Answer: Option B. -> lungs
:
B
Forests absorb the carbon dioxide released by animals from the atmosphere and produce oxygen for respiration. In this manner they maintain the balance of these gases in the atmosphere. Hence, they are known as the green lungs of the Earth.

Answer: Option B. -> desertification
:
B
The process by which fertile land becomes arid and finally converts to a desert, as a result of deforestaion, or inappropriate agriculture is known as desertification.

Answer: Option B. -> nutrients
:
B
Decaying animal dung acts as a natural manure. It provides essential nutrients for the seedlings for their growth.

Answer: Option A. -> Dead plants and animals
:
A
Decomposers feed on dead plants and animal tissues. They convert them into humus. This activity also helps in increasing the soil fertility.

Answer: Option A. -> True
:
A

Forests act as a natural absorber of rainwater and allows it to seep. When rainwater falls on leaves of trees and plants, it does not fall directly on the ground. It drips slowly on the forest ground and does not stagnate. Thus trees prevent flooding. 

Answer: Option C. -> desertification
:
C

Turning forests into pastures leads to soil erosion. As a result of which, removal of the top layer of soil exposes the lower, hard and rocky layers. This soil has less humus and is less fertile. Gradually the fertile land gets converted into deserts. This is called desertification.

Answer: Option C. -> desertification
:

Canopy is formed by the mass of intertwined branches, twigs and leaves of mature trees. The branches of tall trees look like a roof over the other plants in the forest.

Answer: Option C. -> desertification
:

Food: 2 Marks
Microorganisms feed upon dead plants and animal tissues and convert them into a dark coloured substance called humus.

Answer: Option C. -> desertification
:
Each point: 0.5 Mark
 Animals dwelling in the forests are instrumental in the forest's growth and regeneration. For example:
(i) Herbivorous animals clear the land by eating grass for the new growth of vegetation.
(ii) Animals help in seed dispersal and pollination.
(iii) Dead and decaying bodies of animals get converted to humus after decomposition, which increases the fertility of the soil of the forest.
(iv) Dung of animals provide nutrients to various types of seedlings to grow.

Answer: Option C. -> desertification
:

Each point: 1 Mark
1) Forests are the dominant terrestrial ecosystem of Earth, and are distributed across the globe

2) Forests account for 75% of the gross primary productivity of the Earth's biosphere, and contain 80% of the Earth's plant biomass.