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Compensation Point
The light compensation point (''I''c) 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). In assimilation terms, at the compensation point, the net carbon dioxide assimilation is zero. Leaves release CO2 by photorespiration and cellular respiration, but CO2 is also converted into carbohydrate by photosynthesis. Assimilation is therefore the difference in the rate of these processes. At a given partial pressure of CO2 (0.343 hPa in 1980 atmosphere), there is an irradiation at which the net assimilation of CO2 is zero. For ins ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Light Curve (botany)
In botany, a light curve shows the photosynthetic response of leaf tissue or algal communities to varying light intensities. The shape of the curve illustrates the principle of limiting factors; in low light levels, the rate of photosynthesis is limited by the concentration of chlorophyll and the efficiency of the light-dependent reactions, but in higher light levels it is limited by the efficiency of RuBisCo and the availability of carbon dioxide. The point on the curve where these two differing slopes meet is called the light saturation point and is where the light-dependent reactions are producing more ATP and NADPH than can be utilized by the light-independent 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 ...s. Since photosynthesis is also limited by ambient carbon d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Partial Pressure
In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas mixture is the sum of the partial pressures of the gases in the mixture ( Dalton's Law). The partial pressure of a gas is a measure of thermodynamic activity of the gas's molecules. Gases dissolve, diffuse, and react according to their partial pressures but not according to their concentrations in gas mixtures or liquids. This general property of gases is also true in chemical reactions of gases in biology. For example, the necessary amount of oxygen for human respiration, and the amount that is toxic, is set by the partial pressure of oxygen alone. This is true across a very wide range of different concentrations of oxygen present in various inhaled breathing gases or dissolved in blood; consequently, mixture ratios, like that of breat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Critical Depth
In biological oceanography, critical depth is defined as a hypothetical surface mixing depth where phytoplankton growth is precisely matched by losses of phytoplankton biomass within the depth interval."Critical depth" is an important term in ocean acoustics defining the lower limit of the full deep sound channel. That depth lies below the axis of the main duct of sound speed minimum. It is the point at which sound speed equals the maximum found above the axis in the surface layer. See SOFAR channel. This concept is useful for understanding the initiation of phytoplankton blooms. History Critical depth as an aspect of biological oceanography was introduced in 1935 by Gran and Braarud. It became prominent in 1953 when Harald Sverdrup published the "Critical Depth Hypothesis" based on observations he had made in the North Atlantic on the ''Weather Ship M''. Sverdrup provides a simple formula based on several assumptions that relates the critical depth to plankton growth and l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photophosphorylation
In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation. Cyclic photophosphorylation occurs in both aerobic and anaerobic conditions, driven by the main primary source of energy available to living organisms, which is sunlight. All organisms produce a phosphate compound, ATP, which is the universal energy currency of life. In photophosphorylation, light energy is used to pump protons across a biological membrane, mediated by flow of electrons through an electron transport chain. This stores energy in a proton gradient. As the protons flow back through an enzyme called ATP synthase, ATP is generated from ADP and inorganic phosphate. ATP is essential in the Calvin cycle to assist in the synthesis of carbohydrates from carbon dioxide and NADPH. ATP and reactions Both the structure of ATP synthase and its underlying gene are remarkably similar in all known forms of life. ATP synthase is powered by a transmembr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isopycnal
Isopycnals are layers within the ocean that are stratified based on their densities and can be shown as a line connecting points of a specific density or potential density on a graph. Isopycnals are often displayed graphically to help visualize "layers" of the water in the ocean or gases in the atmosphere in a similar manner to how contour lines are used in topographic maps to help visualize topography. Types Oceanography Water masses in the ocean are characterized by their properties. Factors such as density, temperature, and salinity can all be used to identify these masses and their origins as well as where they are in the water column. Density plays a large role in stratifying the ocean into layers. In a body of water, as the depth increases, so does the density; water masses with the highest density are at the bottom and the lowest densities are at the top. Typically, warm freshwater is less dense than cold salty water, thus the colder water will sink below the warmer w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Phytoplankton obtain their energy through photosynthesis, as do trees and other plants on land. This means phytoplankton must have light from the sun, so they live in the well-lit surface layers ( euphotic zone) of oceans and lakes. In comparison with terrestrial plants, phytoplankton are distributed over a larger surface area, are exposed to less seasonal variation and have markedly faster turnover rates than trees (days versus decades). As a result, phytoplankton respond rapidly on a global scale to climate variations. Phytoplankton form the base of marine and freshwater food webs and are key players in the global carbon cycle. They account for about half of global photosynthetic activity and at least half of the oxygen production, desp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plankton
Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucial source of food to many small and large aquatic organisms, such as bivalves, fish and whales. Marine plankton include bacteria, archaea, algae, protozoa and drifting or floating animals that inhabit the saltwater of oceans and the brackish waters of estuaries. Freshwater plankton are similar to marine plankton, but are found in the freshwaters of lakes and rivers. Plankton are usually thought of as inhabiting water, but there are also airborne versions, the aeroplankton, that live part of their lives drifting in the atmosphere. These include plant spores, pollen and wind-scattered seeds, as well as microorganisms swept into the air from terrestrial dust storms and oceanic plankton swept into the air by sea spray. Though many p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ribulose-1,5-bisphosphate
Ribulose 1,5-bisphosphate (RuBP) is an organic substance that is involved in photosynthesis, notably as the principal acceptor in plants. It is a colourless anion, a double phosphate ester of the ketopentose (ketone-containing sugar with five carbon atoms) called ribulose. Salts of RuBP can be isolated, but its crucial biological function happens in solution. RuBP occurs not only in plants but in all domains of life, including Archaea, Bacteria, and Eukarya. History RuBP was originally discovered by Andrew Benson in 1951 while working in the lab of Melvin Calvin at UC Berkeley. Calvin, who had been away from the lab at the time of discovery and was not listed as a co-author, controversially removed the full molecule name from the title of the initial paper, identifying it solely as "ribulose". At the time, the molecule was known as ''ribulose diphosphate'' (RDP or RuDP) but the prefix di- was changed to bis- to emphasize the nonadjacency of the two phosphate groups. Role in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rubisco
Ribulose-1,5-bisphosphate carboxylase-oxygenase, commonly known by the abbreviations RuBisCo, rubisco, RuBPCase, or RuBPco, is an enzyme () involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is converted by plants and other photosynthetic organisms to energy-rich molecules such as glucose. In chemical terms, it catalyzes the carboxylation of ribulose-1,5-bisphosphate (also known as RuBP). It is probably the most abundant enzyme on Earth. Alternative carbon fixation pathways RuBisCO is important biologically because it catalyzes the primary chemical reaction by which inorganic carbon enters the biosphere. While many autotrophic bacteria and archaea fix carbon via the reductive acetyl CoA pathway, the 3-hydroxypropionate cycle, or the reverse Krebs cycle, these pathways are relatively small contributors to global carbon fixation compared to that catalyzed by RuBisCO. Phosphoenolpyruvate carboxylase, unlike RuBisCO, only tempora ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Part Per Million
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement. Commonly used are parts-per-million (ppm, ), parts-per-billion (ppb, ), parts-per-trillion (ppt, ) and parts-per-quadrillion (ppq, ). This notation is not part of the International System of Units (SI) system and its meaning is ambiguous. Overview Parts-per notation is often used describing dilute solutions in chemistry, for instance, the relative abundance of dissolved minerals or pollutants in water. The quantity "1 ppm" can be used for a mass fraction if a water-borne pollutant is present at one-millionth of a gram per gram of sample solution. When working with aqueous solutions, it is common to assume that the density of water is 1.00 g/mL. Therefore, it is common to equate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pascals
The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI), and is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is defined as one newton per square metre and is equivalent to 10 barye (Ba) in the CGS system. The unit of measurement called standard atmosphere (atm) is defined as 101,325 Pa. Common multiple units of the pascal are the hectopascal (1 hPa = 100 Pa), which is equal to one millibar, and the kilopascal (1 kPa = 1000 Pa), which is equal to one centibar. Meteorological observations typically report atmospheric pressure in hectopascals per the recommendation of the World Meteorological Organization, thus a standard atmosphere (atm) or typical sea-level air pressure is about 1013 hPa. Reports in the United States typically use inches of mercury or millibars (hectopascals). In Canada these reports are given in kilopasc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C2 Photosynthesis
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 plants. Photorespiration involves a complex network of enzyme reactions that exchange metabolites between chloroplasts, leaf peroxisomes and mitochondria. The oxygenation reaction of RuBisCO is a wasteful process because 3-phosphoglycerate is created at a lower rate and higher metabolic cost compared with RuBP carboxylase activity. While photorespiratory carbon cycling resu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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