Water is capable of dissolving a large number of substances. As water flows over the rocks containing soluble minerals, some of them get dissolved in the water. Thus, rivers carry many nutrients from land to the sea.

Loss of top soil can be prevented by
(i) increasing the vegetational cover
(ii) checking the falling of trees
(iii) by preventing excessive grazing by animals

Addition of undesirable chemicals like pesticides, fertilizers, industrial waste and domestic wastes not only kill the organisms, they also cause diseases to the aquatic organisms. Besides, the requirement of oxygen by aquatic organisms is also increased. There is a reduction in the dissolved oxygen in water which adversely affects the aquatic organisms

The water from surface of a lake keeps on evaporating. This create a cooling effects in the surrounding. Due to this, when we go near a lake we feel relief from heat.

Air above the land gets heated quickly during day and starts rising. This creates a region of low pressure as a result air over sea rushes into this area of low pressure. This movement of air from one region to the other creates winds. During night, as water cools down slowly, the air above water is warmer than the air on land. So, air moves from land to sea creating winds

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.

Ans. Lichens and Mosses (a) and (b). Lichens and mosses release substances which break down the stones resulting in the formation of soil.

Abiotic factors making soil— sun, water, wind
Biotic factors— lichens, mosses and trees

C, N, S, P, H and O are the basic components of various biomolecules. Living being are made up of numerous biomolecules. Most of these components come to the living world via plants. Carbon comes through photosynthesis. Nitrogen is fixed in soil by nitrogenfixing bacteria so that plants can absorb nitrogenous compounds. Sulphur and phosphorus are available as minerals in soil and are absorbed by plant; along with water. Hydrogen and oxygen enter in the plants when they absorb water. Animal also obtain hydrogen and oxygen when they drink water. Oxygen is also taken up by living beings during inhalation. Finally, these elements are taken up by animals when they take food either directly or indirectly from plants.