B3/ Further additional science

Rhythms

A circadian rhythm is a change in biological rhythms over a 24 hour period.

The Human brain contains a timing mechanism called a biological clock, which regulates what happens in the body in the 24 hour period. This includes the release of hormones.

Even though the body has a biological clock, it stills needs to have regular exposure to night-day to keep in sync with the 24 hour cycle. If a person is travelling they may experience jet lag. This is when a person is less alert and less able to think. This is due to travelling west to east or vice versa and losing track of the day to night cycle.

A hormone is a chemical messenger that is made in the body. An example of a hormone is melatonin. This is the hormone responsible for making us feel sleepy. The amount of melatonin levels increase at night, so we go to sleep. In the morning the levels decrease so we wake up.

Photoperiodism

Plants also have circadian rhythms as well as yearly rhythms. Responses to changing day lengths in plants is called photoperiodism.

Many species of plant species die in the tough winter conditions, but their seeds survive. In spring, as the days get longer, the seeds sense this and germinate.

Some plants may grow all through the winter, and respond to the lengthening days by growing faster. In autumn, as the days get shorter, other plants stop growing and get ready to survive the harder times ahead.

In many plant species, flowering is controlled by the length of dark or light in the 24 hour period.