Life Support Systems
By Tas - tas@oustudent.me.uk
Essential Elements
While energy, in the form of food, is often thought of as the only essential nutrients for life this is not the case. Out of the 92 naturally occurring elements there are thirty or forty that are considered essential for life (Westcott, R., p 23).
These essential elements can be broken down into ones that are required in large quantities (major elements or macronutrients), such as carbon, nitrogen, oxygen etc. and elements that are required in trace amounts (minor elements or micronutrients) such as iron and zinc (Westcott, R., p 23).
Unlike energy, which flows through the ecosystem on a constant basis (providing effectively unlimited quantities) in a variety of forms, the matter which makes up the essential elements are finite and must be constantly cycled through the system if life is to survive. The basic cycle these minerals follow is the autotrophs take up the elements from the soil in which they grow. The elements are passed up each trophic level in the chain. Eventually the organism at the top of the food chain dies and the process of decomposition returns the elements to the soil (Westcott, R., p 23). This allows the cycle to begin again.
Suitable Temperature
The vast majority of the cycles and flows that are required by life on Earth also require a suitable ambient temperature for them to occur in. The water cycle (hydrological cycle) is dependant on the temperature being sufficiently warm enough for water to be fluid (i.e. above 0oC) yet must be sufficiently cool so that not all the water is evaporated. The term suitable temperature doesn’t imply one single temperature is ideal for all organisms or cycles – however it does imply that the ecosystem is capable of maintaining temperature within certain boundaries.
The energy provided by the Sun’s radiation is the primary source of heat on Earth and in normal circumstances the atmosphere is sufficient to retain and control the planetary heat levels.
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Reference
Westcott, R., ed. (2004) T210 Block One: The Environment, Risk and Public Health, Milton Keynes, The Open University.
