Phototaxis

As a phototaxis by differences in illuminance ( Beleuchtungsstärkengradient ) is referred influenced in its direction of locomotion of organisms. We distinguish the positive phototaxis ( movement toward higher luminosity ) and the negative phototaxis ( movement toward lower illuminance).

Organisms may also react differently at different illumination intensities. So show some flagellates in low light a positive phototaxis, with stronger lighting a negative phototaxis. Some organisms react differently or in different wavelengths of light. So phototrophic bacteria often respond positively phototactic to wavelengths of light that are absorbed by their phototrophic pigments, while they do not respond or negative phototaxis in light of other wavelengths.

Some organisms move in certain angles to the light; in this case one speaks of slide or Transversalphototaxis.

The first description of phototaxis was by Gottfried Reinhold Treviranus 1803 green enthusiasts. Since then phototactic reactions in almost all groups of animals have been found. All of these organisms must necessarily have some form of light receptors.

The phototaxis should not be confused with the photokinetics. This form of the response to light is independent of variations of the illuminance, it depends on the absolute illuminance. Photokinetics is a function of the speed of movement of the intensity of the light radiation. With a positive PhotoKinesis an organism moves faster in stronger light, in the negative Photokinese slower. A number of organisms moves in the dark not at all ( dark Rigid ), others take their movement at a light ( light rigid ). The resulting curve of Photokinese is an optimum curve in the rule.