Photorespiration occurs in all plants using conventional
photosynthesis - called C3 photosynthesis because the first
products detected after RuBisCO fixes CO2 are 3-carbon
molecules. Some plants, however, escape the problem. Instead
of using RuBisCO to capture atmospheric CO2, these plants use
an enzyme that doesn't bind oxygen. The enzyme fixes CO2 in a
reaction that transforms a 3-carbon molecule into a 4-carbon
molecule - hence the name, C4 photosynthesis.
C4 plants haven't abandoned RuBisCO. C4 photosynthesis is
effectively the normal, C3 version of photosynthesis, but with
the addition of a CO2 pump. The pump operates across two
types of cell. First, mesophyll cells in the leaf capture CO2 to
produce 4-carbon molecules. These are then exported to
neighbouring bundle sheath cells, which strip CO2 from the 4-
carbon molecules and feed it to RuBisCO. The process converts
the 4-carbon molecules to 3-carbon molecules, which are
recycled back to mesophyll cells to help capture more CO2.
Photorespiration occurs in all plants using conventionalphotosynthesis - called C3 photosynthesis because the firstproducts detected after RuBisCO fixes CO2 are 3-carbonmolecules. Some plants, however, escape the problem. Insteadof using RuBisCO to capture atmospheric CO2, these plants usean enzyme that doesn't bind oxygen. The enzyme fixes CO2 in areaction that transforms a 3-carbon molecule into a 4-carbonmolecule - hence the name, C4 photosynthesis.C4 plants haven't abandoned RuBisCO. C4 photosynthesis iseffectively the normal, C3 version of photosynthesis, but withthe addition of a CO2 pump. The pump operates across twotypes of cell. First, mesophyll cells in the leaf capture CO2 toproduce 4-carbon molecules. These are then exported toneighbouring bundle sheath cells, which strip CO2 from the 4-carbon molecules and feed it to RuBisCO. The process convertsthe 4-carbon molecules to 3-carbon molecules, which arerecycled back to mesophyll cells to help capture more CO2.
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