Circadian Rhythms
Many plant processes are affected by external conditions such as light, temperature and humidity. These processes include transpiration and the synthesis of some enzymes. These factors are easily controllable by growing plants in rigidly controlled conditions. But there are other processes, such as the opening and closing of the stomata and the production of photosynthetic enzymes that are not affected by external conditions. Another example is that legumes lower their leaves in the evening and raise them again in the morning. Even if they are kept in complete darkness or light then they will still continue these patterns because the leaves do not simply respond to sunrise or sunset. These cycles have a duration of approximately 24 hours and are not controlled by any known environmental variable. They are know as Circadian Rhythms. They are common to all eukaryotic organisms. Things such as blood pressure, temperature, cell division and metabolic rate are all examples of human processes that fluctuate in a circadian manner.
When organisms are kept in a constant environment the circadian rhythms deviate from the 24 hour period. They can vary from 21 to 27 depending on the rhythmic response. These are known as free-running periods. For example the deviation of bean plants have a period of 26 hours if the plants are kept in constant darkness. Their internal clocks are still keeping perfect time, they just aren't synchronized with the real world. Desynchronization also happens to humans. For example when we cross several time zones when on an airplane and when we reach our destination the time there is not the same as the that our internal clock says it is.
When organisms are kept in a constant environment the circadian rhythms deviate from the 24 hour period. They can vary from 21 to 27 depending on the rhythmic response. These are known as free-running periods. For example the deviation of bean plants have a period of 26 hours if the plants are kept in constant darkness. Their internal clocks are still keeping perfect time, they just aren't synchronized with the real world. Desynchronization also happens to humans. For example when we cross several time zones when on an airplane and when we reach our destination the time there is not the same as the that our internal clock says it is.