how to explain c4 cycle
Answers
thank you for asking this question.
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C4 cycle occurs in plants which have modified themselves in a way that photorespiration does not occur. As RuBisCO tends to act as oxygenase when the temperature goes up or oxygen is in high level.
Photorespiration is a wasteful process as the ATP and NADPH formed in the light reaction are utilized.
Moreover, glucose isn't formed and CO2 is released out.
the adaptations include:
- kranz anatomy.
- dimorphic chloroplasts are found.
the chloroplasts can be granal ( mesophyll where light reactions take place. ) or agranal ( bundle sheath cells where dark reactions take place. )
the dark reactions involve the functioning of RuBisCO. In the bundle sheath cells the temperature is low which is the reason why photorespiration does not occur as the enzyme can't act as oxygenase in lower temperature.
calvin's cycle is not a light dependent process.
this pathway is also known as hatch and sla.ck cycle.
it is seen in monocots such as sugarcane, maize etc.
now i will explain what actually happens in the calvin cycle of C4 plants.
first things first, the CO2 has got to enter the plant.
it enters the mesophyll cells first where water is present so, the CO2 decides to get converted into HCO3-
it happens this way-
H2O + CO2 under the action of enzyme called carbonic anhydrase forms H2CO3 which splits up into H+ and HCO3- ions.
the HCO3- ion is accepted by PEP ( phosphoenol pyruvate ( 3c compound )) and forms a 4C compound called OOA oxaloacetic acid.
which is the reason why the cycle is called C4 cycle.
as OOA is first stable compound.
this stable compound is formed by the help of PEPcarboxylase.
the OOA can change into malic acid or aspartic acid.
they would diffuse from mesophyll into the bundle sheath cell.
this 4C compound gives 1 molecule of CO2 and a 3C compound called pyruvic acid.
this pyruvic acid would diffuse back into mesophyll cell.
and it would undergo phosphorylation where ATP is converted to AMP and formation of PEP ( now has 3 phosphate ) takes place.
talking about the bundle sheath cell in which 4C compound was splitted into CO2 and pyruvic acid.
the CO2 now released is taken up by RUBP and the enzyme req. is RuBisCO.
the enzyme will now act as carboxylase and not oxygenase because the temp. is low and CO2 concentration is more.
now, the whole C3 cycle takes place to produce glucose.
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god bless..!!