NCERT Exemplar Class 9 Science Solutions Chapter 14 Natural Resources

NCERT Exemplar Class 9 Science Solutions Chapter 14-MCQ

Question:1

The atmosphere of the earth is heated by radiations which are mainly
(a) radiated by the sun
(b) re-radiated by land
(c) re-radiated by water
(d) re-radiated by land and water
Answer: D
The radiation from the sun reaches to the earth surface.
Most of the incident radiation get reflected from earth surface and water.
If there will be no atmosphere around the earth, most of the radiation will reflect back to space.
But this reflected radiation from water and land get trapped in atmosphere.
This re- radiation warms the atmosphere around the earth.
Hence the correct option of this question is option D

Question:2

If there were no atmosphere around the earth, the temperature of the earth will
(a) increase
(b) go on decreasing
(c) increase during day and decrease during night
(d) be unaffected
Answer: C
If there will be no atmosphere around earth, Day time will be warmer because of direct radiation coming from the sun.
But nights will be colder as there is no trapped radiation in the atmosphere.
Hence the correct option of this question is option C

Question:3

What would happen, if all the oxygen present in the environment is converted to ozone?
(a) We will be protected more
(b) It will become poisonous and kill living forms
(c) Ozone is not stable, hence it will be toxic
(d) It will help harmful sun radiations to reach earth and damage many life forms.
Answer: B
Most of the living beings on earth require oxygen to live.
If all the oxygen will convert in ozone, undoubtedly ozone layer will be thick but due to absence of oxygen in environment, life will be destroyed.
Absence of oxygen in environment can be seen as that the whole environment will be poisonous.
Trees and plants helps to maintain oxygen level on earth.
Hence the correct option of this question is option B

Question:4

One of the following factors does not lead to soil formation in nature
(a) the sun
(b) water
(c) wind
(d) polythene bags
Answer: D
Soil formation is a process in which stones and rocks get converted into very tiny particles.
The warmth of the sun, the flow of water and wind are the main parameters in formation of soil.
On the other hand plastic bags pollutes the soil.
Hence the correct option of this question is option D

Question:5

The two forms of oxygen found in the atmosphere are
(a) water and ozone
(b) water and oxygen
(c) ozone and oxygen
(d) water and carbon-dioxide
Answer: C
Oxygen does not exist in atomic form.
Pure oxygen atoms are found in molecular form.
A molecular form in which two oxygen atoms comes together is called oxygen gas.
A molecular form in which three oxygen atoms comes together is called ozone.
Hence the correct option of this question is option C

Question:6

The process of nitrogen-fixation by bacteria does not take place in the presence of
(a) molecular form of hydrogen
(b) elemental form of oxygen
(c) water
(d) elemental form of nitrogen
Answer: B
Nitrogen fixation is a process by which nitrogen () in the atmosphere is converted into ammonia (). Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is converted to ammonia by an enzyme called nitrogenase. Enzymes responsible for nitrogenase action are very susceptible to destruction by oxygen. Many bacteria cease production of the enzyme in the presence of oxygen. Many nitrogen-fixing organisms exist only in anaerobic conditions, respiring to draw down oxygen levels, or binding the oxygen with proteins.
Hence the correct option of this question is option B

Question:7

Rainfall patterns depend on
(a) the underground water tables
(b) the number of water bodies in an area
(c) the density pattern of human population in an area
(d) the prevailing season in an area
Answer: B
The process of rainfall can be easily understood by water cycle.
This water cycle has steps:
Evaporation, Condensation, Precipitation and Surface run off.
Water gets evaporated from the water bodies like Ponds Rivers lakes et cetera.
Therefore we can say the rain pattern will depend on number of water bodies in the area.
Hence the correct answer of this question is option B

Question:8

Among the given options, which one is not correct for the use of large amount of fertilizers and pesticides?
(a) They are eco-friendly
(b) They turn the fields barren after some time
(c) They adversely affect the useful component from the soil
(d) They destroy the soil fertility
Answer: A
Uses of fertilizer and pesticide definitely helps the crops to grow and save them from insects.
Excessive use of fertilizers may make the land infertile or barren as these fertilizers and pesticides destroy the useful components of the soil.
These fertilizers and pesticides are definitely not eco-friendly.
Has the correct option of this question is option A

Question:9

The nitrogen molecules present in air can be converted into nitrates and nitrites by
(a) a biological process of nitrogen fixing bacteria present in soil
(b) a biological process of carbon fixing factor present in soil
(c) any of the industries manufacturing nitrogenous compounds
(d) the plants used as cereal crops in field
Answer: A
Nitrogen fixation process converts nitrogen present in atmosphere into nitrogen compounds.
Nitrogen fixation can be done by non-biological and biological process both.
Lightning is a non-biological process which does nitrogen fixation.
Biologically, some bacteria in the soil does this nitrogen fixation.
Hence, the correct option of this question is option A.

Question:10

One of the following processes is not a step involved in the water-cycle operating in nature
(a) evaporation
(b) transpiration
(c) precipitation
(d) photosynthesis
Answer: D
This water cycle has steps:
Evaporation, Condensation, Precipitation and Surface run off.
Transpiration is also kind of evaporation in the trees with the help of leaves.
Photosynthesis is a part of the carbon cycle.
Therefore correct option of this question is option D

Question:11

The term “water-pollution” can be defined in several ways. Which of the following statements does not give the correct definition?
(a) The addition of undesirable substances to water-bodies
(b) The removal of desirable substances from water-bodies
(c) A change in pressure of the water bodies
(d) A change in temperature of the water bodies
Answer: C
Water is polluted when chemical or biological harmful substances contaminate water bodies such as Lakes, ponds, rivers, ocean, underground water etc.
This contamination means addition of undesirable or removal of desirable substances from water.
Change in water temperature can also make it less useful for life, which is also a kind of water pollution.
But pressure in water is never counted as water pollution.
Hence the correct answer of this question is option C

Question:12

Which of the following is not a greenhouse gas?
(a) Methane
(b) Carbon dioxide
(c) Carbon monoxide
(d) Ammonia
Answer: D
Greenhouse gases are those gases which contribute in greenhouse effect.
These gases in atmosphere absorb and radiate the radiation reflected from surface of earth.
Due to these gases the temperature of earth is correct for life on earth.
The main greenhouse gases are Water vapor, ozone, carbon dioxide, methane et cetera.
Ammonia is not a greenhouse gas.
Has the correct option of this question is option D

Question:13

Which step is not involved in the carbon-cycle?
(a) Photosynthesis
(b) Transpiration
(c) Respiration
(d) Burning of fossil fuels
Answer: B
In the process of transpiration trees and plants removes water from it with the help of leaves.
It does not involve emission or absorption of carbon dioxide.
Photosynthesis in plants and respiration in all living organisms are parts of carbon cycle.
Burning of fossil fuels releases carbon dioxide therefore it is also part of carbon cycle.
Has the correct answer of this question is option B

Question:14

‘Ozone-hole’ means
(a) a large sized hole in the ozone layer
(b) thinning of the ozone layer
(c) small holes scattered in the ozone layer
(d) thickening of ozone in the ozone layer
Answer: B
Ozone layer around the earth is very much required for life on earth.
This layer is getting depleted by man-made compounds containing fluorine chlorine etc.
The thickness of ozone layer is decreasing at many part around the earth.
This thinning of ozone layer is also termed as ozone hole
Has the correct option of this question is option B

Question:15

Ozone-layer is getting depleted because of
(a) excessive use of automobiles
(b) excessive formation of industrial units
(c) excessive use of man-made compounds containing both fluorine and chlorine
(d) excessive deforestation.
Answer: C
Ozone layer around the earth is very much required for life on earth.
This layer is getting depleted by man-made compounds containing fluorine chlorine etc.
The thickness of ozone layer is decreasing at many part around the earth.
These man-made chlorine Fluorine compound are generally emitted by refrigerants.
Hence the correct option is option C.

Question:16

Which of the following is a recently originated problem of environment?
(a) Ozone layer depletion
(b) Green house effect
(c) Global warming
(d) All of the above
Answer: D
Ozone layer depletion, greenhouse effect and global warming are currently main problems for life on earth.
All these problems created by human being.
Emission of chlorine fluorine compounds is main cause of ozone layer depletion.
Burning of fossil fuels and deforestation increases the carbon dioxide level in atmosphere.
Carbon dioxide is the main gas responsible for greenhouse effect.
The increase of greenhouse gases is reason of global warming on Earth.
Hence, the correct option of this question is option D

Question:17

When we breathe in air, nitrogen also goes inside along with oxygen. What is the fate of this nitrogen?
(a) It moves along with oxygen into the cells
(b) It comes out with the during exhalation
(c) It is absorbed only by the nasal cells
(d) Nitrogen concentration is already more in the cells so it is not at all absorbed.
Answer: B
Nitrogen is the most abundant gas in nature hence while inhalation nitrogen goes inside our body along with oxygen.
The composition of inhaled air is oxygen, carbon dioxide, nitrogen and trace gases. The composition of exhaled air is oxygen, carbon dioxide, nitrogen and other trace gases. As the exhaled nitrogen is equal to inhaled nitrogen, we can conclude that it is not utilized by our body and is exhaled along with carbon dioxide.
Hence, the correct option of this question is option B

Question:18

Top-soil contains the following
(a) Humus and living organisms only
(b) Humus and soil particles only
(c) Humus, living organisms and plants
(d) Humus, living organisms and soil particles.
Answer: D
Soil is a mix of varying amounts of inorganic matter, organic matter, water, and air.
Topsoil is made of decaying organisms and plant life; it is responsible for plant production.
The organic material of soil, called humus, is made up of microorganisms (dead and alive), and dead animals and plants in varying stages of decay. Humus improves soil structure, providing plants with water and minerals.
The inorganic material of soil is composed of rock, which is broken down into small particles of sand (0.1 to 2 mm), silt (0.002 to 0.1 mm), and clay (less than 0.002 mm).
Hence, the correct option of this question is option D

Question:19

Choose the correct sequences
(a) in atmosphere → decomposers → organic carbon in animals → organic carbon in plants
(b) in atmosphere → organic carbon in plants → organic carbon in animals → inorganic carbon in soil
(c) Inorganic carbonates in water → organic carbon in plants → organic carbon in animals → scavengers
(d) Organic carbon in animals → decomposers in atmosphere → organic carbon in plants
Answer: B
Nutrient cycling is a cyclic process that encompasses the movement of nutrients from the physical environment to living organisms and back to the environment. Nutrients are present on the earth where they are recycled, transformed into different forms and reutilized. Carbon is present mainly as carbon dioxide and methane in the atmosphere.
There is a continuous exchange of carbon between biotic and abiotic components by the process of photosynthesis and respiration.
Slow geological processes, including the formation of sedimentary rock and fossil fuels, contribute to the carbon cycle over long timescales.
Hence, the correct option of this question is option B

Question:20

Major source of mineral in soil is the
(a) parent rock from which soil is formed
(b) plants
(c) animals
(d) bacteria
Answer: A
The bulk of the soil solid fraction is constituted by soil minerals, which exert significant direct and indirect influences on the supply and availability of most nutrient elements.
All soils initially come from rocks; this is termed the ‘parent material’. The Parent Material may be directly below the soil, or great distances away if wind, water or glaciers have transported the soil.
The formation of soils can be seen as a combination of the products of weathering, of structural development of the soil, of differentiation of that structure into horizons or layers, and lastly of its movement or translocation.
Hence, the correct option of this question is option A

Question:21

Total earth’s surface covered by water is
(a)
(b)
(c)
(d)
Answer: A
Earth is known as the "Blue Planet" because 71 percent of the Earth's surface is covered with water. Water also exists below land surface and as water vapor in the air.
The earth has an abundance of water, but unfortunately, only a small percentage (about 0.3 percent), is even usable by humans.
Hence, the correct option of this question is option A

Question:22

Biotic component of biosphere is not constituted by
(a) producers
(b) consumers
(c) decomposer
(d) air
Answer: D
Abiotic factors refer to non-living physical and chemical elements in the ecosystem. Abiotic resources are usually obtained from the lithosphere, atmosphere, and hydrosphere. Examples of abiotic factors are water, air, soil, sunlight, and minerals.
Biotic component of biosphere comprises living entities, air is a non-living component thus air is not a biotic component.
Hence, the correct option of this question is option D

Question:23

An increase in carbon dioxide content in the atmosphere would not cause
(a) more heat to be retained by the environment
(b) increase in photosynthesis in plants
(c) global warming
(d) abundance of desert plants
Answer: D
is a greenhouse gas; thus, its increase will trap more heat and will cause global warming.
Also increased will increase the rate of photosynthesis however, increase doesn't contribute towards deserted conditions
An increase in carbon dioxide content in the atmosphere would not cause abundance of desert plants as when the temperature rises (due to excessive carbon dioxide emission) their ability to take up carbon dioxide reduces.
Hence, the correct option of this question is option D

Question:24

Oxygen is returned to the atmosphere mainly by
(a) burning of fossil fuel
(b) respiration
(c) photosynthesis
(d) fungi
Answer: C
Oxygen has been released mainly by photosynthesis, which involves the consumption of carbon dioxide.
Respiration is a catabolic process while photosynthesis is an anabolic process. During respiration oxygen is taken and carbon dioxide is given out while during photosynthesis carbon dioxide is taken and oxygen is given out.
During photosynthesis, carbon dioxide is fixed to form carbohydrate by the dark reaction. The water molecules are broken down during the light reaction and release oxygen. Thus, the two process helps to maintain the balance of oxygen and carbon dioxide in the atmosphere.
Hence, the correct option of this question is option C

Question:25

Low visibility during cold weather is due to
(a) formation of fossil fuel
(b) unburnt carbon particles or hydrocarbons suspended in air
(c) lack of adequate power supply
(d) none of these
Answer: B
The atmospheric pollutants or gases that form smog are released in the air when fuels are burnt.
The word "smog" is a combination of the words "smoke" and "fog." Smog is a mixture of many pollutants, mainly ground level ozone and fine particulate matter.
Air pollution due to excessive and uncontrolled exhaust emissions from automobiles has reached alarming rate.
The exhaust from diesel vehicles contain unburnt carbon particles and hydrocarbons.
Hence, the correct option of this question is option B

Question:26

Growth of Lichens on barren rocks is followed by the growth of
(a) moss
(b) ferns
(c) gymnosperms
(d) algae
Answer: A
Growth of Lichens on barren rocks is followed by the growth of moss.
While technically moss is a plant, it lacks the parts of a plant that we are used to seeing.
Moss tends to grow in colonies, with several plants growing closely together, which creates the nice, smooth carpet-like appearance that makes moss gardens so beautiful.
An area is initially colonized by certain early-successional species such as Lichens,
Once new soil has formed in an area it gives way over time to mild-successional species, such as mosses and grasses
Hence, the correct option of this question is option A

Question:27

Aquatic organisms are used to a certain range of temperature in the water bodies where they live. Marked temperature changes in aquatic environment can affect
(a) breeding of animals
(b) more growth of aquatic plants
(c) process of digestion in animals
(d) availability of nutrients.
Answer: A
Aquatic animals are highly susceptible to temperature changes.
To lay eggs aquatic animals need optimum temperature.
Thus, any change in temperature hinder the breeding process.
Hence, the correct option of this question is option A

Question:28

Soil erosion can be prevented by
(a) raising forests
(b) deforestation
(c) excessive use of fertilizer
(d) overgrazing by animals
Answer: A
Trees are also being used in both developed and developing countries as windbreaks to shelter crops, prevent erosion and protect the soil.
Forests and trees make an essential contribution to food security by helping to maintain the environmental conditions needed for agricultural production. They stabilize the soil, prevent erosion, enhance the land's capacity to store water, and moderate air and soil temperatures.
Hence, the correct option of this question is option A

Question:29

What happens when rain falls on soil without vegetational cover?
(a) Rain water percolates in soil efficiently
(b) Rain water causes loss of surface soil
(c) Rain water leads to fertility of the soil
(d) Rain water does not cause any change in soil
Answer: B
In agriculture, soil erosion refers to the wearing away of a field's topsoil by the natural physical forces of water.
When rain falls on soil without vegetational cover, rain water causes loss of surface soil or Top soil. Topsoil, which is high in organic matter, fertility and soil life, is relocated elsewhere "on-site" where it builds up over time or is carried "off-site" where it fills in drainage channels.
Hence, the correct option of this question is option B

Question:30

Oxygen is harmful for
(a) ferns
(b) nitrogen fixing bacteria
(c) chara
(d) mango tree
Answer: B
Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is converted to ammonia by a Nitrogenase enzyme. Nitrogenases are rapidly degraded by oxygen. For this reason, many bacteria cease production of the enzyme in the presence of oxygen. Many nitrogen-fixing organisms exist only in anaerobic conditions, respiring to draw down oxygen levels, or binding the oxygen with a protein such as leghemoglobin.
Hence, the correct option of this question is option B

NCERT Exemplar Class 9 Science Solutions Chapter 14-Short Answer

Question:31

Rivers from land, add minerals to sea water. Discuss how?
Answer:

The soil is made up of rocks (which are aggregation of minerals). When rain falls on soil without vegetational cover, rain water causes loss of surface soil or Top soil. As water flows over the rocks containing soluble minerals, some of them get dissolved in the water. River discharge constitutes the main source for the oceans.

Question:32

How can we prevent the loss of top soil?
Answer:

We can’t completely eliminate soil erosion, but we can reduce the loss of top soil. Maintaining grass waterways in low areas of the fields reduce water runoff and mean fewer nutrients leaving fields. Crops planted in narrow rows canopy provide more protection of the soil. Planting crop rows perpendicular to slopes tends to decrease water runoff and increase infiltration. Conventional tillage produces a smooth surface that leaves soil vulnerable to erosion.

Question:33

How is the life of organisms living in water affected when water gets polluted?
Answer:

Different pollutants affect the aquatic environment in different ways. While at low concentrations many pollutants (e.g. organic materials, N and P) may be beneficial, at high levels they can adversely affect the ecology of the system. Excess pollution in a river can damage the plant and animal life present in the river by reducing the oxygen content of the water. Many of the toxic pollutants in effluents are synthetic, and therefore do not easily biodegrade naturally.
The effects of physical pollution on the ecology of a river system can be complex, affecting the feeding and breeding habits of the different species.

Question:34

During summer, if you go near the lake, you feel relief from the heat, why?
Answer:

During summer, the warm air over land rises, and gets replaced by the relatively cool air which resides immediately above the lake surface. We can thank "lake breezes" for these cooler temperatures. Lake breezes are also responsible to keeping lake shores less cloudy, due to the fact that the cooler air found in a lake breeze tends to rise into cloud cover less readily. if you go near the lake, you feel relief from the heat.

Question:35

In coastal area, wind current moves from the sea towards the land during day; but during night it moves from land to the sea. Discuss the reason.
Answer:

The differential heating of land and sea results in the formation of a breeze, usually in the coastal areas. Land and sea breezes are the winds of a periodic type. Land and sea breezes occur daily. A land breeze is created when the land is cooler than the water such as at night and the surface winds have to be very light. When this happens the air over the water slowly begins to rise, as the air begins to rise, the air over the surface of the ocean has to be replaced, this is done by drawing the air from the land over the water. A sea breeze is created when the surface of the land is heated sufficiently to start rising of the air. As air rises, it is replaced by air from the sea. Sea breezes tend to be much stronger and can produce gusty winds as the sun can heat the land to very warm temperatures, thereby creating a significant temperature contrast to the water. So that is the reason wind current moves from the sea towards the land during day; but during night it moves from land to the sea.

Question:36

Following are a few organisms
(a) lichen (b) mosses (c) mango tree (d) cactus
Which among the above can grow on stones; and also help in formation of soil? Write the mode of their action for making soil.
Answer:
Organisms that can colonize bare rock are called pioneer species. Lichens are usually the first pioneer species, and they look like colour splotches on the surface of rocks - white, green, grey, yellow or even orange.
Once lichens have been growing on rocks for a while, mosses are able to survive there too. Mosses are plants that don't have flowers or stems or roots - just tiny green leaf-like structures and microscopic hair-like structures. Mosses build habitat for small flowering plants; the flowering plants provide habitat and food for more creatures. Flowering plants have roots that hold the soil in place, and they also add to the soil as they die back each winter and decompose. Their decay and decomposition lead to an increase in organic content of the soil which paves way for other forms of vegetation.

Question:37

Soil formation is done by both abiotic and biotic factors. List the names of these factors by classifying them as abiotic and biotic?
Answer:
Abiotic factors involved in soil formation are
(a) Rocks
(b) Water
(c) Sun
(d) Wind
Biotic factors involved in soil formation are
(a) Lichens
(b) Bryophytes
(c) Bacteria
(d) Fungi
(e) Nematodes
(f) Earthworm
(g) Arthropods

Question:38

All the living organisms are basically made up of C, N, S, P, H and O. How do they enter the living forms? Discuss.
Answer:
These chemical elements tend to circulate in the biosphere in a characteristic cyclic path, i.e., from environment to living organisms and back to the environment. These circular paths are called biogeochemical cycles or nutrient cycles.
In other words, these elements are absorbed by the plants from nature and convert them into food. This food passes through different trophic levels of various food chains for utilization by consumers. Finally, the decomposers return the inorganic nutrient to the environment by decomposing the dead bodies and excreta of various consumers.

Question:39

Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere?
Answer:
The atmosphere is composed of a mix of several different gases in different amounts. The permanent gases whose percentages do not change from day to day are nitrogen, oxygen and carbon dioxide. The cycling of oxygen, nitrogen and carbon dioxide between the atmosphere and the biosphere results in relatively constant proportions of these compounds in the atmosphere over time. For example, the carbon cycle, as it relates to the biosphere, is simple in its essence. Inorganic carbon (carbon dioxide) is converted to organic carbon (the molecules of life). To complete the cycle, organic carbon is then converted back to inorganic carbon. The nitrogen cycle begins with the fixing of inorganic atmospheric nitrogen () into organic compounds. These nitrogen-containing compounds are used by organisms and, through the process of denitrification, are converted back to inorganic atmospheric nitrogen.

Question:40

Why does moon have very cold and very hot temperature variations eg, from to even though it is at the same distance from the sun as the earth is?
Answer:
Earth’s atmosphere is a thin blanket of gases and tiny particles - together called air. Temperatures on the moon are extreme, ranging from boiling hot to freezing cold depending on where the sun is shining. There is no significant atmosphere on the moon, so it cannot trap heat or insulate the surface.

Question:41

Why do people love to fly kites near the seashore?
Answer:
The differential heating of land and sea results in the formation of a breeze, usually in the coastal areas. A land breeze is created when the land is cooler than the water such as at night and the surface winds have to be very light. When this happens the air over the water slowly begins to rise, as the air begins to rise, the air over the surface of the ocean has to be replaced, this is done by drawing the air from the land over the water. People love to fly kites near the seashore because it helps in the flying of kites to great heights.

Question:42

Why does Mathura refinery pose problems to the Taj Mahal?
Answer:
Mathura oil refinery and other industries of the neighboring towns which burn fossil fuels are responsible for the discoloration of Taj Mahal. These industries release soot particles and gases like Sulphur dioxide and nitrogen oxides into the atmosphere. The soot particles turn the color of the marble to yellow and the gases react with water to form acid rain which corrodes the marble of the monument. This phenomenon is also called “marble cancer”.

Question:43

Why do not lichens occur in Delhi whereas they commonly grow in Manali or Darjeeling?
Answer:
Lichens are bio-indicators of air pollution. They are sensitive to Sulphur dioxide (SO2) which occurs in sufficient quantity in the atmosphere of Delhi due to large number of vehicles, factories using fossil fuels etc. Moreover, Delhi occurs in semi-arid area where atmospheric moisture is low. In Manali and Darjeeling, the atmosphere is humid and Sulphur dioxide pollution is comparatively low.

Question:44

Why does water need conservation even though large oceans surround the land masses?
Answer:
Water covers about of the earth's surface but only of the earth's water is fresh and more over of the earth's water is available fresh water. of the earth's fresh water is unavailable: locked up in glaciers, polar ice caps, atmosphere, and soil; highly polluted; or lies too far under the earth's surface to be extracted at an affordable cost. Marine water is not useful for human and plant life directly due to high salt content. Water conservation is important because fresh clean water is a limited resource, as well as a costly one.

Question:45

There is mass mortality of fishes in a pond. What may be the reasons?
Answer:
One reason for the mass mortality of fishes in a pond is eutrophication. Eutrophication is a process by which plant growth increases in a water body like ponds or lakes. The increased growth and overcrowding of plants is due to either natural fertilizing agents that are washed off from the soil or the runoff of chemical fertilizers applied to agricultural lands. As the overcrowd plants die off, the dead and decaying vegetation depletes the pond’s oxygen supply. This in turn leads to the mass scale death of fish in the pond.
Any change in the water quality necessarily influences the whole of surrounding environment. Hence to maintain a well-defined environment, the ecology of an ecosystem should not be disturbed. Some other reason may be Poor water quality, Poor pond hygiene, Presence of Pests, etc.

Question:46

Lichens are called pioneer colonizers of bare rock. How can they help in formation of soil?
Answer:
Organisms that can colonize bare rock are called pioneer species. Lichens are usually the first pioneer species, and they look like color splotches on the surface of rocks - white, green, grey, yellow or even orange.
Once lichens have been growing on rocks for a while, mosses are able to survive there too. Mosses are plants that don't have flowers or stems or roots - just tiny green leaf-like structures and microscopic hair-like structures. Mosses build habitat for small flowering plants; the flowering plants provide habitat and food for more creatures. Flowering plants have roots that hold the soil in place, and they also add to the soil as they die back each winter and decompose. Their decay and decomposition lead to increase in organic content of the soil which paves way for other forms of vegetation.

Question:47

“Soil is formed by water.” If you agree to this statement then give reasons
Answer:
The soil is made up of rocks (which are aggregation of minerals). As water flows over the rocks containing soluble minerals, some of them get dissolved in the water. Water is an essential constituent of healthy, productive soils. It serves to bind and secure the physical particulates in soil structure and is the medium by which natural chemicals and essential trace element nutrients are transported to plants. Water enters soil both downwardly, though precipitation, or it is drawn up from deposits in underlying layers of rock or subsoil. This movement has the effect of binding the minerals together as it occupies the microscopic porous spaces between the mineral particles. The importance of water cannot be overstated; in addition to sustaining all life on Earth it plays an important role in formation of soil.

Question:48

Fertile soil has lots of humus. Why?
Answer:
Healthy, fertile soil is a combination of water, air, organic matter, and nutrient minerals. Organic matter comes from decomposing plant and animal materials. Organic matter is the name for a plant and animal when it is in the process of decomposing. It's called humus when it has completely decomposed. Humus contains many nutrient minerals that improves the health and fertility of the soil. Carbon is critical for healthy soil conditions, and humus is roughly 60 percent carbon.

Question:49

Why step farming is common in hills?
Answer:
Step farming is common in hills because of its benefits. The major benefit, of course, is the conservation of soil and water. Terraces reduce both the amount and velocity of water moving across the soil surface, which greatly reduces soil erosion. Terracing thus permits more intensive cropping than would otherwise be possible. Due to the reduction in soil erosion and having high water holding capacity, terrace farming improves soil fertility and land productivity. It enhances biodiversity and helps in ecosystem restoration and enhances biodiversity.

Question:50

Why are root nodules useful for the plants?
Answer:
Root nodules are specialized organs developed by the host plant, mostly legumes. Rhizobia are diazotrophic bacteria that fix nitrogen after becoming established inside the root nodules of legumes Rhizobium is a genus of bacteria associated with the formation of root nodules on plants. These bacteria live in symbiosis with legumes. They take in nitrogen from the atmosphere and pass it on to the plant, allowing it to grow in soil low in nitrogen. Thus, root nodules useful for the plants.

NCERT Exemplar Class 9 Science Solutions Chapter 14-Long Answer

Question:51

How do fossil fuels cause air pollution?
Answer:
Most of this air pollution we cause results from the burning of fossil fuels, such as coal, oil, natural gas, and gasoline to produce electricity and power our vehicles. Although fossil fuels are mainly composed of carbon, it contains impurities such as Sulphur and nitrogen atoms. As the fuel gets burnt the Sulphur and nitrogen combines with oxygen to from Sulphur dioxide (SO2) and nitrogen oxide respectively which gets released into the air, which contribute to the formation of smog and acid rain. The most common nitrogen-related compounds emitted into the air by human activities are collectively referred to as nitrogen oxides. Ammonia is another nitrogen compound emitted to the air, primarily from agricultural activities, but also from fossil fuels. Most of the nitrogen oxides released is due to human activity are from the burning of fossil fuels associated with transportation and industry.

Question:52

What are the causes of water pollution? Discuss how you can contribute in reducing water pollution.
Answer:
It is sometimes caused by nature, such as when mercury filters from the Earth's crust, polluting oceans, rivers, lakes, canals and reservoirs. However, the most common cause of poor-quality water is human activity and its consequences such as:

1. Global warming: Rising global temperatures caused by emissions heat the water, reducing its oxygen content.

2. Deforestation: Felling forests can exhaust water resources and generate organic residue which becomes a breeding ground for harmful bacteria.

3. Industry, agriculture and livestock farming: Chemical dumping from these sectors is one of the main causes of eutrophication of water.

4. Rubbish and fecal water dumping: of the world's sewage finds its way into seas and rivers untreated.

5. Maritime traffic: Much of the plastic pollution in the ocean comes from fishing boats, tankers and cargo shipping.

We must prevent water pollution with measures like the following:

1. prevent global warming and acidification of the oceans.emissions to Reduce

2. Reduce the use of chemical pesticides and nutrients on crops.

3. Reduce and safely treat waste water so that, as well as not polluting, it can be reused for irrigation and energy production.

4. Restrict the use of single-use plastics that end up floating in rivers, lakes and oceans, many as microplastics.

5. Encourage sustainable fishing to ensure the survival of species and avoid depletion of the seas.

Question:53

A motor car, with its glass totally closed, is parked directly under the sun.
The inside temperature of the car rises very high. Explain why?
Answer:
Infrared radiations in sunlight pass through the glass and heat the interior of the car. The radiation emitted by upholstery and other inner parts of the car cannot pass out of the glass, so the heat trapped inside raises the temperature of the interior. This is because glass is transparent to infrared radiation from the Sun having smaller wavelengths than that emitted by the interior of the car which are of longer wavelengths to which the glass is opaque.

Question:54

Justify “Dust is a pollutant”?
Answer:
The air we breathe indoors and outdoors always contains particle pollution. Some particles, such as dust, dirt, soot, or smoke, are large enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope. Dust particles, often referred to as particulate matter (PM), in the atmosphere arise from a wide variety of sources. Given the wide variety of pollutants and chemical compositions involved, dust particles play a role in many air pollution issues. Human health effects of particles; respiratory and heart problems caused by inhalation of small particles has been related to the mass concentration of particles below 10 µm diameter. Deposition of regional pollutants causing acidification and eutrophication. Breathing low levels of household or urban dust does not cause health problems in most individuals but anyone who is exposed to high levels of dust may be affected – the longer you breathe in the dust, then the greater the chance that it will affect your health. The Department of Health recommends that you think about using dust control and personal protective equipment whenever you undertake dusty activities at home or at work.
People more likely to develop health problems from long term exposure to high levels of dust include: babies and young children, elderly people (65 years and over), people with pre-existing respiratory conditions (e.g. asthma, bronchitis), including smokers, heart conditions

Question:55

Explain the role of the Sun in the formation of soil.
Answer:
Soil forms through the interaction of the major soil-forming factors--parent material, climate, vegetation and animal life, relief, and time. Relief, or the shape of the landscape, influences soil formation, mainly through its effect on drainage and erosion, and partly through variations in exposure to the sun and wind and in air drainage. Under the influence of solar radiations, the rocks heat up and expand. At night, these cool down and contract. Since all parts of the rocks do not expand and contract at the same rate, cracks appear in the rocks and ultimately the large rocks break up into smaller pieces. Exposure to the sun is closely related with temperature which also has a profound effect on weathering. Warm temperatures, coupled with high moisture, will increase weathering processes. Therefore, in the warm, wet climates of the tropics, it is typical to have well-developed, highly weathered soils. In places with extreme climatic conditions, such as the arctic circle or the arid region, the rocks are subjected to sudden expansion and contraction, which results in the loosening of their particles and increase in the air content. Over time, the effect significantly reduces a rock to loosen soil. The rocks swell when they are wet and shrink back when dry. Regular wetting and drying of rocks result in the loosening of its grains. Therefore, sun has important role to play in the formation of soil.

Question:56

Carbon dioxide is necessary for plants. Why do we consider it as a pollutant?
Answer:
We commonly think of pollutants as contaminants that make the environment dirty or impure. A vivid example is Sulphur dioxide, a by-product of industrial activity. High levels of Sulphur dioxide cause breathing problems. Too much causes acid rain. Sulphur dioxide has a direct effect on health and the environment. Carbon dioxide, on the other hand, is a naturally occurring gas that existed in the atmosphere long before humans. Plants need it to survive. During the process of photosynthesis, cells use carbon dioxide and energy from the Sun to make sugar molecules and oxygen. The level of atmospheric carbon dioxide in the atmosphere has remained at relatively stable levels. However, human Carbon dioxide emissions over the past few centuries have upset this balance. The increase in Carbon dioxide has some direct effects on the environment. For example, as the oceans absorb Carbon dioxide from the atmosphere, it leads to acidification that affects many marine ecosystems. However, the chief impact from rising Carbon dioxide is warmer temperatures. Rising levels causes an enhanced greenhouse effect. This leads to warmer temperatures which has many consequences. Some effects are beneficial such as improved agriculture at high latitudes and increased vegetation growth in some circumstances. However, the negatives far outweigh the positives. Coast-bound communities are threatened by rising sea levels. Melting glaciers threaten the water supplies of hundreds of millions. Species are becoming extinct at the fastest rate in history.