9.7: C4 Pathway and CAM Overview. It is one of three known processes for carbon fixation These plants fix CO2 into a four carbon compound (C4) called oxaloacetate. This occurs in cells called mesophyll cells. Oxaloacetic add is the first product in c4 pathway. Plants that use the c4 pathway produce a 4-carbon sugar as the first stable molecule. C4 is the alternative pathway of Calvin cycle (C3 cycle) taking place during the dark phase of photosynthesis. The image below illustrates the pathway we just described: 1. Thus in C4 plants, C4 carbon fixation has a net added cost of 1 ATP for every CO2 delivered to rubisco; however, C4 plants are less likely to die of dehydration compared to C3 plants in dry conditions. These plants like hot temperatures. These plants are very efficient in hot, dry climates and make a lot of energy. ADVERTISEMENTS: In this article, we will discuss about the C4 – Dicarboxylic Acid Pathway (Hatch–Slack Pathway). In c3 pathway, ribulose biphosphate is the first acceptor of CO2. (a) The CAM pathway fixes CO{eq}_2 {/eq} onto the three-carbon molecule to make the four-carbon molecule at night, when it is cooler and stomata are open. Figure \(\PageIndex{1}\): The C4 Pathway The C4 pathway is designed to efficiently fix CO2 at low concentrations and plants that use this pathway are known as C4 plants. In the C4 cycle the first stable compound is 4 carbon compound, namely oxaloacetic acid. For considerable period of time the Calvin cycle as described earlier was thought to be the only photosynthetic reaction sequence operating in higher plants and algae. They have their stomata open for shorter periods during the day to stop the lose of off too much H2O because of the hot temperatures. 2. But in 1965 Kortschak, Hartt and Burr reported that 4-C containing dicarboxylic acids, […] The cycle begins with CO 2 from the atmosphere entering mesophyll cells where it is used to generate oxaloacetate—a four-carbon molecule—from phosphoenolpyruvate (PEP). C4 carbon fixation or the Hatch-Slack pathway is a photosynthetic process in some plants. It is the first step in extracting carbon from carbon dioxide to be able to use it in sugar and other biomolecules. In c3 pathway, Phosphoglyceric acid is the first product. ). It is a process of carbon dioxide fixation. Difference between C3 and C4 pathway. Overview of C4 Pathway Photosynthesis The Calvin cycle was believed to be the only photosynthetic reaction series operating in higher plants and algae for a significant amount of time. 3. In c4 pathway, phosphoenol pyruvate is the first acceptor of CO2, while ribulose biphosphate is the second acceptor. 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