The biological world and ecology

Living systems, as far as is known, are limited to this planet. The power of living systems is immense if their activities are considered on the global scale. The biosphere, or the environment in which life exists, is a rather limited part of the planet, the most important of which is that near or on surface, or in the oceans. 

Evidence for activity of living processes appears to expand steadily. There is good evidence that life can successfully exist in pressurised water at 120°C, in ice at - 10°C, and at extremes of pH (1-11), in saturated salt solutions and even when subjected to high levels of radiation. 

The carbon cycle is illustrated in Fig. 5.2. All living systems require an external source of energy, either in the form of chemical bond energy, as chemical (redox) potential or as some form of electromagnetic radiation usually in or near the visible light region. 

The biosphere has a complex chemistry and many aspects of the processes and their consequences are not fully understood. However, pollution arises from the cyclic processes being out of balance, or from the accumulation of other undesirable materials. Indeed, a major perception of pollution is the disruption of these cycles. The activities of man are now on such a scale that they significantly affect the environment and its chemistry. 

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