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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