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