Principles of the Interaction of Light and Matter

This chapter deals with those principles of spectroscopy and photochemistry that form the logical basis for a molecular approach to photophysiological processes. It is a familiar fact that most plants operate through a photosynthetic apparatus that stores light energy, absorbed by chlorophyll, as chemical energy in the form of carbohydrates produced from carbon dioxide and water. There are also other light-mediated processes in the plant kingdom, such as phototropism (bending of organisms) and phototaxis (locomotion of organisms), which arise from a spatial imbalance of a growth hormone (auxin), and, in many species of plants, the processes of flowering, seed germination, and other photoperiodic effects appear to be controlled by a photosensitive hormone, phytochrome. In the animal kingdom photoperiodism is also observed, but the principal photophysiological process here is vision, and it is largely this process that has guided the development of this chapter.