An Introduction to Chlorophyll Fluorescence

Abstract

Photosynthesis is a physiological process that couples the energy of light to certain metabolic changes in biochemical reactions, via photochemical processes. Importantly, these metabolic changes would be endothermic in the absence of light, meaning that they would not proceed spontaneously. It is by this means that plants, algae, photosynthetic bacteria, and other organisms that have some kind of photosynthetic ability, are able to assemble energy-rich molecules, such as carbohydrates or lipids, from energy-poor starting materials, such as carbon dioxide or water. Even if these biochemical transformations are spatially and also partly temporally removed from the photochemical events, they are dependent upon physical and chemical changes that follow the absorption of light. This coupling permits the free-energy of light to produce metabolic change. This physiological trick is the energetic foundation of most life on earth. Only chemosynthetic organisms (e. g. non-photosynthetic sulphur bacteria) and those that prey upon them are fundamentally independent of the energy of light. It is the purpose of this chapter to lay out the basic physical and physiological processes associated with this coupling, and to show how these changes are linked to other physical processes that allow us to measure the operation and progress of the coupling of light-absorption to physiology. The essential raw material for this process is light itself, so we shall begin with a brief overview of light, especially in relation to energy.