How do fossil fuels cause air pollution?
Soln:
When we burn fossil fuels carbon dioxide, nitrous oxide and other chemicals are released which increase the green-house effect and contribute to global warming. Nitrous oxide forms smog and results in acid rain.
32. How can we prevent the loss of topsoil?
Soln:
Loss of topsoil can be stopped by 1) Afforestation 2) Crop rotation 3) Counter farming 4) proper irrigation methods.
33. How is the life of organisms living in water affected when water gets polluted?
Soln:
Addition of pollutants like fertilizers and chemicals to the water bodies will cause diseases in aquatic organisms. Pollutants increase the biological oxygen demand of organisms living in water, since, the dissolved oxygen in the water reduces drastically.
34. During summer, if you go near the lake, you feel relief from the heat, why?
Soln:
Lake water gets evaporated and vapours formed due to evaporation create a cooling effect near lake. Hence we feel relieved from heat.
35. In coastal area, wind current moves from the sea towards the land during the day; but during the night it moves from land to the sea. Discuss the reason.
Soln:
During day time land heats more than the sea. This creates low pressure on the land and wind always moves from the region of low pressure to high pressure. Similarly in the night land cools faster and sea remains hot making wind to move from sea to land.
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 the formation of soil? Write the mode of their action for making soil.
Soln:
Answers are (a) lichen (b) mosses
Explanation:
Lichens grow on rocks and release certain enzymes which favour the growth of mosses. Mosses form clumps of soil from the rock which results in the formation of topsoil.
37. Soil formation is done by both abiotic and biotic factors. List the names of these factors by classifying them as abiotic and biotic?
Soln:
Abiotic factors;
Sun, water and wind
Biotic Factors:
Lichens, mosses and trees.
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.
Soln:
C, N, S, P, H and O enters the living community through plants. Carbon comes through photosynthesis and nitrogen is obtained through nitrogen-fixing bacteria. Sulphur and Phosphorus are absorbed from the soil. Hydrogen and oxygen are obtained by water. These nutrients are obtained by animals from plants.
39. Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere?
These gases are used by human beings for their growth and development. But these are returned to the environment in one or other form. This process of using natural resources and giving them back to nature is called a biogeochemical cycle. Because of the biogeochemical cycle percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same 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?
Soln:
Earth has an atmosphere which prevents overheating of the earth during day time. On the other hand, Moon does not have atmosphere hence it appears to be hotter during day time. Lack of atmosphere in the moon also allows the heat to escape during the night because of this phenomenon temperature varies on the moon surface.
41. Why do people love to fly kites near the seashore?
Soln:
Near the seashore, breeze blows during day time which is ideal for flying kites.
42. Why does Mathura refinery pose problems to the Taj Mahal?
Soln:
Mathura refinery releases oxides of Sulphur which causes acid rain. Acid rain corrodes the marble of Tajmahal hence Mathura refinery pose problems to Tajmahal.
43. Why do not lichens occur in Delhi whereas they commonly grow in Manali or Darjeeling?
Soln:
Lichens are sensitive to Sulphur oxide released by automobiles. Delhi has more number of automobiles which increases pollution. Pollution avoids lichens in Delhi.
44. Why does water need conservation even though large oceans surround the landmasses?
Soln:
Seawater is not suitable for the livelihood of humans and plants. Freshwater resources are limited hence they need to be conserved.
45. There is mass mortality of fishes in a pond. What may be the reasons ?
Soln:
Reasons for mortality of fishes in a pond are i) Thermal pollution ii) addition of mercuric compounds and other toxic chemicals iii) Blockage of gills by pollutants.
46. Lichens are called pioneer colonisers of bare rock. How can they help in the formation of soil?
Soln:
Lichens release enzymes that break the rock into smaller pieces and helps in the formation of soil.
47. “Soil is formed by water.” If you agree to this statement then give reasons
Soln:
Water causes soil formation by following steps.
- Water causes wear off of rock for a long period of time.
- Water makes rubbing between the rocks to smaller particles which are deposited as soil.
- On freezing, water expands to cause breaks in the rock.
48. Fertile soil has lots of humus. Why?
Soln:
Fertile soil has a number of microorganisms that decompose dead and organic matter to convert to humus. Humus provides nutrients, absorb water and makes soil porous.
49. Why step farming is common in hills?
Soln:
In hills, there are steep slopes which risk washout of topsoil by wind and rain. In order to conserve topsoil, step farming is done in hills.
50. Why are root nodules useful for the plants?
Soln:
Root nodules are the home for nitrogen-fixing bacteria called a Rhizobium. Rhizobium fixes atmospheric nitrogen thereby increasing soil fertility.
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