Wednesday, March 18, 2015
IMPORTANCE OF WATER AT MOLECULAR LEVEL
Water is the medium of life. It is the most abundant compound in all organisms. It varies from 65 to 89 percent in different organisms. Human tissues contain about 20 per cent water in bone cells and 85 per cent in brain cells. Almost all reactions of a cell occur in the presence of water. It also takes part in numerous biochemical reactions such as hydrolysis of macromolecules. It is also used as a raw material for photosynthesis. Following are a few important points of water..
Solvent properties:
Due to its polarity, water is an excellent solvent for polar substances. Ionic substances when disbanded in water, dissociate into positive and negative ions. Non-ionic substances having charged groups in their molecules are spread in water. When in solution, ions and molecules move randomly and are in a more favorable state to react with other molecules and ions. It is for this reason property of water that almost all reactions in cells occur in aqueous media. In cells, all chemical reactions are catalyzed by enzymes which work in an aqueous environment. Non-polar organic molecules, such as fats, are insoluble in water and help to maintain membranes which make compartments in the cell.
Heat Capacity:
Water has great ability of absorbing heat with a minimum of change in its own temperature. The specific heat capacity of water is - the number of calories required to raise the temperature of water from 15 to 16°C and is 1.0 cal. This is because much of the energy is utilized to break hydrogen bonds. Water thus works as temperature stabilizer for organisms in the environment and hence protects living material against sudden thermal changes.
Heat Of Vaporization:
Water absorbs considerable heat as it changes from liquid to gas. Heat of vaporization is given in calories absorbed per gram vaporized. The specific heat of vaporization of water is 574 Kcal/kg, which plays an important part in the regulation of heat produced by oxidation. It also provides cooling effect to plants when water is transpired or to animals when water is perspired. Evaporation of only 2 ml out of one litre of water, lowers the temperature of the remaining 998 ml by 1°C.
Protection:
Water is an effective lubricant that provides protection against damage resulting from friction. For example, tears protect the surface of the eye from the rubbing of eyelids, water also forms a fluid cushion around organs that helps to protect them from trauma.
Diffusion:
Water not only diffuses itself but also assists the diffusion of other molecules. Molecules of other substances are dissolved in water. Diffusion is the movement of concentration from an area of higher concentration to an area of lower concentration. Diffusion causes equal distribution of molecules. Diffusion of water diffuses not only itself but also causes the diffusion of ions and molecules of other substances. Hence, water also helps with the transport.
Organizes non-polar molecules:
Non-polar molecules such as oil do not form hydrogen bonds with water which is a polar molecule. Instead, the water molecules form hydrogen bonds with each other, causing the water to be excluded the non-polar molecules. It means non-polar molecules move away from water, so they are known as being "hydrophobic" which means "water fearing". Non-polar molecules form bonds with each other in a water solution and become organized. This bonding of non-polar molecules is known as hydrophobic bonding.
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