Although 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 called that contain . In plants, these proteins are held inside called , while in bacteria they are embedded in the . Some of the light energy gathered by chlorophylls is stored in the form of (ATP). The rest of the energy is used to remove 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 , but different sets of reactions are found in some bacteria, such as the in . Many photosynthetic organisms have that concentrate or store carbon dioxide. This helps reduce a wasteful process called that can consume part of the sugar produced during photosynthesis.
Photosynthesis (from the [photo-], "light," and [synthesis], "putting together", "composition") is a process that converts into , especially , using the energy from sunlight. Photosynthesis occurs in , , and many species of , but not in . Photosynthetic organisms are called , since they can create their own food. In plants, algae and photosynthesis uses carbon dioxide and , releasing as a waste product. Photosynthesis is vital for . As well as maintaining the normal level of oxygen in the , nearly all life either depends on it directly as a source of energy, or indirectly as the ultimate source of the energy in their food (the exceptions are that live in rocks or around deep sea ). The amount of energy trapped by photosynthesis is immense, approximately 100 : which is about six times larger than the . As well as energy, photosynthesis is also the source of the carbon in all the organic compounds within organisms' bodies. In all, photosynthetic organisms convert around 100,000,000,000 of carbon into per year.
The incorporation of chloroplasts within the cells of Elysiachlorotica allow the slug to generate energy directly fromlight, as most plants do, through the process known as .This is significantly beneficial for Elysia chloroticabecause during time periods where algae is not readily available asa supply, the Elysiachlorotica can survive for months on the sugars producedthrough performed by their own . Keptwithin the slug's own cells, it has been found that thechloroplasts can survive and function for up to nine or even 10months.In one study Elysia chlorotica were deprived of algaingestion for a period of eight months. After the eight monthperiod, despite the fact that the Elysia chlorotica wereless green and more yellowish in colour, the majority of the within the slugs appeared tohave remained intact while also maintaining their finestructure.Although Elysia chlorotica are unable to synthesize theirown , the ability to maintain the acquired from in a functional state indicates that Elysiachlorotica must possess photosynthesis-supporting genes withinits own nuclear ; mostlikely acquired through .Since chloroplast alone encodesfor just 10% of the required for proper photosynthesis, scientists investigated theElysia chlorotica for potential genes that could supportchloroplast survival and photosynthesis. The researchers found avital algal gene, psbO (a encoding for a -stabilizingprotein within the complex)in the sea slug's DNA, identical to the algal version. Theyconcluded that the gene was likely to have been acquired through , asit was already present in the eggs and sex cells of Elysiachlorotica.
Photosynthetic organisms are , which means that they are able to food directly from carbon dioxide using energy from light. However, not all organisms that use light as a source of energy carry out photosynthesis, since use organic compounds, rather than carbon dioxide, as a source of carbon. In plants, algae and cyanobacteria, photosynthesis releases oxygen. This is called oxygenic photosynthesis. Although there are some differences between oxygenic photosynthesis in , and , the overall process is quite similar in these organisms. However, there are some types of bacteria that carry out , which consumes carbon dioxide but does not release oxygen.
Carbon dioxide is converted into sugars in a process called . Carbon fixation is a reaction, so photosynthesis needs to supply both a source of energy to drive this process, and also the electrons needed to convert carbon dioxide into , which is a . In general outline, photosynthesis is the opposite of , where glucose and other compounds are oxidized to produce carbon dioxide, water, and release chemical energy. However, the two processes take place through a different sequence of chemical reactions and in different cellular compartments.
began the research of the process in the mid-1600s when he carefully measured the of the soil used by a plant and the mass of the plant as it grew. After noticing that the soil mass changed very little, he hypothesized that the mass of the growing plant must come from the water, the only substance he added to the potted plant. His hypothesis was partially accurate—much of the gained mass also comes from carbon dioxide as well as water. However, this was a signaling point to the idea that the bulk of a plant's comes from the inputs of photosynthesis, not the soil itself.
chemically fix carbon dioxide in the cells of the by adding it to the three-carbon molecule , a reaction catalyzed by an enzyme called and which creates the four-carbon organic acid, . Oxaloacetic acid or synthesized by this process is then translocated to specialized cells where the enzyme, rubisco, and other Calvin cycle enzymes are located, and where CO2 released by of the four-carbon acids is then fixed by rubisco activity to the three-carbon sugar . The physical separation of rubisco from the oxygen-generating light reactions reduces photorespiration and increases CO2 fixation and thus photosynthetic capacity of the leaf. C4 plants can produce more sugar than C3 plants in conditions of high light and temperature. Many important crop plants are C4 plants including maize, sorghum, sugarcane, and millet. Plants lacking PEP-carboxylase are called because the primary carboxylation reaction, catalyzed by rubisco, produces the three-carbon sugar 3-phosphoglyceric acids directly in the Calvin-Benson Cycle.
and , along with , elucidated the path of carbon assimilation (the photosynthetic carbon reduction cycle) in plants. The carbon reduction cycle is known as the , which inappropriately ignores the contribution of Bassham and Benson. Many scientists refer to the cycle as the Calvin-Benson Cycle, Benson-Calvin, and some even call it the Calvin-Benson-Bassham (or CBB) Cycle.