Class 7 Science Forests Our Lifeline Notes

Plants depend on animals for carbondioxide

Plants need carbon dioxide for manufacturing food by photosynthesis. Animals release carbondixoide into the atmosphere through respiration. Human activities like burning of wood, coal, petrol, gas, etc., also release carbon dioxide into air.

Plants depend on animals for pollination and seed dispersal

Bees, wasps, butterflies and moths visit flowers for collecting nectar and in this act they help in the transfer of pollen from one flower to another. For attracting these insects, plants have colourful and scented flowers. Some animals feed on fruits and deposit seeds at different places. Seeds of some plants cling to the body of animals and are carried away to new places. This helps in the dispersal of seeds.

Animals provide nutrients to plants

The bodies of dead and decaying animals and the dropping of animals are acted upon by microbes. They reduce them to inorganic compounds. These compounds get percolated into the soil and provide nutrients to the plants. This is called recycling of nutrients. Therefore, plants depend on animals for inorganic nutrients. Living organisms cannot survive alone. They have to interact with each other and with their environment. Successful survival of a biological community depends upon interaction of its members and a balance between their activities.

Why should we preserve our forest?

Forests are an important natural resource. They are essential for the preservation of environment and survival of all the animals including man.

1. Forests purify air and provide clean and fresh air for breathing to all living being

2. Forests regulate climate by reducing temperature and help in rainfall.

3. Trees bind the soil and control soil erosion.

4. Forests control and prevent flood by holding water and not allowing its free flow.

5. Trees make the soil fertile by recycling the nutrient

6. Forests help in reducing pollution.

7. Forests provide animals with a place to live (shelter).

8. Forests provide us food, wood, rubber gum, resin, non-edible oils, honey, beewax, lac, bamboo, fuel etc.

9. Some forests have been developed into recreational parks where people enjoy camping and trekking. Some forests have been made wildlife reserves where animals and plants are protected.

10. Some ancient tribes live in forest The forests provide them everything they need like food, shelter, water and medicines. Products obtained from forests are a source of steady income for tribals.

What will happen if forests disappear?

1. Disappearance of forests will severely disturb the ecosystem and the ecological balance in nature.

2. Wildlife may also not be able to survive in the absence of forest

3. There will be a shortage and scarcity of forest product

4. Since forests play a major role in keeping the environment cool and regulating the rainfall, their absence will lead to reduced rainfall and increased temperature.

5. It will be very difficult to recharge the existing water resources without forest

6. Unpredictable changes will take place in weather and climate patterns across the world.

7. Soil erosion will increase. This will adversely affect soil fertility and productivity.

8. Global warming will lead to flooding of low lying areas, as ice caps and glaciers melt. This is already happening. Two islands in the Andamans have vanished under-water.

9. Disappearance of forests will cause drastic increase in air pollution which will ultimately threaten the very existence of life on the earth.

Forests are the green lungs

Forests are the lungs of the earth. Just like human lungs do, it turns carbon dioxide into clean oxygen. Every living creature in this world needs oxygen. Without trees and forests, our earth would be running out of oxygen. Forest absorbs carbon dioxide from atmosphere by doing photosynthesis, a simple chemical reaction that produces energy in the presence of light by chlorophyll. The main substance for this reaction is carbon dioxide and water. A by-product of photosynthesis is, of course, oxygen. Over 40 percent of the world’s oxygen is produced from the forests. Another major function of the forest, directly connected to its function as the Earth’s lungs is to keep the planet cool. It helps stop global warming, also known as greenhouse effect. As we already understand, trees are an important part of the carbon cycle, a process that keeps the atmospheric concentration of carbon dioxide under control. Carbon dioxide in the atmosphere traps heat, like a blanket and causing the earth temperature to rise.

Destroying the forest is the same as destroying our own life-support system. A single tree in the park can only produce little amount of oxygen, while a forest which contains thousands or even millions of trees can produce millions times more. Earth’s population is keep growing, and our technology is rapidly increasing. This situation leads to the rise of carbon dioxide concentration in the atomosphere. However, over the past half century, the Earth’s forests have been reduced greatly. The destruction about 14.6 million hectares of forest in the last dozen years makes the earth getting hotter. The average global temperature over the past 50 years has increased at fastest rate in recorded history. And the trend is accelerating, the 10 hottest years on record have all occurred since 1990. If this situation continues, scientists believe that the average global temperatures could be 3 to 9 degrees higher by the end of the century. We can take another point of view to understand the cause of forest destruction. Consider the earth as a living organism, and the forest as its lungs. If the lungs have been destroyed, all cells inside the organism wouldn’t be able to get clean oxygen and eventually die. In this case, we - all living creatures on earth - are the cells.

Food Chain and Food Web

The nature, the organisms, are in constant interaction with the non living part of the physical environment. The organisms include the green plants which are the producers and animals which form the consumer category.

The non-living part of the environment includes factors like light, temperature, soil and water. Such factors are important to all living organisms for their survival. Thus interdependence of living organisms with the non- living part of the environment is important for a system to sustain. Such a system is referred to a ecosystem.