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What is the definition of a C4 pathway?

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The C4 pathway is a method plants use to convert atmospheric carbon dioxide into a chemical compound containing four carbons. About.com explains that plans that utilize this pathway usually originate in subtropical areas. Examples include maize, sugarcane, sorghum, millet and papyrus. These plants commonly grow at latitudes below 45 degrees, in the tropics.

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While photosynthesis normally takes place in the leaves of plants, in those plants using the C4 pathway, it takes place in a special leaf structure, the Kranz anatomy, which includes vascular bundles surrounded by sheath cells. Once the fixation of carbon dioxide completes, transforming it into the four-carbon compound through tehmesophyll cells, the plant transports it to the sheath cells where ribosco, the enzyme necessary for photosynthesis, is stored. This process prevents exposing the enzyme to oxygen and conserves energy for the plant.

Reference.com says that C4 photosynthesis gives plants an advantage over those using the classic C3 type of photosynthesis in drought conditions as well as in locations where carbon dioxide and nitrogen are limited. In C3 plants, as much as 97 percent of the water is lost due to transpiration. C4 plants make up approximately 5 percent of the world's biomass yet fix 30 percent of terrestrial carbon.

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