Photosynthesis is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their activities. Photosynthesis usually refers to oxygenic photosynthesis, a process that produces oxygen.
Photosynthetic organisms store the chemical energy they produce in photosynthesis, within intracellular organic compounds like sugars, glycogen, cellulose and starches. To use this stored chemical energy, the organisms' cells metabolize the organic compounds through another process called cellular respiration. Photosynthesis plays a critical role in producing and maintaining the oxygen content of the Earth's atmosphere, and it supplies most of the biological energy necessary for complex life on Earth.
C4 carbon fixation or the Hatch–Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. It owes the names to the 1960s discovery by Marshall Davidson Hatch and Charles Roger Slack.
Photorespiration (also known as the oxidative photosynthetic carbon cycle or C2 cycle) refers to a process in plant metabolism where the enzyme RuBisCO oxygenates RuBP, wasting some of the energy produced by photosynthesis. The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin–Benson cycle, but approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), creating a product that cannot be used within the Calvin–Benson cycle. This process lowers the efficiency of photosynthesis, potentially lowering photosynthetic output by 25% in C3 plants. Photorespiration involves a complex network of enzyme reactions that exchange metabolites between chloroplasts, leaf peroxisomes and mitochondria.
C3 carbon fixation is the most common of three metabolic pathways for carbon fixation in photosynthesis, the other two being C4 and CAM. This process converts carbon dioxide and ribulose bisphosphate (RuBP, a 5-carbon sugar) into two molecules of 3-phosphoglycerate through the following reaction:
The Calvin cycle, light-independent reactions, bio synthetic phase, dark reactions, or photosynthetic carbon reduction (PCR) cycle of photosynthesis is a series of chemical reactions that convert carbon dioxide and hydrogen-carrier compounds into glucose. The Calvin cycle is present in all photosynthetic eukaryotes and also many photosynthetic bacteria. In plants, these reactions occur in the stroma, the fluid-filled region of a chloroplast outside the thylakoid membranes. These reactions take the products of light-dependent reactions and perform further chemical processes on them. The Calvin cycle uses the chemical energy of ATP and reducing power of NADPH from the light dependent reactions to produce sugars for the plant to use. These substrates are used in a series of reduction-oxidation (redox) reactions to produce sugars in a step-wise process; there is no direct reaction that converts several molecules of CO2 to a sugar. There are three phases to the light-independent reactions, collectively called the Calvin cycle: carboxylation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration.
The light compensation point (Ic) is the light intensity on the light curve where the rate of photosynthesis exactly matches the rate of cellular respiration. At this point, the uptake of CO2 through photosynthetic pathways is equal to the respiratory release of carbon dioxide, and the uptake of O2 by respiration is equal to the photosynthetic release of oxygen. The concept of compensation points in general may be applied to other photosynthetic variables, the most important being that of CO2 concentration – CO2 compensation point (Γ).Interval of time in day time when light intensity is low due to which net gaseous exchange is zero is called as compensation point.
Howard Griffiths is a physiological ecologist. He is Professor of Plant Ecology in the Department of Plant Sciences at the University of Cambridge, and a Fellow of Clare College, Cambridge. He formerly worked for the University of Dundee in the Department of Biological Sciences. He applies molecular biology techniques and physiology to investigate the regulation of photosynthesis and plant water-use efficiency.
A Dynamic Global Vegetation Model (DGVM) is a computer program that simulates shifts in potential vegetation and its associated biogeochemical and hydrological cycles as a response to shifts in climate. DGVMs use time series of climate data and, given constraints of latitude, topography, and soil characteristics, simulate monthly or daily dynamics of ecosystem processes. DGVMs are used most often to simulate the effects of future climate change on natural vegetation and its carbon and water cycles.
Min Chen is an Australian plant physiologist. She was born in China and educated in Northeast Normal University China - BSc in 1984 and MSc in 1987 and received her PhD in 2003 from The University of Sydney Australia. She is a full professor and Australian Research Council Future Fellow in the School of Biological Sciences at the University of Sydney. Her research is primarily concerned with elucidating the molecular and biochemical mechanism of the energy-storing reactions in photosynthetic organisms, especially the function of novel photopigments in oxygenic photosynthetic bacteria.
Photosynthesis systems are electronic scientific instruments designed for non-destructive measurement of photosynthetic rates in the field. Photosynthesis systems are commonly used in agronomic and environmental research, as well as studies of the global carbon cycle.
Graham Douglas Farquhar, is an Australian biophysicist, Distinguished Professor at Australian National University, and leader of the Farquhar Lab. In 2018 Farquhar was named Senior Australian of the Year.
The Mehler reaction is named after Alan H. Mehler, who, in 1951, presented data to the effect that isolated chloroplasts reduce oxygen to form hydrogen peroxide. Mehler observed that the H
2O
2 formed in this way does not present an active intermediate in photosynthesis; rather, as a reactive oxygen species, it can be toxic to surrounding biological processes as an oxidizing agent. In scientific literature, the Mehler reaction often is used interchangeably with the Water-Water Cycle to refer to the formation of H
2O
2 by photosynthesis. Sensu stricto, the Water Water Cycle encompasses the Hill reaction, in which water is split to form oxygen, as well as the Mehler Reaction, in which oxygen is reduced to form H
2O
2 and, finally, the scavenging of this H
2O
2 by antioxidants to form water.
Marilyn Ball is a professor at the College of Medicine, Biology and Environment at the Australian National University (ANU), and leader of the Ball (Marilyn) Lab for Ecophysiology of Salinity and Freezing Tolerance.
Jane Alison Langdale, is a British geneticist and academic. She is Professor of Plant Development in the Department of Biology at the University of Oxford and a Professorial Fellow at The Queen's College, Oxford.
Thomas D. Sharkey is a plant biochemist who studies gas exchange between plants and the atmosphere. His research has covered (1) carbon metabolism of photosynthesis from carbon dioxide uptake to carbon export from the Calvin-Benson Cycle, (2) isoprene emission from plants, and (3) abiotic stress tolerance. Four guiding questions are: (1) how leaf photosynthesis affects plant yield, (2) does some carbon fixation follow an oxidative pathway that reduces sugar output but stabilizes photosynthesis, (3) why plants make isoprene, and (4) how plants cope with high temperature.
Photosynthesis converts carbon dioxide to carbohydrates via several metabolic pathways that provide energy to an organism and preferentially react with certain stable isotopes of carbon. The selective enrichment of one stable isotope over another creates distinct isotopic fractionations that can be measured and correlated among oxygenic phototrophs. The degree of carbon isotope fractionation is influenced by several factors, including the metabolism, anatomy, growth rate, and environmental conditions of the organism. Understanding these variations in carbon fractionation across species is useful for biogeochemical studies, including the reconstruction of paleoecology, plant evolution, and the characterization of food chains.
Sabeeha Sabanali Merchant is a professor of plant biology at the University of California, Berkeley. She studies the photosynthetic metabolism and metalloenzymes In 2010 Merchant led the team that sequenced the Chlamydomonas genome. She was elected a member of the National Academy of Sciences in 2012.
Charles Roger Slack was a British-born plant biologist and biochemist who lived and worked in Australia (1962–1970) and New Zealand (1970–2000). In 1966, jointly with Marshall Hatch, he discovered C4 photosynthesis.
Donald Richard Ort is an American botanist and biochemist. He is the Robert Emerson Professor of Plant Biology and Crop Sciences at the University of Illinois at Urbana-Champaign where he works on improving crop productivity and resilience to climate change by redesigning photosynthesis. He is a member of the National Academy of Sciences (NAS) and a fellow of the American Association for the Advancement of Science (AAAS) and American Society of Plant Biologists (ASPB).
Anne-Sophie Dielen is a researcher, scientist communicator and policy maker. Her research focuses on generating and regulating sodium/proton antiporters in plant chloroplasts. She is the Founder of The League of Remarkable Women in Science.
