These NCERT Solutions for Class 7 Science Chapter 17 Forests: Our Lifeline Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.
Forests: Our Lifeline NCERT Solutions for Class 7 Science Chapter 17
Class 7 Science Chapter 17 Forests: Our Lifeline Textbook Exercise Questions and Answers
Explain how animals dwelling in the forest help it grow and regenerate.
Animals which live in the forest help it grow and regenerate in following ways:
- By eating vegetation, they clear the land for fresh growth.
- Animals help flowering plants in pollination and seed dispersal.
- Dead remains of animals make humus after decomposition. This increases soil fertility.
Explain how forests prevent floods.
Forest acts as a natural absorber of rainwater and allows it to seep underground. It helps in controlling the flow of water and slows it down which helps in preventing floods. Also, the trees present in the forest prevents the rain from directly hitting the ground and bind the soil together which helps in absorption of the rainwater and thus prevent flood.
What are decomposers? Name any two of them. What do they do in the forest?
The organisms which decompose the dead remains of plants and animals are called decomposers. Fungi and bacteria are examples of decomposers. They clear the debris of dead remains and convert them into humus which enriches the topsoil.
Explain the role of forest in maintaining the balance between oxygen and carbon dioxide in the atmosphere.
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 the atmosphere.
Explain why there is no waste in a forest.
Forest works like a self sustaining system. Whatever is produced in the forest is utilised by different components of the forest. Even the waste is converted into beneficial substances in a forest. Due to this, there is no waste in a forest.
List five products we get from forests.
- We get medicines from forests.
- We get gum from forests.
- We get wood which is used for many purposes like making furniture, paper, etc.
- We get food for animals from forests.
- We get sealing wax from forests.
Fill in the blanks:
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 ………………..
(b) water and air,
Why should we worry about the conditions and issues related to forests far from us?
We should worry about the conditions and issues related to forests far from us because, more or less, we are dependent on them because of the following reasons:
- The amount of carbon dioxide in air will increase if forests will disappear and thus less oxygen will be there in the atmosphere.
- There will be more soil erosion and thus increase in floods as soil will not be able to hold water.
- Increase in the percentage of carbon dioxide will also leads to global warming.
- Deforestation will endanger our life and environment and also there will be no shelter for animals.
- There will also be an imbalance in the nature and thus causing climate changes and less rainfall.
Explain why there is a need of variety of animals and plants in a forest.
There is a need of variety of animals and plants in a forest as each of them contribute for maintaining the ecosystem of the forest. They also help forests in regeneration and growth. Herbivores are needed to eat green plants and to provide food for the carnivores and carnivores are needed to eat herbivores and check their population. Also, decomposers are needed to maintain the supply of nutrition to the soil and to the growing plants.
In fig. 17.15 (NCERT textbook), 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.
Which of the following is not a forest product?
c. Sealing wax
Which of the following statements is not correct?
a. Forests protect the soil from erosion.
b. Plants and animals in a forest are not dependent on one another.
c. Forests influence the climate and water cycle.
d. Soil helps forests to grow and regenerate.
b. Plants and animals in a forest are not dependent on one another.
Micro-organisms act upon the dead plants to produce
NCERT Extended Learning Activities and Projects
The Department of Environment is to decide whether some portion of a forest in your area could be cleared for a housing complex. Write a letter to the department explaining your point of view as a concerned citizen.
The Department of Environment
Subject: Deforestation in ……… area.
As an aware resident of our society, I have come to know that your department has granted the permission to clear some forest area of our residence. I want to draw your attention towards some points, i.e., the after-effects of your decision.
- If you cut the forest area, then the wild animals will move towards the residential area, which is very dangerous to people and animals also.
- Due to deforestation, the climate will be affected the most. There will be more carbon dioxide and other dangerous gases in the environment.
- Loss of trees and other vegetation may cause soil erosion.
- Due to deforestation, the people won’t get the fresh air and health problems will increase day by day.
These are the points which may cause danger to our lives and environment due to deforestation. 1 request to reconsider your decision in the public interest.
A concerned citizen
Visit a forest. Here is a list of points that would make your visit more fruitful.
a. Make sure that you have permission to go into the forest.
b. Make sure that you can find your way around. Get a map and go along with someone who is familiar with the area.
c. Keep a record of the things you see and do. Observations make the visit interesting. Sketches and photographs are useful.
d. You may record bird calls.
e. Collect different kinds of seeds or hard fruits like nuts.
f. Try to recognise various types of trees, shrubs, herbs, etc. Make lists of plants from different places in the forest and of different layers. You may not be able to name all the plants, but it is worth recording and seeing where they grow. Make a record of approximate height of plants, crown shape, bark texture, leaf size and flower colour.
g. Learn to recognise the animal’s droppings.
h. Interview the forest officials and the people of surrounding villages and other visitors.
Do it yourself.
Objective: To verify the fact that the decaying organic matter is always moist and warm.
Materials Required: Khurpi, leaves, water, etc.
- Dig a small pit with the help of a khurpi.
- Fill the vegetable wastes, dry leaves, etc., in this pit and cover it with soil. Pour some water over it.
- After 3-4 days, remove the upper layer of soil and observe the decaying matter.
Observation: We observe that the decaying matter is moist and warm.
Conclusion: The decaying organic matter is always moist and warm.
Forests are Green Lungs: Plants take up carbon dioxide and release oxygen during photosynthesis. The plants keep balance of carbon dioxide and oxygen in the atmosphere. This is a reason why forests are called green lungs of the earth.
Forests as Dynamic Living Entity: By harbouring a greater variety of plants, the forests provide greater opportunities for food and habitat for herbivores. Larger number of herbivores means increased availability of food for a variety of carnivores. The wide variety of animals helps the forest to generate and grow. Decomposers help in maintaining the supply of nutrients to the growing plants in the forest. Therefore, the forest is a called ‘dynamic living entity’ which means ‘full of life and vitality’.
Soil Erosion: Washing away of the top fertile layer of soil by water or wind is called soil erosion. Soil helps the forest to grow and regenerate. Forests protect the soil and avoid soil erosion.
Deforestation: Large scale cutting of trees to clear land for human use is called deforestation. Deforestation may lead to floods, global warming, danger to environment and our life.
Afforestation: It refers to the large scale planting of trees. It helps in increasing the forest land and thus helps in improving the environment of the earth. It also leads to several benefits that the forests provide us.
Significance of Forests: Forest plays an important role in preserving environment. Green plants take solar energy and convert it into chemical energy while making food during photosynthesis. Thus, solar energy is transferred to other living beings through the green plants. Green plants utilise carbon dioxide during photosynthesis and release oxygen. That is how the green plants maintain the balance of carbon dioxide and oxygen in the environment. It also protects the soil and increase underground water table. It is a home to a wide variety of fauna.
Class 7 Science Chapter 17 Forests: Our Lifeline Additional Important Questions and Answers
Very Short Answer Type Questions
Cutting and destroying of the forest is called deforestation.
What is meant by afforestation?
Planting more and more trees by which we can preserve our forest wealth is called afforestation.
What are producers?
Green plants are called producers.
What are herbivores?
The organisms which directly depend on plants for their food are called herbivores.
What are carnivores?
The organisms which are flesh-eaters and depend on other animals for their food are called carnivores.
Draw any simple food chain going on in the forests?
Grass → Insects → Frogs → Snake → Eagle
What happens if an animal dies in the forest?
Dead animals become food for vultures, crows, jackals and insects.
What is known as the crown of the tree?
Branchy part of a tree above the stem is known as the crown of the tree.
What is canopy?
Branches of the tall trees look like a roof over the other plants in the forest. This is called a canopy.
What is humus?
Humus is a dark-coloured substance which is formed from the decomposition of dead bodies of plants and animals.
What are known as understroyes in a forest?
Trees have crowns of different types and sizes. These create different horizontal layers in the forest. These are known as understroyes.
What is the effect of deforestation on soil?
Roots of trees normally bind the soil together, but in their absence, the soil is washed away or eroded.
In which layer of the soil would you find humus? What is its importance to the soil?
Humus is found in the top, organic layer of soil. Humus provides many useful nutrients to the soil.
Would you see similar kinds of trees and animals in every forest?
No, we don’t see similar kinds of trees and animals in every forest.
What do you mean by food chain?
The organisms which take their food from plants get eaten by other organisms and so on. This chain of eating and being eaten is called food chain.
Name some factors responsible for clearing of forests.
Construction of roads and buildings, industrial development, increasing demands of wood, etc.
What role does a decomposer play in forest?
Decomposers convert dead leaves and dead animals into humus.
How will water pollution be affected with the depletion of forests?
Without trees, there will be no roots holding the soil in a forest. Soil will run into the river and will cause water pollution.
How do animals help forest to grow?
The animals disperse the seeds of certain plants and help the forest to grow and regenerate.
How can we recognise the presence of an animal in the forest?
By its droppings and footprints, we can recognise the presence of an animal in the forest.
Short Answer Type Questions
Why does the forest floor seem to be dark-coloured?
The forest floor seems to be dark-coloured as it is covered with a layer of dead and decaying leaves, fruits, seeds, twigs and small herbs. The decaying matter is moist and warm.
How are the trees planted in a forest?
In nature, trees produce enough seeds. The forest floor provides favourable conditions for them to germinate and develop into seedlings and saplings. Some grow up into trees.
Why even after heavy rainfall, water does not stagnate in the forest?
Forest acts as a natural absorber of rainwater and allows it to seep. It helps maintain the water table throughout the year. Forests not only help in controlling floods but also help maintain the flow of water in the streams so that we get a steady supply of water.
Why are forests called the green lungs?
Plants release oxygen through the process of photosynthesis. The plants help to provide oxygen for animal respiration. They also maintain the balance of oxygen and carbon dioxide in the atmosphere. That is why forests are called the green lungs.
Why raindrops do not hit the forest floor directly?
The uppermost layer of the forest canopy intercept the flow of raindrops and most of the water come down through the branches and the stems of the trees. From the leaves it drips slowly over branches of the shrubs and herbs. Thus, raindrops do not hit the forest floor directly.
Why are forests disappearing?
Forests are disappearing due to:
- construction of roads, buildings, industrial development and increasing demand of wood.
- overgrazing of animals and indiscriminate felling of trees for agricultural land.
Explain the importance of forests.
Forests are very important to us. They provide us with oxygen. They protect soil and provide habitat to a large number of animals. They help in bringing good rainfall in neighbouring areas. They are a source of medicinal plants, timber and many other useful products.
Explain how forest affects food chain.
All animals, whether herbivores or carnivores, depend ultimately on plants for food. Organisms which feed on plants often get eaten by other organisms, and so on. For example, grass is eaten by insects, which in turn, is taken by the frog. The frog is consumed by snakes. This is said to form a food chain: Grass → insects → frog → snake → eagle. Many food chains can be found in the forest. All food chains are linked. If any one food chain is disturbed, it affects other food chains. Every part of the forest is dependent on the other parts.
Define deforestation. Write its causes and consequences also.
The excessive cutting of forests and trees is called deforestation.
Causes of deforestation:
- Trees are used for charcoal, fuel, timber, etc.
- The cleared land is used as pasture for livestock, plantations of commodities, and settlements.
Consequences of deforestation:
- The removal of trees resulted in damage to habitat, biodiversity loss and aridity.
- It has adverse impacts on bio-sequestration of atmospheric carbon dioxide.
- Deforested regions may degrade into wasteland due to soil erosion.
How do forests maintain the water cycle?
The role of rainforests in the water cycle is to add water to the atmosphere through the process of transpiration (in which plants release water from their leaves during photosynthesis). This moisture contributes to the formation of rain clouds which release the water back onto the rainforests. This maintains the water cycle and water level in the environment.
How are the nutrients of the soil’ related to decomposers?
Different animals and plants live in forests. When they die, nobody cremates their dead bodies. They keep on lying there. Scavengers like vultures, eagle, etc., eat their dead bodies. They eat flesh and other soft organs. The rest of the dead bodies are broken down by various microorganisms called decomposers. They decompose the dead bodies of plants and animals into a dark substance called humus which maintains the nutrient level of the soil.
Long Answer Type Questions
Explain why forest is called “the dynamic living entity”?
The wide variety of animals helps the forest to regenerate and grow. In forest, plants produce food. All animals, whether herbivores or carnivores, depend ultimately on plants for food. Organisms which feed on plants often get eaten by other organisms, and so on. This is said to form a food chain.
Decomposers feed upon the dead plant and animal tissues and convert them into a dark coloured substance called humus. By harbouring greater variety of plants, the forest provides good opportunities for food and habitat for the herbivores. Larger number of herbivores means increased availability of food for a variety of carnivores. Thus forest is the dynamic living entity, that is, full of life and vitality.
What would happen if forests disappear?
The conditions and issues we have to face when forests disappear are:
- Soil erosion: Trees in a forest hold the soil with their roots. If trees are gone, soil will be washed away.
- Landslides: Without trees, land will be very unstable and easily move down the slope.
- Water pollution: Without tree roots holding the soil in a forest, soil will run into the river by flowing water and wind.
- Loss of biodiversity: Plants and animals will lose their food and shelter.
- Floods: Bald hills and mountains can no longer hold back sudden flows of water, which may cause floods.
- Increase in carbon dioxide: Depletion of forests results in increase in carbon dioxide which will cause global warming.
Why is replenishment of forests necessary?
Forests need to be replenished because of the following reasons:
- Rainfall: During transpiration, trees give out enormous amount of water vapour. This water vapour helps in the formation of rain clouds. So, if trees are cut and not replenished, the rainfall in the area will reduce.
- Natural rate of tree growth: Forests cannot be regrown in a few days or months as trees take many years to grow fully. Thus, it becomes necessary to replenish the forests periodically.
- Soil erosion: If a large number of trees are cut, the soil becomes naked. The topsoil, which is rich in organic matter will be washed away by water or carried away by wind. Trees help in binding the soil.
- Carbon dioxide-oxygen balance: Forests have a very large number of trees which give out O2 and take in CO2 by photosynthesis. In this way, they help in maintaining the carbon dioxide-oxygen balance in the atmosphere.
- Timber and fuel: Forests are the best suppliers of timber for furniture and fuel. So, for their constant supply, forests need to be replenished.
What are the various steps, we can take to conserve our forests?
- We should mindfully celebrate the Van Mahotsav Day.
- We should lay emphasis on tree plantation.
- We should discourage the use of wooden furniture.
- We should impose strict environmental laws.
- Educating and sensitising people regarding the role of forests in maintaining stable ecosystem should be done.
Draw a diagram of different types of crowns of trees.
Draw a diagram to show canopy and understorey.
Observe the following figure and label its various components.
1. Carbon dioxide