Ex

  Biology (NTSE/Olympiad)  

6. Natural Resources

Water : A World Liquid

Water : A World Liquid
Water is one of the basic necessities of life. It is an inexhaustible natural resource which is liquid between 0ºC and 100ºC. We need water for various activites such as drinking, cooking of food, bathing and washing. It is also needed for irrigation of crop in agriculature, as an essential requirement in industries, and for navigation.
Water plays a vital role in the metabolic reactions taking place within the organism’s body. It acts as a universal solvent, providing a medium for the chemical reactions to occur. In fact, all the chemical reactions that occur within body cells involve substances that are dissolved in water. Substances are also transported from one part of the body to the other in dissolved form.
97.5% of the water on the planet earth is found in seas and oceans as saline water and is not available to us for use directly. Only 2.5% of the total water resources of the world consist of fresh water. Majority of it (about 2%) is found frozen in the ice-caps at the two poles and on snow-covered mountains. Remaining (0.6% of the total) is available to support terrestrial life. Majority (90%) of this fresh water is found underground as ground water and only 10% occurs as surface water in lakes, ponds, streams, rivers etc. Limited amount of fresh water is available to us as a renewable souce through water cycle but its distribution is uneven.

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