SCIENCE KCT - 1 Question Paper 2024-25

7 Sci Chp 17 solusn

Solutions for Class 7th: Ch 17 Forests: Our Lifeline Science

 Exercises

1. Explain how animals dwelling in the forest help it grow and regenerate.

Answer

Animals dwelling in the forest help in various way for growth and regenerate. Some of them are:

(i) Herbivores animals clear the land by eating grass for the new growth of vegetation.

(ii) Animals also help in the seed dispersal and pollination.

(iii) Dead and decaying bodies of animals convert to humus after decomposition which increase the fertility of the soil of the forest.

(iv) Dungs of animals provide nutrient to various types of seedling to grow.

2. Explain how forests prevent floods.

Answer

Forest  acts as a natural absorber of rainwater and allows it to seep. It helps in controlling the flow of water and slows it down which helps in preventing flood. Also, the trees present in the forest prevents the rain from directly hitting the ground and bind the soil together which helps in absorption of the rain water and thus prevent flood.

3. What are decomposers? Name any two of them. What do they do in the forest?

Answer

The micro-organisms which convert the dead plants and animals to humus are known as decomposers.

Bacteria and fungi are the two examples of decomposers.

They play an important role in the decomposition of dead remains of the plants and animals

 and converting them to humus which add nutrient to the soil.

4. Explain the role of forest in maintaining the balance between oxygen and carbon dioxide in the atmosphere.

Answer

Forest play an important role in maintaining the balance between oxygen and carbon dioxide in the atmosphere. The green plants and trees present in the forest take in carbon dioxide which is released by the animals and release oxygen through the process of photosynthesis which are breathe in by the animals and thus maintains the balance between oxygen and carbon dioxide in the atmosphere.

5. Explain why there is no waste in a forest.

Answer

There is no waste in a forest because whatever produced here are utilized by the other organisms or plants for sustainability. Even the waste materials and dead remains which are produced are bodegradable and converted into humus which returns back the nutrient back to the soil.

6. List five products we get from forests?

Answer

Five products we get from forests are:

(i) Wood

(ii) Resins

(iii) Gum

(iv) Honey

(v) Medicines

7. Fill in the blank:

(a) The insects, butterflies, honeybees and birds help flowering plants in ___________ .

(b) A forest is a purifier of _____________ and _______________ .

(c) Herbs form the ______________ layer in the forest.

(d) The decaying leaves and animal droppings in a forest enrich the ______________ .

Answer

(a) The insects, butterflies, honeybees and birds help flowering plants in pollination .

(b) A forest is a purifier of water and air .

(c) Herbs form the lowest layer in the forest.

(d) The decaying leaves and animal droppings in a forest enrich the soil .

8. Why should we worry about the conditions and issues related to forests far from us?

Answer

We should worry about the conditions and issues related to forests far from us because more or less we are dependent on it because:

(i) The amount of carbon dioxide in air will increase if forest will disappear and thus less oxygen in atmosphere o breathe in.

(ii) There will be more soil erosion and thus increase in floods as soil will not able to hold water.

(iii) Increase in the percentage of carbon dioxide will also leads to global warming.

(iv) Deforestation will endanger our life and environment and also there will be no shelter for animals.

(v) There is also imbalance in nature and thus causing climate changes and less rainfall.

9. Explain why there is a need of variety of animals and plants in a forest.

Answer

There is a need of variety of animals and plants in a forest as each of them contribute their for maintaining the ecosystem of the forest. It also helps forest in regeneration and growth. Herbivores are needed to eat green plants and to provide food for the carnivores and Carnivores are needed to eat herbivores and check their population. Also, decomposers are needed to maintain the supply of nutrients to the soil and to the growing plants.

10. In Fig. 17.15, the artist has forgotten to put the labels and directions on the arrows. Mark the directions on the arrows and label the diagram using the following labels:

clouds, rain, atmosphere, carbon dioxide, oxygen, plants, animals, soil, roots, water table.

Answer

11. Which of the following is not a forest product?

(i) Gum

(ii) Plywood

(iii) Sealing wax

(iv) Kerosene

► (iv) Kerosene

12. Which of the following statements is not correct?

(i) Forests protect the soil from erosion.

(ii) Plants and animals in a forest are not dependent on one another.

(iii) Forests influence the climate and water cycle.

(iv) Soil helps forests to grow and regenerate.

► (ii) Plants and animals in a forest are not dependent on one another.

13. Micro-organisms act upon the dead plants to produce

(i) sand 

(ii) mushrooms

(iii) humus

(iv) wood

► (iii) humus

7 sci Chp 16 solusn

 

Solutions for Class 7th: Ch 16 Water: A Precious Resource Science

Exercises

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

(a) The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. (T/F)

(b) Water shortage is a problem faced only by people living in rural areas. (T/F)

(c) Water from rivers is the only source for irrigation in the fields. (T/F)

(d) Rain is the ultimate source of water. (T/F)

Answer

(a) T

(b) F

(c) F

(d) T

2. Explain how groundwater is recharged?

Answer

The rainwater and water from other sources such as rivers and ponds seeps through the soil and fills the empty spaces and cracks deep below the ground. The process of seeping of water into the ground is called infiltration. The groundwater thus gets recharged by this process.

3. There are ten tubewells in a lane of fifty houses. What could be the long term impact on the water table?

Answer

This will lead to exploitation of water resource present underground if people of all the fifty houses in the lane use the ten tubewells regularly. In long term, the water level will go below and thus the depletion of tubewells.

4. You have been asked to maintain a garden. How will you minimise the use of water?

Answer

For minimising the use of water in maintenance of garden, i will use the technique of drip irrigation. In this method, required amount water is supplied directly to the roots of the plants using narrow pipes thus preventing the loss of water.

5. Explain the factors responsible for the depletion of water table.

Answer

Factors responsible for the depletion of water level:

(i) Increase in the demand of water due to overpopulation.

(ii) Deforestation leads to less rainfall which affect the recharge of river and pounds.

(iii) Increase the number of industries as they use a lot of water for their purpose.

(iv) Insignificant uses in agriculture activities as in many parts of the world people uses old techniques which waste a lot of water.

(v) Lack awareness in people is also a main reason behind the depletion of water level as they waste water without any uses.

6. Fill in the blanks with the appropriate answers:

(a) People obtain groundwater through________ and ________ .

(b) Three forms of water are ________, ________ and ________.

(c) The water bearing layer of the earth is ________.

(d) The process of water seepage into the ground is called ________.

Answer

(a) People obtain groundwater through tube wells and hand pumps.

(b) Three forms of water are ice, water and vapour.

(c) The water bearing layer of the earth is aquifer.

(d) The process of water seepage into the ground is called infiltration.

Page No: 204

7. Which one of the following is not responsbile for water shortage?

(i) Rapid growth of industries

(ii) Increasing population

(iii) Heavy rainfall

(iv) Mismanagement of water resources

Answer

(iii) Heavy rainfall

8. Choose the correct option. The total water

(i) in the lakes and rivers of the world remains constant.

(ii) under the ground remains constant.

(iii) in the seas and oceans of the world remains constant.

(iv) of the world remains constant.

Answer

(iv) of the world remains constant.

9. Make a sketch showing groundwater and water table. Label it.

Answer

7 Sci Chp 15 Solusn

 

Solutions for Class 7th: Ch 15 Light Science

Exercises

1. Fill in the blanks:

(a) An image that cannot be obtained on a screen is called ____________.

(b) Image formed by a convex __________ is always virtual and smaller in size.

(c) An image formed by a __________ mirror is always of the same size as that of the object.

(d) An image which can be obtained on a screen is called a _________ image.

(e) An image formed by a concave ___________ cannot be obtained on a screen.

Answer

(a) An image that cannot be obtained on a screen is called virtual image.

(b) Image formed by a convex mirror is always virtual and smaller in size.

(c) An image formed by a plane mirror is always of the same size as that of the object.

(d) An image which can be obtained on a screen is called a real image.

(e) An image formed by a concave lens cannot be obtained on a screen.

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

(a) We can obtain an enlarged and erect image by a convex mirror. (T/F)

(b) A concave lens always form a virtual image. (T/F)

(c) We can obtain a real, enlarged and inverted image by a concave mirror. (T/F)

(d) A real image cannot be obtained on a screen. (T/F)

(e) A concave mirror always form a real image. (T/F)

Answer

(a) F

(b) T

(c) T

(d) F

(e) F

3. Match the items given in Column I with one or more items of Column II.

Column I	Column II
(a) A plane mirror	(i) Used as a magnifying glass.
(b) A convex mirror	(ii) Can form image of objects spread over a large area.
(c) A convex lens	(iii) Used by dentists to see enlarged image of teeth.
(d) A concave mirror	(iv) The image is always inverted and magnified.
(e) A concave lens	(v) The image is erect and of the same size as the object.
-	(vi) The image is erect and smaller in size than the object.

Answer

Column I	Column II
(a) A plane mirror	(v) The image is erect and of the same size as the object.
(b) A convex mirror	(ii) Can form image of objects spread over a large area.
(c) A convex lens	(i) Used as a magnifying glass.
(d) A concave mirror	(iii) Used by dentists to see enlarged image of teeth.
(e) A concave lens	(vi) The image is erect and smaller in size than the object.

4. State the characteristics of the image formed by a plane mirror.

Answer

Characteristics of the image formed by a plane mirror:

(i) The image formed is virtual

(ii) The image is laterally inverted.

(iii) It is of the same size as the object.

(iv) The image is situated at the same distance from the mirror as the object.

(v) The image is erected.

5. Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.

Answer

A, H, I, M, O, T, U, V, W, X, Y are the letters of English alphabet in which the image formed in a plane mirror appears exactly like the letter itself.

Discuss with your classmates to find the same types of words from other languages.

6. What is a virtual image? Give one situation where a virtual image is formed.

Answer

The image which cannot be formed or obtained on the screen is called virtual image.

When we stand in front of our dressing table mirror, we use to see our virtual image. The virtual image is formed in case of plane and convex mirror.

7. State two differences between a convex and a concave lens.

Answer

Convex lens	Concave lens
(i) Convex lens converges the light falling on it.	(i) Concave lens diverges the light falling on it.
(ii) Convex lens is thicker in the middle.	(ii) Concave lens is thinner in the middle.

8. Give one use each of a concave and a convex mirror.

Answer

Concave mirror forms large images therefore it is used by dentists to see enlarged image of teeth.

Convex mirror forms diminished image therefore it used as rear view mirror in vehicles.

9. Which type of mirror can form a real image?

Answer

Concave mirror can form a real image.

10. Which type of lens forms always a virtual image?

Answer

Concave lens forms always a virtual image.

Choose the correct option in questions 11–13

11. A virtual image larger than the object can be produced by a

(i) concave lens

(ii) concave mirror

(iii) convex mirror 

(iv) plane mirror

Answer

(ii) concave mirror can produce a virtual image larger than the object.

12. David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be

(i) 3 m 

(ii) 5 m

(iii) 6 m

(iv) 8 m

Answer

(iii) 6 m

In case of plane mirror, the image is situated at the same distance from the mirror as the object.

Initial distance between David and the mirror = 4 m

Final distance between David and the mirror = 4-1 = 3 m

Therefore, distance between David and his image = 3+3 = 6m

13. The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be

(i) 1 m/s 

(ii) 2 m/s

(iii) 4 m/s 

(iv) 8 m/s

Answer

(iii) 4 m/s

In case of plane mirror, the distance is always doubled therefore the speed is in case between the image and the object. So, when driver is reversing his car at a speed of 2 m/s, then the image is also coming closer to the mirror by 2m/s. Thus, it seems that the image of the truck appears to approach the driver at 4 m/s.