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ScienceClass 9CBSE

Lichens are called pioneer colonisers of bare rock. How can they help in formation of soil?

Lichens releases enzymes that break the rock into smaller pieces and helps in formation of soil.

ScienceClass 9CBSE

There is mass mortality of fishes in a pond. What may be the reasons ?

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.

ScienceClass 9CBSE

Why does water need conservation even though large oceans surround the land masses?

Sea water is not suitable for livelihood of humans and plants. Fresh water resources are limited hence they need to be conserved.

ScienceClass 9CBSE

Why do not lichens occur in Delhi whereas they commonly grow in Manali or Darjeeling?

Lichens are sensitive to Sulphur oxide released by automobiles. Delhi has more number of automobiles which increase the pollution. Pollution avoids lichens in Delhi.

ScienceClass 9CBSE

Why does Mathura refinery pose problems to the Taj Mahal?

Mathura refinery releases oxides of Sulphur which causes acid rain. Acid rain corrodes the marble of tajmahal hence Mathura refinery pose problems to Tajmahal.

ScienceClass 9CBSE

Why do people love to fly kites near the seashore ?

Near the sea shore breeze blows during day time which is ideal for flying kites.

ScienceClass 9CBSE

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?

Earth has atmosphere which prevents over heating 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 moon also allows the heat to escape during night because of this phenomenon temperature varies on moon surface.

ScienceClass 9CBSE

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 back to environment in one or other form. This process of using natural resources and giving them back to nature is called as Bio-Geo Chemical cycle. Because of Bio-Geo Chemical cycle percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere.

ScienceClass 9CBSE

All the living organisms are basically made up of C, N, S, P, H and O. How do they enter the living forms? Discuss.

C, N, S, P, H and O are enter the living community through plants. Carbon comes through photosynthesis and nitrogen are obtained through nitrogen fixing bacteria. Sulphur and Phosphorus are absorbed from soil. Hydrogen and oxygen are obtained by water. These nutrients are obtained by animals from plants.

ScienceClass 9CBSE

Soil formation is done by both abiotic and biotic factors. List the names of these factors by classifying them as abiotic and biotic?

Abiotic factors; Sun, water and wind Biotic Factors: Lichens, mosses and trees.

ScienceClass 9CBSE

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.

Answers are (a) lichen (b) mosses Explanation: Lichens grow on rocks and releases certain enzymes which favor the growth of mosses. Mosses forms clumps of soil from rock which results in formation of top soil.

ScienceClass 9CBSE

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.

During day time land heats more than sea .This create a low pressure in the land and wind always move from low pressure to high pressure regions. Similarly in the night land cools faster and sea remains hot making wind to move from sea to land.

ScienceClass 9CBSE

During summer, if you go near the lake, you feel relief from the heat, why?

Lake water gets evaporated and vapors due to evaporation creates a cooling effect near lake. Hence we feel relieved from heat.

ScienceClass 9CBSE

How is the life of organisms living in water affected when water gets polluted?

Addition of pollutants like fertilizers and chemicals to the water bodies will bring disease to aquatic organisms. Pollutants increases the oxygen requirement in aquatic life. Pollutants also decrease the dissolved oxygen in the water which will affect the aquatic life adversely.

ScienceClass 9CBSE

How can we prevent the loss of top soil?

Loss of top soil can be stopped by 1) Afforestation 2) Crop rotation 3)Counter farming 4) proper irrigation methods.

ScienceClass 9CBSE

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

Soln: Answer is (b) nitrogen fixing bacteria Explanation: Nitrogen fixing bacteria are anaerobic, they get killed when exposed to oxygen hence oxygen is harmful for them

ScienceClass 9CBSE

How do fossil fuels cause air pollution?

When we burn fossil fuels carbon-do-oxide, 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.

ScienceClass 9CBSE

1. 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

Explanation: b) Rain water causes loss of surface soil Explanation: Roots hold on the surface soil and helps them to get washed away from current of water due to rainfall. When there is no vegetation surface soil gets washed away.

ScienceClass 9CBSE

Soil erosion can be prevented by (a) raising forests (b) deforestation (c) excessive use of fertilizer overgrazing by animals

Soln: Answer is (a) raising forests Explanation: Trees in the forest hold on the soil by its roots. Hence growing forest can prevent soil erosion.

ScienceClass 9CBSE

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.

Soln: Answer is (a) breeding of animals Explanation: Most aquatic animals are cold blooded. Their egg and larvae are highly susceptible to temperature changes hence breeding of animals gets affect from temperature changes.

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