2. Feeding activity is circadian, although the circadian rhythm is most obvious in animals that don't get enough food. If an animal gets too little to eat, but gets food at certain times of the day, their activity will increase at that time of the day, even if they don't get any food, at it will go on for several days. Plants, of course, don't 'eat' (and they don't sleep either), but metabolism is regulkated by the circadian rhythm in plants. Photosyntesis consists of a light reaction and a dark reaction, and they occur at different times of the circadian day. That it is regulated by the circadian rhythm rather than by the presence or absence of light can be shown by growing plants in constant light conditions or in artificial conditions with much shorter days and nights than normal. In these situations, they still shopw a circadian rhythm.
3. The first circadian behaviour that was reported was actually reported in a plant. It was the ancient Greek philosopher Androsthenes of Thassos that described how various plants open and close their leaves depending on the time of day. This process has later been shown to be regulated by a circadian rhythm. This is, perhaps, the closest you can get to a 'behaviour' of a plant.
4. Body temperature in animals (and humans) are regulated by a circadian rhythm. Our body temperature is as lowest in the very early morning, and a s highest in the evenings.
5. The signal that tells trees when to lose their leaves is that the days get shorter. The trees use their circadian rhythm to track the length of the day. Migratory birds use a similar way of knowing when to migrate.
there are some plants (mostly flowers) that close at night. while there is a specific word for that nyctinasty its still an example of the plants having a circadian rhythm. and what about animals that are nocturnal? that's a great example. they have to know when the day is over in order to be active at night.
