NCERT Solutions for Class 7 Science Chapter 17 Forests Our Lifeline

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

Answer:

Animals play a number of roles in helping the forests regenerate. The herbivores restrict the overgrowth of the grass and other plants by devouring them as food. The herbivores themselves support the survival of carnivores by being their food.

Their wastes help maintain the nutrition of the soil and once they die their carcasses are degenerated by microorganisms and this enriches the soil. The flora and fauna flourish by being mutually beneficial for each other.

2 . Explain how forests prevent floods.

Answer:

Forests prevent floods by the following way

1. Forests don't let the rainwater directly reach the ground and much of it remains on the canopy of the forest.

2. The roots of the trees and plants absorb large amounts of groundwater thus maintaining the level of water in the soil.

3. The roots also bind the soil without which rain will cause the soil to erode and wash away.

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

Answer:

Decomposers are microorganisms which decompose the dead bodies of plants and animals. They not only just clean the environment by decomposing the dead bodies but meanwhile also give back the nutrients to the soil thus maintaining the nutrition of the soil.

Examples of decomposers include bacteria and some fungi like the water fungus.

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

Answer:

Oxygen is essential for the survival of all animals. This oxygen required is released by plants and trees during the process of photosynthesis. Other animals inhale this oxygen and exhale carbon dioxide during respiration. This carbon dioxide serves as raw material to the plants for photosynthesis.

This cycle helps maintain the levels of oxygen and carbon dioxide in the atmosphere and a high number of trees ensure that this cycle is run properly.

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

Answer:

There is no waste in forests as all the body waste generated by the animals and the dead bodies of plants and animals are decomposed by microorganisms and thus no waste piles up in the forests.

6. List five products we get from forests?

Answer:

Five products which we get from the forest are:

(i) Medicines.

(ii) Firewood or wood for making furniture and paper.

(iii) Honey.

(iv) Gum and wax.

(v) Fruits

7. Fill in the blanks:

(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 air and water .
(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 be worried about the conditions and issues related to forests far from us because deforestation would lead to a decreased level of oxygen in the atmosphere which is essential for the survival of all living beings. Deforestation also would lead to increased amounts of carbon dioxide in the atmosphere which causes the greenhouse effect and thus results in global warming.

Lack of forests would lead to floods, soil erosion and disturbance of the ecosystem and thus the destruction of the forests would certainly harm the humans directly or indirectly and this, therefore, must be a matter of concern for us all.

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

Answer:

All organisms residing at a different level of the food chain have some role or the other to play required for a balanced ecosystem. For example, plants and grass serve as food for the herbivores which serve as food for the carnivores and when these herbivores and carnivores die their dead bodies are devoured by microorganisms and insects living the soil and once these dead bodies are decomposed this enriches the soil which is essential for the plants.

Thus there is a need for a variety of animals and plants in a forest.

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:

The following is the labelled diagram:

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

(i) Gum
(ii) Plywood
(iii) Sealing wax
(iv) Kerosene

Answer:

Kerosene is not a forest product.

(iv) is the correct answer.

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.

Answer:

Plants and animals in a forest are dependent on one another.

(ii) is the correct answer.

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

(i) sand (ii) mushrooms (iii) humus (iv) wood

Answer:

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

(iii) is the correct answer.