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Life Support Systems

By Tas -


Water is also an essential component of life on Earth, as it is used for respiration, nutrient transport and a variety of other essential functions. Water is processed through a complex cycle, known as the hydrological cycle. This cycle takes waters from the oceans and through evaporation into clouds deposits it on the land, where it returns to the oceans as run off or subsurface water (Westcott, R., p 27). It is important that the water returns to its large reservoirs (the oceans), as the Earth is a “closed loop cycle” as far as water is concerned. Unlike energy, which is constantly being provided by the Sun’s rays, there is no extra-planetary source of water. This means any water lost to the cycle is permanently lost and the overall stocks will deplete.

The Earth’s surface is approximately 70% water, however most animals and plant’s require fresh water to survive (Westcott, R., p 27). Only about 3% of the planets water supply is actually fresh water, most of this is stored as ice or snow on the poles or is deep under the surface and inaccessible (Westcott, R., p 28). This means supplies of fresh water are always important and throughout history access to fresh water has been a source of conflict.

Possibly as a result of the importance of fresh water, and the lack of natural reserves, the natural environment has developed an efficient system of purifying waste water products. A good example is how water consumed by animals and used for nutrient transport around the body is returned to the reservoirs. Animals excrete water, which is contaminated with metabolic by-products (urine). This is turned into water vapour (pure water) by natural evaporation and then returns to the Earth as rain. In addition to this, microbes in the soil convert the waste products (mostly urea) into a form that is useable by plants to create new tissue. Finally, the waste products in the urine can be electrostatically filtered by particles of clay in the soil, leaving pure water, which then runs downstream to the reservoirs (Westcott, R., p 18).

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Westcott, R., ed. (2004) T210 Block One: The Environment, Risk and Public Health, Milton Keynes, The Open University.

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