ADDITIONAL QUESTIONS AND ANSWERS :
A. Observe the correlation between the words of the first pair and complete the second pair :
1. Type of soil : size of soil particles :: Quality of soil : ………..
2. The water present on the earth: hydrosphere::Outer crust of the earth : …………
3. .…………: Atmosphere of carbon dioxide:: Earth: Atmosphere of oxygen, nitrogen, carbon dioxide and water vapour
4. Carbon dioxide: Greenhouse effect:: CFC: ……………._
Ans: 1. Humus and microscopic organisms 2. Lithosphere
3. Mars or Venus 4. Depletion of ozone layer.
B. Name the following :
1. The component of the biosphere consisting of living things.
Ans: Biotic component
2. The blanket of air around the earth.
Ans: Atmosphere
3. Two planets where the major component of the atmosphere is carbon dioxide
Ans: Venus and Mars.
4. The process of converting carbon dioxide into glucose by green plants in the presence of sunlight.
Ans: Photosynthesis.
5. The oxygen molecule having three atoms of oxygen.
Ans: Ozone.
6. The poisonous substance used in the paper industry.
Ans: Salts of mercury.
7. The component of the soil that decides soil structure.
Ans. Humus.
8. The type of plants whose roots contain nitrogen fixing bacteria.
Ans: Leguminous plants.
9. The substance, present in the life-forms which perform photosynthesis in the presence of sunlight.
Ans: Chlorophyll.
10. Man-made compounds responsible for depletion of the ozone layer.
Ans: CFCs (Chloro Fluoro Carbons)
11. Life supporting zone where the lithosphere, hydrosphere and atmosphere interact to make life possible.
Ans: Biosphere.
12. Visible indication of air pollution.
Ans: Smog
13. The factors or forces that cause soil erosion.
Ans: Water and wind.
14. The winds that bring rain to India.
Ans: South-west and north-east.
15. The greenhouse gas present in the atmosphere.
Ans: Carbon dioxide
16. The factors on which the biodiversity of a particular region depends.
Ans:
(i) Availability of water
(ii) Proper temperature
(iii) Nature of the soil
17. The property of air which keeps the temperature fairly steady on the earth.
Ans: Air is a bad conductor of heat.
18. The oxygen molecule having three atoms of oxygen.
Ans: Ozone.
19. Name the part of the earth over which there is a hole in the ozone layer.
Ans: Antarctica.
20. Any two biotic components.
Ans: Plants, animals.
21. Any two abiotic components.
Ans: Temperature, rainfall, soil
22. The part of the root of leguminous plants where bacteria responsible for fixation of nitrogen are found.
Ans: Root nodules.
C. Answer the following in a word:
1. An enclosure to keep tropical plants warm during winter.
Ans: Greenhouse.
2. Air in motion.
Ans: Wind.
3. Increase in the contents of harmful substances in the air.
Ans: Air pollution.
4. Removal of fertile topsoil by various agents or forces.
Ans: Soil erosion
5. Conversion of atmospheric nitrogen into its compounds.
Ans: Fixation
6. Preparation of glucose from carbon dioxide in the presence chlorophyll and sunlight.
Ans: Photosynthesis
D. Answer the following :
1. Any two processes that produce carbon dioxide.
Ans: Respiration and combustion or burning are the processes that produce carbon dioxide.
2. The factors that influence the direction of winds.
Ans: The factors that influence the direction of winds are: Rotation of the earth. Presence of mountain ranges in the path of the wind.
3. The importance of vegetation with reference to the soil.
Ans: The importance of vegetation with reference to the soil: The roots of plants hold the soil in place. It helps water to percolate into the deeper layers of the earth.
4. The composition of air on the earth is a result of life existing on the earth. Justify the statement
Ans: It is due to the constant interaction between biotic and abiotic components and due to biogeochemical cycles. Oxygen, nitrogen and carbon dioxide is used by living organisms through several processes. But the same is returned to the atmosphere by some other processes. Therefore the composition remains more or less the same.
5. Though carbon dioxide is added to the atmosphere by different processes, the percentage of carbon dioxide is a mere fraction of a per cent. Why ?
Ans: It is because carbon dioxide is being constantly utilised by green plants during photosynthesis. Also, many marine animals use carbon dioxide dissolved in water to make their shells.
6. Why is condensation of water vapour into drops faster when dust particles are present ?
Ans: Condensation of water vapour is faster when dust particles are present because the dust particles serve as nuclei for condensation of water vapour.
7. The atmosphere is clear after a rainfall. Why ?
Ans: Dust particles present in the atmosphere serve as nuclei for condensation of water vapour during the formation of rain. Thus the dust particles come down along with rain and the percentage of dust particles in the atmosphere decreases.
8. Why does wind blow from the sea to the land during day time ?
Ans: During day time air over the land is heated faster by the heat re-radiated from the land. Hence the air rises and causes a low pressure over the land. The air over the sea, which is comparatively less heated, moves to the low pressure area. This causes Wind to blow from the sea to the land during day time.
9. Why does wind blow from the land to the sea during night time ?
Ans: The land masses cool faster than water. Therefore air over the heat re-radiated from the land. Hence the air rises and causes a low pressure over the land. The air over the sea, which is comparatively less heated, moves to the low pressure area. This causes wind to blow from a the sea to the land during the day time
10. Why do deserts have extreme climate ?
Ans: The sand which constitutes the deserts is heated quickly as well as cooled quickly. Therefore it will be very hot during day time and quite cool during night time.
11. When is air said to be polluted ?
Ans: Air is said to be polluted when there is an increase in the contents of harmful substances in air.
12. How is acid rain caused ?
Ans: Fossil fuels like petroleum and coal contain small amounts of nitrogen and sulphur. When fossil fuels are burnt, nitrogen and sulphur contained in the fossil fuels form their respective Oxides. They dissolve in rain water to form acids and come down as acid rain.
13. Living organisms have to maintain a certain level of water within their body. Give a reason.
Ans: All cellular process take place in a water medium. All reactions in the body and within the cells take place between the substances which are dissolved in water. Different substances are transported from one part of the body to the other in water in a dissolved form.
14. Why cannot terrestrial life-forms survive in saline water ?
Ans: Terrestrial life-forms cannot survive in saline water because they cannot tolerate or get rid of the high amounts of dissolved salts in saline water.
15. Why do the Western Ghats have a richer biodiversity than the Deccan Plateau ?
Ans: The number and variety of plants and animals in a given area depends upon the amount of available water. The Western Ghats receive heavier rainfall than the Deccan plateau. Hence, due to greater availability of water there is a rich biodiversity in the Western Ghats.
16. Leena regularly waters the plants in her backyard while Meena does not. It is observed that many new plants are coming up besides what were planted in Leena’s backyard.Why are new plants seen growing in Leena’s backyard ?
Ans: The biodiversity at a place depends upon the amount of available water. Since Leena is regularly watering her plants, the amount of available water is more. Hence new plants are seen growing in her backyard.
17. What are the factors that decide the biodiversity of a region ?
Ans: The factors that decide the biodiversity of a region are :
(i) Amount of available water (ii) Temperature (iii) Nature of the soil.
18. When is water said to be polluted ?
Ans: Water is said to be polluted when: Undesirable substances are added to water bodies. Desirable substances are removed from water bodies. Temperature of water is changed due to human activities.
19. How do modern agricultural practices contribute to water pollution ?
Ans: In modern times chemical fertilisers and pesticides are used in agriculture. Some percentage of these fertilisers and pesticides are washed into water bodies which causes pollution of water. aquatic life.
20. What is the effect of sudden change in the temperature of water on aquatic life ?
Ans: A sudden change in temperature affects the breeding of aquatic organisms since eggs and larvae of various aquatic animals are susceptible to temperature changes.
21. What is humus ?
Ans: Humus is the bits of decayed living organisms.
22. Why does humus decide the structure of the soil ?
Ans: Humus decides the structure of the soil because it makes the soil porous and allows the water to penetrate to a depth underground.
23. What is topsoil ?
Ans: The topmost layer of the soil containing humus, living organisms and soil particles is called topsoil.
24. What is soil erosion ?
Ans: Soil erosion is the removal of fertile topsoil by various agents or forces.
25. What is soil pollution ?
Ans: Soil pollution is the removal of useful components of the soil and the addition of other substances that adversely affect the fertility of soil and kill various micro-organisms that live in it.
26. Why does deforestation lead to soil erosion ?
Ans: The roots of plants hold the soil in place and prevent it from being carried away. Deforestation amounts to removal of the vegetative cover. The soil, without a cover of trees and plants, 1 s likely to be removed quickly and leads to soil erosion.
27. What are the disadvantages of deforestation ?
Ans: The disadvantages of deforestation are: It destroys biodiversity. It enhances soil erosion .It slows down the percolation of water.
28. Why do cracks in the rocks widen when water in them freezes ?
Ans: Cracks in the rocks widen when water filled in them freezes because water expands on freezing
29. Give examples to show how living organisms help in the process of making soil.
Ans: When living organisms like lichens grow on the surface of the rocks they release certain substances which powder down the rock surface. The moss growing on such a powdered surface breaks down the rock further. The roots of the trees enter the cracks and widen them as the roots grow in size.
30. Earthworms should be allowed to multiply in agricultural lands. Why ?
Ans: Earthworms add humus to the soil thereby improving the structure of the soil. Therefore earthworms should be allowed to multiply in agricultural lands.
31. How does modern farming destroy the soil structure ?
Ans: In modern farming excessive quantities of fertilisers and pesticides are used. Prolonged use of fertilisers and pesticides kills micro-organisms and earthworms living in the soil which make rich humus. Thereby the structure of the soil is destroyed.
32. What are biogeochemical cycles ?
Ans: Biogeochemical cycles are the cyclic pathways through which chemical elements circulate from the environment to organisms and back to the environment.
33. How does the sun act as an agent of soil formation.
Ans: During day time rocks expand due to the heat of the sun and contract during night time as they cool. But the expansion or contraction is not uniform in all parts of the rocks. The unequal expansion and contraction develops cracks in them. With such repeated processes over a considerable period of time, the rocks finally break up into smaller pieces forming soil particles.
34. Why is soil erosion more in hilly areas ?
Ans: Soil erosion is more in hilly areas because the process of soil erosion is accelerated by the high speed of water due to the sloppy terrain.
35. What is fixation of nitrogen ?
Ans: Fixation of nitrogen is the process of converting atmospheric nitrogen into water soluble nitrates and nitrites.
36. Some gases prevent the escape of heat from the earth. What are such gases called. Give an example.
Ans: The gases which prevent the escape of heat from the earth are called greenhouse gases.
Example: carbon dioxide, methane.
37. Why does an increase in carbon dioxide in the atmosphere cause global warming ?
Ans: Carbon dioxide prevents the escape of heat radiated from the earth. If the percentage of carbon dioxide in the atmosphere increases, more heat is prevented from being lost and the temperature world-wide increases resulting into global warming.
38. The use of chlorofluorocarbons is to be banned or to be limited. Why ?
Ans: Chlorofluorocarbons are stable and not degraded by biological processes. When they reach the ozone layer, they react with the ozone molecules resulting in the reduction of the ozone layer which protects the life on earth from harmful radiations. Therefore the use of chlorofluorocarbons is to be banned or to be limited.
39. Though ozone is poisonous, the ozone layer around the earth is extremely important for life on the earth. Why ?
Ans: Ozone is poisonous but it has the property of absorbing the harmful radiations coming from the sun. This prevents harmful radiations from reaching the earth. Thus the life forms are saved from the damages of harmful radiations.
40. Draw a diagram to show the oxygen cycle formed by green plants and aerobic organisms.
Ans: OXYGEN CYCLE IN NATURE
41. What do you mean by biosphere ?
Ans: Biosphere is the life supporting zone of the earth where the atmosphere the hydrosphere and the lithosphere interact and make life possible.
42. Sand is deposited on roads close to beaches, as we see at Miramar beach near Panaji. Why ?
Ans: The blowing wind constantly carries the sand particles with it and deposits them on near by roads from the beach
43. Why are trees grown on sloppy terrains ?
Ans: In sloppy terrains the water has more speed. Therefore the soil erosion is faster. To check soil erosion trees are grown on sloppy terrains so that the roots of the trees hold the soil and prevent erosion.
ANSWER THE FOLLOWING :
1. The depression in the Bay of Bengal causes rain or cyclones in the eastern parts of India.
a) What do you mean by depression ?
Ans: Depression means low pressure
b) Why does a depression in the Bay of Bengal cause cyclones in the eastern parts of India ?
Ans: A cyclone is a storm or wind with high speed. When there is low pressure, the air from the surrounding high pressure areas rushes towards the area with low pressure. The speed of wind depends upon the difference in pressure. If the difference in pressure is considerable the speed of wind is high causing a cyclone.
2. Burning of fossil fuels cause atmospheric pollution.
a) What do you mean by atmospheric pollution ?
Ans: Atmospheric pollution is an increase in the contents of harmful substances in air.
b) How is pollution caused by burning of fossil fuels ?
Ans: Fossil fuels contain small amounts of sulphur and nitrogen. When these fuels are burnt sulphur and nitrogen produce their respective Oxides. The inhalation of these gases is dangerous. In addition they dissolve in rain water and cause acid rain. Combustion of fossil fuels release unburnt hydrocarbons or carbon particles which remain suspended in air.
3. Modern agricultural practices cause soil pollution.
a) What is soil pollution ?
Ans: Soil pollution is the removal of useful components of the soil and addition of other substances that adversely affect the fertility of soil and kill various micro-organisms that live in it.
b) How do modern agricultural practices cause soil pollution ?
Ans: Modern agriculture makes use of large amounts of fertilisers and pesticides. Prolonged use of fertilisers and pesticides kills micro-organisms living in the soil. It also kills earthworms which make humus. Thereby the soil structure is destroyed.
4. Describe the fixation of nitrogen in nature as a:
(i) biological process and (ii) physical process.
Ans: Biological process: The nitrogen fixing bacteria may be free living or found in root nodules of leguminous plants. These bacteria convert atmospheric nitrogen into nitrates and nitrites.
Physical process: During lightning, due to high temperature and pressure, the atmospheric nitrogen and oxygen combine to form oxides of nitrogen. These oxides dissolve in rain water to form nitrous and nitric acid and come down on the earth.
5. Describe how the sun and water help in the formation of soil.
Ans:
(a) The Sun: The rocks expand when they are heated during daytime and contract during night time due to cooling. But the expansion or contraction 1 S unequal in different parts of a rock. This develops cracks in them. With such prolonged processes, the rocks finally break up into smaller pieces.
(b) Water: (i) Water fills the cracks formed in the rocks. When water freezes it expands and widens the cracks.
(ii) The flow of water over the rocks for a long time wears out the rocks to form fine particles of soil. When water flows, it carries with it big and small particles of rocks which rub against other rocks. This abrasion causes wearing of the rocks into smaller and smaller particles.
6. Describe how human activities are responsible for water pollution water.
Ans: Some of the human activities add undesirable substances to water and thereby pollute it as under: Some percentage of fertilisers and pesticides used during farming are washed into water bodies.
Poisonous substances, like mercury salts used in the paper industry, are added to water when industrial effluents flow into water bodies. Disease causing organisms like bacteria which cause cholera are added to water when sewage from towns and cities is released into rivers and lakes.
7. The Railway Ministry has decided to withdraw about ten thousand air conditioned coaches from operation. These coaches were manufactured prior to 1994 and were using refrigerant having harmful effects on the atmosphere. This decision has been taken in accordance to the Montreal Protocol, which has been signed by India.
a) Name the refrigerant having a harmful effect on the atmosphere.
Ans: CFC
b) Which component of the atmosphere is affected by the refrigerant ?
Ans: Ozone layer.
c) What is the importance of that component on the atmosphere ?
Ans: The ozone layer absorbs harmful radiations coming from Sun.
d) What harmful effect will there be on the living world if the use of such a refrigerant is continued ?
Ans: If the use of such a refrigerant is continued, the ozone layer will be exhausted. The harmful radiations coming from the sun will no longer be absorbed and the living world on the earth will
will be exposed to such harmful radiations.
8. How is rain formed ?
Ans: The sun heats water bodies during day time, as a result the water evaporates and a large amount of water vapour goes into the air. The air is also heated and the hot air rises up. As the air rises it expands and cools. Water vapour in the air condenses to tiny droplets due to the cooling of air. Condensation of water vapour is accelerated if dust or other suspended particles are present in air because such particles serve as a nucleus for the droplets to be formed. These droplets grow in size due to condensation. As they grow in size, they become heavy and come down in the form of rain.