What is Biological rhythms?
'''Biological rhythms''' are the repeating cycles of activity which occur in living organisms. The best-known example is the daily or ''[[circadian rhythm]]'', which fits the cycle of day and night. Most forms of life have natural rhythms which fit them to natural changes in their [[environment]]. Animals are most active in part of the day, and rest or sleep at other times. They may be: * [[Diurnal]], which describes organisms active during daytime * [[Nocturnal]], active in the night * [[Crepuscular]], active during the [[dawn]] and [[dusk]] hours. Plants undergo daily cycles as well. [[Photosynthesis]] has parts which need light, called [[light-dependent reactions]], and parts which can continue at night ([[light-independent reactions]]). Many other important cycles are also studied,<ref>Refinetti, Roberto 2006. ''Circadian physiology''. CRC Press/Taylor & Francis Group. {{ISBN|0-8493-2233-2}} [http://www.circadian.org/dictionary.html Lay summary]</ref> including: * cycles longer than a day, such as the annual [[migration]] or reproduction cycles found in certain animals or the human [[menstrual cycle]]. * cycles shorter than 24 hours, such as the 90-minute [[REM]] cycle, the 4-hour [[nasal cycle]],<ref>This is the alternating congestion and decongestion of each side of the nasal cavity.</ref> or the 3-hour cycle of [[growth hormone]] production. * [[Tide|Tidal rhythms]] are often seen in marine life, which follow the roughly 12.4-hour transition from high to low tide and back. * [[Lunar rhythms]], which follow the [[lunar month]] (29.5 days). They are relevant for marine life, as the level of the tides is affected by the lunar cycle. * [[Gene]] oscillations – some genes are [[gene expression|expressed]] more during certain hours of the day than during other hours. == References == {{reflist}} [[Category:Physiology]]