Physical Factors of the Environment

The subject of this section, namely the influence of physical factors on biological systems belongs to environmental biophysics on the one hand and, on the other hand, is important for applications in medicine and biotechnology.

The input of energy from the environment into biological systems can lead to different consequences:

- It can directly interact with the energetics of the organism. This can occur in a specific way, as in the case of photosynthesis, or nonspecifically, for example, just by heating the organism.

- Very small amounts of energy, occasionally being absorbed at particular targets, can significantly disturb biological mechanisms of control. The place of interaction in this case is not a specific receptor, but rather a crucial point in the network of reactions. An example of this is the induction of mutations by ionizing radiation.

- Environmental energy can act as a carrier of information. In this case specific receptors are activated by negligible amounts of energy input.

According to the so-called Grotthus-Draper principle it is not the energy penetrating the organism which is effective, but that part of the energy which is absorbed in the system. Investigations into the mechanism of interaction, therefore, start with the question: how, and where is this kind of energy absorbed? Eventually it must be clarified whether alterations are induced by the absorbed energy, and how these influence the biological system. In some cases, biological cascades of amplification exist. The theory of biological amplification was first developed in radiation biology. It is, however, also crucial for a number of other physical influences.

When discussing possible influences of weak physical energies on biological systems, its relation to thermic noise (kT, Sect. 2.3.4) is frequently stressed. This is correct from the physical point of view, assuming the following circumstances are taken into account:

- To relate the energy input to the energy of thermic noise, the primary mechanism must be known which leads to the absorption of this kind of energy in the biological system.

- It must be considered that cooperative effects may be included in these processes. Such interactions are quite probable in more highly organized molecular systems. This sort of cooperation can significantly promote low energetic influences. - It must be considered that the organism has developed a multitude of filter systems against thermic noise along the path of evolution. The best example of this is the human ear.

In this context it should be pointed out that the organism has and is adapting through evolution to all physical parameters of its environment. So, for example, the double strand of the DNA is an adaptation to overcome single strand breaks by ionizing radiation. Additionally, a large number of mechanisms have been developed to repair these kinds of damage. On the other hand, during evolution an astonishing number of mechanisms have been developed to sense minimal amounts of energy, in the form of receptors for vibration, for temperature, for light and for other kinds of radiation.

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