Forests: Our Lifeline | Chapter 17, Class 7 Science | Ncert Answers Cbse Guide Cbse Notes

 

Forests: Our Lifeline

CBSE Guide for Class 7 NCERT Science


Terms & Definitions

Canopy: The branches of the tall trees look like a roof over the other plants in the forest. This is called canopy.
Crown: Branchy part of a tree above the stem is known as the crown of the tree.
Understories: Trees in a forest have crowns of different types and sizes. These are known as understories.

NCERT Solutions of Textbook Exercise (Important Questions Only)


Question.1: Explain how animals dwelling in the forest help it grow and regenerate.
Answer: Animals constitute an important component of the forest. The wide variety of animals helps the forest to regenerate and grow in various ways. We can see a bunch of seedlings growing in a decaying heap on animal droppings. These seedlings are generally herbs and shrubs which feed, develop and grow on heap of animal dropping especially in rainy seasons. Moreover animals also help in seed-dispersal of certain plants and help the forest to grow and regenerate. The decaying animal dung also provides nutrients to the seedlings to grow. Microorganisms such as, decomposers also help in maintaining the supply of nutrients to the growing plants in the forest.

Question.2: Explain how forests prevent floods.
Answer: Raindrops in a forest do not hit the ground directly. The uppermost layer of the forest canopy intercept the flow of raindrops and most of the water comes down through the branches and the stems of the trees. From the leaves it drops slowly over the branches of herbs and shrubs. Thus a forest act as a natural absorber of rain water and allows it to seep and therefore help in controlling floods.

Question.3: What are decomposers? Name any two of them. What do they do in the forest?
Answer: Decomposers are the microorganisms which convert the dead plants and animals to Humus. Examples are tiny insects, millipedes, ants, beetle etc. Decomposers feed upon the dead plant and animal tissues and convert them into dark coloured substance called Humus, which acts as nutrients for the soil. These nutrients are again absorbed by the roots of the living plants.
In this way decomposers act an important role in maintaining the balance by the supply of nutrients to the growing plants after decomposing the dead plants and animals into humus.

Question.4: Explain the role of the forest in maintaining the balance between oxygen and carbon dioxide in the atmosphere.
Answer: The plants release oxygen through the process of photosynthesis. Animals require oxygen for respiration and release carbon dioxide to the environment. This carbon dioxide is again absorbed by the plants in the process of photosynthesis. Thus plants help in maintaining the balance of oxygen and carbon dioxide in the atmosphere. 

Question.5: Explain why there is no waste in a forest?
Answer: Forest is a system comprising plants, animals and microorganisms. All these are inter-dependant on one another and ultimately help in growing and regenerating the forest. The dead animals become food for vultures, crows, jackals and insects. Moreover, the decomposers convert the dead plants and animals to humus which enrich the soil nutrients. The droppings of animals also cause feeding and sprouting of seedlings especially in rainy season. Even the decaying animal dung also provides nutrients to the seedlings to grow. So nothing goes waste in the forest.

Question.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) pollination (b) air, water (c) lowest (d) soil.

Question.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 even far from us because forests play an important role for the sustenance of life on earth. The following points illustrate the importance of forests for us:
  • Forests help in maintaining the ratio of oxygen and carbon dioxide in air.
  • Forests provide the habitat to a wide variety of plants and animals.
  • Forests provide firewood, timber, medicines, fruits, rubber, gum, resins, honey, bee-wax, lac and many other things.
  • It also purifies the air and keeps the environment cool.
  • Forests absorb noise pollution.
  • It protects the soil and prevents the flood.

 CBSE Guide NCERT Answers for CBSE Hots


Additional Short Type CBSE Questions
Question.1: Choose the true and false statements:
(i) We get various useful products from the forests surrounding us.
(ii) Forest is a system comprising various plants, animals and microorganisms.
(iii) Forests must be cleared to make the human life safe and comfortable.
(iv) Different layers of vegetation provide food and shelter foe animals, birds and insects.
(v) The various components of forest are inter-dependant on one another.
(vi) In the forest there is interaction between soil, water, air and living organisms.
Answer: (i) T (ii) T (iii) F (iv) T (v) T (vi) T

Additional Long Type CBSE Questions
Question.1: What is soil erosion? How do the forests prevent soil erosion?
Answer: Washing away of the fertile layer of the soil is known as the soil erosion.

During rains the uppermost layer of the forest canopy intercept the flow of rain drops, and most of the water come down and most of the water comes down through the branches and the stems of the trees. If the trees are not present rain hits the ground and damages the soil. Also roots of trees normally bind the soil together, in absence of which the soil will be eroded. Thus we can say forests are of great importance in preventing the soil erosion.       

Question.2: “The forest is a dynamic living entity - full of life and vitality.” Explain or justify.
Answer: Forest is a system comprising various plants, animals and microorganisms. By giving harbouring to a 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. The wide variety of animals helps the forest to regenerate and grow. Decomposers help in maintaining the supply of nutrients to the growing plants in the forest. In one sentence forests are the lifeline for the forest-dwelling communities. Therefore, the forest is a dynamic living entity - full of life and vitality. 

Question.3: Why the forests are called “green lungs”?
Answer: The plants release oxygen through the process of photosynthesis. The plants provide oxygen for animal respiration and also absorb carbon dioxide from the atmosphere. In this way plants help in maintaining the balance of oxygen and carbon dioxide in the atmosphere. Forests also influence climate, water cycle and air-quality. That is why forests are called “green lungs”.

Question.4: If there were fewer trees, how will the water-cycle be affected?   
Answer: Trees take in water from the roots which are present in the soil and release water vapour into the air through evaporation. In this way trees contribute in running the water-cycle. So, if there were fewer trees, both climate and water-cycle will be affected and we will get less and uneven rain.



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