Class 7 Science Chapter 12 Question Answers - Forests - Our Lifeline

Q1. Forests are valuable resources. Explain.
Ans: Forest products play a vital role in socio-economic development. We get food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes) and products of medicinal importance. It is also the home of diverse wildlife, which maintains the ecosystem. Thus, forests are valuable resources.

Q2. Forests are called green lungs. Why?
Ans: The forests provide us with oxygen to breathe. If we rapidly cut down forests, it means we are cutting down the oxygen supply to us. That is why they are called green lungs.

Q3. Write the differences between decomposers and scavengers.
Ans: The difference between decomposers and scavengers is

Q4. Plants are known as the producers of a food chain. Give reason.
Ans: Plants are known as the producers of a food chain. It is because green plants (autotrophs) make their own food from carbon dioxide and water in the presence of sunlight and chlorophyll by a process called photosynthesis and provide food to all living organisms which live in the forest.

Q5. How could a pipal sapling have grown on a side wall of some old buildings?
Ans: Animals disperse the seeds of certain plants with the help of their droppings. Therefore, pipal seed would have come to the wall by a bird dropping. On coming in contact with water and a suitable nutrient medium, it would have grown into a pipal sapling.

Q6. State the role of scavengers in cleaning our environment.
Ans: Scavengers eat the dead animals and act as the cleaning agents of our environment. Some of these animals (scavengers) are vultures, crows, jackals, hyenas, some insects, etc.

Q7. Explain how the root system of plants helps prevent floods.
Ans: The root system helps water to seep down into the ground. It helps to maintain the water table throughout the year. Roots of trees normally bind the soil together and stop the erosion of soil.

Q8. Life would be impossible without plants. Explain how.
Ans: All green plants are producers. They make food through the process of photosynthesis using water, CO2, and sunlight. All forms of animals depend on plants for food. So, if there are no plants, no food will be there. Plants are also given oxygen during photosynthesis, and there would be no oxygen in the absence of a plant. These two basic needs make plants important to us, and we cannot think of life without plants.

Q9. What happens when an animal dies in the forest?
Ans: The body of the dead animal is eaten up by scavengers like vultures, jackals, hyenas, etc.
These animals clean the forest. This also shows that nothing goes to waste in the forests.

Q10. Is it possible to construct a food chain without a producer? State the reason to support your answer.
Ans: No, in any food chain, producers are always at the beginning. It is the producer which provides food to all living organisms. In a food chain, if the producer is absent, then there will be no flow of energy. So, we can say that it is not possible to construct a food chain without a producer.

Q11. If one component of the forest is removed, what would its effect be on the ecosystem?
Ans: Every component of the forest depends on the others. If we remove one, the other will be affected, e.g. if we remove top carnivores (lion/tiger) in a forest, herbivores will increase, and if they increase, they will end up eating all plants, so the ecosystem will get disturbed.

Q12. The crown is different from the canopy. Explain how.
Ans: The part of the tree with branches is known as the crown. When the crown of tall trees in the forests forms a roof-like covering over the other plants, it is known as a canopy.

Q13. Sketch a diagram to show how plants maintain the balance between carbon dioxide and oxygen in the atmosphere.
Ans:

Q14. Write the major steps by which we can conserve the forest.
Ans: Forests maintain balance in nature. Their conservation is the need of the hour. We should take the following steps to conserve the forests.
(i) Planned harvesting An efficient way to get wood from forests for our requirements is to cut only some of the trees in an area. The uncut trees prevent erosion. The fruits of these trees produce seeds that will help new trees grow. This way, the forest cover is maintained.
(ii) Afforestation This is the practice of renewing a forest by planting seedlings or small trees. These days, in our country, planned afforestation is being done not only by the government but also by private organisations for commercial purposes. Selective cutting of trees in these plantations provides wood for construction and also keeps the forest cover intact.
(iii) Protection from fire Huge forest areas are destroyed by fire every year. Fire may occur due to the carelessness of people due to lightning during a storm or by friction between dry stems and dry branches of trees.
Forest fires are controlled by spraying fire extinguishing solutions from aircraft or by changing the direction of wind by using strong blowers.

Q15. Cycling of papers helps conserve forests. Justify.
Ans: The papers are made from wood pulp. We derive wood by cutting down trees. If we recycle the existing quantity of paper in the market and do not let it decompose, we can stop cutting down forest trees for new raw materials required for paper making.
It takes years to grow a tree, and cutting a tree takes only a few minutes.
So, we should give serious thought before cutting a single tree even and should encourage the recycling of paper everywhere in our country and in the world.

Q16. Differentiate between autotrophs and heterotrophs.
or
Differentiate between producer and consumer.
Ans:

Q17. Give an example of a food chain.
Ans: Grass is eaten by insects, which, in turn, is taken by the frog. The frog is consumed by snakes. This is an example of a food chain.

Q18. Name any four birds which you expect to see in a forest.
Ans: Kingfisher, blue jay, hornbill and jungle crow.

Q19. What does the forest floor look like?
Ans: The forest floor looks dark-coloured and covered with a layer of dead and decaying fruits, plants, leaves, twigs and small herbs, which is quite moist and warm.

Q20. What do you mean by deforestation? Give some causes of deforestation.
Ans: The excessive cutting of trees for personal or commercial purposes is called deforestation.
Two causes of deforestation are as follows:

• The land is required to be cleared for cultivation, construction of houses, roads, etc.
• Forest fires cause huge loss of forest cover, which may be natural or by man.
• Overpopulation, too, directly affects forest cover with the expansion of its habitat.
• The reckless felling of trees to obtain timber also causes deforestation.

Q21. What is the importance of dense bushes and tall grasses for animals living in the forests?
Ans: The dense bushes and tall grasses provide the animals with food and shelter. Moreover, they protect the herbivores from carnivores living in the forest.

Q22. Why is it dark inside a forest?
Ans: It is dark inside the forest because sun rays are hardly able to penetrate through the dense covering of leaves. The canopy of tall trees forms a roof over the other plants. The trees also get covered with different types of creepers and climbers.

Q23. How do forests help in bringing rain?
Ans: Trees absorb water from the soil through their roots, and the excess water is released into the atmosphere through transpiration in the form of water vapour. This released water vapour forms clouds, which later bring rainfall.

Q24. How do forests sustain a large variety of animals?
Ans: Different types of animals live in the forest, like herbivores, carnivores, scavengers, etc. Forest provides them with suitable living conditions. The animals get their food in the forest itself. Herbivores feed on plants. Carnivores eat herbivores and thus survive. When these animals die, various scavengers, like vultures, eagles, etc., feed on their dead bodies.
Numerous microorganisms also live in the forest and convert dead and decaying plant and animal tissues into humus. They are called decomposers. Thus, they provide a hostile condition for all the animals.

Q25. As an active citizen, elaborate on your role in protecting the forests.
Ans: At my level, I will do the following things to protect the forest:

• Use less paper and try to recycle it.
• Do not buy any products made up of or obtained from the killing of wild animals.
• Try to plant as many trees as I can.
• Aware people of the importance of forests in our lives.
• Reduce the use of artificial items as they also create stress for the forest.

Q26. How do forests prevent soil erosion? Explain.
Ans: The removal of the top layer of fertile soil by the action of wind, river or rain is known as soil erosion. This can change a fertile land into a desert. This happens in areas that are not covered with vegetation, such as trees and plants.
The roots of plants and trees bind the soil particles together firmly. Owing to this, strong winds and flowing rivers find it very difficult to take away the particles of soil. In this way, soil erosion is prevented.
When it rains heavily in a forest, the rainwater is first intercepted by the canopy, and then it comes down through the stems, branches and leaves of the forest plants. Over this process, the speed of the rainwater slows down. In this way, the rainwater does not hit the floor of the forest directly. The forest floor covered with fallen leaves and twigs absorbs water readily and does not allow it to flow, thus preventing soil erosion.