How do photosynthetic organisms detect light?

Answer 1

Detection implies consciousness, which photosynthetic organisms don't have. Everything that they do is an automatic process, built in to their biochemistry, rather than being a decision based upon something that they have observed. In the case of plants that grow toward the light, that has to do with growth hormone in strategic locations, which alters the way the plant grows. The plant does not actually know where to secrete the growth hormone, that is just an automatic response to certain envrionmental conditions. In the case of growing in an upward direction, that is easy, the growth hormone just sinks downward under the influence of gravity. The lowest part of the plant then grows the fastest, causing the plant to turn upward. And for plants whose leaves angle toward the sunlight, you just need a hormone secretion where the rate of photosynthesis is lower.

Answer 2

Photosynthetic organisms have light-sensitive pigments called photoreceptors that are able to detect light. The most common photoreceptor in plants is called phytochrome, which absorbs red and far-red light. When light is absorbed by these pigments, it triggers a series of chemical reactions that ultimately lead to the activation of photosynthesis.

Answer 3

by chemical photoreceptors
Plants detect light by chemical photoreceptors.