Photosynthesis: The Complex Path from Light to Carbon Fixation

The summary reaction of photosynthesis belies the complexities of the underlying processes. This chapter provides a brief introduction to the processes of photosynthesis, the concepts of reaction centers, light harvesting centers, and photosynthetic units. The fundamentals of the functioning of the electron transport chain and the carbon assimilation processes are reviewed. Most algae do not live in a condition of steady-state growth where elemental supply, energy balance, and the production of ATP and NADPH are all balanced. Consequently, there are many alternate pathways by which cells can rebalance and protect their photosynthetic machinery from overexcitation and/or photoinhibition. These pathways function in both the electron transport chains of respiration and photosynthesis. These light-dependent and light-independent respiration reactions are also reviewed here. Finally, this chapter characterizes the fundamental relationships between photosynthesis and irradiance as well as respiration and irradiance.