Photorespiration and loss of 50% of carbon fixed in the Calvin cycle?
The oxidative photosynthetic carbon cycle reaction is catalyzed by Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) activity: RuBP + O2 → Phosphoglycolate + 3-phosphoglycerate Photorespiration is said to be an evolutionary relic. The early atmosphere in which primitive plants originated contained very little oxygen, so it is hypothesized that the early evolution of RuBisCO was not influenced by its lack of discrimination between O2 and carbon dioxide. Another theory postulates that it may function as a "safety valve," preventing excess NADPH and ATP from reacting with oxygen and producing free radicals, as these can damage the metabolic functions of the cell by subsequent reactions with lipids or metabolites of alternate pathways.
How do plants adapt themselves to avoid photorespiration?
Here is my answer to a similar question.C3 carbon fixing plants are adapted to environments where they are able to keep their stomata open long enough during the day so natural circulation of gases keeps concentrations of CO2 and O2 in the leaf at proportions where photorespiration is less compromising and productivity is sufficient.The problem of photorespiration increases when stomata must be closed to conserve water, reducing transpiration on hot and dry days. Under those circumstances, natural circulation of gases in the leaf is restricted, trapping O2 and lowering CO2 concentration, thus increasing photorespiration and compromising production efficiency.C4 and CAM carbon fixing plants are adapted to climates where the need for water conservation limits the natural circulation of gases in the leaf because stomata must be restricted or closed during the day to reduce transpiration. C4 and CAM plants have evolved methods to supplement CO2 concentrations, minimizing the compromise of photorespiration and raising production efficiency in these climates.…RuBisCO is the enzyme involved in carbon fixing in the Calvin cycle of photosynthesis. RuBisCO has the capability of carboxylating or oxygenating RuBP, the substrate recycled in the Calvin cycle. Carboxylation of RuBP proceeds through the Calvin cycle producing PGA for sugar production. Oxygenation of RuBP is more costly and produces less PGA for sugar production. This is called photorespiration because it produces CO2. Photorespiration is counter productive to carbon fixing in the Calvin cycle. The two processes occur simultaneously.At ambient levels of carbon dioxide and oxygen, the ratio of the reactions is about 4 to 1, which results in a net carbon dioxide fixation of only 3.5.This is a satisfactory compromise in C3 carbon fixing productivity. However, C4 and CAM plants reduce the effect by increasing CO2 concentrations, maximizing carboxylation of RuBP by RuBisCO because stomata are restricted or closed during the day to conserve transpiration of water.Although C3 and C4 carbon fixing plants are found together in many climates, their production efficiencies are nevertheless optimum relative to their respective adaptations.2.2.3 - Energetics of C4 photosynthesisWilliam Halmeck's answer to How do C3 plants minimize photorespiration?
Plants produce carbon dioxide as a product of cellular respiration; but they release oxygen rather than carbon dioxide. How is this possible?
Hey BrittneeMost plants take in carbon dioxide during photosynthesis during the day and release carbon dioxide during respiration at night. This said, plants take up much more carbon dioxide during the process of photosynthesis than they give off in respiration.Image from www.buzzle.comSo. during their lifetimes, plants generally give off about half of the carbon dioxide (CO2), that they absorb, although this varies a great deal between different kinds of plants. Once they die, almost all of the carbon that they stored up in their bodies is released again into the atmosphere.As you may know, plants use the energy in sunlight to convert CO2 (from the air) and water (from the soil) into sugars. This is called photosynthesis. Plants use some of these sugars as food to stay alive, and some of them to build new stems and leaves so they can grow. When plants burn their sugars for food, CO2 is produced as a waste product, just like the CO2 that we exhale is a waste product from the food we burn for energy. This happens day and night, but since photosynthesis is powered by sunlight, plants absorb much more CO2 than they give off during the daytime. At night, when photosynthesis is not happening, they give off much more CO2 than they absorb. While they're alive, overall, about half of the CO2 that plants absorb is given off as waste.Photosynthesis: Useing energy from the sun to turn CO2 (carbon dioxide) and H2O (water) into sugar (C6H12O6) with oxygen (O2) left over.Cellular Respiration: Breaking down the sugar (C6H12O6) into CO2 (carbon dioxide) and H2O (water), but they need (O2) oxygen to do it.When you look at a tree, almost all of the body of the tree is made of sugars, which are made from carbon (from CO2) and hydrogen and oxygen (from water). When the tree dies, it rots as decomposers, like bacteria, fungi,and insects eat away at it. Those decomposers gradually release almost all of the tree's stored carbon back into the atmosphere as CO2. Only a very small portion of the carbon in the tree ends up staying in the soil or washing out to sea without changing back into CO2.Hope this helps.
Does photosynthesis and/or cell respiration happen at night time?
Photosynthesis and cell respiration are two separate biochemical processes that function in different ways.Photosynthesis can occur during the night, but requires light for the process to begin. The light independent portion of the cycle is called the dark reaction/ Calvin cycle and is a continuation of photosynthesis from light dependent stages. The dark reaction is not a separate cycle, but a continuation of photosynthesis and is independent of the presence of light.Cell respiration occurs continually during the plant life cycle because it produces the energy necessary for the plant to maintain itself through grow and development. If the plant didn’t have this energy available, it would die.
Does photosynthesis produce glucose and carbon dioxide?
Photosynthesis consists of multiple steps.The first step, the light-dependent reaction, uses sunlight to split water into oxygen and hydrogen. The oxygen is immediately released from the cell. The hydrogen passes through some molecular machinery which harvest the energy released to energize molecules of ATP and then joins to NADP to form NADPH.In the light-independent reaction, the ATP and NADPH are used to assemble carbon dioxide into three-carbon sugar phosphate molecules in a tremendously complex multi-step circular chain of chemical reactions.Glucose is not generated immediately, but the three-carbon molecules created in the light-independent reaction can be assembled into glucose elsewhere in the plant cell. So though it is a bit of an oversimplification, you could say that photosynthesis turns water and carbon dioxide into oxygen and glucose, even if it’s not that simple.
Descibe the purpose of photosynthesis.how does the process change during a full day?
Photosynthesis can happen in different ways in different species, some features are always the same. For example, the process always begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls. In plants, these proteins are held inside organelles called chloroplasts, while in bacteria they are embedded in the plasma membrane. Some of the light energy gathered by chlorophylls is stored in the form of adenosine triphosphate (ATP). The rest of the energy is used to remove electrons from a substance such as water. These electrons are then used in the reactions that turn carbon dioxide into organic compounds. In plants, algae and cyanobacteria this is done by a sequence of reactions called the Calvin cycle, but different sets of reactions are found in some bacteria, such as the reverse Krebs cycle in Chlorobium. Many photosynthetic organisms have adaptations that concentrate or store carbon dioxide. This helps reduce a wasteful process called photorespiration that can consume part of the sugar produced during photosynthesis. Overview of cycle between autotrophs and heterotrophs. Photosynthesis is the main means by which plants, algae and many bacteria produce organic compounds and oxygen from carbon dioxide and water (green arrow).Photosynthesis evolved early in the evolutionary history of life, when all forms of life on Earth were microorganisms and the atmosphere had much more carbon dioxide. The first photosynthetic organisms probably evolved about 3,500 million years ago, and used hydrogen or hydrogen sulfide as sources of electrons, rather than water. Cyanobacteria appeared later, around 3,000 million years ago, and changed the Earth forever when they began to oxygenate the atmosphere, beginning about 2,400 million years ago. This new atmosphere allowed the evolution of complex life such as protists. Eventually, no later than a billion years ago, one of these protists formed a symbiotic relationship with a cyanobacterium, producing the ancestor of the plants and algae. The chloroplasts in modern plants are the descendants of these ancient symbiotic cyanobacteria.
How many photons does it take to make one glucose molecule through photosynthesis?
Biochem two, here I come! Ok, photosynthesis of sugar occurs in two steps: electron transport and carbon fixation (known as the light and dark cycles). The Calvin cycle, as the carbon fixation is called, requires 9ATP to transfer dihydroxy acetone into the cytosol. Two processes are required to make glucose, so this is an overall cost of 18 ATP and 12 NADPH (the equivalent of 36 ATP). In the photosystem II and I (in order, confusing I know), 8 photons of light are use to produce approximately 3 ATP and 2 NADPH (the equivalent of 6 ATP in total).So I'd have to say that a regular C3 pathway plant would need 48 photons to complete a glucose molecule. You can do the math for more complicated molecules. Plants need the sunlight!