NATURAL
RESOURCES
NCERT
Textbook Questions
Q.1.
How is our atmosphere different from the atmosphere on Venus and
Mars?
Answer:
On
the planets Venus and Mars carbon dioxide forms the major component
constituting upto 95-97% of the atmosphere. No life is known to exist
there. On the contrary, on the Earth, air forms the blanket around
the Earth having nitrogen (78.08%), oxygen (20.92%), carbon dioxide
(0.03%), argon (0.93%) and trace components (0.04%). It has life on
it.
Q.2.
How does the atmosphere act as a blanket?
Answer: The
mass or body of gases that surrounds the Earth or any heavenly body
is called atmosphere.
Earth’s
atmosphere extends from the surface to a height of more than 1000 km,
beyond which it merges gradually with solar atmosphere.
Earth’s
atmosphere acts as a protective blanket for the organisms to exist.
It keeps the average temperature of the Earth fairly steady during
the day and even during the course of whole year. In addition, the
ozone shield (i.e.,
high
concentration of ozone about 18-26 km above the surface of the Earth)
of the atmosphere absorbs most of the harmful UV radiations coming
from the sun thereby protecting human beings and animals from their
harmful effects.
Q.3.
What causes winds?
Answer: The
movement of air from one region to another creates winds. When the
solar radiations fall on the Earth, some are absorbed and majority of
these are reflected back or reradiated by the land and water bodies.
These reflected or re-radiated solar radiations heat up the atmosphere
from below. As a result, convection currents are set up in the air.
But since land gets heated faster than the water, the air above the
land gets heated faster than the air over water bodies. During the
day, the air above the land gets heated faster and starts rising,
creating a region of low pressure below. As a result, the air over
the sea moves into this region of low pressure and forms the wind.
Q.4.
How are clouds formed?
Answer: When
the water bodies are heated with solar radiations during the day, a
large amount of water evaporates and goes in the air. The air
carrying water vapours also gets heated. This hot air rises up
carrying water vapours with it. As the air rises, it expands and
cools. This cooling causes the water vapours in the air to condense
as tiny droplets. Dust or other suspended particles present in the
air act as the “nucleus”
for
these droplets to form around. These droplets of water once formed
slowly grow bigger by the condensation of more water droplets. An
enormous collection of tiny droplets of water appear as clouds.
When
the droplets have grown big and heavy, they fall down in the form of
rain.
Q.5.
List any three human activities that you think would lead to air
pollution.
Answer:
1.
Burning of fossil fuel (coal, petroleum products) in automobiles,
generators, thermal power plants.
2.
Smoke from industries (e.g.
brick-kiln,
crashers, etc.)
3.
Burning of fuelwood and dung cakes in household cooking.
Q.6.
Why do organisms need water?
Answer: Organisms
need water because it plays a vital role in the reactions taking
place within organism’s cells and body. Water acts as a universal
solvent, providing a medium for the chemical reactions to occur.
Substances are also transported from one part of body to the other in
the dissolved state. Therefore, it is necessary for the organisms to
maintain a distinct level of water within their bodies in order to
stay alive.
Q.7.
What is the major source of fresh water in the city/town/village
where you live?
Answer: Major
sources of fresh water in the city/town/village where we live is
underground water.
Q.8.
Do you know of any activity which may be polluting this water source?
Answer: Percolated
dissolved fertilizers and pesticides from the fields, sewage and
wastes from factories (which are often stored in underground tanks)
are the major sources of underground water pollution.
Q.9.
How is soil formed?
Answer: Soil
is a mixture of small particles of rocks and humus (i.e,
organic
matter obtained from decaying of living organisms or their wastes).
Temperature variations due to radiations of the sun, rain water,
winds and living organisms influence the formation of soil from the
rocks involving two processes: weathering and paedogenesis.
Breakdown
of bigger rocks into small, fine soil particles is called weathering.
It
may occur due to physical, chemical or biological means. Under the
influence of solar radiations, rocks heat up and expand. At night,
these rocks cool down and contract. Since all the parts of rocks do
not expand and contract at the same rate, cracks appear in the rocks
and ultimately the large rocks breakdown into smaller pieces. Flow of
water through or over the rocks make the cracks bigger.
Flowing/falling water also has a erasing effect on the rocks. On
freezing the water expands in rock crevices and break the rocks.
Similarly, strong winds continue to rub against hard rocks and erode
them. Growth of lichens, mosses and other plants also influence the
formation of soil by eroding the rocks over which they are growing.
Paedogenesis
involves
the decomposition
of
organic materials by bacteria and fungi and humification
and
mineralization
of
decomposed organic matter. Earthworms also play an important role in
the soil formation.
Q.10.
What is soil erosion?
Answer: The
topmost layer of the soil that contains humus and living organisms
(bacteria, fungi, nematodes, earthworms, etc.) in addition to the
mineral particles is called topsoil.
The
removal and transportation of top soil from its original position to
another place with the help of certain agents such as strong winds
and fast running waters, is called soil
erosion. Action
of walking and grazing by the hoofed animals (e.g.,
sheep,
goats, donkeys, horses, mules, cattles, etc.) too result in soil
erosion.
Q.11.
What are the different methods of preventing or reducing soil
erosion?
Answer: Soil
erosion can be effectively prevented by adopting the following
measures:
1. Intensive cropping;
2. Sowing grasses and planting
xerophytes;
3. Terrace farming;
4. Proper drainage canals around the
fields;
5. Making strong embankments along the river banks; and
6.
Checking the overgrazing.
Q.12.
What are the different states in which water is found during the
water cycle?
Answer:
(i)
Water vapours in the air which ultimately form clouds, and
(ii)
Rain water that falls on Earth and is available to us in water bodies
or as underground water.
(iii)
Dew, snow, sheet or hail.
Q.13.
Name two biologically important compounds that contain both oxygen
and nitrogen.
Answer:
(i)
Nucleic acids (DNA and RNA);
(ii)
Proteins.
Q.14.
List any three human activities which could lead to an increase in
carbon dioxide content of air.
Answer:
(i)
Burning of fossil fuels (coal and petroleum products) in homes,
industries and automobiles.
(ii)
Burning associated with agricultural practices.
(iii)
Deforestation.
Q.15.
What is the greenhouse effect?
Answer: Heat
is trapped by glass, and hence the temperature inside a glass
enclosure will be much higher than the surroundings. This phenomenon
was used to create an enclosure where tropical plants could be kept
warm during the winters in colder climates. Such enclosures are
called greenhouses.
Greenhouses
have also lent their name to an atmospheric phenomenon. Some gases
such as carbon dioxide (CO2),
methane (CH4),
chlorofluorocarbons (CFCs), etc., are present in the Earth’s
atmosphere prevent the escape of heat from the Earth. An increase in
the percentage of such gases in the atmosphere would cause the
average temperatures to increase worldwide and this is called
greenhouse
effect. Carbon
dioxide, methane and chlorofluorocarbons, are such greenhouse
gases. An
increase in the carbon dioxide content in the atmosphere, for
example, would cause more heat to be retained by the atmosphere and
lead to global warming.
Q.16.
What are two forms of oxygen found in the atmosphere?
Answer: Molecular
oxygen (O2)
and ozone (O3).
NCERT
Exercises
Q.1.
Why is the atmosphere essential for life?
Answer: The
multilayered gaseous envelope (or blanket) surrounding the planet
Earth is called atmosphere.
Atmosphere
filters sunlight reaching the Earth affect climate and is a reservoir
of several elements which are essential for life. Oxygen is required
by most living beings for respiration and for burning (combustion) of
materials. Air contains about 20% oxygen and its percentage in air is
balanced by the process of photosynthesis. Photosynthesis occurs in
chloroplasts of green plants and this metabolic activity requires
CO2,
water and sunlight but release oxygen gas. Ozone umbrella of
atmosphere does not allow penetration of ultraviolet light of solar
radiations to reach the Earth. These solar radiations otherwise
affect organisms adversely (e.g.,
UV
rays may cause skin cancer in human beings).
Q.2.
Why is water essential for life?
Answer: Organisms
need water because it plays a vital role in the reactions taking
place within organism’s cells and body. Water acts as a universal
solvent, providing a medium for the chemical reactions to occur.
Substances are also transported from one part of body to the other in
the dissolved state. Therefore, it is necessary for the organisms to
maintain a distinct level of water within their bodies in order to
stay alive.
Q.3.
How are living organisms dependent on the soil? Are organism that
live in water totally independent of soil as a resource?
Answer: The
top surface layer of Earth capable of supporting plant life is called
soil.
Soil
is a complex mixture, comprising of minerals (45%), organic matter
(5%), water (25%), air (25%) and living organisms. It is an important
resource that determines the diversity of life in an area. Plants are
dependent on the soil from where they obtain various types of
minerals, water and air. All these three components are essential for
the growth of plants. Animals (herbivores) depend on plants for food.
Other animals (carnivores) depend on these herbivores. Hence, all
living organisms directly or indirectly depend on the soil.
Aquatic
organisms are not entirely independent of soil as a resource.
Microscopic decomposers (e.g.,
fungi,
archaebacteria and bacteria) present in the bottom sediments of water
bodies decompose dead, decaying organic matter into simple, inorganic
substances (minerals). The latter get dissolved in water and are
available as nutrients for aquatic plants and then indirectly through
plants to animals.
Q.4.
You have seen weather reports on television and in newspapers. How do
you think we are able to predict the weather?
Answer: We
daily see weather reports on television and newspapers. These
informations about the weather are recorded by meteorological
laboratories present in different cities of the country. Information
such as direction and speed of wind, average daily minimum and
maximum temperature, relative humidity, patterns of cloud formation,
depression zones over an area, etc., are recorded with the help of
instruments and then displayed on television, published in newspapers
or broadcasted on the radio. This meteorological information helps us
to predict the weather and to act accordingly. For example a farmer
can decide his next step for agriculture according to latest weather
report and may be benefitted.
Q.5.
We know that many human activities lead to increase levels of
pollution of air, water bodies and soil. Do you think that isolating
these activities to specific and limited areas would help in reducing
pollution?
Answer: We
have studied that many human activities lead to increase the levels
of pollution of the air, water bodies and soil. Isolating such
activities to specific and limited areas may help in reducing only
soil pollution. However, air and water pollution cannot be checked.
For instance air pollution brings about global environmental changes
such as
(i)
acid rainfalls;
(ii)
global warming due to increase in the concentration of green house
gases (carbon dioxide, methane and chlorofluorocarbons) in the
atmosphere;
(iii)
depletion of ozone layer.
In
the same way, water keeps moving in streams, rivers and oceans. It
distributes wastes to far off places from the point of their
discharge. Similarly, underground water pollution due to sewage,
industrial wastes and agricultural percolation (of fertilizers and
pesticides) will affect large areas.
Q.6.
Write a note on how forests influence the air, soil and water
resources.
Answer: Forest
is a large area covered thickly with trees and other plants such as
shrubs and grasses. Any forest is a renewable natural resource.
Forests influence the air, water and soil resources in following
ways:
1.
Forests shape natural environment by influencing such factors as
temperature, humidity and precipitation.
2.
Forests shape the soil environment by affecting its composition,
structure, the chemical properties, water content, etc.
3.
Forests play important role in running the biogeochemical cycles of
water, carbon, nitrogen, oxygen, and other elements.
4.
Forest plants maintain the CO2
and
O2
balance
in the atmosphere.
5.
Roots of forest plants bind the soil and do not allow erosion of soil
by fast winds or fast moving water. In this way they help in
maintaining the fertility of soil. Many bacteria present in root
nodules (e.g., Rhizobium
bacteria
in root nodules of leguminous plants) replenish to the soil.
6.
Forests check flooding, landslides and shifting of sand and silting
of rivers.
Questions
Based on NCERT Question Bank (Exemplar Problems in Science)
Q.1.
How can we prevent loss of top soil?
Answer: We
can prevent loss of top soil by following methods:
a.
Intensive cropping: It means growing of more crops in the same fields
and not leaving them unused. If the fields remain covered with crops
throughout the year, top soil will not be exposed to winds or rains.
b.
Planting grasses and xerophytes: Planting grass and xerophytes on
barren soil will bind the loose soil. This will help in reducing the
soil erosion.
c.
Terrace farming: In hilly regions, small fields are formed in the
form of steps or terraces for cultivation of crops. Such farming in
hilly regions is called terrace farming. This technique reduces the
flow of rain water down the slopes of hills.
d.
Proper drainage canals: The excess rain water can be drained out
through small drainage canals formed around the fields without
causing damage to main fields.
e.
Making embankments along the river banks: This method involves the
formation of strong embankments of stones, sand bags, etc. on both
the sides of the rivers particularly in erosion prone areas. This
will check soil erosion by the fast moving river water.
Q.2.
Rivers from land and minerals to sea water. Discuss how.
Answer: Rivers
are formed from melting snow, springs, and rain water flowing over
land as run off. While passing through and over the rocks, the
flowing water picks up minerals, silt and sand. These dissolved and
suspended substances are carried by rivers to sea and make them
available to marine organisms.
Q.3.
How is life of organisms living in water affected when water gets
polluted?
Answer: Water
gets polluted from domestic wastes (loaded with detergents, faecal
matter, etc.), fertilisers and pesticides from crop fields and
industrial wastes (heavy metals, waste heat).
(i)
Fertilisers and domestic wastes cause eutrophication or increased
organic loading and excessive growth of algae (algal bloom). This
ultimately reduces oxygen available to aquatic animals (fish,
molluscs) and kill them.
(ii)
Domestic wastes also carry pathogens of a number of human diseases.
Some of them can cause diseases of animals as well.
(iii)
Pesticides and pollutants of industrial wastes directly harm the
aquatic organisms and humans.
Q.4.
During summer, if you go near the lake, you feel relief from heat.
Why?
Answer: During
day time, air over the land becomes heated up by sun rays, it rises
up and creates area of low pressure. Water of lake is not heated up
by sun rays so quickly. Evaporation of water from its surface also
cools up the lake water. So, air over the surface of lake is cooler.
It moves towards the land where low pressure exists. Therefore,
during day time a cool breeze flows from lake to the nearby land.
Q.5.
In coastal areas, wind current moves from sea towards the land during
day but during night it moves from land to the sea. Discuss the
reason.
Answer: Air
moves from a region of high pressure to a region of low pressure.
During the day, the air above the land gets heated faster than air
above the sea or water. The warm air rises up creating low pressure.
The
air pressure over the water is higher with cold dense air, which
moves to occupy the space created over the land. The wind blows from
the sea to land. This is called sea breeze. During the night, the
land cools faster than water body. There cold air above land and warm
air above sea. The warm air above sea rises up and cold air from the
land pushes in above sea to take its place. Therefore, the movement
of wind is from land towards the sea. This is called land breeze.
Q.6.
Following are a few organisms: (a)
Lichens; (b)
Mosses; (c)
Mango tree; (d)
Cactus, which among the above can grow on stones, help in formation
of soil? Write the mode of their action for making the soil.
Answer: Lichens
can grow on stones. These are a close association of a fungus and an
algae. Lichens are the pioneer plants on barren rocks and hard rocky
soil. Their continuous growth can even disintegrate rocks which helps
in soil formation. They do this by secreting some organic acids. The
disintegrated rock particles and the decaying of lichen form a
fertile layer of soil where other plants particularly mosses can
colonise.
Q.7.
Soil formation is done by both abiotic and biotic factors. List the
name of these factors by classifying them as abiotic and biotic.
Answer:
(i)
Abiotic
factors of soil formation: Sun,
water, wind.
(ii)
Biotic
factors of soil formation: Lichens,
mosses, herbs, shrubs, trees and animals (earthworms).
Q.8.
All the living organisms are basically made up of C,N, S, P, H and O.
How they enter the living forms?
Answer: Most
of these elements first enter plants and become components of organic
material during the process of photosynthesis. Thus, they enter from
air (CO2),
water (H2O)
and ions (N, S, P) from the soil. From plants the chemicals pass on
to other organisms through the food chains.
Q.9.
Why does the percentage of gases such as oxygen, nitrogen and carbon
dioxide remain almost the same in the atmosphere?
Answer: The
composition of gases such as O2,
N2
and
CO2
remains
same in atmosphere due to the process of biogeochemical cycles.
During
these cycles, occur the repeated circulation of biogenetic nutrients
between abiotic and biotic components of the environment.
Q.10.
Why does moon have very cold and very high temperature variations,
e.g., from –190°C to 110°C even though it is at the same distance
from the sun as the Earth is?
Answer: Atmosphere
of Earth is a bad conductor so acts as a temperature buffer. However,
moon lacks an atmosphere around it. Therefore, moon gets heated up as
sun rays fall on its surface. It cools down drastically when there is
no sunlight, causing wide fluctuations in its temperature.
Q.11.
Why do people love to fly kites near the sea shore?
Answer:
(i)
There is a regular unidirectional wind from the sea to land. It helps
in flying the kite high.
(ii)
The wind is cooler and provide comfort to kite flyers even in bright
sun.
Q.12.
Why does Mathura refinery pose problems to the Taj Mahal?
Answer: Mathura
refinery emits hydrocarbons and sulphur oxides in its exhaust/fumes.
Hydrocarbons induce the formation of ozone which is highly oxidizing.
Sulphur dioxide produces acid rain which has a corroding effect on
marble. As a result, Mathura refinery does pose problems to Taj
Mahal.
Q.13.
Why do not lichens occur in Delhi where as they commonly grow in
Manali or Darjeeling?
Answer: Lichens
act as indicators of air pollution. They are sensitive to sulphur
dioxide which occurs in sufficient quantity in the atmosphere of
Delhi due to large number of vehicles, homes and factories using
fossil fuels. Also Delhi exists in semiarid area where atmospheric
moisture is low. In Manali and Darjeeling, the atmosphere is humid
and has comparatively low contents of sulphur dioxide.
Q.14.
Why does water need conservation even though large oceans surround
the land masses?
Answer: Salt
water of seas and oceans is unfit for consumption by humans, animals,
land plants or industries. Therefore, terrestrial biota and human
beings have to depend upon fresh-water resources available on land
(such as water present in rain, snow, springs, river, lakes, ponds
and other freshwater bodies (only about 0.5% of the total water on
earth). As a result, freshwater needs its conservation.
Q.15.
There is a mass mortality of fish in a pond. What may be the reasons?
Answer: In
a pond, a mass mortality of fish may occur due to following seasons.
(i)
Passage of pesticide rich water from crop fields.
(ii)
Release of toxic industrial waste.
(iii)
Pouring of hot water from an industry or thermal power plant.
(iv)
Release of waste rich in heavy metals and mercury.
(v)
Blockage of gills of fish by some suspended pollutant such as oil.
Q.16.
Lichens are called pioneer colonisers of bare rock. How can they help
in formation of soil?
Answer: Lichens
release small quantity of acids which corrode the surface of rock
creating minute pores and releasing minerals. With the passage of
time these minerals deposit on rock to form a thin layer of soil.
Q.17.
“Soil is formed by water.” If you agree with this statement, then
give reasons.
Answer: Yes,
water causes weathering of rocks by following three methods.
1.
Wetting and drying. Certain
constituents of rocks can pick up moisture and swell up. They
contract on drying. Such components (i.e.,
chemicals) help in breaking of rocks.
2.
Frost action. Water
seeps into rock crevices and cracks and may freeze if the temperature
goes below O°C. Frozen water expands and exerts a huge pressure
sufficient to break all rocks.
3.
Abrasion. Beating
of rocks by rain and hail, wave action on shores and abrasion caused
by trumbling rock fragments in running water batter and grind the
rocks into smaller and smaller particles. Water carries these
particles depositing them downstream. This produces soil (e.g.,
sand particles) at a far away place from the parent rock.
Q.18.
Fertile soil has lots of humus. Why?
Answer: Fertile
soil contains sufficient amount of humus because (i)
Humus is required for binding soil particles into crumbs. Crumb
formation helps in both hydration and aeration of soil. (ii)
Humus makes the soil porous for easy passage of plant roots. (iii)
Humus is a source of mineral. (iv)
Humus contains chemicals that promote growth of plants.
Q.19.
Why step farming is common in hills?
Answer: Step
farming is also called terracing. It is carried out in the hills
because terracing slows down the speed of rain water currents, checks
soil erosion and increase water absorption by the soil.
Q.20.
Why are root nodules useful for the plants?
Answer: Root
nodules mostly occur in the legume plants. These nodules contain
nitrogen fixing bacteria named Rhizobium.
The
bacteria picks up nitrogen from soil atmosphere and convert it into
organic compounds. The same pass into the plant so that legumes
(e.g.,
pea, gram) become rich in proteins and other nitrogen compounds.
Q.21.
How do fossil fuels cause air pollution?
Answer: Coal
and petroleum are the fossil fuels. They are burnt to get energy.
Combustion of fossil fuels produces:
(i)
suspended particles,
(ii)
sulphur oxides;
(iii)
nitrogen oxides;
(iv)
carbon dioxide;
(v)
carbon monoxide;
(vi)
vapours of hydrocarbons.
All these are air pollutants. Hydrocarbons
act as a source of cancer. Along with nitrogen oxides, they produce
ozone and smong. Sulphur and nitrogen oxides give rise to acid rain.
They are also irritatants and damage eyes and nasal tract.
Q.22.
Discuss how you can contribute in reducing water pollution.
Answer: Reduction
in Water Pollution
(i)
Sewage. The
authorities can be persuaded not to pass untreated effluents into
water body. Dairy owners of city can be prevailed upon not to pass
dung of cows and buffaloes into municipal waste water lines
especially during monsoon days.
(ii)
Garbage. Domestic
waste or garbage should not be thrown on the banks of water bodies.
(iii)
Industrial effluents. Asking
the industrial houses not to release untreated effluents into water
body.
(iv)
Washing clothes. Washing
clothes should be discouraged on the banks of water bodies as
detergents are a source of entrophication.
(v)
Vegetation cover. Grasses,
herbs, shrubs and trees should be planted on the banks of water
bodies. This will check soil erosion and siltation of water bodies.
It may also reduce run off from crop fields. Such runoffs are often
laden with fertilizers and toxic pesticides which are potent water
pollutants.
Q.23.
A motor car with its, glass totally closed, is parked directly under
the sun. The inside temperature of the car rises very high. Explain.
Answer:
Glass
is transparent to sunlight allowing it to pass into the interior of
the car. It heats up the interior. But heat waves do not escape from
the car due to glass being opaque to the same. As a result, the
interior of the car placed in the sun will become very hot. It is
similar to glass house effect.
Q.24.
Justify “Dust is a pollutant”.
Answer:
(i)
Dust consists of suspended particles. The latter pass into nasal
tract and cause a lot of discomfort including allergic asthma,
bronchitis, cough and cold
(ii)
Dust reduces light intensity
(iii)
Dust particles are eye irritants.
(iv)
Dust particles settle over plant foliage and reduce photosynthetic
activity
(v)
Dust particles block stomata reduces gaseous exchange in plants
(vi)
Dust particles can pick up toxic metals and chemicals being emitted
by industries.
Q.25.
Explain the role of the sun in the formation of soil.
Answer: Sun
plays an important role in weathering of rocks for soil formation. It
heats up the rocks during the day. Heating causes the rocks to
expand. During night, the rocks cool down and contract. Different
parts of a rock expand and contract at different rates resulting in
its cracking and breaking up into smaller pieces or fragments
(boulders).
Q.26.
Carbon dioxide is necessary for plants. Why do we consider it as a
pollutant?
Answer: Carbon
dioxide gas is essential for photosynthesis by plants. It is also a
green-house gas (GHG). Upto 350 ppm (ppm = parts per million)
concentration in the atmosphere, CO2
is
both a good raw material as well as essential for keeping the Earth
warm. However, when concentration of CO2
rises
(as presently it is 387 ppm), it becomes a pollutant because it
results in global warming. The global warming is quite dangerous
because it tends to melt polar ice and glaciers existing on
mountains, raise in the water level of oceans and submerge severals
coastal areas and islands.
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