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) re-radiated by land and water
[ The sun's radiation is absorbed by land and water, which then re-radiate long-wave heat, mainly warming the atmosphere from below. ]
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) increase during day and decrease during night
[ Without the atmosphere, heat would not be trapped. Earth would become very hot in the day and very cold at night. ]
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) It will become poisonous and kill living forms
[ Ozone is toxic in large amounts. If all oxygen becomes ozone, breathing will be impossible and most living organisms will die. ]
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) polythene bags
[ Soil forms due to natural factors like the sun, water, and wind breaking rocks. Polythene bags are man-made and do not help in soil formation.]
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) ozone and oxygen
[ In the atmosphere, oxygen exists as oxygen (O₂) and ozone (O₃). Ozone forms a protective layer that absorbs harmful ultraviolet rays from the Sun. ]
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) elemental form of oxygen
[ Nitrogen-fixing bacteria work in anaerobic conditions. The presence of oxygen inhibits the nitrogenase enzyme, so nitrogen fixation does not occur.]
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
Answer: (d) the prevailing season in an area .
[ Rainfall mainly depends on seasonal winds and climate conditions, so the prevailing season determines rainfall patterns.]
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
Answer: (a) They are eco-friendly
[ Large amounts of fertilisers and pesticides harm soil fertility, kill useful microbes and can make fields barren. They are not eco-friendly. ]
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) a biological process of nitrogen fixing bacteria present in soil
[ Nitrogen-fixing bacteria in soil convert atmospheric nitrogen into nitrates and nitrites that plants can absorb and use. ]
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) photosynthesis
[ The water cycle includes evaporation, transpiration, and precipitation. Photosynthesis is a plant process and not a step of the 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
Answer : (c) A change in pressure of the water bodies
[ Water pollution means adding harmful substances or changing temperature/composition of water. Change in pressure does not define water pollution. ]
12. Which of the following is not a green house gas?
(a) Methane (b) Carbon dioxide (c) Carbon monoxide (d) Ammonia
Answer: (c) Carbon monoxide
[ Methane (CH₄), carbon dioxide (CO₂), and ammonia (NH₃) are recognized greenhouse gases. Carbon monoxide (CO) is not a significant greenhouse gas. ]
13. Which step is not involved in the carbon-cycle?
(a) Photosynthesis (b) Transpiration (c) Respiration (d) Burning of fossil fuels
Answer: (b) Transpiration
[ The carbon cycle includes photosynthesis, respiration, and burning of fossil fuels. Transpiration is related to the water cycle, not the 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
Answer: (b) thinning of the ozone layer
[ “Ozone hole” means the thinning of the ozone layer in the atmosphere, which allows more harmful ultraviolet rays to reach Earth. ]
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) excessive use of man-made compounds containing both fluorine and chlorine
[ Compounds like CFCs (chlorofluorocarbons) release chlorine and fluorine that destroy ozone molecules, causing depletion of the 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
Answer: (d) All of the above
[ Ozone layer depletion, greenhouse effect, and global warming are all recent environmental problems caused mainly by human activities. ]
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.
Answer: (b) It comes out with the CO₂ during exhalation
[ Nitrogen is an inert gas and not used by the body, so it enters with air and leaves unchanged 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.
Answer: (d) Humus, living organisms and soil particles
[ Topsoil contains humus (organic matter), soil particles, and many living organisms like bacteria, fungi, and earthworms. ]
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
Answer: (b) CO₂ in atmosphere → organic carbon in plants → organic carbon in animals → inorganic carbon in soil
[ Plants fix CO₂ by photosynthesis → animals eat plants → decomposition returns carbon to soil as inorganic carbon. ]
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) parent rock from which soil is formed
[ Minerals in soil mainly come from the weathering of parent rocks from which the soil is formed. ]
21. Total earth’s surface covered by water is
(a) 75% (b) 60% (c) 85% (d) 50%
Answer: (a) 75%
[ About three-fourths (around 75%) of the Earth’s surface is covered by water, mainly in oceans, seas, rivers, and lakes. ]
22. Biotic component of biosphere is not constituted by
(a) producers (b) consumers (c) decomposer (d) air
Answer: (d) air
[ Biotic components are living organisms: producers (plants), consumers (animals) and decomposers (bacteria/fungi). Air is an abiotic (non-living) component of the biosphere. ]
23. An increase in carbondioxide 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) abundance of desert plants
[ More CO₂ can increase heat retention and global warming, and may increase photosynthesis. But it does not directly cause abundance of desert plants. ]
24. Oxygen is returned to the atmosphere mainly by
(a) burning of fossil fuel (b) respiration (c) photosynthesis (d) fungi
Answer: (c) photosynthesis
[ During photosynthesis, green plants release oxygen into the atmosphere, which maintains the oxygen balance in air. ]
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) unburnt carbon particles or hydrocarbons suspended in air.
[ During cold weather, smoke, unburnt carbon particles, and hydrocarbons remain suspended in air, forming smog or fog, which reduces visibility. ]
26. Growth of Lichens on barren rocks is followed by the growth of
(a) moss (b) ferns (c) gymnosperms (d) algae
Answer: (a) moss
[ Lichens break down rocks and form a thin soil layer. After this, moss grows on the surface during ecological succession. ]
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.
Answer: (a) breeding of animals
[ Large temperature changes in water disturb the breeding and reproduction cycles of aquatic animals, affecting their survival. ]
28. Soil erosion can be prevented by
(a) raising forests (b) deforestation (c) excessive use of fertilizer (d) overgrazing by animals
Answer: (a) raising forests
[ Planting trees (forests) holds the soil with roots and reduces the effect of wind and water, thus preventing 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
Answer: (b) Rain water causes loss of surface soil
[ Without vegetational cover, rainwater washes away the top fertile layer of soil, causing soil erosion. ]
30. Oxygen is harmful for
(a) ferns (b) nitrogen fixing bacteria (c) chara (d) mango tree
Answer: (b) nitrogen fixing bacteria
[ Oxygen inhibits the nitrogenase enzyme in nitrogen-fixing bacteria, so high oxygen levels are harmful for their nitrogen fixation process. ]
31. Rivers from land, add minerals to sea water. Discuss how?
Answer: Rivers flow over rocks and soil on land. During this flow, they dissolve small amounts of minerals and salts from rocks. These dissolved minerals are carried along with the river water and finally enter the seas and oceans, increasing the mineral content of sea water.
32. How can we prevent the loss of top soil?
Answer: Loss of top soil can be prevented by maintaining good vegetative cover on land. Plants and trees hold the soil with their roots and reduce soil erosion. Avoiding large-scale deforestation and growing more plants help protect the top layer of soil and allow water to slowly percolate into deeper layers.
33. How is the life of organisms living in water affected when water gets polluted?
Answer: When water gets polluted by fertilizers , pesticides, sewage and industrial waste, it changes the conditions of the water. Hot water released from industries or cold water from dams can also affect temperature. These changes may help some organisms grow but harm others, disturbing the natural balance of life in water bodies.
34. During summer, if you go near the lake, you feel relief from the heat, why?
Answer: During summer, the water in a lake absorbs heat from the surroundings and evaporates slowly. Evaporation uses heat energy from the nearby air, which makes the surrounding area cooler. Therefore, when we go near a lake, we feel cool and get relief from the heat.
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: During the day, land heats up faster than the sea. The warm air over land rises, so cooler air from the sea moves towards the land (sea breeze). At night, land cools faster than the sea. Warm air rises over the sea, so cooler air from land moves towards the sea (land breeze).
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: Lichen and mosses can grow on stones and help in soil formation.
Lichens grow on rocks and release substances that slowly break the rock into powder, forming a thin layer of soil. After this, mosses grow on the surface and further break the rock, helping more soil to form.
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: Soil formation is influenced by both abiotic and biotic factors.
Abiotic factors: Temperature changes, water, wind, and sunlight which break rocks into small particles.
Biotic factors: Living organisms such as lichens, mosses, plants, animals, and microorganisms that help break rocks and add organic matter to form soil.
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: Elements like C, N, S, P, H and O enter living organisms through air, water and soil. Plants take carbon dioxide from air, water from soil, and minerals like nitrogen, sulphur and phosphorus from the soil. Animals get these elements by eating plants or other animals. In this way, these elements enter living forms through food chains and natural cycles.
39. Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere?
Answer: The percentage of gases like oxygen, nitrogen, and carbon dioxide remains almost the same because they are continuously recycled through natural cycles. Processes like photosynthesis, respiration, decomposition, and the nitrogen cycle keep a balance between the use and release of these gases in the atmosphere.
40. Why does moon have very cold and very hot temperature variations eg, from -190°C to 110°C even though it is at the same distance from the sun as the earth is?
Answer: The Moon has extreme temperature variations because it lacks an atmosphere. On Earth, the atmosphere traps heat during the night and moderates temperature during the day, keeping it steady. Without this protective layer, the Moon’s surface heats up quickly to 110°C in sunlight and cools rapidly to –190°C at night.
41. Why do people love to fly kites near the seashore ?
Answer: People love to fly kites near the seashore because the strong and steady sea breeze provides continuous airflow, which helps kites stay high in the air easily.
42. Why does Mathura refinery pose problems to the Taj Mahal?
Answer: Mathura refinery emits sulphur dioxide and other pollutants into the air. These gases combine with moisture to form acid rain, which damages the marble of the Taj Mahal, causing discoloration and erosion of the monument’s surface.
43. Why do not lichens occur in Delhi whereas they commonly grow in Manali or Darjeeling?
Answer: Lichens do not occur in Delhi because the air is highly polluted with smoke, dust, and harmful gases. In contrast, Manali and Darjeeling have clean, fresh air, which allows lichens to grow easily. Lichens are sensitive indicators of air quality.
44. Why does water need conservation even though large oceans surround the land masses?
Answer: Water needs conservation because only a small fraction of Earth's water is fresh and usable. Most water is in oceans and is salty, while rivers, lakes, and groundwater are limited. Overuse, pollution, and climate change reduce this fresh water, so we must save and use it wisely for drinking, farming, and daily life.
45. There is mass mortality of fishes in a pond. What may be the reasons ?
Answer: Mass mortality of fishes in a pond may occur due to:
(i) Water pollution: Chemicals, pesticides, or sewage reduce water quality.
(ii) Lack of oxygen: Overgrowth of algae or excessive decomposition consumes dissolved oxygen.
(iii) Sudden temperature changes: Sharp rise or fall affects fish survival.
(iv) Disease outbreak: Pathogens or parasites can kill many fishes quickly.
46. Lichens are called pioneer colonisers of bare rock. How can they help in formation of soil?
Answer: Lichens are called pioneer colonisers because they are the first to grow on bare rocks. They secrete acids that slowly break rocks into tiny particles. When lichens die, they add organic matter (humus), gradually forming a thin layer of soil that allows mosses and other plants to grow.
47. “Soil is formed by water.” If you agree to this statement then give reasons.
Answer: Yes, soil is formed by water because rain and flowing water break rocks into small particles through weathering. Water also transports minerals and sediments, deposits them, and helps in mixing organic matter, which gradually leads to the formation of fertile soil.
48. Fertile soil has lots of humus. Why?
Answer: Fertile soil has lots of humus because humus is decayed organic matter that provides essential nutrients to plants. It also improves soil structure, water retention, and aeration, making the soil ideal for plant growth.
49. Why step farming is common in hills?
Answer: Step farming is common in hills because it reduces soil erosion and helps retain water on sloped land. Terraces create flat surfaces for growing crops, making farming easier and more productive in hilly regions.
50. Why are root nodules useful for the plants?
Answer: Root nodules are useful because they house nitrogen-fixing bacteria that convert atmospheric nitrogen into usable forms (like nitrates) for the plant. This provides essential nitrogen, which helps in growth and protein synthesis, improving soil fertility naturally without chemical fertilizers.
51. How do fossil fuels cause air pollution?
Answer: Burning fossil fuels like coal and petroleum releases nitrogen and sulphur oxides, which can cause acid rain. It also produces suspended particles like unburnt carbon and hydrocarbons, reducing visibility and forming smog. Breathing this polluted air can lead to allergies, cancer and heart diseases. The increase of these harmful substances in air is called air pollution.
52. What are the causes of water pollution? Discuss how you can contribute in reducing water pollution.
Answer: Water pollution is caused by:
(i) Addition of harmful substances : Chemicals like fertilizers, pesticides, industrial wastes, and disease-causing organisms enter water bodies.
(ii) Removal of useful substances: Dissolved oxygen and essential nutrients decrease, affecting aquatic life.
(iii) Change in temperature: Sudden changes harm aquatic organisms, especially eggs and larvae.
We can help to reduce water pollution by:
(i) Avoiding disposal of chemicals and plastics into rivers, lakes, or drains.
(ii) Using fertilizers and pesticides carefully in farming or gardening to prevent runoff.
(iii) Conserving water so less wastewater enters water bodies.
(iv) Participating in cleaning drives for local ponds, rivers, and lakes.
(v) Spreading awareness about the harmful effects of water pollution.
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: When sunlight enters the car through glass, it is absorbed by the seats and floor and converted into heat. This heat cannot escape easily because the glass traps it, a process similar to the greenhouse effect, causing the temperature inside the car to rise sharply.
54. Justify “Dust is a pollutant” ?
Answer: Dust is a pollutant because it suspends in the air, reduces air quality, and can enter our respiratory system, causing breathing problems and allergies. It also settles on plants, water, and buildings, affecting health, crops, and the environment.
55. Explain the role of the Sun in the formation of soil.
Answer: The Sun plays a key role in soil formation by heating rocks and the Earth’s surface, causing them to expand and contract. This temperature change leads to cracking and breaking of rocks (physical weathering). Combined with water, wind, and organisms, this process gradually forms soil that supports plant life.
56. Carbon dioxide is necessary for plants. Why do we consider it as a pollutant?
Answer: Carbon dioxide is necessary for plants for photosynthesis, but excess CO₂ from industries and vehicles traps heat in the atmosphere, causing global warming and climate change. Its high concentration disturbs the balance of gases, making it a pollutant even though it is naturally essential for life.
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