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The biological clock

Janet E. Harker
Science Progress (1933-)
Vol. 61, No. 242 (Summer 1974), pp. 175-189
Stable URL: http://www.jstor.org/stable/43420237
Page Count: 15
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The biological clock
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Abstract

The ability of living organisms to maintain accurately timed rhythms, in the absence of normal environmental time-cues, has led to the proposal that such rhythms are driven by a biological 'clock'. The nature of the processes involved in the timing system has been explored, indirectly, by observing the effect of changes in the physical environment on the period and phase-setting of circadian rhythms, and, more directly, by observing the effect on such rhythms of blocking certain metabolic processes and of removing a variety of organs and cell organelles. The question is raised as to how far the results of such experiments reflect their effect on the coupling processes between the biological clock and the observed rhythmical process rather than their effect on the biological clock itself. Finally the proposition that the ultimate control of timing may depend not on a biological clock but on a sensitivity to uncontrollable environmental variables is discussed.

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