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How is our atmosphere different from the atmosphere on Venus and Mars?

Atmosphere of the earth consists of a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour that helps life to exist on the earth. The major component of the atmosphere found on Venus and Mars is carbon dioxide (95-97%) and as such it does not support life.


How does the atmosphere act as a blanket?

Our atmosphere acts as a blanket because:
It keeps the average temperature of the earth fairly constant during the day.
The atmosphere prevents the sudden increase in temperature during the daylight hours.
During the night, it slows down the escape of heat into outer space.


What causes winds? 

The air above the land gets heated faster and being light starts rising. As the air rises, a region of low pressure is created. Due to this, the air which moves over the sea moves into this area of low pressure. The movement of air from one region to the other creates wind.


How are clouds formed?

A large amount of water evaporates and goes into the air. Some amount of water vapour also gets into the air due to various biological activities. The hot air rises up carrying the water vapour with it . On rising up air expands and cools. Cooling causes the water vapour in the air to condense in the form of tiny droplets around dust and other suspended particles in the air. This leads to the formation of clouds.


List any three human activities that you think would lead to air pollution.

The human activities that lead to air pollution are
burning of diesel and petrol in vehicles,
burning of coal in factories, engines and thermal power stations and 
deforestation by human beings.


Why do organisms need water?

Organisms need water for
Cellular processes which take place in a water medium.
Transportation of substances from one part of the body to the other.


What are the major sources of fresh water in the city/town/village where you live?

Rivers and lakes are the major sources of fresh water in the city where we live.


Do you know  any activity which may be polluting this water source?

Washing and bathing near the well will pollute well water. Stagnation of water near a well also causes pollution of the water resource.


How is soil formed? 

The following are the factors or processes which make the soil:

i. The sun: The sun causes heating of rocks during the day. As a result they expand. These rocks cool down at night and contract. Since, all parts of the rock do not expand and contract at the same rate, it results in the formation of cracks. Finally huge rocks break up into smaller pieces.

ii. Wind: Strong winds and storms also erode rocks down. The strong wind carries small rock pieces and sand from one place to the other like water.

iii. Living organisms: The lichens grow on the surface of rock. They release certain substances that cause the rock surface to powder down to form a thin layer of soil.

iv. Water: Water gets into cracks of rock formed due to uneven heating by the sun. In winter, this water freezes and causes widening of cracks. It is because water expands on freezing.

v. Trees: The roots of big trees sometimes go into the cracks of the rock. As these roots grow bigger, the cracks widen.


What is soil erosion?

Removal of fertile top soil is called soil erosion.


What are the methods of preventing or reducing soil erosion.

The following are some of the methods which can prevent or reduce soil erosion:

vi. To keep vegetation cover on the ground which reduces soil erosion by wind and water.

vii. Intensive cropping and maintaining soil fertility.

viii. Afforestation , the roots of trees check the flow of running water. Trees also check the speed of strong winds, thus preventing the erosion of soil.


What are the different states in which water is found during the water cycle?

Water is found during the water cycle in three states, namely solid ( ice or snow) liquid and vapour.


Name two biologically important compounds that contain both oxygen and nitrogen.

Proteins and nucleic acids (DNA and RNA)


List any three human activities which would lead to an increase in the carbon dioxide content of air.

Burning of wood and charcoal for heating, cooking etc.
Deforestation that reduces the green plants and tree population , consequently lessening the utilization of atmospheric CO
Burning of fossil fuels such as petrol, diesel and coal in various activities like transportation and industrial processes.


What is green house effect?

The concentration of carbon dioxide in the atmosphere is increasing due to the current global trend in deforestation and increasing combustion of fossil fuels. The heating of the atmosphere due to the absorption of infrared radiations by CO2 molecules is called the green house effect. This will ultimately increase earth’s temperature and may cause melting of glaciers and thereby flooding the coastal plains.


What area the two forms of oxygen found in the atmosphere?

Oxygen is found in the atmosphere in the form of diatomic molecule as oxygen and tri-atomic molecule as ozone.


Why is the atmosphere essential for life?

The atmosphere keeps the average temperature of the earth fairly steady. The atmosphere prevents the sudden increase in temperature during the daylight hours. It also slows down the escape of heat into outer space during the night.


Why is water essential for life?

All life processes that take place in the cells require water medium. Water is needed for transportation of substances from one part of the body to the other in a dissolved form.


How are living organisms dependent on the soil? Are organisms that are living in water totally independent of soil as resource? 

Living organisms directly or indirectly depend on the soil. For the food all the living beings in the earth depend on the soil. Plants need soil for their survival  since soil provides the plants with the nutrients to prepare food through photosynthesis for self and other organisms. Thus all living organisms depend on the soil. Organisms living in water depend on green plants for materials and energy. Aquatic green plants get dissolved mineral from water. If there is no continuous supply of minerals from the soil to water bodies, the minerals present in the water will exhaust. The organisms living in water will not survive for a long time.


You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?

In large parts of India, rain is  brought mainly by the South-West or North West monsoons. Prediction of weather can be done by studying wind patterns that decide rainfall patterns. It also shows areas of low pressure and high pressure.


We know that human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?

Isolating the activities to specific and limited areas would not help in reducing pollution.


Write a note on how forests influence the quality of our air, soil and water resources.

Forests do influence the quality of our air, soil and water resources.
The ways in which they influence are:
Carbon dioxide- oxygen balance in the atmosphere: Forests have a large number of trees, shrubs and herbs. They take in CO2 and give oxygen during photosynthesis in daylight. Thus, oxygen consumed during combustion and respiration is replenished by forests.

Prevention of soil erosion: Trees and other roots of plants bind the soil particles. They form a vegetation cover over the fertile top soil. Trees of the forest check the speed of running water and wind thus preventing the removal of top soil and consequently soil erosion.

Replenishment of water resources: Trees in the forest are large in number and give out enormous amount of water during transpiration in the form of water vapour. The water vapour helps in the formation of clouds, which on precipitation cause rain. If forests are cut and not replenished, there will be reduction in rainfall and change in the climate.

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