CBSE - Natural Resources

Earth's atmosphere is a mixture of nitrogen (79%), oxygen (20%), and a small fraction of carbon dioxide, water vapours and other gases. This makes the existence of life possible on Earth. However, the atmospheres on Venus and Mars mainly consist of carbon dioxide. The amount of carbon dioxide on these planets can range from 95% to 97%.

The atmosphere acts as a blanket by performing the following functions:
→ It keeps the average temperature of the Earth fairly constant during day time and even during the course of whole year.
→ It prevents a sudden increase in the temperature during day time.
→ It slows down the escape of heat from the surface of the Earth into outer space during night time.

An uneven heating of the Earth's surface causes winds. On being heated, air becomes lighter and rises up. As a result, a region of low pressure is created. Then, air from a high pressure region moves to a low pressure region, causing wind.

During day time, on being heated, a large amount of water evaporates from various water bodies and goes into the air. A part of this water vapour also reaches the atmosphere through biological activities such as transpiration and respiration. This causes the air in the atmosphere to heat up. When this heated air rises, it expands and cools, which results in the condensation of water vapour forming water droplets. The presence of dust and other suspended particles in air also facilitates the process of condensation. The formation of water droplets leads to the formation of clouds.

Three human activities leading to air pollution are:
→ Smoke from industries e.t.c.
→ Burning of fossil fuels like coal and petroleum→ Deforestation.

The organisms need water:
→ For different cellular process.
→ For transportation of substance from one place to another inside the body.

Rivers.

The discharge of waste water from homes, industries, hospitals, etc. into the river pollutes this fresh water source.

Soil is formed by breaking down of rocks at or near the surface of the Earth through various physical, chemical, and biological processes by various factors such as the sun, water, wind, and living organisms.→ Sun: During day time, the rocks are heated up by solar rays. This causes the rocks to expand. During night time, these rocks cool down and contracts, thus the cracks devlop in the rock and they break down.
→ Water: It helps in breaking of rocks in two ways:
(i) It goes into the cracks and crevices formed in the rocks. When this water freezes, its volume increases. As a result, the size of the cracks also increases. This helps in the weathering of rocks.
(ii) Water moving in fast speed carries big and small particles of rock downstream. These rocks rub against each other, resulting in breaking down of rocks.These smaller particles are carried away by running water and deposited down its path.→ Wind: Strong winds carry away rocks, which causes rubbing of rocks. This results in the breaking down of rocks into smaller and smaller particles.
→ Living Organism: Some living organisms like lichens help in the formation of soil. Lichens grow on rock surfaces and converts them into powdery form and make soil layer. In the same way, the plants like moss also help in the making of fine soil particles.

The blowing away or washing away of land surface bywind or water is known as soil erosion.

The methods of preventing or reducing soil erosion are:
→ Plantation of tress and plants→ Prevention of deforestation
→ Prevent excessive grazing

Water is found in three different states during the water cycle:
→ Solid (Snow, Ice)
→ Liquid Water (ground water, river water, etc.)
→ Gaseous State (Water vapours)

Two biologically important compounds that contain both oxygen and nitrogen are:
(i) Amino acids
(ii) Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA)

Three Human activities are:

→ Burning of fuels in various processes like heating, cooking, transportation, and industry.
→ Human induced forest fires
→ The process of deforestation includes the cutting down of trees. This decreases the uptake of carbon dioxide for photosynthesis. Eventually, the content of carbon dioxide increases

Some gases like carbon dioxide, methane, nitrous oxide prevent the escape of heat from the Earth's surface by trapping it. This increases the average temperature of the Earth. This is called the green house effect. 

The two forms of oxygen found in the atmosphere are:
→ Diatomic molecular form with chemical formula O₂.
→ Triatomic molecular form with chemical formula O₃known as ozone.

The atmosphere is essential for life because it maintains an appropriate climate for the sustenance of life by carrying out the following activities:
→ Atmosphere keeps the average temperatureof the Earth fairly constant during day time.
→ It prevents a sudden increase in temperature during day time.
→ It also slows down the escape of heat from the surface of the Earth into outer space during night time.

Water is essential for life because of the following reasons:
→ Most biological reactions occur when substances are dissolved in water. Thus, all cellular processes need water as a medium to take place.
→ Transportation of biological substances needs water as a medium.

Almost all living organisms are dependent on soil. Some depend directly, while some depend indirectly.
Plants need soil for getting support as well as nutrients to prepare their food.
On the other hand, organisms depend on plants for food and other substances that are essential for life. Herbivores depend directly upon plants, and carnivores depend upon animals, which in turn depend upon plants for food. This makes them depend on soil indirectly.
Organisms that live in water are not totally independent of soil as a resource. These organisms depend on aquatic plants for food and other substances. These aquatic plants in turn require minerals for their sustenance. These minerals are carried to water bodies from soil by rivers, rain water, etc. Without the supply of minerals from the soil to the water bodies, it is impossible to imagine aquatic life.

The meteorological department of the government collects data on the elements of weather such as maximum and minimum temperatures, maximum and minimum humidity, rainfall, wind speed, etc. They are able to study these elements using various instruments. The maximum and minimum temperature of a day is measured by a thermometer known as the maximum-minimum thermometer. Rain fall is measured by an instrument known as the rain gauge. Wind speed is measured by anemometers. There are various instruments used to measure humidity.

Forests influence the quality of our air, soil, and water resources in various ways. Some of them are:
→ Forests balance the percentages of carbon dioxide and oxygen in the atmosphere. The increasing amount of carbon dioxide caused by human activities is balanced by a larger intake of carbon dioxide by plants during the process of photosynthesis. Simultaneously, a large amount of oxygen is released.
→ Forests prevent soil erosion. Roots of plants bind the soil tightly in a way that the surface of the soil cannot be eroded away by wind, water, etc.
→ Forests help in the replenishment of water resources. During the process of transpiration, a huge amount of water vapour goes into the air and condenses to form clouds. These clouds cause rainfall that recharge water bodies

Yes. Isolating human activities to specific areas would help in reducing levels of pollution. For example, setting up of industries in isolated regions will control pollution to some extent. The pollution caused by these industries will not contaminate water resources, agriculture land, fertile land, etc.

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
Ans. (d) re-radiated by land and water
Explanation: The hear from the sun reaches the earth and heats up the land and water. After that, heat from land and water is re-radiated to heat up the atmosphere.

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
Ans. (c) increase during day and decrease during night Explanation: This is because of the atmosphere that the earth is saved from becoming too hot during day time. This happens because a significant amount of heat is prevented from reaching the earth’s surface by the atmosphere. Moreover, the atmosphere prevents the heat from escaping during night. Thus, an ambient temperature is maintained on the earth throughout the 24-hour period.

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.
Ans. (b) It will become poisonous and kill living forms
Explanation: Living being need oxygen for respiration. Lack of oxygen will kill all living beings.

4. One of the following factors does not lead to soil formation in nature
(a) the sun
(b) water
(c) wind
(d) polythene bags
Ans. (d) polythene bags
Explanation: Polythene bags end up contaminating the soil and turning the soil barren

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
Ans. (c) ozone and oxygen
Explanation: Ozone is an allotrope of oxygen.

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
Ans. (b) elemental form of oxygen

7. Rainfall patterns depend on
(a) the underground water table
(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
Ans. (b) the number of water bodies in an area
Explanation: Water bodies provide water for evaporation. Water vapour, formed after evaporation condense to cause rainfall. Lack of water bodies in an area would reduce humidity in air and thus will adversely affect the rainfall.

8. Among the given options, which one is not correct for the use of large amount of fertilisers and pesticides?
(a) They are eco-friendly
(b) They turn the fields barren after some time
(c) They adversally affect the useful component from the soil
(d) They destroy the soil fertility
Ans. (a) They are eco-friendly
Explanation: Adverse effects mentioned in other options make the fertilizers and pesticides non-friendly to the ecosystem.

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
Ans. (a) a biological process of nitrogen fixing bacteria present in soil  
Explanation: Cereal crops themselves cannot fix nitrogen. They harbour nitrogen fixing bacteria in their root nodules. So, option (d) is incorrect. Factories cannot utilize nitrogen in the air to produce nitrogenous compounds; they use petrochemicals for this purpose. Hence, option (c) is incorrect. Option (b) talks about carbon fixation and hence is
incorrect.

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
Ans. (d) photosynthesis
Explanation: Photosynthesis is involved in carbon cycle and not in water cycle.

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
Ans. (c) A change in pressure of the water bodies
Explanation: A change in pressure of the water bodies can happen because of physical causes and it does not result in contamination of water.

12. Which of the following is not a greenhouse gas?
(a) Methane
(b) Carbon dioxide
(c) Carbon monoxide
(d) Ammonia
Ans. (d) Ammonia

13. Which step is not involved in the carbon-cycle?
(a) Photosynthesis
(b) Transpiration
(c) Respiration
(d) Burning of fossil fuels
Ans. (b) Transpiration
Explanation: Transpiration is involved in water cycle and not in carbon cycle.

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
Ans. (b) thinning of the ozone layer
Explanation: Mention of the term ‘hole’ rules out options ‘a’ and ‘c’. Thickening is similar to strengthening and hence options ‘d’ is ruled out.

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.
Ans. (c) excessive use of man-made compounds containing both fluorine and chlorine Explanation: Compounds which contains both fluorine and chlorine are called chlorofluorocarbons (CFCs). Chlorine and fluorine react with ozone to convert it into
oxygen and thus they result in depletion of ozone layer.

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
Ans. (d) All of the above
Explanation: All the problems mentioned here have originated after the industrial revolution.

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 CO2 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.
Ans. (b) It comes out with the CO2 during exhalation
Explanation: Nitrogen is the most abundant gas in the air and hence it goes inside our body during inhalation. But nitrogen is not utilized by the body and comes out during exhalation.

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.
Ans. (d) Humus, living organisms and soil particles.

19. Choose the correct sequences
(a) CO2 in atmosphere →decomposers → organic carbon in animals → organic carbon in plants
(b) CO2 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 → CO2 in atmosphere → organic carbon in plants 
Ans. (b) CO2 in atmosphere →organic carbon in plants → organic carbon in animals → inorganic carbon in soil
Explanation: Carbon dioxide from the atmosphere is utilized by green plants during photosynthesis. Thus, organic compounds are made in plants. When an animal takes food, organic compounds from plants go to the body or animal (directly or indirectly). Once an animal or a plant dies; decomposition of the dead remains result in formation of inorganic carbon in soil.

20. Major source of mineral in soil is the
(a) parent rock from which soil is formed
(b) plants
(c) animals
(d) bacteria
Ans. (a) parent rock from which soil is formed

21. Total earth’s surface covered by water is
(a) 75%
(b) 60%
(c) 85%
(d) 50%
Ans. (a) 75%

 22. Biotic component of biosphere is not constituted by
(a) producers
(b) consumers
(c) decomposer
(d) air
Ans. (d) air
Explanation: Biotic components comprise of living beings. Air is a non-living thing and hence cannot be a part of biotic components.

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
Ans. (d) abundance of desert plants
Explanation: Desert does not have suitable condition for abundant growth of plants. A part from carbon dioxide; a plant also needs oxygen, water and minerals form proper growth and development. But water is a scarce resource in deserts.

24. Oxygen is returned to the atmosphere mainly by
(a) burning of fossil fuel
(b) respiration
(c) photosynthesis 
(d) fungi
Ans. (c) photosynthesis
Explanation: Agents in other options return carbon dioxide to the atmosphere.

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
Ans. (b) unburnt carbon particles or hydrocarbons suspended in air
Explanation: Unburnt carbon particles and hydrocarbons suspended in air create smog. Smog result in low visibility.

26. Growth of Lichens on barren rocks is followed by the growth of
(a) moss
(b) ferns
(c) gymnosperms
(d) algae
Ans. (a) moss
Explanation: Lichens secrete certain enzymes which break the rocks and make it suitable for growth of masses. Mosses further pave the way for formation of soil and for growth of higher plants.

27. 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.
Ans. (a) breeding of animals
Explanation: Temperature change my hamper the growth of aquatic plants. Availability of nutrients in water does not depend on temperature but an availability of mineral in the substratum. Temperature change in water way affect digestion in aquatic animals but it will have no effect on digestion in land animals. Thus, other options can be ruled out.

28. Soil erosion can be prevented by
(a) raising forests
(b) deforestation
(c) excessive use of fertilizer
(d) overgrazing by animals
Ans. (a) raising forests
Explanation: Agents in other options will increase soil erosion.

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
Ans. (b) Rain water causes loss of surface soil
Explanation: plants hold top soul with their roots and thus prevent top soil from getting washed away by rain.

30. Oxygen is harmful for
(a) ferns
(b) nitrogen fixing bacteria
(c) chara
(d) mango tree
Ans. (b) nitrogen fixing bacteria

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, rivers carry many nutrients from land to the sea.

Loss of top soil can be prevented by
(i) increasing the vegetational cover
(ii) checking the falling of trees
(iii) by preventing excessive grazing by animals

Addition of undesirable chemicals like pesticides, fertilizers, industrial waste and domestic wastes not only kill the organisms, they also cause diseases to the aquatic organisms. Besides, the requirement of oxygen by aquatic organisms is also increased. There is a reduction in the dissolved oxygen in water which adversely affects the aquatic organisms

The water from surface of a lake keeps on evaporating. This create a cooling effects in the surrounding. Due to this, when we go near a lake we feel relief from heat.

Air above the land gets heated quickly during day and starts rising. This creates a region of low pressure as a result air over sea rushes into this area of low pressure. This movement of air from one region to the 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

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.

Ans. Lichens and Mosses (a) and (b). Lichens and mosses release substances which break down the stones resulting in the formation of soil.

Abiotic factors making soil— sun, water, wind
Biotic factors— lichens, mosses and trees

C, N, S, P, H and O are the basic components of various biomolecules. Living being are made up of numerous biomolecules. Most of these components come to the living world via plants. Carbon comes through photosynthesis. Nitrogen is fixed in soil by nitrogenfixing bacteria so that plants can absorb nitrogenous compounds. Sulphur and phosphorus are available as minerals in soil and are absorbed by plant; along with water. Hydrogen and oxygen enter in the plants when they absorb water. Animal also obtain hydrogen and oxygen when they drink water. Oxygen is also taken up by living beings during inhalation. Finally, these elements are taken up by animals when they take food either directly or indirectly from plants.

These elements are continuously utilized by living beings. But these elements undergo a cyclic process which ensures that they are returned to the atmosphere through various processes. This cyclic process of utilizing various elements and returning them to the atmosphere is called biogeochemical cycle. Due to this, the percentage of oxygen, nitrogen and carbon dioxide remains almost the same in the atmosphere.

The moon does not have atmosphere. Due to this, there is no mechanism to prevent overheating of the surface during daytime; unlike what happens on the earth. Moreover, lack of atmosphere allows all the heat to escape during night. Due to this there are wide variations in temperature on the moon

In coastal areas, sea breeze blows during daytime. The sea breeze has ideal speed for kite flying. Hence, people love to fly kites near the seashore.

Mathura refinery releases toxic gases (like oxides of sulphur) which causes acid rain and hence corrosion of the marbles of Taj Mahal.

It is a bio-indicator and sensitive to SO2 pollution from automobiles. Delhi has maximum number of automobiles, hence has a highly polluted environment.

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

 (i) Thermal pollution
(ii) Addition of poisonous (mercury) compounds in water
(iii) Due to blockage of gills with any pollutant. 

Lichens release chemical substances to break the rocks into smaller particles and hence make soil.

Water helps in formation of soil in following ways
(i) Water causes ‘wear off’ of rocks over a long period of time.
(ii) It also causes the rocks to rub against other rocks creating small particles which are
taken away downstream and deposited as soil.
(iii) Water expands on freezing in crevices of rocks and cracks rocks into smaller pieces. 

Fertile soils are rich in organisms that decomposes dead organic matter forming humus. Humus gives minerals, absorbs water and makes soil porous.

Farms in hills have steep slopes. There is always a risk of top soil being washed away by rainwater because of steep slope. Steps are made to prevent soil erosion. Hence, step farming is common in hills.

In root nodules nitrogen fixing Rhizobium bacteria are present which increases the soil fertility.

The fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur. When fossil fuels are burnt, it produces oxides of nitrogen and sulphur. These gases cause inhalation problems and in presence of rain forms acid rain. Burning of fossil fuels also increase the amount of suspended particles in air that reduce the visibility.

Water pollution can be caused by addition of
(i) undesirable substances like fertilizers and pesticides or any poisonous substances.
(ii) sewage directly entering a water body.
(iii) hot water from the power plant that increases the temperature and reduces the dissolved oxygen in water thus killing the aquatic organisms.
(iv) industrial effluents or radioactive substances in water body. We can take following measures to check water pollution
(i) The sewer lines should not be directly connected to the water body.
(ii) We should not throw our garbages or domestic waste in the water body.
(iii) Prevent dumping of toxic compounds in the water bodies.
(iv) Washing of clothes should be avoided near water bodies as it adds lot of detergents to it.
(v) Plant trees near the banks of the river to check soil erosion otherwise erosion leads to siltation of water body. 

Infra-red 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 wavelength than that emitted by the interior of the car which are of longer wavelength to which the glass is opaque

Dust remains present in air as suspended particles can cause allergy and other respiratory diseases. It also affects plant growth, by covering stomata on leaf surface. It acts as the carrier of toxic compounds like heavy metals.

The rocks are heated by the sun; they contract during night but not at same rate — resulting in cracks in rocks and ultimately to smaller particles

Increasing concentration (more than normal) of CO₂ is harmful and considered as a pollutant. Higher concentrations of CO₂ is one of the causes of greenhouse effect/global warming.