Learning outcomes
- 1.31 Be able to explain the importance of photoperiodicity in plants, including:
- a) plant germination
- b) growth
- c) reproduction
- 1.32 Be able to demonstrate an understanding of circadian rhythms in living organisms.
Chronobiology is a field of biology that examines periodic (cyclic) phenomena in living organisms and their adaptation to solar- and lunar-related rhythms. These cycles are known asbiological rhythms. Chronobiology comes from the ancient Greek χρόνος (chrónos, meaning "time"), and biology, which pertains to the study, or science, of life.
The variations of the timing and duration of biological activity in living organisms occur for many essential biological processes.
These occur
(a) in animals (eating, sleeping, mating, hibernating, migration, cellular regeneration, etc.),
The most important rhythm in chronobiology is the circadian rhythm, a roughly 24-hour cycle shown by physiological processes in all these organisms. The term circadian comes from the Latin circa, meaning "around" and dies, "day", meaning "approximately a day." It is regulated by circadian clocks cool, complex molecular circuits.
Here are some circadian rhythms of humans.
The circadian rhythm can further be broken down into routine cycles during the 24-hour day:[2]
- Diurnal, which describes organisms active during daytime
- Nocturnal, which describes organisms active in the night
- Crepuscular, which describes animals primarily active during the dawn and dusk hours (ex: white-tailed deer, some bats)
WHY WE GET JETLAG
Chronobiology of Plants
Many plants detect and respond to changes in the length of daylight to control their growth and reproduction. This is called ‘photoperiodicity’. This process helps plants to flower and reproduce, germinate, grow roots and shoots, and drop their leaves at the appropriate time.
Many flowering plants (angiosperms) use a photoreceptor protein, to sense seasonal changes in night length, or photoperiod, which they take as signals to flower.
Long-day plants flower when the night length falls below their critical photoperiod. These plants typically flower in thenorthern hemisphere during late spring or early summer as days are getting longer. In the northern hemisphere, the longest day of the year (summer solstice) is on or about 21 June.[6] After that date, days grow shorter (i.e. nights grow longer) until 21 December (the winter solstice). This situation is reversed in the southern hemisphere (i.e., longest day is 21 December and shortest day is 21 June).
Long-day plants flower when the night length falls below their critical photoperiod. These plants typically flower in thenorthern hemisphere during late spring or early summer as days are getting longer. In the northern hemisphere, the longest day of the year (summer solstice) is on or about 21 June.[6] After that date, days grow shorter (i.e. nights grow longer) until 21 December (the winter solstice). This situation is reversed in the southern hemisphere (i.e., longest day is 21 December and shortest day is 21 June).
A cool use of chronobiology - a clock made of flowers!
A circadian cycle was first observed in the 18th century in the movement of plant leaves by the French scientist Jean-Jacques d'Ortous de Mairan (for a description of ). In 1751 Swedish botanist and naturalist Carolus Linnaeus (Carl von Linné) designed a flower clock using certain species of flowering plants. By arranging the selected species in a circular pattern, he designed a clock that indicated the time of day by the flowers that were open at each given hour. For example, among members of the daisy family, he used the hawk's beard plant which opened its flowers at 6:30 am and the hawkbit which did not open its flowers until 7 am.
References: Wikipedia.
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