17. Forests: Our Lifeline Class 7 Science Solutions English Medium-NCERT Exercise

Exercise 

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

Answer:

Animals help in dispersing seeds of certain plants. The decaying animal dung also privides nutrients to the seedling to grow. This is how animals help the forest to grow and regenerate.  

2. Explain how forests prevent floods.

Answer:

Plants act as a natrual observer of rainwater and allow water to seep slowly to recharge ground water. This is how forest help preventing flood.  

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

Answer:

The micro-organism which convert the dead plants and animals to humus are known as decomposers. Bacteria, mushroom, etc. are and provide nutrient to trees.

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

Answer:

Plants take in carbon-die- oxide and release oxygen in the process of photosynthesis. Thus, they maintain the balance of oxygen and carbon-dioxide in the atmosphere.

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

Answer:

The decomposers decompose the dead organisms. The decomposed matter is absorbed by plants as nutrients. So, there is no waste in forests.

6. List five products we get from forests? Keywords Canopy Crown Decomposers Seed dispersal Soil erosion Understorey Deforestation Humus Regeneration.

Answer:  

Wood, medicine, spice, fodder. and honey.

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) pollination, (b) water, air (c) ground (d) soil.

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

Answer:

Forests are very helpful for us. They clean air, play a vital role in water cycle, provide variious items and so on. So, we should worry about the conditions and issues related to forests far from us.  

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

Answer:

(i) Variety of animals are necessary for their survival and maintainance of food chain.

(ii) For example: grass is eaten by insects, which in turn, is eaten by frog.

(iii) The frog is consumed by snakes which is eaten by eagles.Thus, it is made a food chain:

 Grass - insects - frog - snake - eagle

Many food chain can be found in the forest. All food chains are linked. If any one food chain is distrubed, It effects other food chains. Every part of the forest is depandet on each other parts. If we remove one component, say trees, all other components would be affected. 

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.

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

(i) Gum

(ii) Plywood 

(iii) Sealing wax

(iv) Kerosene

Answer:

(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 depedent on one another.

(iii) Forests influence the climate and water cycle.

(iv) Soil helps forests to grow and regenerate

Answer:

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

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

(i) Sand

(ii) Mushroom

(iii)Humus

(iv) Wood

Answer:

(iii) Humus.