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It forms a protective covering on the leaf vein and consists of one or more cell layers, usually parenchyma. Loosely-arranged mesophyll cells lie between the bundle sheath and the leaf surface. The Calvin cycle is confined to the chloroplasts of these bundle sheath cells in C 4 plants. C 2 plants also use a variation of this structure. [1]
D: Bundle sheath cell E: Stoma F: Vascular tissue 1. CO 2 is fixed to produce a four-carbon molecule (malate or aspartate). 2. The molecule exits the cell and enters the bundle sheath cells. 3. It is then broken down into CO 2 and pyruvate. CO 2 enters the Calvin cycle to produce carbohydrates. 4.
In the C4 pathway, a layer of mesophyll cells encircles bundle sheath cells that have large chloroplasts necessary for the Calvin cycle. A: Mesophyll Cell B: Chloroplast C: Vascular Tissue D: Bundle Sheath Cell E: Stroma F: Vascular Tissue: provides continuous source of water 1) Carbon is fixed to produce oxaloacetate by PEP carboxylase.
During C 4 photosynthesis, an evolved pathway to increase localized CO 2 concentrations under the threat of enhanced photorespiration, CO 2 is captured within mesophyll cells, fixed as oxaloacetate, converted into malate and released internally within bundle sheath cells to directly feed RuBisCO activity. [9]
C 4 plants, in contrast, concentrate CO 2 spatially, with a RuBisCO reaction centre in a "bundle sheath cell" being inundated with CO 2. Due to the inactivity required by the CAM mechanism, C 4 carbon fixation has a greater efficiency in terms of PGA synthesis.
[2] [3] The Casparian strip is impervious to water so can control the transportation of water and inorganic salts between the cortex and the vascular bundle, preventing water and inorganic salts from being transported to the stele through the apoplast, so that it must enter the cell membrane and move to the stele through the symplastic pathway ...
In PEPCK-type C 4 plants the oxaloacetate is then converted to aspartate, which travels to the bundle sheath. In the bundle sheath cells, aspartate is converted back to oxaloacetate. PEPCK decarboxylates the bundle sheath oxaloacetate, releasing carbon dioxide, which is then fixed by the enzyme Rubisco.
Perimysium is a sheath of dense irregular connective tissue that groups muscle fibers into bundles (anywhere between 10 and 100 or more) or fascicles. Studies of muscle physiology suggest that the perimysium plays a role in transmitting lateral contractile movements .