Phototactic Behavior: Searching for Light

Abstract All organisms respond in some way to light; they move, orient, swim, or fly to or away from the light—they are phototactic. Organisms have evolved photoreceptors for detecting light, measuring its intensity, and selecting the wavelengths of light for function—all in search of an optimal environment for survival. Phototactic behavioral responses are described as phototropism and phototaxis. Phototropism, as defined here, is simply a positive or negative orientation of a part or of the whole organism to move toward or away from light. The bending and twisting of a plant leaf to present its surface to the light is an example of positive phototropism. This ability of a plant to orient in search of light increases its efficiency for photosynthesis, which in effect determines the plant’s biochemistry and growth.