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

Total Earth’s surface covered by water is (a) 75% (b) 60% (c) 85% (d) 50%

‘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

Top-soil contains the following (а) Humus and living organisms only (b) Humus and soil particles only (c) Humus, living organisms and plants (d) Humus, living organisms and soil particles.

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

Oxygen is returned to the atmosphere mainly by (a) burning of fossil fuel (b) respiration (c) photosynthesis (d) fungi

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

Biotic component of the biosphere is not constituted by (a) producers (b) consumers (c) decomposer (d) air

Major source of mineral in soil is the (a) parent rock from which soil is formed (b) plants (c) animals (d) bacteria

The temperature ranges from …………… to …………… on the moon as it does not have atmosphere.

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

Marked temperature changes in an aquatic environment can affect (a) breeding of animals (b) more growth of aquatic plants (c) process of digestion in animals (d) availability of nutrients.