Ncert solution of class 9 chapter 14 natural resources
Page no. 193
Question
1: How is our atmosphere different from the atmospheres on Venus and
Mars?
Answer 1: Earth’s atmosphere is different from those of Venus and Mars. This
difference lies essentially in their compositions. Earth’s atmosphere is a
mixture of nitrogen (79%), oxygen (20%), and a small fraction of carbon
dioxide, water vapours and other gases. This makes the existence of life
possible on Earth. However, the atmospheres on Venus and Mars mainly consist of
carbon dioxide. The amount of carbon dioxide on these planets can range from
95% to 97%.
Question
2: How does the atmosphere act as a blanket?
Answer 2: The atmosphere acts as a blanket by performing the following
functions:
(a) It keeps the average
temperature of the Earth fairly constant during day time and even
during the course of whole
year.
(b) It prevents a sudden
increase in the temperature during day time.
(c) It slows down the
escape of heat from the surface of the Earth into outer space during
night time.
Question
3: What causes winds?
Answer 3: An uneven heating of the Earth’s surface causes winds. On being
heated, air becomes lighter and rises up. As a result, a region of low pressure
is created. Then, air from a high pressure region moves to a low pressure
region, causing wind.
Question
4: How are clouds formed?
Answer 4: During day time, on being heated, a large amount of water
evaporates from various water bodies and goes into the air. A part of this
water vapour also reaches the atmosphere through biological activities such as
transpiration and respiration. This causes the air in the atmosphere to heat
up. When this heated air rises, it expands and cools, which results in the
condensation of water vapour forming water droplets. The presence of dust and
other suspended particles in air also facilitates the process of condensation.
The formation of water droplets leads to the formation of clouds.
Question
5: List any three human activities that you think would lead to air
pollution.
Answer 5: The following three human activities would lead to air pollution:
(i) Burning of fossil
fuels such as coal and petroleum
(ii) Industrialization
(iii) Deforestation
Page no. 194
Question
1: Why do organisms need water?
Answer 1: Organisms need water for the following reasons:
(i) All cellular processes
need water as a medium. Usually, the reactions that take
place in our body or
within the cells occur between substances that are dissolved in water.
(ii) Since most of the
substances are transported in a dissolved form, water is necessary.
Question
2: What is the major source of fresh water in the city/town/village
where you live?
Answer 2: River is a major source of fresh water.
Question
3: Do you know of any activity which may be polluting this water
source?
Answer 3: The discharge of waste water from homes, industries, hospitals,
etc. into the river pollutes this fresh water source.
Page no. 196
Question
1: How is soil formed?
Answer 1: Soil is formed by breaking down of rocks at or near the surface of
the Earth through various physical, chemical, and biological processes by
various factors such as the sun, water, wind and living organisms.
(i) Sun: During day time, the rocks are
heated. This causes the rocks to expand. During night time, these rocks cool
down and contract. Since all parts of the rock do not undergo expansion and contraction
at the same rate, this causes the formation of cracks in these rocks. These
cracks lead to the breaking up of huge rocks into smaller pieces.
(ii) Water: Water catalyses the process of
formation of soil in two ways.
(a) Water
goes into the cracks and crevices formed in the rocks. When this water freezes,
its volume increases. As a
result, the size of the cracks also increases. This helps in the weathering of
rocks.
(b) Running
water wears away hard rocks over long periods of time. Water moving in fast
speed carries big and
small particles of rock downstream. These rocks rub against each other,
resulting in breaking down
of rocks. These smaller particles are carried away by running water
and deposited down its
path.
(iii) Wind: Strong winds carry away rocks,
which causes rubbing of rocks. This results in the
breaking down of rocks
into smaller and smaller particles.
(iv) Living organisms: Some living organisms like
lichens help in the formation of soil. Lichens
also grow on rocks. During
their growth, lichens release certain substances, which cause the rock
surface to powder down
forming a thin layer of soil. On this thin layer of soil, some small plants
like moss also grow. They further cause the
breaking down of the rock particles.
Question
2: What is soil erosion?
Answer 2: The blowing away or washing away of land surface by wind or water
is known as soil erosion.
Question
3: What are the methods of preventing or reducing soil erosion?
Answer 3: The methods of preventing or reducing soil erosion are:
(i) Prevention of deforestation
(ii) Plantation of trees
Page no. 201
Question
1: What are the different states in which water is found during the
water cycle?
Answer 1: During the water cycle, water is found in solid state (snow, ice,
etc.), liquid state (ground water, river water, etc.), and gaseous state (water
vapours).
Question
2: Name two biologically important
compounds that contain both oxygen and nitrogen.
Answer 2: Two biologically important compounds that contain both oxygen and
nitrogen are:
(i) Amino acids
(ii) Deoxyribonucleic acid
(DNA) and Ribonucleic acid (RNA)
Question
3: List any three human activities which would lead to an increase in
the carbon dioxide content of air.
Answer 3:
(i) Burning of fuels in
various processes like heating, cooking, transportation, and industry.
(ii) Human induced forest
fires.
(iii) The process of
deforestation includes the cutting down of trees. This decreases the uptake of
carbon dioxide for photosynthesis.
Eventually, the content of carbon dioxide increases.
Question
4: What is the greenhouse effect?
Answer 4: Some gases like carbon dioxide, methane, nitro us oxide prevent
the escape of heat from the Earth’s surface by trapping it. This increases the
average temperature of the Earth. This is called the greenhouse effect. An
increase in the content of such gases would lead to a situation of global warming.
Question
5: What are the two forms of oxygen found in the atmosphere
Answer 5: The two forms of oxygen found in the atmosphere are:
(i) Diatomic molecular
form with chemical formula O2.
(ii) Triatomic molecular form with chemical
formula O3 known as ozone.
Exercise
Question
1: Why is the atmosphere essential for life?
Answer 1: The atmosphere is essential for life because it maintains an
appropriate climate for the sustenance
of life by carrying out
the following activities:
(i) Atmosphere keeps the
average temperature of the Earth fairly constant during day time.
(ii) It prevents a sudden
increase in temperature during day time.
(iii) It also slows down
the escape of heat from the surface of the Earth into outer space during
nighttime.
Question
2: Why is water essential for life?
Answer 2: Water is essential for life because of the following reasons:
(i) Most biological
reactions occur when substances are dissolved in water. Thus, all cellular
processes need water as a
medium to take place.
(ii) Transportation of biological substances
needs water as a medium.
Question
3: How are living organisms dependent on the soil? Are organisms that
live in water totally independent of soil as a resource?
Answer 3: Almost all living organisms are dependent on soil. Some depend
directly, while some depend indirectly. Plants need soil for getting support as
well as nutrients to prepare their food. On the other hand, organisms depend on
plants for food and other substances that are essential for life. Herbivores
depend directly upon plants, and carnivores depend upon animals, which in turn depend
upon plants for food. This makes them depend on soil indirectly. Organisms that
live in water are not totally independent of soil as a resource. These
organisms depend on aquatic plants for food and other substances. These aquatic
plants in turn require minerals for their sustenance. These minerals are
carried to water bodies from soil by rivers, rain water, etc. Without the
supply of minerals from the soil to the water bodies, it is impossible to
imagine aquatic life.
Question
4: You have seen weather reports on television and in newspapers. How
do you think we are able to predict the weather?
Answer 4: The meteorological department of the government collects data on
the elements of weather such as maximum and minimum temperatures, maximum and
minimum humidity, rainfall, wind speed, etc. They are able to study these
elements using various instruments. The maximum and minimum temperature of a
day is measured by a thermometer known as the maximum−minimum thermometer. Rain
fall is measured by an instrument known as the rain gauge. Wind speed is measured
by anemometers. There are various instruments used to measure humidity.
Question
5: 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 5: Yes. Isolating human activities to specific areas would help in
reducing levels of pollution. For example, setting up of industries in isolated
regions will control pollution to some extent. The pollution caused by these
industries will not contaminate water resources, agriculture land, fertile land,
etc
Question
6: Write a note on how forests influence the quality of our air, soil
and water resources.
Answer 6: Forests influence the quality of our air, soil, and water
resources in various ways. Some of them are:
(i) Forests balance the
percentages of carbon dioxide and oxygen in the atmosphere. The
increasing amount of
carbon dioxide caused by human activities is balanced by a larger intake of
carbon dioxide by plants
during the process of photosynthesis. Simultaneously, a large amount of
oxygen is released.
(ii) Forests prevent soil
erosion. Roots of plants bind the soil tightly in a way that the surface of
the soil cannot be eroded
away by wind, water, etc.
(iii) Forests help in the
replenishment of water resources. During the process of transpiration, a
huge amount of water
vapour goes into the air and condenses to form clouds. These clouds cause
rainfall that recharge
water bodies.
