Question 1:
How is our atmosphere different from atmosphere on Venus and Mars?
Answer:
Our atmosphere consists of nitrogen, oxgen, carbon dioxide, water vapours etc which help in the existence of life. But the atmosphere on Vanus and Mars is largely consist of carbon dioxide (95% to 97%).
Question 2:
How does atmosphere act as a blanket?
Answer:
Atmosphere acts as a blanket because of the following reasons:
(a) Air is a bad conductor of heat.
(b) It keeps the average temperature of the Earth fairly steady during the day and even
during the course of whole year.
(c) It prevents sudden increase or decrease in the temperature.
Question 3:
What causes winds?
Answer:
Movement of air or winds are caused by the uneven heating of the atmosphere in different regions of the Earth. Air above the land gets heated faster and, being light, starts rising. As the hot air rises, a region of low pressure is created. Due to this, cooler air over the sea moves into this area of low pressure.
Other factors which control wind are:
(a) The rotation of the Earth and presence of mountain ranges
(b) Uneven heating of land in different parts of the world
(c) Differences in heating and cooling of land and water bodies
Question 4:
How are clouds formed?
Answer:
Clouds are formed by the condensation of water droplets in the air. Large amount of water evaporates and goes into the air. As air rises up, it expands and cools. This cooling of air causes water vapour present in the air to condense and form tiny droplets of water. These water droplets get bigger and form clouds.
Question 5:
List any three human activities that you think would lead to air pollution.
Answer:
(a) Combustion of fossil fuels (b) Industrialisation (c) Deforestation
Question 6:
Why do organisms need water?
Answer:
Water is necessary for living organisms because:
(a) All cellular processes take place in water.
(b) Water is the universal solvent. All reactions that take place within our bodies and
within the cells occur between substances that are dissolved in water.
(c) Substances are transported from one part of the body to the other in a dissolved form,
which requires water.
(d) Water helps in maintaining the temperature of the body.
Question 7:
What is the major source of fresh water in the city/town/village where you live?
Answer:
The major sources of fresh water are underground water, surface water like rivers, lakes, ponds, stored rain water, etc. Also, drinking water is supplied by the local municipal corporation.
Question 8:
Do you know of any activity which may be polluting this water sources?
Answer:
Yes, the water is being polluted by:
(a) Sewage from towns and cities
(b) Bathing and washing clothes in ponds and rivers
(c) Dumping of factory wastes in water bodies
(d) Excessive use of fertilisers and pesticides and their run off into water bodies
(e) Discharging of hot water into water bodies
Question 9:
How is soil formed?
Answer:
The breaking up of rocks at or near the surface of Earth over long periods of time results in
soil formation. The rocks are broken down by various physical, chemical and biological
processes. The end products of this breaking down are the fine particles of soil.
Other factors which play a vital role in the formation of soil are:
(a) Heat from the Sun heats up the rocks causing them to crack and ultimately break into
smaller pieces.
(b) Water breaks rocks both by freezing and by its fast flow.
(c) Wind causes erosion of rocks.
(d) Living organisms such as lichens and mosses grow in the cracks in rocks. As they grow,
they widen these cracks and ultimately break down the rocks.
Question 10:
What is soil erosion?
Answer:
Removal of the top fertile layer and useful components of the soil, which adversely affects the fertility of the soil is called soil erosion.
Question 11:
What are the methods of preventing or reducing soil erosion?
Answer:
(a) Soil erosion can be prevented by planting trees and sowing grasses.
(b) It can be prevented by intensive cropping.
(c) It can be prevented by providing proper drainage canals around the fields.
(d) It can be prevented by constructing strong embankments along river banks.
(e) Soil erosion in hilly areas can be prevented by practising terrace farming.
Question 12:
What are different states in which water is found during water cycle?
Answer:
Water is found in all three states—gaseous, liquid and solid during the water cycle in the form of ground water, surface water, water vapour, water droplets, clouds, etc.
Question 13:
Name two biologically important compounds that contain both oxygen and nitrogen.
Answer:
Proteins and nucleic acids (DNA and RNA)
Question 14:
List any three human activities which would lead to an increase in the carbon dioxide content of air.
Answer:
a) Burning fossil fuels b) Respiration c) Deforestation
Question 15:
What is greenhouse effect?
Answer:
The increase in global temperature due to a rise in CO2 levels is called greenhouse effect. It causes global warming.
Question 16:
What are two forms of oxygen found in the atmosphere?
Answer:
The two forms of oxygen found in the atmosphere are diatomic form as oxygen (O2) and triatomic form ozone (O3)
Question 17:
Why is the atmosphere essential for life?
Answer:
(a) The atmosphere acts as a blanket and keeps the average temperature of the Earth steady
during day and night and even during the course of the year.
(b) Oxygen present in the atmosphere is essential for respiration and combustion; whereas
carbon dioxide is essential for photosynthesis.
(c) Rain and rainfall patterns are decided by the atmosphere.
(d) Ozone layer present in the atmosphere absorbs ultraviolet rays and thus, protects living
organisms from their harmful effects.
Question 18:
Why is water essential for life?
Answer:
Refer to NCERT IN-TEXT QUESTIONS, Question 1 of Page 194.
Question 19:
How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Answer:
All living beings, directly or indirectly, depend upon plants for their food.
Soil plays an important role in plant growth by providing water, nutrients and
anchorage.
Soil also supports the growth of crops, grasslands and forests, which provide us food,
fibre, wood and building materials.
Soil is an important resource and decides the diversity of life in an area. It is the
habitat of a wide variety of terrestrial organisms.
Organisms that live in water get dissolved minerals from water. These minerals come from the
soil.
Question 20:
You have seen weather reports on television and in newspapers. How do you think that we are able to predict the weather?
Answer:
Weather can be predicted on the basis of the following:
(a) Movement of air which is due to the uneven heating of the atmosphere in different
regions of the Earth
(b) Rainfall patterns, which are decided by the prevailing wind pattern
(c) Relative humidity
(d) Pattern of cloud formation
Question 21:
We know that many 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?
Answer:
Limiting activities that cause pollution to certain areas will not have long lasting benefits. This is because polluted air and water can be carried to far off places. Similarly, pollutants from the soil can leach into underground water or can be absorbed by the plants growing in the polluted soil. Thus, the pollutants will enter many different food chains and affect many living organisms.
Question 22:
Write a note on how forests influence the quality of our air, soil and water resources.
Answer:
Forests influence the quality of air, soil and water resources in the following ways:
(a) Forests are the lungs of the Earth. The plants in the forests take in CO2 for
photosynthesis and release O2. Thus, they not only reduce air pollution but also
help in maintaining a balance between O2 and CO2 in the
atmosphere.
(b) Forests prevent soil erosion. The roots of trees, plants and grasses hold the soil
firmly and thus, prevent its erosion.
(c) Forests help in recharging water bodies and play an important role in maintaining the
water cycle.