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

Forests: Our Lifeline Exercise 217

Solution 1

The animals in forests are of various types. These could be herbivores, carnivores, micro-organisms, etc. which play an important role in maintaining the food chains.
(i) Micro-organisms convert the dead plants and animals to humus which helps in returning the nutrients back to the soil. Thus, they act as decomposers.
(ii) The animals also help in dispersing the seeds of certain plants.
(iii) The decaying animal dung provides nutrients to various types of seedlings to grow.
All these activities of animals dwelling in the forest help it to grow and regenerate.

Concept insight: Animals are biotic component of an ecosystem.

Solution 2

Firstly forest cover prevents rain water from directly hitting the ground thus soil is able to absorb large amount of water slowly. Humus also increases absorbing power of soil. Thus, forests prevent direct hitting of water to the ground and thus prevent floods.

Concept insight: Firstly forest canopy do not let rain direct hit the forest floor. Secondly humus absorbs are large amount of water so it does not let rain water run off.

Solution 3

Decomposers are micro-organisms that convert the dead plants and animals to humus.
Bacteria and fungi are the two types of decomposers.
They help in the process of recycling of nutrients by decomposing various dead organisms such as plants and animals to form humus.

Concept insight:  Decomposers decompose dead and decaying matter and release nutrients in the soil.

Solution 4

Forests are called the green lungs. This is because plants in forests release oxygen through the process of photosynthesis and help in providing oxygen to animals for respiration. Plants consume carbon dioxide released by the animals. In this way, Plants help in maintaining a balance of oxygen and carbon dioxide in atmosphere.   

Concept insight: Plants take in carbon dioxide and release oxygen.

Solution 5

There is no waste in a forest because all waste generated is biodegradable on which micro-organisms act and convert them into humus. This humus ensures that the nutrients are returned back to the soil.

Concept insight: All the wastes generated in the forest are biodegradable which are decomposed by decomposers.

Solution 6

(i) Medicines
(ii) Wood
(iii) Paper
(iv) Oil
(v) Gum

Concept insight: Importance of forests.

Forests: Our Lifeline Exercise 218

Solution 7

(a) Pollination
(b) Air, water
(c) Lowest
(d) Soil

Concept insight: Important from Exam Point of View.

Solution 8

There are various reasons for which we should be vigilant about matters related to forests.
i.A decrease in forest area would lead to an increase in carbon dioxide in air. This will increase the temperature of earth's atmosphere.
ii.Soil erosion would occur if there are no forests.
iii.Floods would be more frequent in absence of forests.
iv.Forests provide shelter and food to animals. When forests are adversely affected, the habitats of wild animals are also adversely affected.
v.Due to deforestation many areas will slowly get converted into deserts.
Therefore, we need to conserve our forests.

Concept insight: Cutting of forests will disturb our ecosystem.

Solution 9

A greater variety of plants and animals in the forests helps it to regenerate and grow. Greater variety of plants means more food and habitat for the herbivores. An increase in herbivores means more food for carnivores. Decomposers help to maintain the supply of nutrients to the soil and to the growing plants. This wide variety makes forest a dynamic living entity.

Concept insight: Greater variety of plants and animals provide variety of food to herbivores and carnivores.

Solution 10

Concept insight: Important from Exam Point of View.

Solution 11

(iv) Kerosene

Concept insight: All are forest products except kerosene which is obtained by petroleum refining.

Solution 12

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

Concept insight: All biotic and abiotic components in a forest are dependent on each other.

Forests: Our Lifeline Exercise 219

Solution 13

(iii) humus

Concept insight: Micro-organisms decompose dead plants to produce humus.