Goa Board Class 7 Solutions for Science – Forests: Our Lifeline (English Medium)
Page No. 217:
Question 1:
Explain how animals dwelling in the forest help it grow and regenerate.
Solution :
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.
Question 2:
Explain how forests prevent floods.
Solution :.
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.
Question 3:
What are decomposers? Name any two of them. What do they do in the forest?
Solution :
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.
Question 4:
Explain the role of forest in maintaining the balance between oxygen and carbon dioxide in the atmosphere.
Solution :
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.
Question 5:
Explain why there is no waste in a forest.
Solution :
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.
Question 6:
List five products we get from forests.
Solution :
(i) Medicines
(ii) Wood
(iii) Paper
(iv) Oil
(v) Gum
Concept insight: Importance of forests.
Page No. 218:
Question 7:
Fill in the blank:
(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 _______.
Solution :
(a) Pollination
(b) Air, water
(c) Lowest
(d) Soil
Concept insight: Important from Exam Point of View.
Question 8:
Why should we worry about the conditions and issues related to forests far from us?
Solution :
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.
Question 9:
Explain why there is a need of variety of animals and plants in a forest.
Solution :
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.
Question 10:
In Fig. 17.15, the artist has forgotten to put the labels and directions on the arrows. Mark the directions on the arrows and label the diagram using the following labels.
Clouds, rain, atmosphere, carbon dioxide, oxygen, plants, animals, soil, roots, water table
Solution :
Concept insight: Important from Exam Point of View.
Question 11:
Which of the following is not a forest product?
(i) Gum
(ii) Plywood
(iii) Sealing wax
(iv) Kerosene
Solution :
(iv) Kerosene
Concept insight: All are forest products except kerosene which is obtained by petroleum refining.
Question 12:
Which of the following statements is not correct?
(i) Forests protect the soil from erosion.
(ii) Plants and animals in a forest are not dependent on one another.
(iii) Forests influence the climate and water cycle.
(iv) Soil helps forests to grow and regenerate.
Solution :
(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.
Page No. 219:
Question 13:
Micro-organisms act upon the dead plants to produce
(i) sand
(ii) mushrooms
(iii) humus
(iv) wood
Solution :
(iii) humus
Concept insight: Micro-organisms decompose dead plants to produce humus.