Friday, 8 July 2011

Chapter 17. Forests : Our Lifeline | Science | Class VII (7th) Lesson Exercises

1.Question :  Explain how animals dwelling in the forest help it grow and regenerate.
Answer : The wide variety of animals helps the forest to regenerate and grow.  In forest, plants produce food. All animals, whether herbivores or carnivores, depend ultimately on plants for food.Organisms which feed on plants often get eaten by other organisms, and so on. For example, grass is eaten by insects, which in turn, is taken by the frog. The frog is consumed by snakes. This is said to form a food chain:
Grass→ insects→ frog→ snake→ eagle.
Many food chains can be found in the forest. All food chains are linked. If any one food chain is disturbed, it affects other food chains. These food chains produces a lot of supplementary products which are vital for the plants growth.The micro-organisms which convert the dead plants and animals to humus are known as decomposers. Decomposers help in maintaining the supply of nutrients to the growing plants in the forest.Decaying heap of animal dropping are good source of nutrition for plants in the forest. The decaying animal dung also provides nutrients to the seedlings to grow. The animals also disperse the seeds of certain plants and help the forest to grow .

2.Question :   Explain how forests prevent floods.
Answer : The forests prevent floods in many ways. The forest  acts as a natural absorber of rainwater and allows it to seep. In deep forest, during heavy rain,  the raindrops do not hit the forest floor directly. The uppermost layer of the forest canopy intercept the flow of raindrops, makes its impact slow. On the ground it is obsorbed by heaps of decaying leaves etc. In the absence of trees in the forest, rain may hit the ground directly and may flood the area around it. Heavy rain may also damages the soil. Roots of trees normally bind the soil together, but in their absence the soil is washed away or eroded.

3.Question :   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. These micro-organisms play an important role in the forest.They feed upon the dead plant and animal tissues and convert them into a dark coloured substance called humus. The presence of humus ensures that the nutrients of the dead plants and animals are released into the soil. From there, these nutrients are again absorbed by the roots of the living plants.
For example :
  1. Fungi  grow on decaying fruits and vegetables and convert them into humus.
  2. Some kinds of bacteria, prefer breaking down meat or waste from carnivores.
  3. Actinolites only break down dead plants, including hard to break down plants and the waste of herbivores.
  4. Worms are also considered decomposers, as they act as scavengers.

4. Question :  Explain the role of forest in maintaining the balance between oxygen and carbon dioxide in the atmosphere.
Answer : The forest play an important role in maintaining the balance between oxygen and carbon dioxide in the atmosphere. As we know plants for their food nutrition requirement make use of process of photosynthesis, in which they consume Carbon Dioxide, released by the living organism from the environment.As a result of photosynthesis, plants release oxygen which is again consumed by living beings for  respiration and this cycle goes on. .

5.Question :   Explain why there is no waste in a forest.
Answer : The forests are perfect recycling factories of nature. Here nothing goes waste. Forest is a system comprising various plants, animals and micro-organisms.The various components of the forest are interdependent on one another.All animals, whether herbivores or carnivores, depend ultimately on plants for food.Organisms which feed on plants often get eaten by other organisms, and so on. For example, grass is eaten by insects, which in turn, is taken by the frog. The frog is consumed by snakes. This is said to form a food chain. Many food chains can be found in the forest. All food chains are linked.
The  micro-organisms called decomposers  play an important role in the forest. The presence of humus ensures that the nutrients of the dead plants and animals are released into the soil. From there, these nutrients are again absorbed by the roots of the living plants.The dead animals become food for vultures, crows, jackals and insects. In this way, the nutrients are cycled. So, nothing goes waste in a forest

6. Question :  List five products we get from forests?
Answer :
  1. Wood for building constructions, making furniture,  paper, fuel wood,
  2. Edible Fruits , Nuts and spices
  3. Gums and resins
  4. Oil seeds like Sal, Mahua, Karanj, Kusum, Neem, Mango
  5. Fodder for animals
  6. Medicinal plants


7. Question :  Fill in the blank:
(a) The insects, butterflies, honeybees and birds help flowering plants in Pollination .
(b) A forest is a purifier of air and ground water .
(c) Herbs form the lowest layer in the forest.
(d) The decaying leaves and animal droppings in a forest enrich the soil nutrition in the form of humus.

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8.Question :   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 forests influence climate, water cycle and air quality of planet earth in a big way.Forests provide us with oxygen.If forests disappear, the amount of carbon dioxide in air will increase, resulting in the increase of earth’s temperature. They provide habitat to a large number of animals  In the absence of trees and plants, the animals will not get food and shelter. They protect soil . In the absence of trees, the soil will not hold water, which will cause floods. Forests help in bringing good rainfall in neighbouring areas. They are a source of medicinal plants, timber and many other useful products.



9. Question :  Explain why there is a need of variety of animals and plants in a forest.
Answer : For a sustainable forest eco system, there has to be variety of animals and plants in a forest.Forest is a system comprising various plants, animals and micro-organisms.The various components of the forest are interdependent on one another.In the forest, there is interaction between soil, water, air and living organisms.
Different layers of vegetation provide food and shelter for animals, birds and insects. All animals, whether herbivores or carnivores, depend ultimately on plants for food.
Organisms which feed on plants often get eaten by other organisms, and thus part of some food chain. Many food chains can be found in the forest. All food chains are linked. Some micro-organisms called decomposer,  like mushroom (fungi), feed upon the dead plant and animal tissues and convert them into a dark coloured substance called humus. Humus enrich the soil with nutrition which helps in plants growth. The dead animals become food for vultures, crows, jackals and insects.By harbouring greater variety of plants, the forest provides greater opportunities for food and habitat for the herbivores. Larger number of herbivores means increased availability of food for a variety of carnivores. Not only this, decaying heap of animal dropping is a source of food to various insects or decomposers which ultimately enrich the soil with nutrition in the form of humus.




10.Question :   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 :

Forest Eco-System

11.Question :   Which of the following is not a forest product?
(i) Gum
(ii) Plywood
(iii) Sealing wax
(iv) Kerosene
Answer : (iv) Kerosene


12. Question :  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 depedent on one another.


13.Question :   Micro-organisms act upon the dead plants to produce
(i) sand (ii) mushrooms (iii) humus (iv) wood
Answer : (iii) humus
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CBSE Class VII (7th) Lesson Exercises | Chapter 17. Forests : Our Lifeline | Science |

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