NCERT Solutions For Class 7 Science Chapter 17
Forests: Our Lifeline

Micro-organisms act upon the dead plants to produce (iii) humus

The incorrect statement is: (ii) Plants and animals in a forest are not dependent on one another.

(iv) Kerosene

The correctly labelled diagram with arrow marks is as shown below:

We should be concerned with the conditions and issues related to forests because of the following reasons:

1. Forests maintain the balance between oxygen and carbon dioxide in the atmosphere. This helps in preventing the increase in temperature of earth’s atmosphere.
2. Forests prevent floods and erosion of soil.
3. Forests provide us with many important products like, timber, firewood, honey, beeswax, herbal medicines etc.
4. Forests help a region in receiving sufficient amount of rainfall.
5. Forests also curb noise pollution.

(a) pollination
(b) air, water
(c) lowest
(d) soil

The five products which we get from the forests are as follows:

1. Timber
2. Firewood
3. Wax
4. Gum
5. Spices

There is no waste in a forest because animal droppings, dead remains of plants and animals, are acted upon by the decomposers which convert them back into useful nutrients. These recycled nutrients are utilised by the plants and microorganisms for growth and reproduction. Thus, all the waste material generated in the forest is converted into useful materials and no waste is left in the forest.

Forests are considered as carbon sinks which absorb carbon dioxide from the atmosphere and utilise it in the process of photosynthesis. In turn, they release oxygen, which is the by-product of photosynthesis formed along with carbohydrates. In this way, forests maintain the balance of oxygen and carbon dioxide in the atmosphere.

Decomposers are the microorganisms, like fungi and bacteria, that breakdown dead and decaying remains of plants and animals into the nutrients to be utilised by other organisms. In this way, decomposers recycle the nutrients and make them available to the soil from which other organisms can uptake and utilize them.

The roots of the trees anchor the top soil firmly and prevent erosion of soil and underlying rocks. Those banks of rivers and streams, which are guarded by forests, delimit them and prevent their overflow. Also, the heavy flow of rain is received by the forest canopy and as water reaches the ground, its flow slows down. This further prevents cutting away of fertile top soil and provide ample time for seepage of water into the ground. Therefore, forests are helpful in preventing floods.

Organic matter, generated by animals in the form of animal droppings and dead remains, contains lots of nutrients. These nutrients are recycled by the decomposers into the soil and made available to young saplings and microorganisms facilitating their growth. This helps forest to regenerate its lost resources. Further, animals also help in dispersal of seeds to larger distances which help in expansion of forest cover. Thus, animals play a vital role in growth and regeneration of forests.

Large variety of plants and animals provide greater choice of food resources to all the life forms. This helps in growth in populations and varieties of both herbivores and carnivores. These animals play important roles in circulation of nutrients and energy through food chain and dispersal of seeds to larger distances. Such processes define and contribute in the growth, expansion, development and regeneration of a forest.