Photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds. Light energy is converted into chemical energy by the green pigment molecule, chlorophyll, and involves two sets of reactions, the light reaction, and the dark usloveescort.com chloroplast contains.
Photosynthesis is the source of most organic carbon on Earth, as well as the oxygen in the air. The overall chemical equation for oxygenic photosynthesis is:. Both are needed for carbon fixation reactions the reduction of inorganic carbon to make organic carbon molecules presented in the next page. An important by-product of the light reactions is the generation of oxygen gas.
In the chemical equation above, the oxygen atoms in water are bolded in red to show that these are the source of the oxygen atoms in oxygen gas. Oxygenic photosynthesis evolved to take electrons from water to make oxygen gas, and ultimately give the electrons to carbon dioxide to form organic reduced carbon molecules food — the exact reverse of aerobic respiration, which takes electrons from organic carbon molecules and ultimately gives them to oxygen gas to make water.
Overview of oxygenic photosynthesis by cyanobacteria and chloroplasts, from Wikipedia. There are two different general components of phothosynthesis: the light reactions and the Calvin cycle. The product of the Calvin cycle is fixed carbon, or sugar. Visible light is a slice of the electromagnetic EM spectrum, from about nm to a little over nm in wavelength.
Light has wave-particle duality, and a quantum of light energy is a photon. Therefore, photons of shorter wavelengths blue-violet have more energy than photons of longer wavelengths red. Biological pigments are molecules that preferentially absorb light at particular wavelengths. Organisms that capture light energy for conversion to chemical energy show evolutionary and phylogenetic differences in the pigments they use. Phototrophic organisms convert light energy into chemical energy in the form of ATP.
The use what is bentonite clay for hair light energy to make ATP is called photophosphorylation. Photophosphorylation is similar to oxidative phophorylation in that both use a proton gradient across a membrane to power similar ATP synthase enzyme complexes. The earliest phototrophs and photosynthetic organisms were prokaryotes with single photosystems that did not generate oxygen.
Two different types of photosystems evolved, that were combined in cyanobacteria. One of the two photosystems in cyanobacteria evolved the power to oxidize water molecules as a source of electrons, releasing O2. No Archaea thus found are truly photosynthetic. Halobacteriumwhich is an Archaeal species despite its name, how to fix a spoiled child bacteriorhodopsina purple-colored membrane protein, as a light-driven proton pump to generate a proton gradient across the plasma membrane and power chemiosmotic ATP synthesis.
Thus Halobacteria are phototrophic, but not photosynthetic, because they do not use light energy to fix carbon dioxide to organic carbon. Phototrophic organisms still depend on organic food molecules to build their own biomass. Photosystems are membrane complexes of proteins and chlorophyll molecules. The chlorophyll molecules absorb photons and funnel the energy to a reaction center chlorophyll, which becomes oxidized loses electrons.
All oxygenic photosynthesizers those that produce oxygen gas as a byproduct; cyanobacteria and chloroplasts have two different types of photosystems coupled together. In contrast, what is through hole soldering anoxygenic do not produce oxygen gas photosynthetic bacteria have just one type of photosystem.
The earliest phototrophs were probably anoxygenic. Photosystem II, upon absorbing light energy, transfers electrons to a membrane-localized electron transport chain, that pumps protons to generate an electrochemical gradient for chemiosmotic ATP synthesis. In cyanobacteria and chloroplasts, oxidized photosystem II splits oxidizes water molecules to regain electrons, and thereby generates oxygen gas.
Figure 2 from Blankenship Electron transport diagram indicating the types or RCs and electron transport pathways found in different groups of photosynthetic organisms.
The color coding is the same as for Figure 1 and highlights the electron acceptor portion of the RC. Figure courtesy of Martin Hohmann-Marriott. How did such a complicated system with two different photosystems evolve? Clues come from the observation that some phototrophic and photosynthetic bacteria have only one photosystem. And they have either a type I or a type II photosystem.
Bacteria that have only a type II photosystem PSIIsuch as the purple bacteria are phototropic: they use light energy to make ATP by photophosphorylation, but they do not use light energy to fix carbon dioxide. Photophosphorylation is very much like oxidative phosphorylation. Light energy oxidizes the reaction center chlorophyll and transfers electrons to an electron transport chain, which generates a proton gradient across the photosynthetic membrane. In other words, purple sulfur bacteria can fix carbon dioxide, but they cannot use their photosystem II to do it; their photosystem II can only be used to make ATP.
Bacteria with only a type I photosystem PSIsuch as green-sulfur bacteria, can be true photoautotrophs: they use light energy both to make ATP and to fix reduce carbon dioxide.
The oxidized reaction center chlorophyll must then be reduced by electrons from a chemical electron donor, such as hydrogen sulfide H2S. The oxidized reaction center chlorophyll pulls electrons from H2S down the photosynthetic electron transport chain, which generates a proton gradient to make ATP.
Thus green-sulfur bacteria use light energy to produce both ATP and reducing power; both are required for carbon fixation reduction of CO2 to carbohydrate. However, they are limited by the availability of a suitable electron donor such as H2S. Approximately 2. In the non-cyclic electron flow scheme often called the Z-schemelight-activated PSII gives its electrons to the electron transport chain to drive photophosphorylation.
Oxidized PSII regains electrons from oxidizing water molecules to generate oxygen gas. The ability of cyanobacteria to extract electrons from water gave them a huge evolutionary advantage over green-sulfur bacteria, which were restricted to locations that had hydrogen sulfide or other suitable electron donors. Photosynthesis in chloroplasts is essentially the same as photosynthesis in cyanobacteria.
The figure below illustrates non-cyclic electron flow during photosynthesis in chloroplasts. Non-cyclic electron flow on the chloroplast thylakoid membrane. The membranes of photosynthetic bacteria are highly convoluted via infolding of the plasma how to connect silverlight application to database, multiplying the surface area for light absorption and photosynthesis.
These infolded membranes are also present in chloroplasts, which evolved from endosymbiotic cyanobacteria. These infolded membranes are called thylakoidsand the lumen of the thylakoid corresponds to the extracellular or periplasmic space of the cyanobacteria. Structure of the chloroplast, from Wikipedia 1.
Blankenship R. Early evolution of photosynthesis. Plant What the new clubland cd called. Fischer, K. Inoue, M. Nakahara, C. Bauer, Molecular evidence for the early evolution of photosynthesis.
Science DOI: You must be logged in to post a comment. Biological Principles. Skip to content. Home What is life? Strong Inference Molecules and Metabolism Chemical context for biology: origin of life and chemical evolution Biological molecules Membranes and Transport Cells Energy and enzymes Respiration, chemiosmosis and oxidative phosphorylation Oxidative pathways: electrons from food to electron carriers Fermentation, mitochondria and regulation Why are plants green, and how did chlorophyll take over the world?
Why are plants green, and how did chlorophyll take over the world? Converting light energy into chemical energy Learning objectives Describe the properties of light as energy Distinguish phototrophism in some archaea versus photosynthesis in cyanobacteria and chloroplasts Distinguish the capabilities of photosystem I vs photosystem II Describe the innovation that led to oxygenic photosynthesis in cyanobacteria Compare photophosphorylation to oxidative phosphorylation Trace the flow of electrons in the light reactions of oxygenic photosynthesis Photosynthesis creates organic carbon Photosynthesis is the source of most organic carbon on Earth, as well as the oxygen in the air.
Absorption spectra of chlorophyll molecules. Photosystem I Structure, from Wikimedia. Cyanobacterial photosystem II, from Wikimedia. Categories eradication of Asian tiger mosquitos gut bacteria and stunted growth gut pathogens and autoimmune disease human milk oligosaccharides Legionella and mitochondria mannosides and uropathogenic E.
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Phototrophic organisms convert light energy into chemical energy in the form of ATP. The use of light energy to make ATP is called photophosphorylation. Photophosphorylation is similar to oxidative phophorylation in that both use a proton gradient across a membrane to power similar ATP synthase enzyme complexes. Photosynthetic organisms (photoautotrophs) use light energy to make both ATP . Photosynthesis is the process by which organisms that contain the pigment chlorophyll convert light energy into chemical energy which can be stored in the molecular bonds of organic molecules (e.g., sugars). Photosynthesis powers almost all trophic chains and food webs on the Earth. Oct 11, · Photosynthesis converts light energy into chemical energy. Only a few energy conversions are percent efficient. Batteries change electricity into chemical energy.
Photosynthesis , the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water , carbon dioxide , and minerals into oxygen and energy-rich organic compounds. Photosynthesis is critical for the existence of the vast majority of life on Earth.
It is the way in which virtually all energy in the biosphere becomes available to living things. Additionally, almost all the oxygen in the atmosphere is due to the process of photosynthesis. This means that the reactants, six carbon dioxide molecules and six water molecules, are converted by light energy captured by chlorophyll implied by the arrow into a sugar molecule and six oxygen molecules, the products.
The sugar is used by the organism, and the oxygen is released as a by-product. The ability to photosynthesize is found in both eukaryotic and prokaryotic organisms.
The most well-known examples are plants, as all but a very few parasitic or mycoheterotrophic species contain chlorophyll and produce their own food. Algae are the other dominant group of eukaryotic photosynthetic organisms. All algae, which include massive kelps and microscopic diatoms , are important primary producers. Cyanobacteria and certain sulfur bacteria are photosynthetic prokaryotes, in whom photosynthesis evolved.
No animals are thought to be independently capable of photosynthesis, though the emerald green sea slug can temporarily incorporate algae chloroplasts in its body for food production.
It would be impossible to overestimate the importance of photosynthesis in the maintenance of life on Earth. If photosynthesis ceased, there would soon be little food or other organic matter on Earth. The only organisms able to exist under such conditions would be the chemosynthetic bacteria , which can utilize the chemical energy of certain inorganic compounds and thus are not dependent on the conversion of light energy.
Energy produced by photosynthesis carried out by plants millions of years ago is responsible for the fossil fuels i. There, protected from oxidation , these organic remains were slowly converted to fossil fuels.
These fuels not only provide much of the energy used in factories, homes, and transportation but also serve as the raw material for plastics and other synthetic products. Unfortunately, modern civilization is using up in a few centuries the excess of photosynthetic production accumulated over millions of years.
Consequently, the carbon dioxide that has been removed from the air to make carbohydrates in photosynthesis over millions of years is being returned at an incredibly rapid rate. Requirements for food, materials, and energy in a world where human population is rapidly growing have created a need to increase both the amount of photosynthesis and the efficiency of converting photosynthetic output into products useful to people.
One response to those needs—the so-called Green Revolution , begun in the midth century—achieved enormous improvements in agricultural yield through the use of chemical fertilizers , pest and plant- disease control, plant breeding , and mechanized tilling, harvesting, and crop processing.
This effort limited severe famines to a few areas of the world despite rapid population growth , but it did not eliminate widespread malnutrition. Moreover, beginning in the early s, the rate at which yields of major crops increased began to decline. This was especially true for rice in Asia. Rising costs associated with sustaining high rates of agricultural production, which required ever-increasing inputs of fertilizers and pesticides and constant development of new plant varieties, also became problematic for farmers in many countries.
A second agricultural revolution , based on plant genetic engineering , was forecast to lead to increases in plant productivity and thereby partially alleviate malnutrition. However, such traits are inherently complex, and the process of making changes to crop plants through genetic engineering has turned out to be more complicated than anticipated. In the future such genetic engineering may result in improvements in the process of photosynthesis, but by the first decades of the 21st century, it had yet to demonstrate that it could dramatically increase crop yields.
Another intriguing area in the study of photosynthesis has been the discovery that certain animals are able to convert light energy into chemical energy. The emerald green sea slug Elysia chlorotica , for example, acquires genes and chloroplasts from Vaucheria litorea , an alga it consumes, giving it a limited ability to produce chlorophyll.
When enough chloroplasts are assimilated , the slug may forgo the ingestion of food. The study of photosynthesis began in with observations made by the English clergyman and scientist Joseph Priestley. Priestley had burned a candle in a closed container until the air within the container could no longer support combustion. He then placed a sprig of mint plant in the container and discovered that after several days the mint had produced some substance later recognized as oxygen that enabled the confined air to again support combustion.
He also demonstrated that this process required the presence of the green tissues of the plant. Gas-exchange experiments in showed that the gain in weight of a plant grown in a carefully weighed pot resulted from the uptake of carbon, which came entirely from absorbed carbon dioxide, and water taken up by plant roots; the balance is oxygen, released back to the atmosphere. Almost half a century passed before the concept of chemical energy had developed sufficiently to permit the discovery in that light energy from the sun is stored as chemical energy in products formed during photosynthesis.
In chemical terms, photosynthesis is a light-energized oxidation—reduction process. Oxidation refers to the removal of electrons from a molecule; reduction refers to the gain of electrons by a molecule. Most of the removed electrons and hydrogen ions ultimately are transferred to carbon dioxide CO 2 , which is reduced to organic products.
Other electrons and hydrogen ions are used to reduce nitrate and sulfate to amino and sulfhydryl groups in amino acids , which are the building blocks of proteins. In most green cells , carbohydrates —especially starch and the sugar sucrose —are the major direct organic products of photosynthesis.
The overall reaction in which carbohydrates—represented by the general formula CH 2 O —are formed during plant photosynthesis can be indicated by the following equation:. This equation is merely a summary statement, for the process of photosynthesis actually involves numerous reactions catalyzed by enzymes organic catalysts. During the first stage, the energy of light is absorbed and used to drive a series of electron transfers, resulting in the synthesis of ATP and the electron-donor-reduced nicotine adenine dinucleotide phosphate NADPH.
This assimilation of inorganic carbon into organic compounds is called carbon fixation. During the 20th century, comparisons between photosynthetic processes in green plants and in certain photosynthetic sulfur bacteria provided important information about the photosynthetic mechanism.
Sulfur bacteria use hydrogen sulfide H 2 S as a source of hydrogen atoms and produce sulfur instead of oxygen during photosynthesis. The overall reaction is. In the s Dutch biologist Cornelis van Niel recognized that the utilization of carbon dioxide to form organic compounds was similar in the two types of photosynthetic organisms.
Suggesting that differences existed in the light-dependent stage and in the nature of the compounds used as a source of hydrogen atoms, he proposed that hydrogen was transferred from hydrogen sulfide in bacteria or water in green plants to an unknown acceptor called A , which was reduced to H 2 A. During the dark reactions, which are similar in both bacteria and green plants, the reduced acceptor H 2 A reacted with carbon dioxide CO 2 to form carbohydrate CH 2 O and to oxidize the unknown acceptor to A.
This putative reaction can be represented as:. By chemists were using heavy isotopes to follow the reactions of photosynthesis. Water marked with an isotope of oxygen 18 O was used in early experiments. Plants that photosynthesized in the presence of water containing H 2 18 O produced oxygen gas containing 18 O; those that photosynthesized in the presence of normal water produced normal oxygen gas.
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External Websites. Articles from Britannica Encyclopedias for elementary and high school students. Coauthor of Photosynthesis of Carbon Compounds; See Article History. Understand the importance and role of chloroplasts, chlorophyll, grana, thylakoid membranes, and stroma in photosynthesis.
The location, importance, and mechanisms of photosynthesis. Study the roles of chloroplasts, chlorophyll, grana, thylakoid membranes, and stroma in photosynthesis.
Diagram of photosynthesis showing how water, light, and carbon dioxide are absorbed by a plant to produce oxygen, sugars, and more carbon dioxide. Top Questions. Read more below: General characteristics: Overall reaction of photosynthesis. Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now. Load Next Page.