In Part I, we considered the underwater light climate: the particular characteristics that it has in different types of natural water bodies, the scattering and absorption processes that take place in the aquatic medium, and the ways that these operate upon the incident light stream to produce the kinds of underwater light field that we observe. Now, in Part II, we turn our attention to the utilization of this underwater light for photosynthesis by aquatic plants. We begin, in this chapter, by asking: with what intracellular structures, from the level of organelles down to that of molecules, do aquatic plants harvest radiant energy from the underwater light field and convert it to chemical energy?

Chloroplasts

In eukaryotic plants, photosynthesis is carried out by the organelles known as chloroplasts, the best known members of the great class of related and interconvertible organelles known as plastids. Detailed accounts of these organelles may be found in Kirk and Tilney-Bassett (1978), Staehelin (1986) and Falkowski and Raven (2007): we shall here content ourselves with a rather brief treatment.