Class 7 Science Chapter 12 Important Questions

A forest is a large area of land covered mainly with trees and other plants. In nature the trees produce enough seeds. The animals and birds of forest, wind and water disperse the seeds of trees and plants on the forest soil. These seeds obtain nutrients and water from the forest soil and germinate to form seedlings. The seedling grows to form saplings and ultimately develop into trees or other plants. The shrubs and herbs also grow in the forest on their own in a similar way.

We know that forest is a big habitat and it is a large area covered with trees and other plants. Due to different climate and soils, there are various types of trees and other plants found in various forest. Forest act as the purified of air and water because the leaves of its trees and plants clean the air by trapping dust from the air. It also puts oxygen in air. The forest act as purifier of water because its trees may suck dirty water from the soil through their roots and make pure water available as rain through the water cycle.

The plants and animals do not live forever. After certain time, the plants and animals die then the microorganisms which breakdown the dead parts of plants and dead bodies of animals into simple substances such as mineral salts or nutrients, carbon dioxide and water which can be used by the plants. The microorganisms such as bacteria and fungi are called “decomposers”. And they are non-green organisms. In this way the nutrients of plants and animals mix with the soil of the forest.

When the animals die in a forest, they are eaten up by some other animals called scavengers. The decomposer organisms such as bacteria and fungi, decompose the dead plant material, dead animals and animal wastes present in the forest into mineral salts or in the form of humans, water and carbon dioxide which go into soil and air. Since, dead animals are eaten up and the materials present in dead animals, dead plants and animal wastes are recycled. Therefore, in a forest there is no waste left.

The human beings and other animals give out carbon dioxide during respiration which goes into atmosphere. The green plants and trees of the forests absorb carbon dioxide from the atmosphere for the process of food making. In this way, the plants reduce the amount of carbon dioxide in atmosphere. So, forest are the major suppliers of oxygen needed by humans and other animals for breathing and respiration. Since, the green plants and trees of the forest are known as “green lungs”. Thus, forest remove carbon dioxide from the atmosphere and put oxygen into the atmosphere. By doing this, forest maintain the balance of carbon dioxide and oxygen in the atmosphere.

The forest plays a major role in maintaining the water cycle in nature. As the forest trees suck water from the soil through their roots and release water vapor into the air through transpiration or evaporation. This water vapor helps in the formation of clouds and bring rain on the earth. In this way, forest help in maintaining a perfect water cycle in nature and meet our fresh water requirements.

Yes, the layer of vegetation in a forest which is just below the canopy is called under-storey. Understorey is above the shrub layer. The understorey layer consists of smaller trees and tree saplings. The understory layer of forest has comparatively much less sunlight. The smaller trees found in the understory grow to become bigger trees only when tall trees die and open gaps in the canopy which can provide more sunlight to the smaller trees needed for their further growth.

The forest floor is covered with a lot of decaying material and small vegetation. Due to which it behaves like a giant sponge. The roots of trees and plants in the forest help this rainwater to seep into the forest ground and raise the water table. By holding back rain water and then releasing it slowly into rivers, the forest prevents the occurrence of floods in the rivers.
If the forests are cut down, then in the absence of trees and plants of the forest, the excessive amount of rain water falling during heavy rains cannot be absorbed into forest ground. The large amount of rain water will then suddenly flow into rivers causing the flooding of rivers which cause a great loss of life and property in the nearby areas.

The removal of fertile top soil from a region by wind, rain or river water is called soil erosion. The cutting down of forest leads to soil erosion. In the absence of trees and plants there are no roots which can bind the soil particles together and prevent them from being carried away by strong winds or heavy rains. This leads to soil erosion.
Forests prevent soil erosion as the roots of trees and plants growing in the forest bind the particles of topsoil and hold the soil together firmly. Due to this, binding of soil particles, the strong winds and flowing rain water are not able to carry away the topsoil and hence the soil erosion is prevented.

Variety of animals and plants living in forest build a rich biodiversity. Different animals and plants play different role in the system of a forest. For example, herbivores are needed to eat green plants and to provide food for the carnivores. Similarly, carnivores are needed to eat the herbivorous and check their pollution. This biodiversity make forests more productive, stable and resilient. If there is no grass, all herbivorous would die. If there are no carnivores, all herbivores would eat up all the plants and there is shortage of food. If there are no decomposers, the dead remains of plants and animals would pollute the environment. Due to such biodiversity a balance in nature is maintained.

Forest provides home or shelter, food and water to the animals living there. There are a large number of various types of animals in the forest. The forests provide “natural habitat” to animals. The different layers of regulation present in a forest provide food and shelter. Forest provides leaves, flowers, fruits, seeds, nuts and bark of trees as food for herbivorous animals. The carnivorous animals hunt and eat herbivorous animals. The dense bushes, tall grasses and thick trees provides shelter and also protection for herbivorous animals.

Forest products play a vital role in socio-economic development. We get food (cereals, pulses and fruits), fire wood, fibre, construction material, industrial products (tannins, lubricants, dyes resins and perfumes) and products of medical importance. It is also the home of diverse wildlife which maintains the ecosystem.
Forests give oxygen to keep us alive and absorb carbon dioxide and it also help in maintaining water cycle in nature. Forests save the soil from erosion and help in maintaining the ground water level.
Thus, forests are valuable resources.

The seedling was being benefited from the animal dung as the decaying animal dung provided nutrients to the growing seedlings. This happens as follows – animal dung or droppings keep on collecting on the forest floor. The decomposer organism (such as bacteria or fungi) act on animal wastes and convert them into humus.
The humus must contain plant nutrients and it mixes with the forest soil and make it fertile, seeds obtain nutrients from forest soil and germinate forms seedlings and seedlings grow to form saplings.

By harboring greater variety of plants, the forest provides greater opportunities for food and habitat for the herbivores. Larger number of herbivores means increased availability of food for a variety of carnivores. The wide variety of animals helps the forest to regenerate and grow. Decomposers help in maintaining the supply of nutrients to the growing plants in the forest. Therefore, the forest is a ‘dynamic living entity’ — full of life and vitality.”

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. Again snakes is eaten by eagle. This is said to form a food chain.
Many food chains can be found in the forest. All food chains are linked. If anyone food chain is disturbed, it affects other food chains. Every part of the forest is dependent on the other parts. If we remove one component, say trees, all other components would be affected.”