Outlines of evolutionary biology / by Arthur Dendy, with glossary of technical terms.

  • Arthur Dendy
Date:
1923
Catalogue details

Licence: In copyright

Credit: Outlines of evolutionary biology / by Arthur Dendy, with glossary of technical terms. Source: Wellcome Collection.

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    of to-day still derive supplies of energy from the same source and lock up in their leaves and stems what they do not them¬ selves expend, while the animals in turn derive their energy from the green plants upon which they directly or indirectly feed. Hence both plants and animals are ultimately dependent upon the sun for their existence. Even the most superficial examination is sufficient to demon¬ strate the fact that the body of any of the more familiar animals or plants is, as we have already indicated, an extremely complicated thing. Whatever may be the degree of complexity, however, and however much one organism may differ from another in details of structure, whether it be a microscopic alga or an oak tree, an Amoeba or a man, there are always certain things which have to be done, certain actions or functions which have to be performed, in order that its life may be maintained. In the first place, the organism must safeguard itself as far as possible from the destructive influences of its environment. It must not only be able to protect itself from such physical agents as heat and cold, mechanical impact and friction, but it may have to select a situation where life is possible, or to escape from other organisms by which it is liable to be attacked. All this involves the expenditure of energy in some form or another; it may be in the manufacture or secretion of protective envelopes or shells, such as we find even in some of the simplest Protozoa, or it may be in actively moving away from the source of danger. Thus it appears that the very first thing necessary for the maintenance of life is the expenditure of energy. This energy, though ultimately derived from the sun, is, as we have already seen, derived immediately from the combustion of fuel, very much as in the case of a steam-engine, but with the important difference that in the living organism the fuel is, at any rate to a large extent, the actual substance of which the body is composed. In this respect the comparison with a candle is especially apt, for it is the combustion of the actual substance of which the candle is composed that liberates the energy manifested in the light and heat of the flame. Now combustion is, of course, simply another name for what chemists term oxidation, or combination with the element oxygen, a process which is often accompanied by the liberation of a considerable amount of energy in the form of heat and light, though this is by no means always the case. In the
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