Abstract:
In organisms we can often observe rhythmic structures. Thus, the visual cells in our eyes are daily renewed, chloroplasts of plants and algae alter their form or position in a daily rhythm, starch is deposited in daily layers, likewise calciumcarbonate in shells of snails and corals. Fossil corals show by their layer depositions, that 400 million years ago a year consistet of 400 days. Depositions in flies and dinosaurs tell us in the same way as annual rings of trees their age. Fairy rings of mushrooms are further examples. In Neurospora the molecular mechanism of the clock is known, which is responsible for the daily spore formation. A marine ameba displays an interesting change in form with an unusual rhythmic behavior. Some proposals for demonstrations, observations and experiments shall motivate the reader, to engage oneself with these interesting topics.