Tuesday, January 6, 2009

Regulation of Water Balance in cells and organisms

Water is a very important element of life. There is a constant and steady loss of water from the body in different ways. For example, transpiration and excretion can reduce the water content of the body substantially and therefore should be replaced. Water is the medium for biochemical reactions and is needed in sufficient quantities for the easy diffusion and flow of dissolved and suspended materials within the body. A disturbance in the water balance in the body can disturb entire metabolic activities.

In animals, the site of homeostasis is the kidney. Kidneys are concerned with the isolation and excretion of metabolic waste products. Kidneys filter a large volume of water, solutes, and wastes everyday. But major amounts of water and solutes are reabsorbed. Only a small amount of water, solutes, and all wastes are excreted as urine. This is enough to create a shift in the water balance of the body. But we take in a lot of water along with food and otherwise. In the case of fresh water fishes, since the solute concentration in the cells is higher than the surrounding water excess water gets into their cells. The excess water is removed by excreting very dilute urine. Whereas, fish living in salt water have a different mechanism for water regulation. They take in a lot of salt water and the excess salt is pumped out through their gills. This is an active mechanism and needs lot of energy. In addition to this they produce highly concentrated urine in their specialized kidneys. Thus, they can remove a lot of salt by conserving water. This is the mechanism of homeostasis in marine organisms.

In plants, different mechanisms and modifications regulate water loss.

Terrestrial plants regulate water balance through roots and leaves. For example, during dry conditions certain plants drop their leaves to check water loss. In certain soil conditions where there is high salt concentration, certain plants actively pump minerals through their roots, which increases the solute concentration of the cell sap in the root hair. As the salt concentration is higher in the cell sap, water diffuses into the cell by osmosis. Plants have several mechanisms to conserve water. In desert plants, there is a very thick waxy coating all over the body to prevent water loss by evaporation. In most cases, stomata are located on the lower side of the leaves and also there is mechanisms to close the stomata during the day in those plants that are growing in dry weather.

Key words: Bio Genetics, Bio Technology

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