesium ribbon, sand paper and candle.
Procedure:

• Get a small piece of a thin strip or ribbon of magnesium.
• Clean its tip with sandpaper.
• Bring the tip near a candle flame.
• Hold it for some time and observe.

Observations: It bums with a brilliant white light. When it is completely burnt, it leaves behind a powdery ash. It is called magnesium oxide.
Conclusion: Heat and light are given out in this process. It is not possible to recover magnesium ribbon in the original form from the white powdery ash. Therefore, burning of magnesium ribbon is a chemical change.

ii. Reaction of copper sulphate with iron is also a chemical change which represents a change is colour by formation of a new substance.

Activity 4

Objective: To study the reaction between copper sulphate solution and iron (iron nail/ shaving blade).
Materials Required: Test tube, copper sulphate, two glass beakers and an iron nail or a shaving blade.
Procedure:

• Dissolve about a teaspoonful of copper sulphate (blue vitriol or neela thotha) in about half a cup of water in a glass tumbler or a beaker.
• Add a few drops of dilute sulphuric acid to the solution. You should get a blue coloured solution.
• Save a small sample of the solution in a test tube or a small glass bottle.
• Drop an iron nail or a used shaving blade into the remaining solution.
• Wait for half an hour or so. Observe the colour of the solution again.
• Compare it with the colour of the sample solution saved separately.

Observations: Take out the nail or the blade. The changes that you noticed are due to a reaction between copper sulphate and iron. The change in colour of the solution from blue to green is due to the formation of iron sulphate, a new substance. The brown deposit on the iron nail is copper, another new substance. Conclusion: It can be said that iron reacts with copper sulphate to form iron sulphate and copper. The equation can be written as:
Copper sulphate solution (blue) + Iron → Iron sulphate solution (green) + Copper (brown deposit)

iii. Reaction between vinegar and baking soda is also a chemical change. Vinegar reacts with baking soda to produce carbon dioxide gas which turns lime water milky. The reaction can be represented as:
Carbon dioxide (CO₂) + Lime water [Ca(OH)₂] → Calcium carbonate [CaCO₃] (milky) + Water (H₂O)

Activity 5

Objective: To study the reaction between vinegar and baking soda.
Materials Required: Vinegar, baking soda, lime water, test tubes, rubber cork and delivery tube.
Procedure:

• Fit one end of the delivery tube into a one-holed cork.
• Fill one test tube with vinegar and add a pinch of baking soda to it.
• Close the mouth of this tube with cork fitted with delivery tube.
• Immerse the other end of the delivery tube into lime water as shown below.

Observation: Bubbles of gas are seen in vinegar. This gas turns lime water milky white in colour.
Conclusion: Carbon dioxide is released in the above reaction which turns lime water milky. It is a chemical change. The equation can be represented as:
Baking soda (NaHCO₃) + Vinegar (CH₃COOH) → Sodium acetate (CH₃COONa) + CO₂ + H₂O

Rusting of Iron: Iron reacts with oxygen and moisture present in the atmosphere to form a brown, flaky substance called rust. Rusting of iron is an undesirable change because the layer of rust formed falls off, exposing the metal to further rusting leading to corrosion of iron. As a result, iron objects become weak with passage of time. The process of rusting can be represented by the following equation:
Iron (Fe) + Oxygen (O₂) + Water (H₂O) → Iron oxide (Fe₂O₃.xH₂O)
The iron oxide is called rust. Rust of iron is chemically different from iron and hence rusting is a chemical change.

Methods to Prevent Rusting: Whenever you get iron, water and oxygen together, you get rust. So the best way to prevent rusting is to keep them apart. There are different methods to prevent rusting:

• Painting: Painting the iron surface will create a barrier between the iron and the atmosphere which will protect the iron from rusting.
• Oiling and Greasing: When the iron objects, such as machines, are coated with a thin layer of oil or grease, it prevents them to come in contact with moist air. Thus, rusting does not take place.
• Galvanisation: Galvanisation is a process in which the iron sheets are coated with a layer of zinc which prevents rusting. Zinc gets oxidised more readily than iron. So, the iron remains protected. It is done in ships and many other articles.
• Electroplating: Iron sheets can be electroplated with a metal which is more reactive than iron so that instead of iron getting oxidised, the other metal gets oxidised (because it is more reactive).
• Alloying: Mixing of two or more metals or metals and non-metals is called alloying and the substance formed is called on alloy. It also prevents rusting. For example, stainless steel is on alloy of iron, carbon, chromium, nickel and manganese. It does not rust.

Crystallisation: Crystallisation is a technique used for the purification of substances. It is a separation technique to separate pure solids from a solution. Crystallisation is an example of a physical change. For example, common salt is obtained from seawater by evaporation and crystallisation. Similarly, when copper sulphate is dissolved in hot acidified water and then cooked, pure crystals of copper sulphate are obtained.

Class 7 Science Chapter 6 Physical and Chemical Changes Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What are the two main kinds of changes?
Answer:
Physical changes and chemical changes.

Question 2.
Which property of water changes during its evaporation?
Answer:
Physical property, i.e., state changes.

Question 3.
Is burning of a piece of paper a reversible or an irreversible change?
Answer:
It is an irreversible change.

Question 4.
What is rust?
Answer:
Iron reacts with oxygen and moisture present in the atmosphere to form a brown, flaky substance called rust. It is chemically iron oxide.

Question 5.
What kind of change is rusting?
Answer:
Chemical change.

Question 6.
What are the essential conditions for rusting?
Answer:
Presence of moisture and presence of oxygen in the air.

Question 7.
What is the nature of aqueous solution of magnesium oxide?
Answer:
When magnesium oxide is dissolved in water, it forms an aqueous solution which is basic in nature. The reaction between magnesium oxide and water is: Magnesium oxide (MgO) + Water (H₂O) → Magnesium hydroxide [Mg(OH)₂] In this reaction a new product is formed, which is magnesium hydroxide which is a base.

Question 8.
Give two examples of physical changes.
Answer:
Boiling of water, mixing sand and water.

Question 9.
Which type of change occurs during crystallisation?
Answer:
Physical change.

Question 10.
Which of the two is a permanent change-chemical change or physical change?
Answer:
Chemical change is a permanent change.

Question 11.
What is the colour of flame when magnesium is burnt?
Answer:
Dazzling white colour.

Question 12.
Name the gas released when baking soda is mixed with vinegar.
Answer:
Carbon dioxide.

Question 13.
What happens when carbon dioxide is passed through lime water?
Answer:
Lime water becomes milky due to the formation of calcium carbonate.

Question 14.
What is blue vitriol?
Answer:
Crystals of copper sulphate pentahydrate are blue in colour. So, solution of copper sulphate in water it is commonly known as blue vitriol.

Question 15.
Name any two methods by which rusting of iron can be prevented.
Answer:
Rusting of iron can be prevented by painting and by galvanisation.

Question 16.
Name the technique for obtaining pure sugar from sugar solution?
Answer:
Crystallisation.

Short Answer Type Questions

Question 1.
Define galvanisation.
Answer:
The process of depositing a coat of zinc layer on articles made of copper, iron other metals, which get corroded when exposed to moist air for long time is called galvanisation. For example: Iron bridges and ships can be protected from rusting by galvanising the iron using zinc.

Question 2.
Define crystallisation.
Answer:
Crystallisation is a process that separates a pure solid in the form of its crystals from a solution. The crystallisation method is used to purify solids. For example, the salt we get from seawater can have many impurities in it. To remove these impurities, the process of crystallisation is used.

Question 3.
What are physical changes?
Answer:
A physical change is a type of change in which the form of matter is altered but one substance is not transformed into another. The size or shape of matter may be changed, but no chemical reaction occurs. Physical changes are usually reversible. For example, melting of ice, formation of steam, etc., are physical changes.

Question 4.
What is a chemical change?
Answer:
A chemical change occurs when one substance is transformed into one or more new products via a chemical reaction. Most chemical changes are not reversible. They involve evolution of heat, light, sound or gas. For example, burning of paper, formation of curd, etc., are all chemical changes.

Question 5.
Write the characteristics of a physical change?
Answer:
The characteristics of a physical change are:

• No new substance is formed in a physical change
• A physical change is a temporary change. It can be easily reversed.
• Very little energy (such as heat, etc.) is either absorbed or evolved in a physical change.
• A temporary change in colour may take place in a physical change.

Question 6.
Why is vapourisation of water a physical change? Explain.
Answer:
Evaporation is a physical change and not a chemical change. It is a physical change because it is going from the liquid phase to the gas phase, i.e., the physical property is being changed. It is not a chemical change because its molecules are still made of two hydrogen atoms and an oxygen atom. Hence, no new substance is formed.

Question 7.
Does the energy change take place both in physical and chemical changes?
Answer:
Yes, all types of changes involve energy changes. During a change, energy is either evolved or absorbed. Burning of candle is a chemical change and energy is evolved in it. Evaporation of liquid is a physical change and energy is absorbed in it.

Question 8.
Write the characteristics of a chemical change?
Answer:
The characteristics of a chemical change are:

• A chemical change is a permanent change. It usually cannot be reversed.
• A lot of energy in the form of heat, light, etc., is either absorbed or given out in a chemical change.
• A permanent change in colour may take palace in a chemical change.
• A change in smell may take place in a chemical change
• A new substance is always formed in a chemical change.
• Sound may be produced or a gas may evolve in a chemical change.

Question 9.
What happens when iron nails are dipped in copper sulphate solution?
Answer:
When iron nails are dipped in copper sulphate solution, then after some time a brown layer of copper gets deposited on iron nails. This change is due to the chemical reaction between copper sulphate solution and iron. The colour of copper sulphate solution also changes from blue to green colour due to the formation of iron sulphate.
Iron nail + Copper sulphate solution (Blue) → Iron sulphate (Green) + Copper (Brown deposit)

Question 10.
Ozone acts as a natural shield against ultraviolet radiations. Explain.
Answer:
Ozone protects us from the harmful ultraviolet radiations which come from the sun. Ozone absorbs this radiation and breaks down to oxygen. If ultraviolet radiations were not absorbed by ozone, it would reach the earth’s surface and cause harm to us and other life forms.

Question 11.
Is burning always a desirable change? Explain.
Answer:
No, it is not always a desirable change. It is desirable during cooking of food, burning of candle, burning of fossil fuels to drive engines and other machines. However, it is undesirable at other times as it causes a lot of damage, e.g., forest fire causes lot of damage to plants, animals and our ecosystem. Therefore, it is not always a desirable change.

Question 12.
State the reason for each of the following:
a. Cooked food is stored in a refrigerator.
b. Common salt is stored in an airtight container during the rainy season.
Answer:
a. Low temperature in a refrigerator slows down the growth and multiplication of microorganisms. This prevents the cooked food from spoilage.
b. Common salt absorbs moisture and becomes wet during rainy season. Therefore, to keep common salt dry (free flowing), it is stored in an airtight container during the rainy season.

Long Answer Type Questions

Question 1.
State four differences between physical and chemical changes.
Answer:

Question 2.
State whether each of the following changes is slow/fast, reversible/ irreversible, desirable/undesirable or physical/chemical.
a. Rusting of iron
b. Melting of ice
c. Lighting of bulb
d. Growth of tree
e. Curdling of milk
Answer:
a. Rusting of iron is a slow, undesirable, irreversible and chemical change.
b. Melting of ice is a fast, undesirable, reversible and physical change.
c. Lighting of bulb is a fast, desirable, reversible and physical change.
d. Growth of tree is a slow, desirable, irreversible and chemical change.
e. Curdling of milk is a slow, desirable, irreversible and chemical change.

Question 3.
Why are chemical changes important in our daily lives?
Answer:
Chemical changes are very important in our lives because all new substances are formed as a result of chemical changes. For example, if a metal is to be extracted from an ore, such as iron from iron ore, we need to carry out a series of chemical changes. A medicine is the end product of a chain of chemical reactions. Useful new materials, such as plastics and detergents, are produced by chemical reactions. Indeed, every new material is discovered by studying chemical changes.

Question 4.
Which gas is released when vinegar and baking soda are mixed? What happens when this gas is passed through lime water?
Answer:
When baking soda and vinegar are mixed with each other, carbon dioxide gas is released. When carbon dioxide is passed through lime water, calcium carbonate is formed. Calcium carbonate, makes lime water appear milky. The turning of lime water into milky solution is a standard test of carbon dioxide. The following reactions take place:
a. Vinegar + Baking soda → Carbon dioxide + Other substance
b. Carbon dioxide (CO₂) + Lime water [Ca(OH₂)] → Calcium carbonate (CaCO₃) + Water (H₂O)

Question 5.
What is rusting? How do we prevent rusting?
Answer:
Iron reacts with oxygen and moisture present in the atmosphere to form a brown, flaky substance called rust. Rust of iron is undesirable because the layer of rust formed falls off, exposing the metal to further rusting. As a result, iron objects become weak with the passage of time.
Iron (Fe) + oxygen (O₂) + water (H₂O) → Iron oxide (Fe₂O₃.xH₂O)
The iron oxide is rust.

Methods to prevent rusting:

• Putting oil or paint over the surface of iron articles.
• By the process of galvanisation.
• By electroplating.
• By using anti-rust solution.

Question 6.
Identify the type of change and state whether energy is absorbed or evolved in each one of the following events: Burning of a candle, lighting of a bulb, preparation of food by green plants, volcanic eruption, lightning.
Answer:

Picture-Based Questions

Question 1.
Observe the following figure and answer the question that follow:

a. What does this figure show?
b. Name the gas released.
c. Write the effect of the gas on lime water.
d. Write the reaction involved in the second test tube.
Answer:
a. This figure shows the reaction of acetic acid with baking soda.
b. The gas is carbon dioxide.
c. The lime water becomes milky.
d. Lime water [Ca(OH)₂] + Carbon dioxide (CO₂) → Calcium carbonate (CaCO₃) (milky) + Water (H₂O)

Question 2.
Identify the changes shown below and state in each case, whether it is a physical or a chemical change

Answer:
a. Rolling of dough into Chapati – physical change.
b. Cooking of Chapati – chemical change.
c. Melting of ice – physical change.
d. Burning of paper – chemical change.

NCERT Solutions for Class 7 Science

• Class 7 Science Chapter 1 Nutrition in Plants
• Class 7 Science Chapter 2 Nutrition in Animals
• Class 7 Science Chapter 3 Fibre to Fabric
• Class 7 Science Chapter 4 Heat
• Class 7 Science Chapter 5 Acids, Bases and Salts
• Class 7 Science Chapter 6 Physical and Chemical Changes
• Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals of Climate
• Class 7 Science Chapter 8 Winds, Storms and Cyclones
• Class 7 Science Chapter 9 Soil
• Class 7 Science Chapter 10 Respiration in Organisms
• Class 7 Science Chapter 11 Transportation in Animals and Plants
• Class 7 Science Chapter 12 Reproduction in Plants
• Class 7 Science Chapter 13 Motion and Time
• Class 7 Science Chapter 14 Electric Current and its Effects
• Class 7 Science Chapter 15 Light
• Class 7 Science Chapter 16 Water: A Precious Resource
• Class 7 Science Chapter 17 Forests: Our Lifeline
• Class 7 Science Chapter 18 Wastewater Story

These NCERT Solutions for Class 7 Science Chapter 5 Acids, Bases and Salts Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Acids, Bases and Salts NCERT Solutions for Class 7 Science Chapter 5

Class 7 Science Chapter 5 Acids, Bases and Salts Textbook Exercise Questions and Answers

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:
Ammonia 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 a natural indicator which is obtained from lichens. It is used to determine whether a given solution is acidic or basic.

Question 4.
Is the distilled water acidic/basic/ neutral? How would you verify it?
Answer:
Distilled water is neutral. One can verify it by showing that neither red nor blue litmus paper changes its colour when dipped in distilled water.

Question 5.
Describe the process of neutralisation with help of an example.
Answer:
The reaction between an acid and a base to form salt and water with the evolution of heat is called neutralisation reaction. For example, when the solution of sodium hydroxide and hydrochloric acid react with each other, the acidic nature of acid and the basic nature of base are destroyed. The resulting solution is a neutral solution.

Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H₂O) + Heat

In this reaction, the hydrogen ions from the acid reacts with the hydroxide ions of the base to from water and salt is formed.

Question 6.
Make ‘T’ if the statement is true and ‘F’ if it is false:
a. Nitric acid turns red litmus blue. (T/F)
b. Sodium hydroxide turns blue litmus red. (T/F)
c. Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)
d. Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
e. Tooth decay is caused by the presence of a base. (T/F)
Answer:
a. F,
b. F,
c. F,
d. T,
e. F.

Question 7.
Dorji has a few bottles of soft drink in his restaurant. But unfortunately, these are not labelled. 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 will take red and blue litmus papers and one by one dip them into each bottle of soft drink. The drink in which red litmus paper turns blue is the bottle of basic drink. The drink in which blue litmus paper turns red is the bottle of acidic drink. The drink in which both litmus papers show no changes in colour is of the neutral drink.

Question 8.
Explain why:
a. An antacid tablet is taken when you suffer from acidity.
b. Calamine solution is applied on the skin when an ant bites.
c. Factory waste is neutralised before disposing it into the water bodies.
Answer:
a. We take an antacid such as milk of magnesia to neutralise the excessive acid released in stomach during acidity.
b. Ant’s sting contains an acid called formic acid and when we apply calamine solution containing a base, it neutralises the effect of acid and prevents irritation.
c. Many factories waste contain acids. If they are allowed to flow into the water bodies, the acids will kill the aquatic life. Therefore, factory waste is neutralised before its disposal.

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:
Dip the turmeric indicator one by one in each liquid. The liquid in which the colour of turmeric indicator changes to red is basic in natural, i.e., sodium hydroxide. Since, we already identified sodium hydroxide. We will pour the sodium hydroxide in other two liquids. The liquid which gets warm after pouring the sodium hydroxide (base) solution in it is of hydrochloric acid as heat gets evolved in the process of neutralisation. The last one which shows no effect is the liquid of sugar solution.

Question 10.
Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Answer:
There can be two cases:

• The solution may be basic because blue litmus paper remains unaffected in basic medium.
• The solution can be neutral. A neutral solution has no effect on any indicator.

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 change 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).

NCERT Extended Learning Activities and Projects

Question 1.
Using the knowledge of acids and bases, write a secret message with the help of baking soda and beetroot. Explain how it works. (Hint: Prepare baking soda solution in water. Use this solution to write the message on a sheet of white paper with a cotton bud. Rub a slice of fresh beetroot over the message.)
Hint:
Beetroot acts as an indicator and changes colour upon reaction with the base, i.e., baking soda solution. Hence, message will reappear after some time.

Question 2.
Prepare red cabbage juice by boiling a piece of red cabbage in water. Use it as an indicator and test the acidic and basic solutions with it. Present your observations in the form of a table.
Hint:
Cut the cabbage leaves into pieces. Boil water in a pan. Place the cabbage pieces in a bowl and pour the boiling water in the bowl. Keep it for thirty minutes so that the cabbage pieces get soaked. Separate the juice from the leaves by squeezing. Place the glass jars about two inches apart. Pour chemicals (lemon juice, vinegar, detergent, soda, etc.) in separate jars.

Now test whether the chemical is a base or an acid. Pour a part of your cabbage into each jar. You may have to swirl your mixture a bit. If the mixture turns pink, the chemical is an acid and if it turns blue, the chemical is a base.

Question 3.
Bring the soil sample of your area, find out if it is acidic, basic or neutral. Discuss with farmers if they treat the soil in any manner.
Hint:
Litmus paper helps to determine whether the soil has the right pH balance for the plants to grow or not.

Dump a small amount of soil, about a teaspoon, into a clean container and add distilled water. The mixture should be soggier than mud but without much water, such that all the soil settles to the bottom quickly. Usually, about twice as much water as soil works well. Stir or shake the mixture to evenly distribute the soil. Dip the end of the litmus paper into the soil and water mixture. Hold it in the mixture for 1 or 2 seconds before pulling it out and then wait for a few seconds until the colour stabilises. If the paper turns red, the soil is acidic. It the paper turns blue, the soil is basic.

Question 4.
Visit a doctor. Find out the medicines, he prescribes to treat acidity. Ask him how acidity can be prevented.
Hint:
The medicines prescribed by the doctors are basic in nature and are called antacids. These medicines neutralise are the effect of acids.
To avoid acidity, one should eat small meals throughout the day instead of a few large meals. Also, one should healthy and avoid junk food.

Activity 1

Objective: To test the acidic or basic nature of the given solutions using litmus as the indicator.
Materials Required: Blue litmus paper, red litmus paper, given solution and dropper.
Procedure:

• Take all the given solutions in the labelled test tubes.
• Take one small piece each of the blue and the red litmus papers.
• Put a drop of the solution over each and observe the change in colour.
• Note down your observations.
• Repeat the same for all the solutions.

Observations:

Conclusion: Acidic substances turn blue litmus red and have no effect on red litmus. Basic substances turn red litmus blue and have no effect on blue litmus. Neutral substances have no effect on both the blue and the red litmus papers.

ii. Turmeric: It turns from yellow to red in alkaline (basic) solutions. While it remains yellow in acidic solutions.

Activity 2

Objective: To test the acidic or basic nature of the given substances by using turmeric paper as the indicator.
Materials Required: Filter/blotting paper, turmeric powder, brush, solutions of different
(acidic/basic) nature.
Procedure:

• Make a thick paste of turmeric powder (20 g) in distilled water.
• Apply this paste on a filter/blotting paper with a brush.
• Allow it to dry. When dry, cut it into strips for testing the solution.
• Take all the given solutions in different labelled test tubes.
• Start from the first solution.
• Take a strip of turmeric paper.
• Put a drop of the given solution over turmeric paper and notice any change in colour.
• Note down your observation.
• Repeat the above three steps for all the solutions one by one.

Observations:

Conclusion: Acidic and neutral solution remain unchanged i.e., yellow, when they react with the turmeric. Basic solutions turn yellow colour of turmeric to bright red when they react with turmeric.

iii. China rose: China rose is also a natural indicator. China rose indicator is a light pink coloured solution which is extracted from the red flowers of China rose plant and mixed with water. It turns acidic solution to dark pick (magenta) and basic solutions to green colour.

Activity 3

Objective: To test the acidic or basic nature of the given solutions by using the china rose extract as the indicator.
Materials Required: China rose indicator, water, beaker, dropper, solutions of different acids and bases.
Procedure:

• Collect some Chine rose petals and keep them in warm water (about 80 mL) for some time.
• When water becomes coloured, fitter out the petals and use the coloured water as indicator.
• Take about 2 mL of the first solution in a test tube.
• Add 5 drops of the China rose indicator to the solution.
• Observe the change in colour.
• Repeat the experiment with other solutions one by one.

Observations: Colour of the China rose indicator is light pink.

Conclusion: When the pink colour of China rose indicator turns magenta or dark pink, then the solution is acidic and when it turns green then the solution is basic. If there is no change in the colour, then the solution is neutral.

Neutral substances: Substances which are neither acidic nor basic are called neutral substances. These substances do not bring about any change in the colour of the indicators. Example of some neutral substances are salt, sugar, glucose, nitrogen, water, oxygen, etc.

Neutralisation: The reaction between an acid and a base to give salt and water is known as a neutralisation reaction. Heat is also evolved in this reaction.

Acids and bases react with each other to nullify the effect of each other. Let us consider a simple reaction between NaOH which is a base and dilute HCl which is an acid.

Salt: Salt is product of neutralisation reaction between an acid and a base. Salt formed because of neutralisation may be acidic or basic in nature. The acidic or basic nature of a salt depends upon the strength of the acid and the base used for neutralisation reaction.

Synthetic Indicators: The indicators prepared by humans in laboratory are called synthetic indicators. Phenolphthalein and methyl orange are some examples of chemicals which act as acid-base indicator. For example, phenolphthalein solution is colourless in acidic solution and it gives pink colour in basic solution. Similarly, methyl orange gives red colour in acidic medium and yellow colour in basic medium.

Neutralisation in Everyday Life:
i. Indigestion: Our stomach produces gastric juices which contain hydrochloric acid. Excess of HCl acid in our stomach causes indigestion and acidity. To relieve indigestion, doctors prescribe antacid tablets or syrup which contain milk of magnesia (magnesium hydroxide) and aluminium hydroxide. Since these are bases, they neutralise the effect of excessive acid in our stomach.

Therefore, while suffering from acidity, it is prescribed to take antacid which is bitter in taste, i.e., it is a base. On entering the body, the base neutralises the excess acid released into the stomach and convert it in salt and water.

ii. Ant Sting: The ant sting contains formic acid which when injected into the skin causes pain and irritation. By applying moist baking soda, which is a base, the effect of the sting can be neutralised.

iii. Soil Treatment: Plants do not grow well in excessive acidic as well as basic soil medium. When soil becomes more acidic, it is retreated with quick lime or slaked lime and when it becomes basic, organic matter is added to it.

iv. Factory Waste: Factory wastes are also treated so as to neutralise the waste. Otherwise it may kill aquatic life.

Class 7 Science Chapter 5 Acids, Bases and Salts Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What are acids?
Answer:
The chemical compounds which are sour in taste are called acids.

Question 2.
What are bases?
Answer:
The substances which are soapy in touch and bitter in taste are called bases.

Question 3.
What are indicators?
Answer:
The substances which are used to test whether the given substance is acidic or basic by indicating a colour change are called indicators.

Question 4.
What are alkalis?
Answer:
The bases which dissolve in water are known as alkalis.

Question 5.
Name the acid present in ant-sting that causes pain.
Answer:
Formic acid.

Question 6.
Why does turmeric stain on white shirt is turned to red when it is washed with soap?
Answer:
It is because the soap solution is basic and turmeric.

Question 7.
Name two synthetic indicators.
Answer:
Methyl orange and phenolphthalein.

Question 8.
What is acid rain?
Answer:
The rain containing excess of acids is called an acid rain.

Question 9.
Which acid is naturally present in our stomach?
Answer:
Hydrochloric acid (HCl).

Question 10.
What is the nature of distilled water?
Answer:
The distilled water is neutral.

Question 11.
State the nature of baking soda.
Answer:
Baking soda is basic in nature.

Question 12.
Where does the word acid come from?
Answer:
The word acid comes from the Latin word acere which means sour.

Question 13.
Why curd, lemon juice, orange juice and vinegar taste sour?
Answer:
These substances taste sour because they contain acids.

Question 14.
Which is the most commonly used natural indicator?
Answer:
The most commonly used natural indicator is litmus.

Question 15.
How acidic soil can be treated?
Answer:
When the soil is too acidic, it is treated with bases such as quick lime (calcium oxide) or slaked lime (calcium hydroxide).

Question 16.
What are salts? Give example.
Answer:
The product formed, other than water, by the neutralisation reaction of an acid a base is called salt. Salt may be acidic, basic or neutral in nature. Example: Sodium chloride.

Question 17.
Name the acid present in the following:
a. Tomato
b. Vinegar
c. Tamarind
Answer:
a. Oxalic acid
b. Acetic acid
c. Tartaric acid

Question 18.
Which base is used for removing grease and stains?
Answer:
Ammonium hydroxide is used for removing grease and stains.

Question 19.
How many types of litmus are there?
Answer:
There are two type of litmus:

1. Red litmus
2. Blue litmus

Question 20.
Name a substance which is used to neutralise the effect of excessive acid in our stomach.
Answer:
Milk of magnesia which contains magnesium hydroxide (base).

Short Answer Type Questions

Question 1.
What is litmus? Give uses of litmus.
Answer:
The most commonly used natural indicator is named as litmus. It is a purple coloured dye extracted from lichens. Uses: Litmus helps in the identification of acids and bases. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue.

Question 2.
Define organic acids?
Answer:
The acids which are found in plants and animals are called organic acids. For example, vinegar contains acetic acid, lemon juice contains citric, etc., are all organic acids.

Question 3.
What do you mean by soil treatment?
Answer:
When a farmer uses excessive chemical fertilisers in the soil, the soil becomes acidic. Plants do not grow well when the soil is either too acidic or too basic. When soil is too acidic, it is treated with bases. If the soil is basic, organic matter is added to it. Organic matter releases acids which neutralise the basic nature of the soil. This process of maintaining soil pH balance is called soil treatment.

Question 4.
Give an example each of acidic salt, basic salt and neutral salt.
Answer:
Salts are the compounds generally formed by neutralisation of an acid with base. They can be acidic, basic as well as neutral. Example of acidic salt is sodium bicarbonate, basic salt: magnesium chloride and neutral salt is sodium chloride.

Question 5.
State few properties of acids.
Answer:
Few properties of acids are:

• Acids are sour in taste.
• Acids turns blue litmus red.
• Acids do not react with ammonium salts.
• Acids are generally found in citrus fruits like lemon, vinegar, curd, amla etc.

Question 6.
State few properties of bases.
Answer:
Few properties of bases are:

• Bases are bitter in taste and soapy in touch.
• Bases turn red litmus blue.
• Bases do react with ammonium salts to give ammonium gas.
• Bases are generally found in soaps, window cleaner, milk of magnesia etc.

Question 7.
What is the effect of ant bite? How is its cured?
Answer:
When an ant bites, it injects the acidic liquid (formic acid) into the skin. It causes irritation and burning effect on the skin. The effect of the acid can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution which contains zinc carbonate. Being bases, they neutralise the effect of formic acid.

Question 8.
How do you prepare lime water?
Answer:
Dissolve some lime (chuna) in water in a bottle. Stir the solution and keep it for some time. Pour a little from the top. This is lime water.

Question 9.
What are the uses of China rose petals as indicators?
Answer:
China rose petals, when added to warm water, form coloured solution which may be used as an indicator. This indicator turns acidic solutions to dark pink and basic solution to green.

Question 10.
What do you understand by synthetic indicators?
Answer:
Indicators which are prepared artificially are called synthetic indicators. Phenolphthalein and methyl orange are examples of synthetic indicators. Phenolphthalein turns colourless in acidic solution and turns pink in basic solutions. Methyl orange turns red in acidic solutions and yellow in basic solutions.

Question 11.
What do you mean by a neutral solution? Give examples.
Answer:
The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. Examples- sugar solution, distilled water, salt, etc.

Question 12.
How does rain become acidic?
Answer:
The rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide (which are released into the air as pollutants) dissolve in raindrops to form carbonic acid, sulphuric acid and nitric acid, respectively, hence making the rain acidic.

Long Answer Type Questions

Question 1.
Mention two uses each of the following :
a. Ammonium hydroxide
b. Hydrochloric acid
c. Magnesium hydroxide
Answer:
a. Uses of ammonium hydroxide:

• To remove grease from window panes.
• To remove ink spots from clothes.

b. Uses of hydrochloric acid:

• It is used for the purification of common salt.
• It is used for cleaning of metals, before soldering, tinning and for galvanisation.

c. Uses of magnesium hydroxide:

• It is used in making antacids.
• It is used as a reagent in the chemistry laboratory.

Question 2.
Common indicators is cannot determine how acidic or basic a solution is. Explain.
Answer:
Common indicators, such as litmus, methyl orange and phenolphthalein can easily tell us whether a solution is acidic or alkaline but they cannot easily tell how much a given acidic solution is stronger than another acidic solution. It means they cannot really tell us the degree of acidic or basic nature of a solution.

Question 3.
How will you obtain China rose indicator solution?
Answer:
China rose is a natural indicator. First collect some China rose petals and put them in beaker. Add some warm water and keep the china rose petals immersed in water for some time till the water in the beaker turns into light pink colour. Remove the petals by filtration. This light pink coloured solution is the china rose indicator used for testing acids and bases. This indicator turns acidic solutions to dark pink (magenta) and basic solution to green.

Picture-Based Questions

Question 1.
a. Identify the indicator shown below.

b. What colour does it produce in acidic and basic solutions.
Answer:
a. It is China rose indicator.
b. It gives dark pink colour in acids and green colour in bases.

Question 2.
a. Identify the image shown below.

b. Which indicator is extracted from this source?
Answer:
a. Lichens.
b. Litmus solution is obtained from lichens that is used as indicator.

NCERT Solutions for Class 7 Science

• Class 7 Science Chapter 1 Nutrition in Plants
• Class 7 Science Chapter 2 Nutrition in Animals
• Class 7 Science Chapter 3 Fibre to Fabric
• Class 7 Science Chapter 4 Heat
• Class 7 Science Chapter 5 Acids, Bases and Salts
• Class 7 Science Chapter 6 Physical and Chemical Changes
• Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals of Climate
• Class 7 Science Chapter 8 Winds, Storms and Cyclones
• Class 7 Science Chapter 9 Soil
• Class 7 Science Chapter 10 Respiration in Organisms
• Class 7 Science Chapter 11 Transportation in Animals and Plants
• Class 7 Science Chapter 12 Reproduction in Plants
• Class 7 Science Chapter 13 Motion and Time
• Class 7 Science Chapter 14 Electric Current and its Effects
• Class 7 Science Chapter 15 Light
• Class 7 Science Chapter 16 Water: A Precious Resource
• Class 7 Science Chapter 17 Forests: Our Lifeline
• Class 7 Science Chapter 18 Wastewater Story

These NCERT Solutions for Class 7 Science Chapter 4 Heat Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Heat NCERT Solutions for Class 7 Science Chapter 4

Class 7 Science Chapter 4 Heat Textbook Exercise Questions and Answers

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

• Both thermometers consist of a long, narrow uniform glass tube.
• Both have a bulb at one end.
• Both contain mercury in bulb.
• Both use Celsius scale on the glass tube.

Differences:

• A clinical thermometer is used to measure human body temperature only while a laboratory thermometer is used to measure temperature of different objects other than human body.
• A clinical thermometer reads temperature between 35°C to 42°C while the range of a laboratory thermometer is -10°C to 110°C.
• Clinical thermometer has a kink near the bulb while there is no kink in a laboratory thermometer.

Question 2.
Give two examples each of conductors and insulators of heat.
Answer:
Conductors – aluminium, iron.
Insulators – plastic, wood.

Question 3.
Fill in the blanks:
a. The hotness of an object is determined by its ……………….
b. Temperature of boiling water cannot be measured by a ………………. thermometer.
c. Temperature is measured in degree ……………….
d. No medium is required for transfer of heat by the process of ……………….
e. A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ……………….
f. Clothes of ………………. colours absorb heat better than clothes of light colours.
Answer:
(a) temperature
(b) clinical
(c) Celsius
(d) radiation
(e) conduction
(f) dark

Question 4.
Match the following:

Answer:
i. (d)
ii. (c)
iii. (b)
iv. (a)

Question 5.
Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.
Answer:
If there is more than one layer of clothes, air would be trapped in between them. Air is a poor conductor of heat. This increases the insulation and thus becomes more comfortable to us by keeping us warm.

Question 6.
Look at figure shown below. 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:
Objects with white surface reflect more heat and absorb less. So, less heat from outside would enter the house through walls.

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) become 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 better conductor of heat than the stainless steel.

NCERT Extended Learning Activities and Projects

Question 1.
Go to the doctor or your nearest health centre. Observe the doctor taking temperature of patients. Enquire:
a. Why the doctor dips the thermometer in a liquid before use.
b. Why is the thermometer kept under the tongue.
c. Whether the body temperature can be measured by keeping the thermometer at some place other than the mouth.
d. Whether the temperature of different parts of the body is the same or different.
Hint:
a. The doctor dips the thermometer in a liquid so that, the mercury drops to 35 degrees and also so that the infections of the previous person who used the thermometer is also removed.
b. The thermometer is kept under the tongue because the intense heat of our body is present under our tongue.
c. We can measure the temperature of the body by keeping thermometer at some place other than mouth like armpit.
d. The temperature of different parts of the body is not exactly the same but it differs slightly.

Question 2.
Go to a veterinary doctor (a doctor who treats animals). Discuss and find out the normal temperature of domestic animals and birds.
Hint:
Normal body temperature varies greatly between animals. Normal temperature of an animal ranges from 38.3°C to 39.2°C. Normal temperature of a bird is around 40°C.

Question 3.
Wrap a thin paper strip tightly around an iron rod. Try to burn the paper with candle while rotating the iron rod continuously. Does it burn? Explain your observation.
Hint:
The paper doesn’t bum. The main reason for this consequence is that the iron rod has a high melting point and is a good conductor of heat and hence absorbs the heat and doesn’t allow the paper to reach its ignition temperature.

Question 4.
Take a sheet of paper. Draw a spiral on it as shown in the figure. Cut out the paper along the line. Suspend the paper, as shown in figure, above a lighted candle. Observe what happens. Think of an explanation.

Hint:
As you suspend the spiral paper above the candle. The air around the lighted candle heats up. Since hot air is lighter than cold air, the air that surrounds the candle rises and pushes on your spiral, causing it to spin. The upward movement of hot air causes the movement in spiral paper.

Question 5.
Take two similar transparent glass bottles having wide mouths. Put a few crystals of potassium permanganate or pour a few drops of ink in one bottle. Fill this bottle with hot water. Fill the other bottle with cold water. Cover the cold water bottle with a thick piece of paper such as a postcard. Press the postcard firmly with one hand and hold the bottle with the other hand. Invert the bottle and palace it on top of the hot water bottle. Hold both the bottles firmly. Ask some other person to pull the postcard. Observe what happens. Explain.
Hint:
It can be observed that the, coloured hot water initially ruses up and the clear cold water sinks down at the bottom of the first bottle. Gradually, they mix together to attain a uniform colour and temperature. This demonstrates the process of convection.

Activity 1

Objective: To find the degree of hotness or coldness by the sense of touch.
Materials required: Three bowls, hot water, ice-cold water and water at room temperature.
Procedure:

• Fill the first bowl with the warm water, the second with the ordinary water and the third with the ice-cold water.
• Dip your right hand into the first jar, then dip your left hand into the third jar. Let it be there for one minute and feel the temperature.
• Lift both of your hands each from the first and the third jar, then put it quickly into the second jar.

Observation: During the third step in the activity above, the right hand feels that water is cooler while the left hand feels the water warmer. It means that the touch-sensory organ gives the relative responses to the temperature. Therefore, it is required to use a device to measure the temperature of a body.

Conclusion: It can be said that our sense of touch fails to give an exact estimation of degree of hotness of a body.

Thermometer: Temperature is measured by a device called thermometer. The thermometer that measures the temperature of our body is called a clinical thermometer.

Clinical Thermometer: It consists of a long, narrow, glass the tube with a bulb at – one end filled with mercury. Thermometers have a narrow kink (or constriction) in the fine capillary tube. This constriction prevents the mercury from contracting and flowing back when it is removed from the human body (temperature of surroundings being lower). This enables the recording of the maximum temperature of the body conveniently. The mercury thread needs to be shaken back into the bulb before the thermometer is used again. There is a scale on the thermometer. The scale we use is Celsius scale, indicated by °C. In a clinical thermometer, the range of temperature is form 35°C to 42°C. The normal temperature of the human body is 37°C.

Reading a Thermometer: First of all, note the temperature difference between two bigger marks and also note the number of divisions between these two marks. For example, if the bigger marks read 1°C and there are 10 divisions between them, then one small division in read as \(\frac {1}{10}\) = 0.1°C.

To use it, the thermometer should be washed with an antiseptic. It should be held firmly and given a few jukes to bring the mercury level below 35°C. Its bulb should then be placed under the tongue for one minute before it is taken out to take the reading.

Precautions while using Clinical Thermometer:

• It should be washed with antiseptic before and after use.
• The initial level of mercury should be kept below 35°C.
• It should not be held by its bulb while reading it.
• It should not be kept in sun or near flame.
• It should be handled with care to avoid breakage.
• It should be used to measure human body temperature only.

Laboratory Thermometer: In a laboratory thermometer, the range is form -10°C to 110°C and there is no kink because of which the level of mercury falls rapidly. Such a thermometer can be safely used for measuring the boiling points, melting points or temperatures of substances other than the human body. They are specifically designed for lab purposes.

Precautions while using Laboratory Thermometer: Following are some precautions in addition to those of a clinical thermometer.

• It should be kept upright and not tilted.
• The bulb should be completely immersed in the substance whose temperature is to be measured.
• The bulb should not touch the container walls or base.

Celsius Scale: The Celsius scale to measure temperature was designed by Andres Celsius in 1742. On this scale, temperature is described in degree Celsius. Here, boiling point of water is taken 100°C while melting point of ice is taken 0°C. The other scale which was in use earlier is the Fahrenheit Scale (°F). It has a range of 32°F to 212°F as opposed to the Celsius scale.

Other Types of Thermometers:
i. Maximum- minimum Thermometer:
This thermometer is used to report the maximum and minimum temperatures of previous day reported in weather reports.
ii. Digital Thermometers: Mercury is a toxic substance and is very difficult to dispose off if the thermometer breaks. These days, digital thermometers are available which do not use mercury.

Transfer of heat: The heat always flows from a hotter object to a cooler object. The flow of heat stops when the two objects attain the same temperature. There are three modes of heat transfer. These are: conduction, convection and radiation.
i. Conduction: It is the process by which heat is transferred from the hotter region of an object to the colder region of the same object. Heat transfer in solids generally occurs through conduction.

Conductors: The materials that allow heat to pass through them easily are called conductors of heat. For example, metals like aluminium, iron, and copper are conductors.
Insulators: The materials that do not allow heat to pass through them easily are called poor conductors of heat or insulators. In other words, insulators are the poor conductors of heat. Objects such as wood, plastic, etc., are insulators.

Activity 2

Objective: To demonstrate the process of conduction.
Materials Required: Five small iron nails, wax, metal rod, burner and a matchbox.
Procedure:

• Fix the heads of the nails on the iron rod with the help of wax at equal distances.
• Arrange the rod as shown in the figure.
• Heat the rod at one end with a burner and observe.

Observation: As heat travels from the left side to the right side along the iron rod, it melts the wax. Due to this, nails fall down one by one.

Conclusion: During conduction, heat is transferred from one particle to the other by means of back and forth vibrations of the particles. There is no actual movement of the particles of the solid from its hotter end to the colder end during the conduction of heat through it.

ii. Convection: It is a type of heat transfer that can only happen in liquids and gases, because it involves movement of particles. Convection happens when there is a difference in temperature between two parts of a liquid or a gas. The hot part of a fluid (liquid or gas) rises up and the cooler part sinks dawn.

Sea breeze: The flow of cool air from the sea towards the land during the day in coastal areas is called sea breeze. The land gets heated faster than water during the day. Hence, air above land becomes hot and rises up creating a low pressure area. Cool air from water rushes in towards land to fill the space. Hence, windows in coastal areas are made to face the sea to receive the cool sea breeze.

Land breeze: The breeze blowing from the land towards the sea at night is called land breeze. During night, the land cools down faster than the water.
Hence, the hot air over the warm sea rises upwards and the cooler air from the land blows in towards the sea in the form of land breeze.

Activity 3

Objective: To show the transfer of heat by convection in air.
Materials Required: A candle.
Procedure:

• Light a candle and place it on a stand.
• Now place one hand above the flame (at a safe distance so that you don’t bum your hand) and the other at the side of the flame.

Observation: The hand kept above the flame feels quite hot but the hand kept on the side of the flame does not feel so hot.
Conclusion: The hand above the flame feels hotter since air gets heated by convection and rises up. On the other hand, the air on the side does not feel as hot because there is no convection.

iii. Radiation: It is the process by which heat is transferred without any contact or medium between the heat source and the heated object. We feel the heat from the sun even though we are not touching it. This heat from the sun reaches us by radiation. Thus, transfer of heat by radiation does not require any medium. For example, solar heater traps heat from the sun which can be used for cooking.

Kinds of Clothes we Wear in Summer and Winter: One should wear light coloured clothes, such as white, light pink, light sky blue and other light shades to keep cool because they reflect most of the sun rays back into the atmosphere. Dark fabrics, on the other hand, tend to absorb these rays and trap their heat making one feel even hotter. That is why we feel more comfortable in light-coloured clothes in summers and prefer to wear dark-coloured clothes in winters.

Woollen clothes are not warm but they keep us warm because wool is a poor conductor of heat and it also has air trapped in between the fibres. The trapped air prevents the flow of heat from our body to the cold surroundings as it is a poor conductor of heat. So, we feel warm after wearing woollen clothes in winters.

Nowadays, buildings are also constructed in such a way to trap layers of air by using hallow bricks to prevent heat transfer. This keeps the house cool in summers and warm in winters.

Class 7 Science Chapter 4 Heat Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is the use of kink in a clinical thermometer?
Answer:
It prevents mercury level from falling on its own when thermometer is removed from the body.

Question 2.
Does transfer of heat by radiation require any medium?
Answer:
The transfer of heat by radiation does not require any medium.

Question 3.
Do all hot bodies radiate heat?
Answer:
Yes, all hot bodies radiate heat.

Question 4.
How does heat transfer take place in liquids and gases?
Answer:
In liquids and gases, heat is transferred by convection.

Question 5.
What is the name of those thermometers which do not use mercury?
Answer:
Digital thermometers.

Question 6.
Why do we wear woollen clothes during winter?
Answer:
The wool is a poor conductor of heat. Also, it traps air between its fibres which acts as an insulator. Hence, woollen clothes keep us warm during winter.

Question 7.
Name the two types of thermometer.
Answer:
Clinical thermometer and laboratory thermometer.

Question 8.
What is the scale of temperature used in clinical thermometers.
Answer:
Degree Celsius (°C) scale.

Question 9.
What is the average body temperature of a healthy person?
Answer:
37°C.

Question 10.
Which of the two absorbs more radiation – a dark coloured object or a light coloured object?
Answer:
A dark coloured object.

Question 11.
What are the various methods of transfer of heat?
Answer:
There are three methods of transfer of heat: conduction, convection and radiation

Question 12.
Which type of clothes should be preferred in the month of June in India?
Answer:
Light-coloured clothes.

Question 13.
Which type of cloths should be preferred in the month of February in India?
Answer:
Dark-coloured clothes.

Question 14.
What is a laboratory thermometer?
Answer:
A laboratory thermometer is used for measuring the temperature of substances in a laboratory.

Question 15.
What is the range of a laboratory thermometer?
Answer:
-10°C to 110°C.

Short Answer Type Questions

Question 1.
What is conductor?
Answer:
The materials that allow heat to pass through them easily are called conductors. For example, metals like aluminium, iron and copper.

Question 2.
Define clinical thermometer. Explain its structure with diagram.
Answer:
The temperature is measured by a device called thermometer. The thermometer that measures our body temperature is called clinical thermometer. It consists of a long, narrow glass tube with a bulb fitted at one end. The bulb is filled with mercury. In a clinical thermometer, the range of temperature is form 35°C to 42°C.

Question 3.
What is conduction?
Answer:
Conduction is a process in which transfer of heat takes place between objects by direct contact. In solids generally, the heat is transferred from the hotter end of an object to its cooler end by the process of conduction.

Question 4.
What is the use of the maximum-minimum thermometer?
Answer:
The maximum and minimum temperature of the atmosphere reported in weather reports is measured by the thermometer called the maximum-minimum thermometer.

Question 5.
What are the different types of thermometers other than clinical and laboratory thermometers?
Answer:
There are two other type of thermometers:

• Maximum- minimum thermometer: This thermometer is used to report maximum-minimum temperature of the day.
• Digital thermometer: Mercury is a toxic substance and is very difficult to dispose off if a thermometer breaks. These days digital thermometers are available which do not use mercury.

Question 6.
Why is conduction only possible in solids?
Answer:
In solids, generally, the heat is transferred by the process of conduction because particles of solids are closely packed and heat is transferred from the hotter end to the colder end of an object. In liquids and gases, the particles are loosely packed and are in motion. Hence, heat transfer by direct contact is difficult.

Question 7.
What is an insulator?
Answer:
The materials that do not allow heat to pass through them easily are called insulators. Insulators are the poor conductors of heat. Materials such as wood, plastic, etc., are insulator.

Question 8.
Why is convection not possible in solids?
Answer:
The molecules of a solid are held strongly and tightly due to intermolecular forces. As these molecules cannot travel to the source of heat energy, convection is not possible in case of solids.

Question 9.
How do woollen clothes keep us warm in the winter?
Answer:
Woollen clothes are not warm but they keep us warm because wool is a poor conductor of heat and it also has air trapped in between the fibre. The trapped air prevents the flow of heat from our body to the cold surroundings. So, we feel warm after wearing woollen clothes.

Question 10.
What is the precaution that one must follow while handling a clinical thermometer?
Answer:
The following precautions must be taken while handling a clinical thermometer:

• Never hold the thermometer by the bulb while reading it.
• Wash the thermometer with water or antiseptic solution before and after use.
• It should be used to measure the temperature of human body only.
• Read the thermometer by keeping the level of mercury along the line of sight.

Question 11.
Why is mercury preferred in thermometers in place of water?
Answer:
Mercury used due to the following reasons:

• It expands uniformly.
• It does not stick to the walls.
• It is shiny and easy to see.
• It remains liquid at room temperature.

Question 12.
What are the precautions needed to be observed while reading a laboratory thermometer?
Answer:
Following precautions are needed to be observed while reading a laboratory thermometer:

• The thermometer should be kept upright and not tilted.
• Bulb should be surrounded from all sides by the substance of which the temperature is to be measured.
• The bulb should not touch the surface of the container.

Long Answer Type Questions

Question 1.
What are the different modes of heat transfer? Explain.
Answer:
Heat flows from a region of higher to lower temperature till both the bodies attain same temperature. There are three modes of transfer of heat:

1. Conduction: Conduction is a process in which transfer of heat takes place between objects by direct contact where heat is transferred from the hotter end of an object to its cooler end. This usually occurs in solids.
2. Convection: It is a type of heat transfer that can only happen in liquids and gases because it requires those liquids or gases physically moving. Convection happens when there is a difference in temperature between two parts of a liquid or a gas. The hot part of a fluid rises, and the cooler part sinks.
3. Radiation: Radiation is the process by which heat is transferred without any contact between the heat source and the heated object. We feel the heat from the sun even though we are not touching it. This heat from the sun reaches us by radiation. Thus, transfer of heat by radiation does not require any medium.

Question 2.
Describe with the help of diagrams, the sea breeze and the land breeze.
Answer:
Sea breeze: The flow of cool air from the sea towards the land during the day in coastal areas is called sea breeze. The land gets heated faster than water during the day. Hence, air above the land becomes hot and rises up creating a low pressure area. Cool air from water rushes in towards land to fill the space. Hence, windows in coastal areas are made to face the sea to receive the cool sea breeze.

Land breeze: The breeze blowing from the land towards the sea is called land breeze. During night, the land cools down faster than the water. Hence, the hot air over the warm sea rises upwards and the cooler air from the land blows in towards the sea in the form of land breeze.

Question 3.
Write the key differences between heat and temperature.
Answer:
The differences between heat and temperature can be drawn clearly on the following grounds:

• Heat is nothing but a form of energy in a body. As against this, temperature is something that measures the intensity of heat.
• The main feature of heat is that it travels from a hotter region to a cooler region unlike temperature, which rises when heated and falls when cooled.
• Heat possesses the ability to work but the temperature is used exclusively to gauge the extent of heat.
• The standard unit of measurement of heat is Joules while that of temperature is Kelvin, but it can also be measured in Celsius and Fahrenheit.
• Calorimeter is a device which is used to measure the heat in a body. On the other hand, temperature can be measured by thermometers.

Question 4.
Demonstrate with the help of an activity how heat travels in water?
Answer:
Take a round-bottom flask and fill it with water. Add a few crystals of potassium permanganate to the flask and heat it on a tripod stand as shown below.

As the water gets heated, the hot water starts rising up and the cold water moves towards the flame. This is seen by the movement of purple lines in the water. Also, this process continues till the entire volume of water gets heated. This process of transfer of heat in liquids is called convection.

Picture-Based Questions

Question 1.
Observe the following picture and tell what does this figure show?

Answer:
In the above picture, a girl is reading the temperature in a thermometer. This is a correct method of reading a clinical thermometer.

Question 2.
What do you observe in the following picture Explain the reason behind it.

Answer:
A metallic cap stuck on a glass bottle can be removed by pouring hot water over the cap. It expands due to a rise in its temperature and can be removed easily.

Question 3.
(a) Observe the following picture and identify (i) and (ii).

(b) Which of the above two occurs during the night time?
Answer:
(a) (i) Sea breeze, (ii) Land breeze.
(b) Sea breeze occurs during daytime and land breeze during night time.

NCERT Solutions for Class 7 Science

• Class 7 Science Chapter 1 Nutrition in Plants
• Class 7 Science Chapter 2 Nutrition in Animals
• Class 7 Science Chapter 3 Fibre to Fabric
• Class 7 Science Chapter 4 Heat
• Class 7 Science Chapter 5 Acids, Bases and Salts
• Class 7 Science Chapter 6 Physical and Chemical Changes
• Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals of Climate
• Class 7 Science Chapter 8 Winds, Storms and Cyclones
• Class 7 Science Chapter 9 Soil
• Class 7 Science Chapter 10 Respiration in Organisms
• Class 7 Science Chapter 11 Transportation in Animals and Plants
• Class 7 Science Chapter 12 Reproduction in Plants
• Class 7 Science Chapter 13 Motion and Time
• Class 7 Science Chapter 14 Electric Current and its Effects
• Class 7 Science Chapter 15 Light
• Class 7 Science Chapter 16 Water: A Precious Resource
• Class 7 Science Chapter 17 Forests: Our Lifeline
• Class 7 Science Chapter 18 Wastewater Story

These NCERT Solutions for Class 7 Science Chapter 3 Fibre to Fabric Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Fibre to Fabric NCERT Solutions for Class 7 Science Chapter 3

Class 7 Science Chapter 3 Fibre to Fabric Textbook Exercise Questions and Answers

Question 1.
You must be familiar with the following nursery rhymes:
i. ‘Baa baa black sheep, have you any wool.’
ii. ‘Marry had a little lamb, whose fleece was white as snow’.
Answer the following:
a. Which parts of the black sheep have wool?
b. What is meant by the white fleece of the lamb?
Answer:
a. The fleece (hair) of the black sheep has wool.
b. White fleece of the lamb means the white coloured hair on the skin of the sheep.

Question 2.
The silkworm is: (i) a caterpillar, (ii) a larva.
Choose the correct option:
a. (i)
b. (ii)
c. Both (i) and (ii)
d. Neither (i) nor (ii)
Answer:
c. Both (i) and (ii)

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: The process of keeping, feeding, breeding and taking medical care of useful animals is called rearing of animals. These animals produce one or more useful products for human use.

b. Shearing: The fleece (hair) of sheep is shaved off along with the thin layer of skin. This is similar to shaving beards or hair and this process is called shearing.

c. Sericulture: The rearing of silkworms for obtaining silk is called sericulture.

Question 5.
Given below is a sequence of steps in the processing of wool. Which are the missing steps? Add them.
Shearing, …………., sorting, …………., …………., ………….
Answer:
Shearing, Scouring, sorting, removing burrs, dying and rolling into yarns.

Question 6.
Make sketches of the 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? Sericulture, Floriculture, Moriculture, Apiculture and Silviculture.
Hints:
a. Silk production involves cultivation of mulberry leaves and rearing silkworms.
b. Scientific name of mulberry is Morus alba.
Answer:
a. Sericulture
b. Moriculture.

Question 8.
Match the words of column I with those given in column II.

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:
1D. Scour 1A. Wool
2D. Silk 2A. Mulberry
3D. Fibre 3A. Caterpillar

NCERT Extended Learning Activities and Projects

Question 1.
Paheli wants to know the maximum length of continuous silk thread that can be obtained from a cocoon. Find out for her.
Hint:
The maximum length of continuous silk that can be obtained from a cocoon is approximately 900 metres.

Question 2.
Boojho wants to know why caterpillars need to shed their skin when they grow bigger but we humans do not. Do you have any idea?
Hint:
The skin of caterpillars does not grow. As their body grows, they have to move out of their skin because it becomes too tight for them. However, humans’ skin also grows with their body and hence is not required to shed.

Question 3.
Boojho wants to know why caterpillars should not be collected with bare hands. Can you help him?
Hint:
Caterpillars are toxic and can cause allergy when touched with bare hands.

Question 4.
Paheli wanted to buy a silk frock and went to the market with her mother. There they found that the artificial (synthetic) silk was much cheaper and wanted to know why. Do you know why? Find out.
Hint:
Artificial silk or rayon is produced in mills in bulk at one time and requires less labour and skill whereas original silk is produced by the silkworms and it requires a lot of skill, labour and time to treat the worms and extract silk from them. Hence artificial silk is cheaper than natural silk.

Question 5.
Someone told Paheli that an animal called ‘Vicuna’ also gives wool. Can you tell her where this animal is found? Look for this in a dictionary or an encyclopaedia.
Hint:
Vicuna are native to the central Andes in South America. They are found in Peru, north-western Argentina, Bolivia, and northern Chile.

Question 6.
When handloom and textile exhibitions are held, certain stalls display real moths of various varieties of silk and their life histories. Try and visit these stalls with elders or teachers and see these moths and stages of their life history.
Hint:
Do yourself.

Question 7.
Look for eggs of any moth or butterfly in your garden or park or any other place full of plants. They look like tiny specks (dots) laid in a cluster on the leaves. Pull out the leaves containing eggs and place them in a cardboard box. Take some leaves of the same plant or another plant of the same variety, chop them and put them in the box. Eggs will hatch into caterpillars, which are busy eating day and night. Add leaves every day for them to feed upon. Sometimes you may be able to collect the caterpillars. But be careful. Use a paper napkin or a paper to hold a caterpillar. Observe everyday. Note the.
a. number of days taken for eggs to hatch,
b. number of days taken to reach the cocoon stage,
c. number of days to complete life cycle.
Hint:
a. The hatching period varies from insect to insect. For example: in houseflies, the eggs hatch out within 10 to 15 hours of copulation.
Eggs of the moth or caterpillars hatch in 2-3 weeks.
b. In common mulberry silk moth, the caterpillar completely transforms into pupa within 12 to 15 days.
c. It depends upon the insect moth or

Activity 1

Objective: To study the burning of different fibres used for making cloth.
Materials Required: One fibre each of wool, silk, rayon and nylon, forceps, candle and a
matchbox.
Procedure:

• Light a candle. Hold a woollen fibre with forceps and bum it in the candle flame.
• Smell the vapours while burning by wafting carefully.
• Similarly bum fibres of silk, rayon and nylon one by one and then smell their vapours by wafting.

Observation: Fibres like silk and wool bum slowly and shrinks or curls away from the flame. On the other hand, fibres like rayon and nylon ignite and bum quickly and can continue to bum after the flame is removed.
Conclusion: Wool and silk are natural fibres. Very little smoke is produced on their burning but it smells like burnt hair (wool) or feathers (silk). Rayon and nylon are synthetic fibres.’ Burning these fibres produces black smoke and hazardous fumes.

Wool: Wool bearing animals have a thick coat of hair on their skin to help them trap a lot of air which keeps these animals warm. The skin of a sheep has two types of fibres:
i. coarse beard hair, and
ii. fine soft under-hair close to the skin. The fine soft hair fibres are used for making wool.

Selective Breeding: The process of selecting parents for obtaining special characters, such as fine soft under-hair in sheep, is termed as selective breeding.

Rearing and Breeding of Sheep: Sheep are herbivorous and prefer to eat grass and leaves. Shepherds in different parts of our country take their herds of sheep for grazing. Apart from this, rearers also feed them on a mixture of pulses, com, jowar, oil cakes and minerals. In winters, they are kept indoors and fed on leaves, grains and dry fodder. Once they develop a thick growth of hair, the hair is shaved off for getting wool.

Several breeds of sheep are found in different parts of our country. Some Indian breeds of sheep which provide wool are given in the table below.

Apart from the fleece of sheep, there are other sources of wool as well. Animals that provide wool are described below.

• Yak is reared in Tibet and Ladakh.
• Angora goats are reared in hilly regions such as Jammu and Kashmir. They provide Angora wool and Mohair.
• The under-fur of Kashmiri goat is very soft and is woven into fine shawls known as Pashmina shawls.
• Camels are reared in Rajasthan. The hair of camel can be woven into light¬weight and durable fabric.
• Alpaca are found in the Andes Mountains of South America. They are domesticated by the natives of Peru to get their soft wool. The woolly hair varies in colour from white to red to dark brown to black.
• Llama is found in mountains of South America. The male is used as a beast of burden. The female is highly valued for her milk, meat, hide and wool.

Processing of Fleece into Woollen Fabric:

• The fleece (hair) of sheep is shaved off along with the thin layer of skin. This is similar to removing beards or hair. This process is called shearing. It is done in hot weather to enable sheep to survive without hair coat. Since the uppermost layer of skin is dead, shearing does not hurt the animal and hair grow again after some time.
• After shearing, the fleece is washed properly to remove dirt and grease. This washing of fleece after shearing is called scouring. This is done in tanks or by machines.
• Clean hairy skin is sent to the factory where the hair of different textures are sorted (separated). This is called sorting.
• The small fluffy fibres, called burrs, are picked out from the hair. The fibres are scoured again and dried.
• After sorting and picking out of burrs, the fibres are dyed in desired colours.
• The fibres are then straightened, combed and rolled into yams. Wool yam is used in knitting sweaters and woollen cloths, i.e., fabric.

The risks faced by the workers in any industry are called occupational hazards. One such hazard is the bacterial disease anthrax. It is caused by a bacterium that lives on the skin of sheep and causes severe fatal blood disease in the workers of wool industry. It is also called sorter’s disease.

Silk: It is another important animal fibre. We get silk from silkworms. Silk fibre is obtained from the cocoons of the silk moth. The silk moth lives on the leaves of mulberry plants. The mulberry silk fibre is soft, lustrous and elastic and can be dyed in beautiful colours. The rearing of silk moth for obtaining silk is called sericulture.

Life Cycle of Silk Moth: There are four stages in the life cycle of a silk moth: egg, larva, pupa and adult.

The life history of a silk moth starts when a female silk moth lays eggs on mulberry leaves. This procedure happens once every year. The larvae or caterpillars hatch from the eggs of the silk moth. These caterpillars or silkworms feed on fresh mulberry leaves. After 25-30 days, the caterpillars grow in size and then become pupa.

In the pupa stage, it weaves a net to hold itself. It then swings its head from side to side, secreting proteinaceous fibres that hardens on coming in contact with air. The caterpillars cover itself completely with silk fibre and turns into a pupa. This covering is known as the cocoon. The moth continues to develop within the cocoon. The silk thread or yam is obtained from the cocoon of the silk moth.

Rearing of Silkworms: For obtaining silk for silk industry, silk moths are reared and their cocoons are collected to get silk thread. In the beginning, the female silk moth lays hundreds of eggs. These eggs are stored over a clean paper or a piece of cloth. These eggs are then sold to the silkworm farmers. The farmers keep the eggs under accurate temperature and humidity at a clean place. Bamboo trays are used to keep these caterpillars and some freshly chopped mulberry leaves are kept in the tray. The caterpillars eat these mulberry leaves day and night and grow in size. After 25-30 days approximately, the caterpillars stop eating the leaves and then move inside the small chambers in the bamboo trays to spin cocoons.

Processing of Silk: The cocoons are used to obtain silk threads. When the cocoons are exposed to the sun or steam or are boiled, the silk fibre gets separated. This process of getting silk threads from the cocoons to use it as silk is known as reeling of the silk. Reeling of the silk is carried out by special machines. These machines unwind the fibres of silk or threads from the cocoon. Silk fibres are then converted into silk threads to make different kinds of silk fabrics.

There is a variety of silk moths which yield different types of silk yarn such as Tassar silk, Mooga silk, Kosa silk. Mulberry silk, etc. They yield different varieties of coarse, smooth or shiny silk.

Silk Producing States of India: Mulberry silk is the main variety of silk produced in India. India is the second largest producer of silk in the world after China. About 90% of the mulberry silk comes from Karnataka, Andhra Pradesh and Tamil Nadu. States like Assam, Madhya Pradesh and Orissa also produce silk.

Discovery of Silk: Silk was discovered in China when the empress Si-Lung-Chi was asked by the emperor Hung-ti to find the cause of damaged leaves of mulberry. The empress found white worms eating those leaves and spinning shiny cocoons. A cocoon fell into her cup of tea and a tangle of delicate threads separated out from the cocoon. Silk industry was hence born and was later introduced to other countries.

Class 7 Science Chapter 3 Fibre to Fabric Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What are fibres?
Answer:
The thin strands of a thread are called fibres.

Question 2.
Name two animals which provide wool.
Answer:
Sheep and yak.

Question 3.
What are the sources of wool and silk?
Answer:
Animals are the sources of wool and silk.

Question 4.
From which animal is silk obtained?
Answer:
Silk Moth.

Question 5.
Where is the yak wool common in India?
Answer:
Ladakh.

Question 6.
What are burrs?
Answer:
The small fluffy fibres in wool are called burrs.

Question 7.
What is cocoon?
Answer:
A cocoon is a covering of silky threads that the larvae of the silk moth make for themselves before they grow into adults.

Question 8.
Where is Alpaca found?
Answer:
Alpaca is found in the Andes mountain of South America.

Question 9.
Where is the Lohi breed of sheep found in India?
Answer:
Lohi breed is found in Gujarat.

Question 10.
What is the most common type silk?
Answer:
Mulberry silk.

Question 11.
In which stage does the silk moth spin the silk fibre around itself?
Answer:
Caterpillar stage.

Question 12.
What is the food of silk moth?
Answer:
Mulberry leaves.

Question 13.
Which stage comes earlier in the life history of a silk moth: pupa or larva?
Answer:
Larva.

Question 14.
State whether the artificial silk is an animal fibre or a plant fibre?
Answer:
Plant fibre.

Question 15.
Which part of the animals is used to get wool?
Answer:
Wool is obtained from the fleece or hair.

Question 16.
What do Angora goats provide us?
Answer:
Angora wool.

Question 17.
How much time does a caterpillar take to turn into a mature pupa.
Answer:
3 to 4 weeks.

Question 18.
Where is cotton grown?
Answer:
Cotton is grown in fields. Cotton plants are grown at places having black soil and warm climate.

Question 19.
What is the scientific name of mulberry?
Answer:
Scientific name of mulberry is Morus alba.

Question 20.
What is sericulture?
Answer:
The rearing of silkworms for obtaining silk is called sericulture.

Short Answer Type Questions

Question 1.
What is sorting?
Answer:
Clean hairy skin sheared off animals is sent to the factory where hair of different textures are sorted (separated). This is called sorting.

Question 2.
Define reeling of silk?
Answer:
The process of taking out the silk fibres from the cocoon for use as silk is called reeling. Reeling is done in special machines which unwind the silk from cocoons.

Question 3.
Explain the process to obtain silk thread from cocoon.
Answer:
Cocoons of silk moth are used to obtain the silk fibres. These Cocoons are kept under the sun or boiled or exposed to steam. The silk fibres are thus separated out. This process of obtaining wool from the cocoons is called reeling of silk. Reeling is done in special machines.

Question 4.
What is scouring?
Answer:
Fleece, after shearing, is washed properly to remove dirt and grease. The washing of fleece, after shearing, is called scouring.

Question 5.
What do sheep feed on?
Answer:
Sheep are herbivores and prefer to eat grass and leaves. Apart from grazing sheep, rearers also feed them on a mixture of pulses, com, jowar, oil cakes (material left after taking out oil from seeds) and minerals.

Question 6.
Where is rearing and breeding of sheep popular in India?
Answer:
Rearing and breeding of sheep is popular in Jammu and Kashmir, Himachal Pradesh, Uttaranchal, Arunachal Pradesh, Sikkim and the plains of Haryana, Punjab, Rajasthan and Gujarat.

Question 7.
What are the two types of fibres that form the fleece of a sheep?
Answer:
The hairy skin of sheep has two types of fibres that form its fleece:

• the coarse beard hair, and
• the fine soft under-hair close to the skin.

Question 8.
What is selective breeding?
Answer:
Some breeds of sheep possess only fine under-hair. Their parents are specially chosen to give birth to sheep which have only soft under-hair. This process of selecting parents for obtaining special characters in their offspring, such as soft under-hair in sheep, is termed as ‘selective breeding’.

Question 9.
What is Angora wool?
Answer:
The wool which is obtained from the Angora goats is called Angora wool. The Angora goats are found in the hilly regions such as Jammu and Kashmir.

Question 10.
List a few animals in different regions that are reared for obtaining wool?
Answer:
Various kinds of animals are reared for wool:

• Yak: Yak wool is common in Tibet and Ladakh.
• Angora goats: They are used to obtain Angora wool. They are found in hilly regions.
• Kashmiri goats: They are used to obtain fur.
• Camel: It also provides fur.
• Llama and Alpaca: They are found in South America and also yield wool.

Question 11.
How are silk fibres of different textures prepared?
Answer:
The silk yam is obtained from the cocoon of the silk moth. There is a variety of silk moths which look very different from one another and the silk yam they yield is different in texture like coarse, smooth, shiny, etc. Thus, Tassar silk, Mooga silk and Kosa silk are obtained from the cocoons spun by different types of moths.

Question 12.
What happens when the silk caterpillar stops feeding?
Answer:
When the silk caterpillar stops feeding, its salivary gland starts secreting a sticky fluids (a protein called fibroin). This fluid hardness on exposure to air and forms a long thread of silk. This thread gets wrapped around its body to form a ball-like structure called cocoon.

Long Answer Type Questions

Question 1.
Explain the process of rearing of silkworms.
Answer:
An egg is laid by a female moth which is mostly the size of small dots. A female moth lays more than 350 eggs at a time in the spring. The eggs hatch due to the warmth in the air. This procedure happens once in every year. Hairy silkworms arise after the eggs crack. In this stage of silkworms, the growth happens. They feed on mulberry leaves and consume a large amount of these leaves for around 30 days before going to the next stage. Silkworms spin a protective cocoon around itself. It is of the size of a small cotton ball and is made of a single thread of silk. The cocoon is exposed to boiling water to unwind the silk thread. Then pupa changes into an adult moth. The female moth lays eggs after mating and thus the life cycle of silkworm begins again.

Question 2.
Name some breeds of sheep reared in our country. Explain the quality of wool they provide and the state where they are found.
Answer:

Question 3.
Explain the various steps involved in the process of making wool?
Answer:
The steps involved in wool production are as follows:

• The fleece (hair) of sheep is shaved off along with the thin layer of skin. This is similar to shaving beards or hair and this process is called shearing.
• Fleece, after shearing, is washed properly to remove dirt and grease. The washing of fleece, after shearing, is called scouring.
• Clean hairy skin is sent to the factory where hair of different textures is sorted (separated). This is called sorting.
• The small fluffy fibres, called burrs, are picked out from the hair. Fibres are again scoured and dried.
• After sorting and picking out of burrs, the fibres are dyed in desired colours.
• The fibres are then straightened, combed and rolled into yarns. Wool yam is used in knitting sweaters and woollen cloths, i.e., fabric.

Question 4.
What do you know about the discovery of silk?
Answer:
According to an old Chinese legend, the empress Si-lung-Chi was asked by the emperor Huang-ti to find the cause of the damaged leaves of mulberry trees growing in their garden. The empress found white worms eating mulberry leaves and spinning shiny cocoons around them. Accidentally, a cocoon dropped into her cup of tea and a tangle of delicate threads separated out from the cocoon. In this way, silk industry began in China and was kept a closely guarded secret for hundreds of years.

Question 5.
Explain the process of obtaining silk from cocoon.
Answer:
A pile of cocoons is used for obtaining silk fibres. The cocoons are kept under the sun or boiled or exposed to steam. The silk fibres separate out. This process of taking out threads from the cocoon for use as silk is called reeling the silk. Reeling is done in special machines, which unwind the threads or fibres of silk from the cocoon. Silk fibres are then spun into silk threads which are woven into silk cloth by weavers.

Picture-Based Questions

Question 1.
Draw a labelled diagram to show the life cycle of a silk moth.
Answer:

Question 2.
Identify the following animals and name the region where they are found.

Answer:
(a) Yak, found in Tibet and Ladakh
(b) Camel, found in Rajasthan.
(c) Alpaca, found in South America

NCERT Solutions for Class 7 Science

• Class 7 Science Chapter 1 Nutrition in Plants
• Class 7 Science Chapter 2 Nutrition in Animals
• Class 7 Science Chapter 3 Fibre to Fabric
• Class 7 Science Chapter 4 Heat
• Class 7 Science Chapter 5 Acids, Bases and Salts
• Class 7 Science Chapter 6 Physical and Chemical Changes
• Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals of Climate
• Class 7 Science Chapter 8 Winds, Storms and Cyclones
• Class 7 Science Chapter 9 Soil
• Class 7 Science Chapter 10 Respiration in Organisms
• Class 7 Science Chapter 11 Transportation in Animals and Plants
• Class 7 Science Chapter 12 Reproduction in Plants
• Class 7 Science Chapter 13 Motion and Time
• Class 7 Science Chapter 14 Electric Current and its Effects
• Class 7 Science Chapter 15 Light
• Class 7 Science Chapter 16 Water: A Precious Resource
• Class 7 Science Chapter 17 Forests: Our Lifeline
• Class 7 Science Chapter 18 Wastewater Story

These NCERT Solutions for Class 7 Science Chapter 2 Nutrition in Animals Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Nutrition in Animals NCERT Solutions for Class 7 Science Chapter 2

Class 7 Science Chapter 2 Nutrition in Animals Textbook Exercise Questions and Answers

Question 1.
Fill in the blanks.
a. The main steps of nutrition in humans are ……………., ……………., ……………., ……………., ……………..
b. The largest gland in the human body is …………….
c. The stomach releases hydrochloric acid and ……………. juices which act on food.
d. The inner wall of the small intestine has many finger-like out growths called …………….
e. Amoeba digests its food in the …………….
Answer:
a. ingestion, digestion, absorption, assimilation, egestion,
b. liver,
c. digestive,
d. villi,
e. food vacuole.

Question 2.
Mark ‘T’ if the statement is true and ‘F’ if it is false:
a. Digestion of starch starts in the stomach.
b. The tongue helps in mixing food with saliva.
c. The gall bladder temporarily stores bile.
d. The ruminants bring back swallowed grass into their mouth and chew it for some time.
Answer:
a. False,
b. True,
c. True,
d. True.

Question 3.
Tick (✓) mark the correct answer in each of the following:
a. Fat is completely digested in the:
(i) stomach
(ii) mouth
(iii) small intestine
(iv) large intestine
Answer:
a. (iii) small intestine

b. Water from the undigested food is absorbed mainly in the:
(i) stomach
(ii) food pipe
(iii) small intestine
(iv) large intestine
Answer:
b. (iv) large intestine

Question 4.
Match the items of column I with those given in column II:

Answer:
1. (b),
2. (c),
3. (a).

Question 5.
What are villi? What is their location and function?
Answer:
Villi are the finger-like projections in the inner walls of the small intestine. Villi increase the surface area for absorption of the digested food into the blood.

Question 6.
Where is the bile produced? Which component of the food does it help to digest?
Answer:
The liver secretes bile juice that is stored in a sac called gall bladder. The bile plays an important role in the digestion of fats.

Question 7.
Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.
Answer:
Cellulose is the carbohydrate that can be digested by ruminants. Ruminants have large sac-like structure called rumen between the small intestine and large intestine. The cellulose of the food is digested by the action of certain bacteria in the rumen which are not present in humans and hence they cannot digest cellulose.

Question 8.
Why do we get instant energy from glucose?
Answer:
We get instant energy from glucose because in the cells, glucose breaks down with the help of oxygen into carbon dioxide and water and energy is released.

Question 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. buccal cavity,
c. stomach,
d. small intestine,
e. large intestine.

Question 10.
Write one similarity and one difference between the nutrition in Amoeba and human beings.
Answer:
One similarity is that both Amoeba and humans have holozoic mode of nutrition. The difference is that human beings have complex structures for ingestion, digestion and egestion of food while Amoeba has simple process in which it engulfs the food with the help of pseudopodia and food gets trapped in the food vacuole.

Question 11.
Match the items of column I with suitable items in column II:

Answer:
a. (iii),
b. (iv),
c. (i),
d. (ii),
e. (v),
f. (vi)

Question 12.
Label the diagram of the digestive system.

Answer:

Question 13.
Can we survive only on raw, leafy vegetables/grass? Discuss.
Answer:
No, we cannot survive only on raw, leafy vegetable or grass. It is because the grass contains cellulose which is a type of carbohydrate that humans are not able to digest due to the absence of cellulose-digesting enzymes. Also, we need all the different types of nutrients for our survival and hence it is necessary to take a balanced diet.

NCERT Extended Learning Activities and Projects

Question 1.
Visit a doctor and find out:
a. Under what conditions does a patient need to be on a drip of glucose?
b. Till when does a patient need to be given glucose?
c. How does glucose help the patient recover?
Hint:
a. The various conditions under which a patient needs to be on a drip of glucose are:
i. when the patient is dehydrated.
ii. when the patient is unable to take his food orally.
iii. before doing any type of surgery.

b. A patient should be given glucose only during recovering stage (from any kind of illness).

c. Glucose mixes in the blood instantaneously as it is in the soluble form. Since in patients, the breakdown of food is slowed down due to illness, hence glucose is given because it releases instant energy.

Question 2.
Find out what vitamins are and get the following information.
a. Why are vitamins necessary in the diet?
b. Which fruits or vegetable should be eaten regularly to get vitamins?
Hint:
Vitamins are organic substances that are necessary for normal health and growth in both the animals and the humans. They are required in small quantities in the body.
a. They prevent diseases such as rickets, osteomalacia and scurvy. They promote absorption of calcium and phosphorus compounds from intestines and enable the body to use these information of teeth and bones. Write a one-page note on the information collected by you. You may take help of a doctor, a dietician, your teacher or any other person or from any other source.

b. Fibre rich fruits and vegetables should be eaten. Fruits should be included in our regular diet, especially citrus fruits like orange, lime, grapes, kiwi etc. Vegetables like carrot, beans, beetroot, lady’s finger, cabbage, etc., are rich in all minerals and vitamins, so they should be eaten regularly.

Question 3.
Collect data from your friends, neighbours and classmates to know more about “milk teeth”.
Tabulate your data. One way of doing it is given below:

Find out from at least twenty children and find the average age at which children lose the milk teeth. You may take help of your friends.
Hint:
Milk teeth are generally shed in 6-8 years of age.

Activity 1

Objective: To study the type of food and mode of feeding of the following animals: snails, ant, eagle, lice, butterfly, housefly, humming-bird, and mosquito.
Procedure: Make a list of various organisms and list their food and mode of feeding as listed below.
Observations:

Conclusion: Different organisms use different methods to consume food.

Interesting facts: Starfish opens the hard shells of animals on which it preys, like oysters. After opening the shell, the starfish pops out its stomach through its mouth and wraps the stomach around the captured animal. The stomach is then withdrawn into the body and the food is slowly digested.

Animal nutrition is a complex process and involves five important steps:

• Ingestion: Ingestion means eating food so as to get energy and carry out the activities of life. Ingestion is the process of taking food into the body.
• Digestion: Food that animals eat consists of large insoluble molecules which cannot be absorbed by their body directly. The breakdown of these large insoluble complex molecules, such as carbohydrates, into simpler soluble and usable forms by the body is called digestion.
• Absorption: After the food molecules become small and soluble, they pass through the walls of intestine and go into the blood. This process is called absorption
• Assimilation: The absorbed food is now carried to all parts of the body and to each and every cell through blood, so as to produce energy and make materials
  for the growth and repair of the body. This process is called assimilation.
• Egestion: The process through which undigested food is moved out of the body is called egestion.

Digestion in Humans: We take food through our mouth, digest and utilise it with the help of our digestive system.
Human digestive system consists of an alimentary canal and its associated glands. Various organs of human digestive system in sequence are: mouth or buccal cavity, oesophagus (food pipe), stomach, small intestine, large intestine, rectum and anus. Associated with the alimentary canal are some glands that secrete digestive juices. These are salivary glands, liver and pancreas. The alimentary canal along with the associated glands is called the digestive system.

Mouth or Buccal Cavity: We take in food through our mouth and the process of taking food into the body is called ingestion. The mouth consists of teeth, tongue and salivary glands that help in this process.
i. Teeth: Teeth are used for cutting, chewing, grinding and tearing the food before you swallow it. There are four types of teeth in humans- incisors, canines, premolars and molars.

Your front four teeth in each jaw are the incisors. They are used for biting and cutting. Next to incisors are canines. These are pointed and two in number on either side in each jaw. They are used for piercing and tearing the pieces of food.

Premolars are behind the canines, two in number on either side in each jaw. Molars are behind the premolars. They are meant for grinding and crushing the food. In an adult, they are six in number in each jaw, three each on either side of the premolars.

In young adults, there are 8 molars in all. The second set of 4 molars appears at the age eighteen or even later. These are called the wisdom teeth. Each jaw in an adult has 16 teeth. Hence, each adult human has 32 teeth in all.

In humans, the first set of teeth grows during infancy and they fall off at the age of 8-10 years. These are called milk teeth. The second set of teeth grows to replace them and are called permanent teeth.

ii. Tongue: It is a muscular organ attached at the floor of the buccal cavity at the back. It helps in mixing the chewed food with saliva and swallowing the food. The tongue has taste buds. These buds distinguish four basic tastes, i.e., salty, sour, sweet, and bitter. In addition, it helps us to speak.

iii. Salivary glands: The salivary glands present in the mouth secrete watery liquid called saliva. Saliva helps in the digestion of food. It contains an enzyme called salivary amylase (also called ptyalin). Salivary amylase acts on complex starch (a carbohydrate) and changes it into simple sugar in the mouth. Besides, saliva also contains enzymes that kill germs and bacteria that may enter the body along with the food. It also softens and lubricates the food for its easy passage along the alimentary canal.

Activity 2

Objective: To show that certain chemicals digest food.
Materials Required: Test tubes (two), test tube stand (one), water, iodine solution, amylase and a potato.
Procedure:

• Place a few potato pieces in a test tube. Add water to it and label this test tube A.
• Place the test tube A in the test tube stand.
• Place some more potato pieces in the second test tube. Now add water to it. Then add the digestive chemical amylase. Label this test tube B.
• Place the test tube B in the test tube stand.
• Let both the test tubes stand for 30 minutes, and then add iodine solution to both the test tubes.

Observations: Potato pieces in test tube A turn blue-black while those in test tube B do not.
Conclusion: Digestion has taken place as the starch in test tube B has been acted upon by amylase and hence it does not give starch test.

Oesophagus (Gullet or Food pipe): The swallowed food passes into the food pipe or oesophagus. Hence, oesophagus leads from the mouth to the stomach and it is made up of muscles. The food that we eat is pushed down the oesophagus to the stomach by peristaltic movements that occur all along the alimentary canal.

Stomach: Stomach is the thick-walled bag-like structure present on the left side of the abdomen. It is the widest part of the alimentary canal, and is roughly J-shaped. The stomach walls contain gastric glands which secrete various digestive juices called gastric juices. The stomach walls also secrete mucous and hydrochloric acid. This acid kills the bacteria that may have entered the body with food while the mucous protects the stomach lining from the damage by acid. The digestive juices digest the proteins by breaking them into simpler substances.

Small Intestine: Small intestine is highly 26 coiled and is about 7.5 m long. After leaving stomach, food enters the small intestine and last step of digestion takes place here. In the small intestine, the food is mixed with bile juice and pancreatic juice. Bile is secreted by the liver (a reddish-brown gland) and is stored in gall bladder while the pancreatic juice is secreted by the pancreas (a large cream-coloured gland below the stomach). These juices are important for the process of digestion. While bile helps in digestion of fats, pancreatic juice helps in the digestion of carbohydrates, proteins and fats. In the lower part of the intestine, various intestinal juices are also mixed with the food to complete the process of digestion. Carbohydrates are broken into simple sugars like glucose, fats into fatty acid and glycerol and proteins into amino acids.

Absorption in Small Intestine: The small intestine absorbs the digested nutrients from the food. The inner walls of the small intestine have thousand of finger¬like projections. These are called villi. The surface of the villi are richly supplied with blood vessels and absorb the digested food materials. The villi increase the surface area for the absorption of the digested food into the blood. The digested food is transported in the entire body through blood and assimilated by the cells. Here, glucose is broken down into carbon dioxide and water to release energy with the help of oxygen.

Large Intestine: The undigested and unabsorbed food enters large intestine. Large intestine has no digestive function to carry out. It is about 1.5 m long and helps in absorbing water from the undigested food material.

Rectum: It is the lowermost part of large intestine. The undigested waste material passes into the rectum, where it is sorted as semi-solid faeces. The faecal matter is passed out through the anus by the process of egestion.

Diarrhoea is a disorder of digestive system where a person needs to pass watery stool frequently. It may be caused by the intake of contaminated food or indigestion. Such patients should be given plenty of Oral Rehydration Solution (ORS) which is prepared by dissolving a pinch of salt or sugar in boiled and cooled water.

Digestion In Grass-eating Animals:
Grass-eating animals like cow, buffaloes, goat, sheep, etc., have a separate part of the stomach called rumen. The rumen contains cellulose digesting bacteria. These bacteria, present in the rumen of an animal, helps to digest cellulose (a carbohydrate) present the in grass food eaten by the animal.

The partially digested food in the rumen of an animal is called cud. Rumination is the process by which cud returns to the mouth in a small lump and the animal chews it. When the cud is thoroughly chewed in themouth of the animal, it is swallowed again. The animals which have rumen and carry out rumination are known as ruminants.

Many other animals such as horses, rabbit, etc., have a structure called caecum that helps in digesting cellulose by the action of various bacteria. Many animals, including humans cannot digest cellulose.

Tooth Decay: After eating food items, sweets, chocolates, cold drink and other sugars, if mouth is not washed properly, some leftover food and sugars remain attached to the teeth. The harmful bacteria breakdown these sugars and release acids. These acids gradually damage the teeth. This is called tooth decay which may lead to toothache and even loss of tooth.

Healthy teeth are white and healthy gums are pink. If proper care is not taken, teeth become yellowish due to the formation of a sticky film containing food particles, saliva and bacteria which may lead to loosening of the teeth. Hence, one should brush teeth at least twice daily and should thoroughly rinse the mouth after every meal.

Nutrition in Amoeba: Amoeba is a microscopic single-celled organism found in pond water. It has a cell membrane, a dense rounded nucleus and many small bubble¬like vacuoles in its cytoplasm. Amoeba constantly changes its shape and positions. Hence, it has no definite shape. It pushes out one or more finger-like projections, called pseudopodia or false feet for movement and capture of food. When it senses food, it pushes out pseudopodia around the food particles and engulfs it. The food becomes trapped in a food vacuole.

Various digestive juices secreted inside the food vacuole digest the ingested food. The digested food is absorbed be the cytoplasm to provide energy to the cell body. The undigested waste is expelled by the body through the vacuole.

Class 7 Science Chapter 2 Nutrition in Animals Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Define the term ingestion.
Answer:
The process of talking food into the body is called ingestion.

Question 2.
What is the other name of food pipe?
Answer:
The other name of food pipe is Oesophagus.

Question 3.
What is the function of salivary glands?
Answer:
Salivary glands secrete saliva that helps in softening and lubricating the food. It also contains salivary amylase that digests starch into simple sugars.

Question 4.
What is the length of small intestine in humans?
Answer:
The length of small intestine in humans is 7.5 cm.

Question 5.
What is the role of rectum in human digestive system?
Answer:
The rectum helps to store undigested waste material until it is passed out through anus.

Question 6.
Name the various types of teeth.
Answer:
The various types of teeth are incisors, canines, premolars and molars.

Question 7.
What is rumen?
Answer:
It is the part of stomach of some animals like cow, buffaloes and other grass-eating animals that contain cellulose digesting bacteria.

Question 8.
What is cud?
Answer:
The partially digested food in the rumen of a ruminant animal is called cud.

Question 9.
Where is the water from undigested food absorbed in the body?
Answer:
It is absorbed in the large intestine.

Question 10.
What are the different organs of alimentary canal?
Answer:
The different organs of the alimentary canal are mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus.

Question 11.
What is digestion?
Answer:
The process in which complex food materials are broken into simpler and absorbable substances is called digestion.

Question 12.
What is the function of digestive juices?
Answer:
The digestive juices convert complex substances of food into simpler, soluble and absorbable forms.

Question 13.
What is the role of incisors?
Answer:
The incisors are used for biting and cutting the food.

Question 14.
What is absorption?
Answer:
After the food molecules become small, they pass through the walls of intestine and go into blood. This process is called absorption.

Question 15.
Name the five stages of the animal nutrition.
Answer:

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

Question 16.
Where does the process of digestion start and where does it end?
Answer:
The digestion starts from the mouth and is completed in the small intestine.

Question 17.
Name the juice secreted by the salivary glands.
Answer:
The juice secreted by the salivary glands is saliva.

Question 18.
What is the function of large intestine?
Answer:
Large intestine absorbs water from the undigested food material.

Question 19.
What is the function of oesophagus?
Answer:
The walls of oesophagus pushes the food from mouth towards the stomach.

Question 20.
What the pseudopodia?
Answer:
The body of amoeba has finger-like projections which are called pseudopodia.

Question 21.
Where is the pancreas located?
Answer:
Pancreas is located just below the stomach in the abdomen.

Short Answer Type Questions

Question 1.
State the various types of teeth and their function in human body.
Answer:
There are four kinds of teeth in human beings. Incisors are four in number in each jaw and help to cut and bite the food. Canines are two in number in each jaw and help to piercing and tearing the food. Premolars are four in number in each jaw and help in chewing and grinding the food. Molars are six in number in each jaw and also help in chewing and grinding the food like premolars.

Question 2.
What is rumination? Explain.
Answer:
The grass-eating animals like cow, buffalo, etc., chew continuously even when they are not eating grass. They store the eaten grass in a separate part of the stomach. The is part is called rumen. Here the food gets partially digested to form cud. Later, the cud returns to the mouth and animals chew it. This process is called rumination and the animals are called ruminants.

Question 3.
What is tongue? Write its function.
Answer:
Tongue is a muscular organ in our mouth. It helps in mixing the chewed food with saliva and swallowing the food. The tongue senses various tastes in the food as it has sense organs called the taste buds.

Question 4.
What is the unique feature of stomach?
Answer:
The stomach is a large organ which expands when food enters into it. The muscular walls of the stomach help in mixing the food thoroughly with more digestive juices. Also, they secrete mucous and hydrochloric acid. The acid kills bacteria and the mucous protects the stomach lining from the action of acid.

Question 5.
Differentiate between absorption and assimilation?
Answer:

Question 6.
What does the gastric juice help to digest?
Answer:
The stomach secretes a digestive juice called gastric juice and hydrochloric acid. Protein present in the food is digested by the gastric juice.

Question 7.
What is cellulose?
Answer:
It is a type of complex carbohydrate. Many animals, including humans, cannot digest cellulose. The rumen in ruminants contain cellulose digesting bacteria.

Question 8.
What is the role of hydrochloric acid in human digestive system?
Answer:
Hydrochloric acid secreted inside the stomach makes the medium acidic for digestion of proteins by the gastric juices. Hydrochloric acid also causes disinfection of the food by killing the germs and bacteria.

Question 9.
How does the small intestine work in digestion of food in humans?
Answer:
The food in the small intestine is mixed with the bile juice from the liver and the pancreatic juice from the small intestine. While bile helps in the digestion of fats, pancreatic juice helps in the digestion of carbohydrates, proteins and fats. Intestinal juices from the small intestine are also mixed with the food and help in completing the process of digestion.

Question 10.
What happens when we do not clean our teeth after eating the food?
Answer:
If we do not clean our teeth after eating the food, then various harmful bacteria begin to live and grow on the food trapped in the teeth. These bacteria breakdown the sugar present in the food into acids and remain attached with teeth. The acid formed gradually damages the teeth. This is called tooth decay. This will eventually lead to pain or even loss of teeth.

Question 11.
At times, we feel burning sensation in our throat due to indigestion. Give the possible reason.
Answer:
It is due to the excessive spicy food we eat. When more amount of HCl is released by the stomach to digest the spicy food, then the mucus present in our stomach is not able to neutralise the effect of HCl. This sometimes gives rise to a burning sensation in our throat due to indigestion.

Question 12.
It is said that, ‘small intestine the site of the complete digestion’. Why it so?
Answer:
The small intestine receives the secretions of the liver and pancreas which help in the complete digestion of carbohydrates, proteins and fats. Hence, the digestion of food is completed here.

Long Answer Type Questions

Question 1.
Briefly explain the process of digestion in ruminants.
Answer:
Many animals including humans cannot digest cellulose. But ruminants can digest it. Ruminants include animals like cows, buffaloes and other grass-eating animals. These animals quickly swallow the grass and store it in a separate part of the stomach called rumen. The rumen contains cellulose digesting bacteria. The bacteria present in the rumen of the animal start to digest cellulose carbohydrate present in the grass food. Thus, the grass is partially digested in the rumen. The partially digested food in the rumen of the animals is called cud. After some time, the cud of the rumen returns to the mouth in small lumps and the animals chew it. This process is called rumination.

Question 2.
What is dental plaque? What harm can it do? How can the formation of plaque be prevented.
Answer:
If the teeth are not cleaned regularly, they become covered with a sticky, yellow layer of food particles and bacterial cells called dental plaque. Since plaque covers the teeth forming a layer over them, the alkaline salts cannot reach the tooth surface to neutralise the acid formed by the bacteria and hence tooth decay sets in. Brushing the teeth regularly after eating food, removes the plaque before bacteria produce acid. This will prevent tooth decay.

Question 3.
Explain the digestion in Amoeba.
Answer:
Amoeba is a microscopic organism and eats tiny plants and animals which float in water in which it lives. The mode of nutrition in amoeba is holozoic. The process of obtaining food by Amoeba is called phagocytosis. When it senses food in its surroundings, it projects various pseudopodia around it and engulf the food particle inside the food vacuole. Digestive juices digest the food inside the vacuole which is then absorbed be the cell cytoplasm. The waste is expelled out of the body by the vacuole.

Question 4.
Explain the human digestive system with the help of a labelled diagram?
Answer:
The human digestive system comprises of a group of organs and associated glands that work together in converting food into energy and other basic nutrients to obtain power for the body. The process of digestion starts from mouth and ends at anus. Alimentary canal is a long, muscular and coiled tube.

There are different organs in alimentary canal: mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus. When we take food in our mouth, salivary glands of mouth secrete saliva which moistens the food and digests starch. The tongue helps in chewing the food. From the mouth, food goes into the food pipe called oesophagus.

The food we eat is pushed down the oesophagus to the stomach by peristaltic movements. In the stomach, the food is churned and converted into a semi-solid paste. The stomach secretes a digestive juice called gastric juice that digests proteins. Then the food goes into the small intestine where the food is mixed with bile juice and pancreatic juice. These juices are important for digestion of fats, carbohydrates and proteins.

The undigested food moves from the small intestine to the large intestine where mainly absorption of water from the undigested food takes place. From the large intestine, the undigested food passes to the rectum which pushes it out of the body through the opening called anus.

Picture-Based Questions

Question 1.
Draw a diagram of tongue and label the regions of salt, bitter, sweet and sour sensations on it.
Answer:

Question 2.
Draw a diagram of arrangement of teeth in the buccal cavity of human beings and label the various types of teeth.
Answer:

Question 3.
a. Label the marks 1 and 2 shown in the diagram of digestive system of the ruminant animal given below.

b. Name the partially digested food in the rumen.
Answer:
a. 1. Rumen 2. Stomach
b. Partially digestive food in rumen is called cud.

NCERT Solutions for Class 7 Science

• Class 7 Science Chapter 1 Nutrition in Plants
• Class 7 Science Chapter 2 Nutrition in Animals
• Class 7 Science Chapter 3 Fibre to Fabric
• Class 7 Science Chapter 4 Heat
• Class 7 Science Chapter 5 Acids, Bases and Salts
• Class 7 Science Chapter 6 Physical and Chemical Changes
• Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals of Climate
• Class 7 Science Chapter 8 Winds, Storms and Cyclones
• Class 7 Science Chapter 9 Soil
• Class 7 Science Chapter 10 Respiration in Organisms
• Class 7 Science Chapter 11 Transportation in Animals and Plants
• Class 7 Science Chapter 12 Reproduction in Plants
• Class 7 Science Chapter 13 Motion and Time
• Class 7 Science Chapter 14 Electric Current and its Effects
• Class 7 Science Chapter 15 Light
• Class 7 Science Chapter 16 Water: A Precious Resource
• Class 7 Science Chapter 17 Forests: Our Lifeline
• Class 7 Science Chapter 18 Wastewater Story