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

Various types of animals are found in forests. These are herbivores, carnivores and microorganisms etc. They all play an important role in balancing the food chain. 

1. Microorganisms convert dead or decay organic matter into compost. The composts helps in returning the nutrients back to the soil. These nutrients absorbed by the plants later.
2. Animals also helps in seed dispersal of certain plants. Animals also helps in pollination.
3. The decaying organic matter provide nutrients to the seedlings for the growth.

Forests contains a variety of flora and fauna. They act as the natural absorber of the water. Forests allow rainwater to seep into the soil. In the absence of trees, the rainwater directly hits the ground, this may leads to flood. However, the presence of trees does not allow rainwater to hit the ground directly. It hits the ground slowly. Before flooding, the rainwater seep through the ground. Tree's roots helps to bind the soil whereas if there are no trees then soil erosion occurs by the heavy rainfall. That's why we can say that forest prevents floods. 

The microorganisms who converts dead and decay organic matter into the humus are known as decomposers. Bacteria and fungi are the two main decomposers. Both of them helps in the decomposition of plants and animals and also helps in the recycling of nutrients; in the forest.

Forests are called the lungs of the earth. Because in forests through the process of photosynthesis plants release oxygen and help animals for the respiration process. Plants utilize carbon dioxide which is released by human beings and animals through the process of respiration. Both plants and animals help each other in exchange of gases. In this way forests maintaining a balance of gases (O₂ and CO₂) in the atmosphere. 

There are a number of microorganisms found in the forest. They decompose the dead and decaying organic waste or matter. They convert them in humus. Through the addition of humus, nutrients get back to the soil. That's why there is no waste in forest.

We get a number of products from the forest, some are as follows:

• We get food from the forests like fruits and vegetables.
• We get medicines from the forest like penicillin.
• We get wood from the forest for making furnitures, house, doors etc.
• We obtain paper through the tree.
• We get oil, rubber from the forests.

(a) Pollination
The pollination (transfer of pollen grains from anther to stigma) which occurs through insects called entomophily and which occurs through ornithophily.

(b) Water and air
A forest is a purifier of water and air.

(c) Understory
Herbs form the understory layer in the forest.

(d) Topsoil
The uppermost layer of the soil is called topsoil that contains decaying leaves and animal droppings (litter).

We should be worried about matters related to forests because of various reasons. These are as follows:

1. If there are no forests that it may lead to soil erosion due to various reasons like floods etc.
2. An increament in carbon dioxide gas in air occurs, if we cut the forests (deforestation). This may lead to increase in temperature of earth.
3. In the absence of forests, floods occurs frequently.
4. If we cut the forest, it will adversely affect the habitat of wildlife animals because forests provide them shelter and food.

That's why we need to conserve the forest for the survival of flora and fauna.

Herbivores get more food and habitat where there is a greater variety of plants. As the number of herbivore increases, then the carnivores gets more food which is important to continue the food chain. In microorganisms, mainly decomposers maintain the supply of nutrients to the soil and helps in the growth of plants. This greater variety of plants and animals makes the forest a dynamic living entity. 

(iv) Kerosene

The things we get from the forests are known as the forest products. Gum, Wood, Wax are the products that we get from the plants.

(ii) Plants and animals in a forest are not depedent on one another.

This statement is false because plants and animals help each other in exchange of gases. The carbon dioxide which is utilized by plants gets from the animals during the respiration process and vice versa. Animals get oxygen which is released by the plants.   

(iii) humus

The microorganisms who acts upon the dead and decay organic matter and converts them into the humus are called decomposers. Through the addition of humus nutrients get back to the soil and helps the plants in growth.