Biological clock - Seibutsu to Kei (English spelling) Biological clock

Japanese: 生物時計 - せいぶつとけい（英語表記）biological clock

Also called the biological clock. A general term for mechanisms of periodicity assumed to exist within living organisms. Periodicities vary in type and period, from short ones such as the periodic change in the reduction degree of redox coenzymes in units of seconds or minutes, heartbeats, and brain waves, to seasonal ones such as the migration and migration of birds and fish, and the flowering of plants, but the most common meaning of the term biological clock is diurnal change. Even when animals and plants are kept under constant light, many of them show diurnal rhythms, such as the concentration of excreted substances in animals, so the existence of an intrinsic clock mechanism is assumed, but the nature of this mechanism is not yet clear. In this case, the rhythm is not exactly 24 hours, but may shift slightly, and in many cases it shifts toward the long-period side, that is, the clock is delayed, so this intrinsic rhythm is called a circadian rhythm. In the actual life of living organisms, there is light and darkness during the day and night to correct the shift. When honeybees dance within the hive to indicate the direction of nectar to their fellow bees, they use the angle of their steps as a reference for the direction of the sun at that time, so it is thought that some kind of clock mechanism is involved in this phenomenon, and in a similar sense in the homing of birds. Examples of long-term clock mechanisms include the mating and egg-laying of marine animals that occur in accordance with the phases of the moon, and the menstrual cycle of women. The phenomenon of diurnal rhythm, in which the formation of flower buds in plants is controlled by day length, is also closely related to clock mechanisms. Biologists have been particularly interested in biological clocks since around the 1960s, and in Japan, a society for chronobiology was founded in the 1970s.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

体内時計ともいう。生物体内に存在の想定される周期性発現機構の総称。周期性には，酸化還元補酵素の秒・分単位での還元度の周期変化，心臓の拍動，脳波など短いものから，鳥や魚の渡りや回遊とか植物の開花などのように季節単位のものまで，種類も周期も多様であるが，生物時計というとき意味することが最も多いのは，日周変化である。動植物を定常光下に保っても，動物での排出物質濃度などのように日周リズムを示すものが多いので，内在的な時計機構の存在が想定されるが，その本体はまだ明らかでない。この場合リズムは，正確に 24時間でなく，少しずつずれることがあり，多くは長周期側，すなわち時計が遅れる方向にずれるので，こうした内在リズムを概日リズム (サーカディアンリズム circadian rhythm) という。実際の生物の生活では，昼夜の明暗があってずれを補正する。ミツバチが巣内でのダンスの歩行角度で蜜の方向を仲間に示すとき，基準はその時刻での太陽の方角なので，こうした現象にも，また同様な意味で鳥の帰巣などにも，なんらかの時計機構の介在が考えられる。海の動物の交尾・産卵が月齢に合せて行われるとか，女性の月経周期とかは，長期の時計機構の例である。植物の花芽形成が日長に支配される，いわゆる日周性の現象も，時計機構と密接に関係している。生物時計に関する生物学者の関心は，1960年頃からことに高まってきて，日本でも 70年代に，時間生物学 chronobiologyの学会が発足するにいたっている。

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