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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 Marine Ecology: Processes, Systems, and Impacts

Primary Production Processes  

This chapter introduces the major factors that control primary production and how to measure it. Primary production is the starting point of all life in marine systems. Primary producers in the oceans span many orders of magnitude. Production is measured using bottled incubations or, increasingly, from space, using (satellite-borne) ocean colour sensors that detect photosynthetic pigments in surface waters. The conversion of inorganic carbon into biomass, its subsequent sinking to the seabed, and sequestration over thousands of years are fundamental to an understanding of the ocean as a potential sink for increasing levels of atmospheric carbon dioxide. About 55% of the total carbon captured on Earth through the process of photosynthesis and production of biomass takes place in marine systems.

Chapter

Cover Biochemistry and Molecular Biology

Raising electrons of water back up the energy scale: photosynthesis  

This chapter explains how photosynthesis occurs in plant cell chloroplasts, noting that the part that is dependent on light is the splitting of water to generate NADPH. It describes chlorophyll, which is a green pigment that receives light energy and is present in the membrane of organelles called thylakoids. When activated by photons, chlorophyll molecules donate electrons to chains of electron carriers arranged in two photosystems: PSI and PSII. The chapter talks about the loss of the electrons by chlorophyll. This makes it a very powerful oxidizing agent, capable of accepting electrons from water in the water-splitting centre. Adenosine triphosphate (ATP) is generated by the chemiosmotic mechanism during the passage of electrons from one photosystem to the other.

Chapter

Cover Pharmaceutical Chemistry

Carbohydrates and Carbohydrate Metabolism  

Alex White and Helen Burrell

This chapter focuses on carbohydrates, which are molecules composed almost exclusively of carbon, hydrogen, and oxygen. Carbohydrate monomers are called monosaccharides and are found throughout nature. The chapter explains how carbohydrates are synthesized in plants during the process of photosynthesis, with their carbon atoms being obtained from atmospheric carbon dioxide. The chapter considers carbohydrates as the main fuel source in human bodies and they are divided into two groups: simple sugars and complex carbohydrates. Simple sugars like glucose are metabolized directly via glycolysis and the citric acid cycle, whereas complex carbohydrates like starch and glycogen are first broken down into simple sugars.

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 Plant Physiology and Development

Photosynthesis: Physiological and Ecological Considerations  

This chapter discusses photosynthesis and refers to the rate of net photosynthesis, the difference between photosynthetic carbon assimilation, and the loss of CO2 via photorespiration and mitochondrial respiration in the light. It focuses on how naturally occurring variation in light and temperature influences photosynthesis in leaves and how leaves in turn adjust or acclimate to such variation. It also explores how atmospheric CO2 and temperature influence photosynthesis, which is an important consideration in a world where CO2 concentrations and temperature are rapidly increasing as humans continue to burn fossil fuels for energy production. The chapter analyzes the leaf anatomy that is highly specialized for light absorption, noting how some plants maximize light absorption by solar tracking. It highlights the carbon isotope ratios of leaves that can be used to distinguish photosynthetic pathway differences among different plant species.

Chapter

Cover Ecology

Coping with Environmental Variation: Energy  

This chapter reviews the different ways in which organisms acquire energy to meet the demands of cellular maintenance, growth, reproduction, and survival. It focuses on the major mechanisms that allow organisms to obtain energy from their environment, including the capture of sunlight and chemical energy and the acquisition and use of organic compounds synthesized by other organisms. The chapter then differentiates between autotrophy and heterotrophy. Autotrophs convert energy from sunlight (by photosynthesis) or inorganic chemicals (by chemosynthesis) into energy stored in the carbon–carbon bonds of carbohydrates. Photosynthetic responses to variation in light levels, water availability, and nutrient availability include both short-term acclimatization and long-term adaptation. Meanwhile, heterotrophs acquire energy by consuming organic compounds from other organisms, living or dead.

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 Physical Chemistry for the Life Sciences

Photoactivation and its consequences  

This chapter discusses photoactivation and its consequences. Processes in photobiology typically involve a competition between chemical reaction and the decay of excitation energy. Molecules that have been excited electronically can either react or lose their excitation energy in other ways, including fluorescence. The chapter shows how the kinetics of the processes that can follow photo-excitation can be explored by setting up rate equations like those used in chemical kinetics, and the influence of specifically introduced quenching molecules can be explored quantitatively. With these processes understood, they can be applied to the central issues of photobiology, including vision, photosynthesis, and the damage to DNA that may result from exposure to sunlight.

Chapter

Cover Biological Science

Metabolism  

Energy Capture and Release from Food

This chapter covers the release of energy from glucose, fats, and amino acids during the process of metabolism. It explains that biological oxidation involves the removal of electrons and their transfer to another acceptor molecule and the enzymatic removal of two hydrogen atoms from a metabolite molecule. The main stages of glucose oxidation include the outline of the pathway of glycolysis in terms of ATP production and reduced coenzymes. The chapter then looks into anaerobic respiration and fermentation, which involves the production of ATP without the use of oxygen. It also explains the synthesis of metabolic fuels by plants through the process of photosynthesis.

Chapter

Cover Photosynthetic Life Origin, Evolution, and Future

The bacterial origins of photosynthesis  

This chapter provides a detailed investigation of where, when, and how photosynthesis originated and then evolved in non-eukaryotic organisms. It looks at some of the best accepted geological evidence for the earliest photosynthesis that comes from marine sedimentary deposits in rocks from the Buck Reef Chert in South Africa dated to 3.4 Ga. It also talks about rocks found in the Isua Greenstone Belt in Greenland, dating back from about 3.8 Ga, which harbour geochemical signatures consistent with photosynthesis. The chapter highlights the possibility that anoxygenic photosynthesis had already evolved well before 3 Ga, at a time when the Earth was still a highly anaerobic planet. It covers the two key evolutionary innovations required for the evolution of photosynthesis: first is the evolution of the reaction centre (RC) proteins, and second is a requirement for the evolution of biosynthetic pathways of chlorophylls and related pigments.

Chapter

Cover Biochemistry

Metabolism: Transforming Energy and Biomolecules  

This chapter evaluates the process of metabolism. Although there are many different sets of reactions, or metabolic pathways, involved here, only a small number are fundamental to all cells. The chapter focuses on two metabolic pathways that are particularly well understood by biochemists because of their importance for life: aerobic respiration and photosynthesis. To appreciate cellular metabolism, it is important to understand how energy is transferred between different molecules and converted to different forms. Moving and transforming energy is fundamental to how cells function, and the biochemists that study this topic describe it as bioenergetics. One of the key theoretical concepts that is particularly useful for understanding this biochemical topic is 'free energy'. This concept helps identify whether biochemical reactions are favourable or not. The chapter looks at adenosine triphosphate (ATP), as well as endosymbiosis.

Chapter

Cover Biochemistry

Solving Tomorrow’s Problems: Bioenergy and the Environment  

This chapter highlights the potential to tackle environmental problems by harnessing human understanding of biochemistry. Biotechnology could help in reducing our crippling dependency on fossil fuels. Biotech, which simply means technology derived from living systems, has already been used to pioneer several different forms of renewable energy. Algae, a diverse group of plant-like organisms, have sparked great interest with their potential to produce carbon-neutral biofuels. Moreover, researchers have been developing artificial photosynthesis, which could also be used to produce alternatives to fossil fuels. Agriculture could also reduce its carbon footprint with help from biotechnology. This field has the potential to produce artificial meat and dairy products, which would reduce our dependence on animals along with our greenhouse gas emissions. Meanwhile, plants have been genetically modified for greater efficiency, to grow in harsh climates, and generally to alleviate the scarcity of food that characterizes a snowballing global population.

Chapter

Cover Biological Science

Metabolism  

Energy Capture and Release from Food

This chapter covers the release of energy from glucose, fats, and amino acids during the process of metabolism. It explains that biological oxidation involves the removal of electrons and their transfer to another acceptor molecule and the enzymatic removal of two hydrogen atoms from a metabolite molecule. The main stages of glucose oxidation include the outline of the pathway of glycolysis in terms of ATP production and reduced coenzymes. The chapter then looks into anaerobic respiration and fermentation, which involves the production of ATP without the use of oxygen. It also explains the synthesis of metabolic fuels by plants through the process of photosynthesis.

Chapter

Cover Fundamentals of Plant Physiology

Photosynthesis: Physiological and Ecological Considerations  

This chapter explores some physiological and ecological considerations concerning photosynthesis. Physiologists wish to understand the direct and indirect responses of photosynthesis to environmental factors. The dependence of photosynthetic processes on environmental conditions is also important to agronomists because plant productivity, and hence crop yield, depends strongly on prevailing photosynthetic rates in a dynamic environment. To the ecologist, photosynthetic variation among different environments is of great interest in terms of adaptation and evolution. The chapter focuses on how naturally occurring variation in light and temperature influences photosynthesis in leaves and how leaves in turn adjust or acclimate to such variation. It also describes how atmospheric CO2 influences photosynthesis, an especially important consideration in a world where CO2 concentrations are rapidly increasing as humans continue to burn fossil fuels for energy production.

Chapter

Cover Fundamentals of Plant Physiology

Water and Plant Cells  

This chapter discusses how water plays a crucial role in the life of the plant. Photosynthesis requires that plants draw carbon dioxide from the atmosphere, and at the same time exposes them to water loss and the threat of dehydration. To prevent leaf desiccation, water must be absorbed by the roots and transported through the plant body. Even slight imbalances between the uptake and transport of water and the loss of water to the atmosphere can cause water deficits and severe malfunctioning of many cellular processes. The chapter then considers how water moves into and out of plant cells, emphasizing the molecular properties of water and the physical forces that influence water movement at the cell level. It looks at how cell walls allow plant cells to build up large internal hydrostatic pressures, called turgor pressure, and differentiates between diffusion and osmosis.

Chapter

Cover Physical Chemistry for the Life Sciences

Electron transport chains  

This chapter considers electron transport chains. Two of the most fundamental metabolic processes, aerobic respiration and photosynthesis, which play such a critical role in maintaining life on Earth, require a succession of electron transfers. In both processes the electron transfers take place in membrane-localized electron transport chains that contain multiple electron carriers. These carriers are proteins and other types of molecules that can cycle between oxidized and reduced forms as electrons pass along the chain. Each couple (the oxidized and reduced forms of the carrier, Ox/Red) has a characteristic potential that corresponds to its reduction half-reaction, and the direction of spontaneous electron transport is typically in the direction of increasing potential. Here, the chapter considers electron transfer between redox centres, before examining the respiratory chain and photosynthesis.

Chapter

Cover The Ecology of Plants

Photosynthesis and Light  

This chapter begins by looking at the interactions plants make with their environment by considering the process by which plants acquire energy and carbon: photosynthesis. It examines how plants capture the energy of sunlight and incorporate carbon from the atmosphere in photosynthesis, their adaptations to the light environment, their water relations, and the mineral nutrients they get from the soil. These processes in turn can play out at the larger scope of ecosystem processes. The chapter also takes a look at the structures in which some of these processes take place and some of the biochemistry involved. It focuses first on processes occurring at the small scale of a cell, a leaf, or an individual plant. Finally, the chapter considers the importance of the forest, where plants have evolved and live in an ecological context. It studies the physical conditions that a plant experiences, determined by the physical features of the environment and by other living organisms in that habitat.

Chapter

Cover Thrive in Cell Biology

Chloroplasts and photosynthesis  

This chapter discusses the chloroplasts of green plants, which are surrounded by a chloroplast envelope which encloses a stroma containing a third type of membrane called the thylakoid system. The chapter explains that the chloroplast envelope consists of outer and inner membranes (OCM and ICM) that are separated by an intermembranous space. It also cites the variations in structure that occur between the chloroplasts of plants, algae, and unicellular eukaryotic photosynthetic organisms. The chapter highlights the two linked processes or sets of reactions of photosynthesis called the light-dependent and light-independent or dark reactions. It notes that light-dependent reactions occur in the thylakoid system, while the independent reactions occur in the stroma.