Introduction

Photosynthesis is fundamental to life on Earth as it establishes access to the main energy source of the biosphere, sunlight (Blankenship, 2002). Photosynthesis is based on the interaction between living matter and the sun's radiation field, mainly visible light. This interaction involves the electrons of biological macromolecules and, accordingly, the process of light absorption is governed by quantum physics. During the course of biological evolution, photosynthetic lifeforms learned to exploit quantum physics in ingenious ways, in particular, under the circumstances of physiological temperature. A description of quantum phenomena under the influence of strong thermal effects as arise under these circumstances is challenging. Indeed, the quantum biology of photosynthesis is an active and fascinating research area.

Photosynthesis, in general, is understood to encompass the various processes in living cells by which lifeforms utilize sunlight to drive chemical synthesis. This involves primary processes of light-harvesting, transformation of electronic excitation energy into a membrane potential, as well as the splitting of water into oxygen, abstracting electrons that are added to molecules of nicotinamide adenine dinucleotide phosphate (NADPH+) at a high redox potential. The membrane potential drives the synthesis of adenosine triphosphate (ATP) which is used to fuel many processes in living cells. In plant photosynthesis NADPH+ and ATP are needed for the synthesis of sugar and starch, the most widely known products of photosynthesis. Because of its fundamental importance in cellular energetics, photosynthesis has been the subject of great evolutionary pressure such that, amidst a deep overall similarity, many variants have developed in the competition for habitats and efficiency.