C4 carbon fixation is a common metabolic pathway found in land [[plant](C4 plants). They are competitively superior to plants possessing the more common C3 pathway under the conditions of drought, high temperatures and nitrogen limitation. It is called "C4" because the product, oxaloacetate, contains four carbon atoms. It occurs in the mesophyll of the leaf. The chemical equation is:
PEP carboxylase + PEP + CO2 → oxaloacetate
The product is usually converted to malate, a simple organic compound that gives up its CO2 to the Calvin cycle after being shipped off to bundle sheath cells surrounding a nearby vein. After losing the CO2, it becomes pyruvate, and can be phosphorylated into PEP at the cost of a phosphorus group and one ATP. It can then be reused in the above equation.
plants both utilize photosynthesis, which is a chemical process in which light energy from the sun is captured and mixed with water and carbon dioxide to make sugars which are used as food for chemical energy.
plants are called temperate or cool season plants and reduce (fix) CO directly by the enzyme ribulose bisphosphate carboxylase in the chloroplast.
plants are often called tropical or warm season plants and reduce carbon dioxide captured during photosynthesis to useable components by first converting carbon dioxide to oxaloacetate, a 4-carbon acid.
The bulk flow of water to the top of a plant is driven by solar energy since evaporation from leaves is responsible for transpiration pull.
A CAM plant is adapted to the hot dry conditions prevalent in desert climes.
These plants have a unique strategy in which their stomata remain closed most of the day when water loss is highest, but can maintain a healthy rate of photosynthesis even though CO is not supplied by gas exchange through these pores.
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