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Chapter

Cover Biochemistry

Photosynthesis  

This chapter considers oxygenic photosynthesis as the most important biochemical process on earth. With a few minor exceptions, photosynthesis is the only mechanism by which an external abiotic source of energy is harnessed by the living world, and it is the source of O2, which sustains all aerobic organisms. It explains photosynthesis as the light-driven biochemical mechanism whereby CO2 is incorporated into organic molecules, such as glucose. The chapter refers to captured light energy that is used to synthesise adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH), which drive the process. The reducing power of NADPH is necessary as a strong electron donor is required to reduce the fully oxidised, low-energy carbon atoms in CO2 to the carbon units of organic molecules.

Chapter

Cover Photosynthetic Life Origin, Evolution, and Future

Photosynthesis, oxygen, and the evolution of life  

This chapter discusses photosynthesis, which involves the use of solar energy to convert simple inorganic substrates into complex carbon-based compounds. It surveys the basic processes involved in the various types of photosynthesis found in bacteria and eukaryotes and the pivotal role played by photosynthesis in the evolution of life on Earth. It also considers the broader significance of photosynthesis in terms of the many important roles that it plays in both the biosphere and the geosphere. The chapter shows how photosynthetic oxygen generated by cyanobacteria led to a global oxygen increase during the GOE1 about 2.4 Ga. It describes the evolution of photosynthetic eukaryotes, which gradually diversified and eventually overtook cyanobacteria as the major oxygen producers.

Chapter

Cover Photosynthetic Life Origin, Evolution, and Future

Eukaryotic photosynthesis  

This chapter argues that oxygenic photosynthesis is the most important form of photosynthesis on Earth, which accounts for an estimated 3000-fold greater amount of carbon fixation. It discusses the emerging evidence that oxygenic photosynthesis might have its origins close to the beginnings of cellular life at around or before 4 Ga. It also recognizes oxygenic photosynthesis as the only form that was acquired by eukaryotes following a unique endosymbiotic event between a eukaryotic heterotroph and a cyanobacterium. The chapter focuses on the mechanisms of oxygenic photosynthesis in eukaryotes, and cites algae and plants. It also presents a comparative analysis of the extant cyanobacterial mechanisms which had a momentous effect on biological evolution.

Chapter

Cover Bioinorganic Chemistry

Photosynthesis  

This chapter looks at the overall involvement of metal centres in photosynthesis, specifically discussing the central role of the chlorophylls on the one hand, and of the oxygen-evolving centre on the other hand. It first gives an overview of the Great Oxygenation Event which happened about 2.4 Ga ago, when photosynthetically active cyanobacteria, also called blue-green algae, started to produce — and to release into the atmosphere — more oxygen than could be eliminated by oxidation processes, such as oxidative decay of organics, or the conversion of ferrous to ferric iron, sulfide to sulfate, ammonia to nitrate, and so forth. This change forced organisms that failed to adapt to the novel situation into oxygen-free niches. Emphasizing that more than one hundred proteins are involved in the global regulation of the photosynthetic machinery, steering over 50 distinct chemical transformations, the chapter looks at relevant reaction pathways. Furthermore, it tackles artificial photosynthesis.

Chapter

Cover Plant Physiology and Development

Photosynthesis: The Carbon Reactions  

This chapter describes the metabolic cycle and shows how this incorporates atmospheric CO2 into organic compounds called the Calvin–Benson cycle. It considers how the unavoidable reaction of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) with molecular oxygen decreases the efficiency of photosynthetic CO2 assimilation. It also explores how photorespiration releases CO2 while recycling the by-products of the oxygenation reaction that would otherwise be unusable by the cell. The chapter examines C4 photosynthesis and crassulacean acid metabolism (CAM), which are CO2-concentrating mechanisms that land plants have evolved for minimizing the oxygenation of Rubisco and the loss of energy and CO2 during photorespiration. It looks at the formation of the two major products of the photosynthetic CO2 fixation: starch and sucrose.