Biology 1002B Lecture Notes - Lecture 25: Circadian Rhythm, Pupa, Today'S Railways
15 Mar 2015
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Document Summary
All life has evolved under rhythmic change of light and day because of earth spinning on its axis. Phenomenon that change daily not constant. Period: between one successive section and the next, trough to trough or peak to peak. Day and night, foraging/predatory behaviour, sleep-wake cycles, body temperature, hormone secretion, photosynthesis, gene expression. What if organism could anticipate environmental change: ex. Abundance of mrna coding for light harvesting (proteins that bind chlorophyll for psi or psii) is dependent on diurnal phenomena. Present before sun rises anticipates rather than responds. Constant light still breaks for dark time. Advantage want ps to work as soon as sun comes up: endogenous biological clock. Biological rhythm with a period of around" a day (24-25hrs) Set it to the external light environment. Once clock is set does not need additional input (external cue) Rhythm isn"t perfect forever but lasts for a long time. Output out of clock: physiological responses.
