Biological Units Modify Their Environments

An engineer ultimately designs for a customer, an artist for an audience. 

Environmental interactions with BU are not jnst one-way. BU are adept at modifying their environments to suit their purposes, and one shonld never assume that the environment will be the same after BU have been introduced. We probably all know the weathering effect that certain plants have on rocks and soils. These plants extract required minerals from the rcKks by secreting acids that dissolve the rocks. Over time, the rocks will diminish and disappear. 

Some plants can alter the immediate environment around their roots by exuding materials that change soil acidity. This enhances, by three or more orders of magnitude, the solubility of such essential elements such as iron. These plants have a finely tuned biofeedback control that enhances soil fertility precisely at the root surface without altering the rest of the soil. This, then, minimizes the energy cost to the plant of soil modification (Olsen et al., 1981). Root crops and rhizosphere bacteria secrete acids into the soil solution to raise the solubility of solid-phase phosphates (highly pH dependent) in their immediate neighborhoods (Russell, 1961). 

At the other end of the scale, trees are responsible for the removal of carbon dioxide and the addition of oxygen to the atmosphere. It is widely believed that all of the oxygen in the Earth s atmosphere is the result of photosynthetic activity by primitive organisms, and that the atmosphere before photosynthesis was much different than it is today (see Section 3.9). 

There is a real possibility that microbes from Earth would find conditions on another heavenly body suitable for them to live. If so, is it ethical for planetary probes from Earth to infect the other world NASA personnel say no. Just as in the TV program Star Trek, the prime directive was to prevent interference with alien societies, especially those less advanced than the one that operated the starship Enterprise there should be no contamination of other places in space. Yet, in reality, there is the possibility that some errant microbe might hitchhike its way on a probe from Earth. So, to what degree should hardware from Earth be sterilized What level of assurance is acceptable (Greenberg and Tufts, 2001)  

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