Class 9 Science Chapter 14 Important Questions

Resources which can replenish themselves by quick recycling are called renewable resources. For example, forests and wildlife.

Growing population and industrialisation.

Caron dioxide

Stratosphere.

Carbon dioxide.

(i) Natural resources like air, land and water.
(ii) Energy of the sun.

Photosynthesis and respiration.

Molecular oxygen and ozone

Anaerobic bacteria.

Nitrogen fixation cannot take place in the presence of oxygen.

Food, water, air and optimum temperature.

Humans make the soil more porous and allows the water and air to penetrate deep in soil.

Ans. Clouds are collection of tiny particles of liquid or solid water occurring in the atmosphere above the Earth’s surface.

Rainwater.

From sea water.

It is used for human consumption and irrigation purposes

Step farming is practiced in hills to check soil erosion through water current on the slopes.

Fertility is the capacity of the soil to sustain plant life with the required nutrients.

The topmost layer of the soil which contains soil particles, human as well as living organism is called topsoil.

They are the pollutants that degrade by natural means. For example, excreta of animals, paper, etc.

Decomposers.

Leguminous plants

Rhizobium bacteria.

CFCs or chlorofluorocarbons are manmade orgno-halogens used in refrigerators that degrade the ozone layer.

Through long wave radiations re-radiated by land and water.

By the biological process of nitrogen fixing bacteria present in soil.

The thinning of ozone layer at few places is called the ozone hole.

The parent rock from which soil is formed.

Breeding of aquatic animals.

Inhaling ozone causes dryness of mucous membrane of the mouth, nose and throat, it changes visual activity; causes headache and pulmonary congestion. It even harms leafy vegetables, field crops, fruits and forest trees.

The major uses of oxygen are:
(i) It is necessary for respiration in the living beings.
(ii) Oxygen is essential for combustion i.e. burning

(i) Green plants convert CO2 into glucose in the presence of sunlight by the process of photosynthesis.
(ii) Many marine animals use carbonates dissolved in sea water to make their cells.

Plants take up C and H by the process of photosynthesis and the rest of the minerals are absorbed from the soil. Consumers take in O and H by the process of respiration and the rest of the minerals are taken via food.

Cycling of these gases maintains consistency of these gases. These are taken up and released by almost every living organism and thus their concentration in the atmosphere is maintained.

Dust is present in air as suspended particles. It can cause allergy and other respiratory diseases. It also affects plant growth by covering stomata on leaf surface and blocking them. It acts as the carries of toxic compounds like heavy metals. Thus dust acts as a pollutant.

The burning of fossils fuels like coal and petroleum produces oxides of nitrogen and sulphur which reach the atmosphere. When they dissolve in rain, they form nitric acid and sulphuric acid and fall as rain acid.

Ozone is present in the upper layers of the atmosphere (stratosphere). Before reaching the Earth, the sunrays through the stratosphere. The ozone layer present there absorbs the harmful UV planet from disastrous effect of UV rays.

Nitrogen is the most abundant gas in our atmosphere. In fact, it makes up 78% of our atmosphere and is also a part of many molecules essential to life like proteins, nuclei acids (DNA and RNA) and some vitamins. Moreover, it is found in other biologically important compounds such as alkaloids and urea. Thus nitrogen is very important for us.

(i) Fixed sources: These are fixed or located at specific sites, like industrial units, electric power plant etc.
(ii) Mobile sources: These include the vehicles and different modes of transport using fossils fuels.

Marine water is not useful for human and plant life directly due to high salt content. Uneven distribution of limited fresh water resources and conservation to cater to the demands.

They are certain chemical like fluorocarbon, released in the air either naturally or by human activities in the form of mist or vapour. Fluorocarbon, which deplete the ozone layer on the atmosphere are emitted by jet aeroplanes in the form of aerosols.

A constant interaction between biotic and abiotic components of biosphere makes it dynamic and stable. Infection consists of transfer of matter and energy between different components of biosphere.

During the daytime the rocks are heated up by the Sun and thus they expand. Whereas at night they cool down and thus contract. Since all parts of the rock do not expand and contract at the same rate it results in cracking of rocks, breaking them into smaller pieces.

Biological nitrogen fixation means the conversion of atmospheric nitrogen into useful nitrogen compounds by bacteria and algae. The bacteria present in the root nodules of leguminous plants like Rhizobium as well as some blue green algae help in the fixation of atmospheric nitrogen.

A large amount of energy is always lost into the atmosphere during its transfer from one level to another. This lost energy cannot be replenished from the atmosphere. Thus the energy flow is unidirectional. On the other hand, the biochemical substances are never lost in the biogeochemical cycle. They are only recycled.

The nitrogen cycle is said to be an ideal cycle in the biosphere because the amount of nitrogen remains constant throughout the entire cycle and no nitrogen is lost. Hence it follows the law of conservation of matter. In the other cycles of biosphere there is either loss of energy or loss of matter.

Plant require CO₂ in an optimum amount for the process of photosynthesis. But high concentration of (more than normal) CO₂ is harmful and considered as a pollutant. Higher concentration of CO₂ is one of the causes of greenhouse effect and global warming as it absorbs the infrared radiations thus increasing the temperature of Earth. This leads to many environmental problems.

Water is capable of dissolving a large number of substances. As water flows over the rocks containing soluble minerals, some of them get dissolved in the water. Thus river carry many nutrients from land to the sea.

The major components of the atmosphere on the Venus and Mars is carbon dioxide. In fact, CO₂ constitutes up to 95 – 97% of the atmosphere on these planets. So no life is known to exist on these planets as O₂ is necessary for maintaining life. On the other hand, the atmosphere on Earth has life supporting gases like nitrogen, oxygen, CO₂ and water vapour. Apart from that water is also present only on Earth.

We all need oxygen to break down glucose molecules and get energy for all our activities. During glucose breakdown, carbon dioxide is released. Moreover, a lot of carbon dioxide is produced during combustion of various industrial and other human activities. Forest fires also produce a lot of carbon dioxide. Combustion in vehicles contributes a large amount of carbon dioxide to the atmosphere.

Air moves from a region of high pressure to a region of low pressure. Air above the land gets heated quickly during day and starts rising. This creates a region of low pressure as a result of which air above the sea rushes into this area of low pressure. This movement of air from one region to other creates winds. During night as water cools down slowly, the air above water is warmer than the air on land. So, air moves from land to sea creating winds.

Addition of undesirable chemicals like pesticides, fertilisers, industrial wastes and domestic wastes not only kill the aquatic organisms they also cause water- borne diseases. With the additions of pollutants, the phytoplankton and other organisms require more oxygen for their degradation thus decreasing the amount of oxygen available in water. Due to this reduction in the dissolved oxygen in water there are adverse effects on the aquatic organisms leading to their deaths.

Some nutrients of the soil get depleted by growing the same crop year after year. So replenishment of the soil is essential to keep it fit for further cultivation.
Two natural ways of soil replenishment are:
(i) Crop rotation and
(ii) Leaving the agricultural land uncultivated for one or two seasons so as to allow it to regain its fertility.

Water helps in formation of soil in the following ways:
(i) Water wears off the rocks over a long period of time.
(ii) Small rocks in the flowing water rub against other rocks creating small particles which are carried away downstream and deposited as soil.
(iii) Water expands on freezing. So when it is deposited in crevices of rocks, rocks crack into smaller pieces.

There is a balance between the CO₂ which occurs at the Earth’s surface, CO₂ dissolved in oceans and that found in marine and terrestrial sediments. The burning of fossil fuels increases the amount of CO₂ in the atmosphere causing air pollution. Plants control air pollution because during the process of photosynthesis, they take in CO₂ from the atmosphere and in turn release O₂. Thus, decreasing the level of CO₂ in the atmosphere.

Oxides of nitrogen combine chemically is sunlight and produce hydrocarbons, peroxyacetal nitrate(PAN), and ozone which are commonly known as photochemical smog. This is very harmful and makes eyes watery, affects the growth of plants by checking the rate of photosynthesis and increases the rate of transpiration.

The following are the major factors which lead to water pollution:
(i) The addition of undesirable substances to water bodies. For example, addition of industrial wastes containing poisonous salts like pesticides, insecticides, etc. are fatal for aquatic life.
(ii) The removal of desirable substance from water bodies. For example, depletion of dissolved oxygen and nutrients have adverse effects on aquatic life.
(iii) Change in temperature of water in the water bodies. The aquatic animals are adapted to live under certain temperature range. A sudden change of temperature may affect breeding of aquatic animals, their eggs and larvae, etc. For example, pouring of water at very high temperature from the nuclear reactors may cause death of fishes and aquatic animals, Similarly, pouring cold water from dams also affect aquatic life adversely.

(i) Polluted water causes a number of water-borne diseases like cholera, typhoid, jaundice, diarrhea, hepatitis and dysentery.
(ii) Presence of acids or alkalies in water destroys certain microorganisms, which carry out the self-purification process in rivers.
(iii) Decrease in the amount of dissolved oxygen in the water body adversely affects the life of aquatic organisms.
(iv) Change in water temperature disturbs the aquatic life as eggs and larvae of various animals are badly affected by such changes.

(i) Rhizobium helps in the fixation of atmospheric nitrogen into ammonia.
(ii) Nitrosomonas converts ammonia to nitrates.
(iii) Nitrobactor converts nitrites into nitrates.

CFC’s contain both chlorine and fluorine. CFC’s are very stable and do not get degraded by any natural process. In the ozone layer present in the outer region of the atmosphere (25 – 40 km above sea level) CFC’s are dissociated by ultraviolet light to release free chlorine atoms. Free chlorine atoms catalyse the breakdown of ozone molecules (O3) into oxygen This results in degradation of the ozone layer. Thinning of the ozone layer would allow penetration of ultraviolet light into Earth’s atmosphere causing blindness, skin cancer and mutations.

An increase in global temperature can cause:
(i) Change in the amount and pattern of precipitation, i.e. rain, snow, etc.
(ii) melting of polar ice and rise of sea level.
(iii) extreme weather conditions like floods, droughts, heat wave, hurricanes and tornado etc.

The carbon in the form of food travels to animals from plants through food chains. In atmosphere the concentration of carbon dioxide is very low – only about 0.03% to 0.04%. Therefore, if carbon dioxide is not circulated back to our nutrient pool, there will be shortage of CO₂ and plants will not be able to carry out photosynthesis and the whole cycle will be disrupted. Combustion of fuels also adds carbon dioxide in the atmosphere. Carbon thus cycles through physical and biological activities.

Industrialisation has led to increase pollution of air in following ways:
(i) Due to industrialisation, the composition of fossil fuels has increased. Combination of fossil fuels has increased production of gases like CO, SO₂, SO₃, NO₂ and CO₂ which are toxic.
(ii) There has been depletion in the ozone layer because of increase in the production of chemicals like chlorofluorocarbons which are used as insulator, refrigerator, solvents and aerosol propellants. This has resulted in the entry of UV rays into Earth’s atmosphere, which has affected various organisms.
(iii) Combustion of fossils fuels also increases the amount of suspended particles in air causing pollution.
Step taken to check air pollution are:
(i) Planting more trees as they purify air by intake of CO₂ gas and release of O₂. This will reduce the greenhouse effect.
(ii) Reducing the composition of fossil fuels.
(iii) Laying emphasis on the use of non-conventional sources of energy like wind energy solar energy, tidal energy, etc. which reduce pollution to great extent.

Water is very essential for the survival and growth of plants.
(i) Seeds are germinating in the presence of water.
(ii) Water helps in the growth of plants.
(iii) Plants manufacture their food by the process of photosynthesis in the presence of sunlight, carbon-dioxide, water and a green pigment called chlorophyll.
(iv) Water dissolves the nutrients present in the soil which is then transported to the various parts of the plant.
(v) Water provides a medium for transportation of food and minerals within the plant.
(vi) Water also helps in maintenance of the plant structure by providing appropriate pressure to the plant tissues.

Carbon is stored in the following ways.
(i) As organic molecules in the living and dead organisms found in the biosphere.
(ii) As carbon dioxide in the atmosphere.
(iii) As organic matter in soils.
(iv) As fossil fuels and sedimentary rock deposits such as lime stone, dolomite and chalk.
(v) In the oceans as dissolved atmosphere carbon dioxide and as carbonate shells in marine organism.

Soil pollution mainly results from the following sources.
(i) Industrial wastes: Wastes discharged from pulp and paper mills, chemical industries, oil refiners, coal and mining industries, etc., are responsible for soil pollution.
(ii) Urban wastes: Solid wastes and refuse in urban areas contribute to soil pollution.
(iii) Radioactive pollutants: Radioactive substances resulting from explosions of nuclear devices, atmospheric fall out from nuclear dust penetrate the soil and pollute it.
(iv) Fertilizers: Excessive application of fertilizers to the soil to increase food and vegetable production causes soil pollution.
(v) Pesticides: Different kinds of pesticides used to control pests cause soil pollution.
(vi) Farm wastes: Wastes from cows, cattle, pigs and poultries are one of the major sources of sil pollution.
(vii) Chemical and metallic pollutants: Synthetic chemicals are a sources of trace metals which are added to the soil either deliberately or as an impurity.
(viii) Biological agents: Soil gets large quantities of human, animal, bird excreta which constitute the major sources of soil pollution by biological agents.

Effects of soil pollution:
(i) Chemicals, pesticides, metals, industrial wastes, animals refuse and other pollutants are extremely toxic to living begins and plant producers and cause severe chronic diseases posing a serious threat to human health.
(ii) Solid wastes result in offensive odour and cause clogging of groundwater filters.
(iii) Polluted soil damages crops and agricultural production due to decreased soil fertility.
(iv) When food containing radioactive substance is consumed by human beings they caused a number of undesirable diseases of the digestive track, thyroid gland etc.
(v) Pesticides not only pose a potential hazard to man, animal, fish and livestock but they severely affect the desired yields of crops, fruits and vegetables, which become unfit for eating.

Following measures may be taken to control soil pollution:
(i) Proper dumping of unwanted materials.
(ii) Organic wastes contained in animal dung can be used for preparation of compost, manure and biogas rather than throwing them as waste and polluted the soil.
(iii) Natural soil microorganism should be used to increase the soil fertility rather than the use of pesticides and insecticides.
(iv) To minimise soil pollution, waste such as paper, plastics, glass, metals, chemicals and industrial wastes should be recycled and reduced instead of throwing in soil.
(v) Use of chemical insecticides, etc. should be banned.

The water cycle is the journey water takes as it circulates from the land to the sky and back again involves the following steps:
(i) The Sun’s heat provides the energy for evaporation of water from the earth surface (oceans, lakes, rivers etc.)
(ii) Plants also water into the air by the process of transpiration.
(iii) Wind carries the moisture laden air. The water vapour eventually condenses forming tiny droplets in clouds. When clouds meet cool air over the land, precipitation (rain, hail or snow) is triggered and water returns to the land in the form of rainfall.
(iv) All water that falls on the land does not immediately flow back into the sea. Some water seeps into the ground. Some of the underground water is trapped between rocks or clay layers. This is called ground water. Some of this ground water finds its way to the surface through springs. We also bring the ground water to the surface for our use through wells or tube wells. Water is also used by terrestrial animals and plants for various life processes. Most of the water flows down the hills as run offs eventually returning to the sea as slightly salty water.

The various steps of nitrogen cycle are as follows:
(i) Nitrogen fixation: It is the conversion of atmospheric nitrogen into water soluble compounds like nitrates and nitrites either by the free living bacteria or Rhizobium that are found in the root nodules of legumes. Atmospheric nitrogen also gets converts into nitrates and nitrites naturally by lightning.
(ii) Ammonification: Death and decay of plant bodies release ammonia into the atmosphere. Animals also give out ammonia along with urea and uric acid as excretory products. These nitrogenous compounds are converted to ammonia by putrefying bacteria and the process if known as ammonification.
(iii) Nitrification: Ammonia is then converted first into nitrites and then into nitrites by the nitrifying bacteria, the process being called as nitrification. Plants generally take up nitrite and nitrates and convert them into amino acid.
(iv) Denitrification: When the animal or the plant dies, denitrifying bacteria in the soil converts the various compounds of nitrogen back into nitrates and nitrites. The nitrates and nitrites are convert into elemental nitrogen by Pseudomonas. This process is called denitrification.

Forests need to be replenished because of following reasons:
(i) Rain fall: During transpiration, tree give out enormous amount of water vapour. This water helps in formation of rain clouds, so if trees are cut and not replenished the rainfall in the area will reduce.
(ii) Natural rate of tree growth: Forests cannot be regrown in a few days or months as trees take many years to grow fully. Thus it becomes necessary to replenish the forests periodically.
(iii) Soil erosion: If a large number of trees are cut the soil becomes naked. The top soil which is rich in organic matter will be washed away by water or carried away by wind. Trees helps in binding the soil.
(iv) Carbo dioxide-oxygen balance: Forests have a very large number of trees which gives out O₂ and take in CO₂ in the day by photosynthesis. In this way they help in maintaining the carbon dioxide-oxygen balance in the atmosphere.
(v) Timber and fuel: Forests are the best suppliers of timber for furniture and fuel. So for their constant supply forests needs to be replenished.

Effects of soil pollution:
(i) Chemicals, pesticides, metals, industrial wastes, animals refuse and other pollutants are extremely toxic to living begins and plant producers and cause severe chronic diseases posing a serious threat to human health.
(ii) Solid wastes result in offensive odour and cause clogging of groundwater filters.
(iii) Polluted soil damages crops and agricultural production due to decreased soil fertility.
(iv) When food containing radioactive substance is consumed by human beings they caused a number of undesirable diseases of the digestive track, thyroid gland etc.
(v) Pesticides not only pose a potential hazard to man, animal, fish and livestock but they severely affect the desired yields of crops, fruits and vegetables, which become unfit for eating.

Following measures may be taken to control soil pollution:
(i) Proper dumping of unwanted materials.
(ii) Organic wastes contained in animal dung can be used for preparation of compost, manure and biogas rather than throwing them as waste and polluted the soil.
(iii) Natural soil microorganism should be used to increase the soil fertility rather than the use of pesticides and insecticides.
(iv) To minimise soil pollution, waste such as paper, plastics, glass, metals, chemicals and industrial wastes should be recycled and reduced instead of throwing in soil.
(v) Use of chemical insecticides, etc. should be banned.

The water cycle is the journey water takes as it circulates from the land to the sky and back again involves the following steps:
(i) The Sun’s heat provides the energy for evaporation of water from the earth surface (oceans, lakes, rivers etc.)
(ii) Plants also water into the air by the process of transpiration.
(iii) Wind carries the moisture laden air. The water vapour eventually condenses forming tiny droplets in clouds. When clouds meet cool air over the land, precipitation (rain, hail or snow) is triggered and water returns to the land in the form of rainfall.
(iv) All water that falls on the land does not immediately flow back into the sea. Some water seeps into the ground. Some of the underground water is trapped between rocks or clay layers. This is called ground water. Some of this ground water finds its way to the surface through springs. We also bring the ground water to the surface for our use through wells or tube wells. Water is also used by terrestrial animals and plants for various life processes. Most of the water flows down the hills as run offs eventually returning to the sea as slightly salty water.

The various steps of nitrogen cycle are as follows:
(i) Nitrogen fixation: It is the conversion of atmospheric nitrogen into water soluble compounds like nitrates and nitrites either by the free living bacteria or Rhizobium that are found in the root nodules of legumes. Atmospheric nitrogen also gets converts into nitrates and nitrites naturally by lightning.
(ii) Ammonification: Death and decay of plant bodies release ammonia into the atmosphere. Animals also give out ammonia along with urea and uric acid as excretory products. These nitrogenous compounds are converted to ammonia by putrefying bacteria and the process if known as ammonification.
(iii) Nitrification: Ammonia is then converted first into nitrites and then into nitrites by the nitrifying bacteria, the process being called as nitrification. Plants generally take up nitrite and nitrates and convert them into amino acid.
(iv) Denitrification: When the animal or the plant dies, denitrifying bacteria in the soil converts the various compounds of nitrogen back into nitrates and nitrites. The nitrates and nitrites are convert into elemental nitrogen by Pseudomonas. This process is called denitrification.

Forests need to be replenished because of following reasons:
(i) Rain fall: During transpiration, tree give out enormous amount of water vapour. This water helps in formation of rain clouds, so if trees are cut and not replenished the rainfall in the area will reduce.
(ii) Natural rate of tree growth: Forests cannot be regrown in a few days or months as trees take many years to grow fully. Thus it becomes necessary to replenish the forests periodically.
(iii) Soil erosion: If a large number of trees are cut the soil becomes naked. The top soil which is rich in organic matter will be washed away by water or carried away by wind. Trees helps in binding the soil.
(iv) Carbo dioxide-oxygen balance: Forests have a very large number of trees which gives out O2 and take in CO2 in the day by photosynthesis. In this way they help in maintaining the carbon dioxide-oxygen balance in the atmosphere.
(v) Timber and fuel: Forests are the best suppliers of timber for furniture and fuel. So for their constant supply forests needs to be replenished.