Dictionary of Human Evolution and Biology

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C4 Photosynthetic Pathway

Set of reactions during diurnal photosynthesis in which a specific enzyme (PEPC) uses carbon atoms from CO2 to produce an initial four-carbon compound (C4) that is later refixed as a C3 compound; this requires two different chloroplasts. Plants that utilize this process are at lower risk of losing carbon through photorespiration. Less than 1% of the earth’s plant species can be characterized as C4 vegetation. The C4 pathway is thought to be a more recent adaptation than the older C3 photosynthetic pathway and CAM photosynthesis pathway, and a selective response to the relatively low atmospheric concentrations of CO2 that have prevailed during the Cenozoic epoch of the earth’s history.

See carbon isotope analysis.

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