Primary Production

Question 1

How does c4 photosynthesis work and how is it better than c3 plants?

Answer 1

So c4 photosynthesis involves mesophyll cells and bundle sheath cells. The mesophyll cell is where PEPC is and it is responsible for fixing C to make a 4C compound. Then the co2 is released in the bundle sheath cell where rubisco is and it enters the Calvin cycle. You have spatial separation of enzymes so they don’t compete for co2 and also it is good in hot environments as the pep enzyme can bring in co2 at a high enough level for rubisco to create sugars.

Question 2

Crassulacean acid metabolism involves what steps?

Answer 2

It happens in one cell and involves fixation of co2 Ito firm oxaloacetate by PEPC then it is changed to malate using mdh. Malate is actively transported into vacuole and then you get malic acid back to malate, then co2 release to enter Calvin cycle. The enzymes to not compete for co2 since they have diurnal regulation. So PEPC active at night when stomata open and rubisco during day when stomata closed. The reason why cam may not be better than c3 despite the increased water efficiency is due to energy needed to transport malate, temporal regulation of PEPC needs energy and also due to complex assimilation of c the cam plants have slower photosynthesis.

Question 3

Explain how c3 photosynthesis works

Answer 3

So you get the light dependent reaction in the thylakoid that converts light energy into the form of chemical energy so atp and nadph. Then the light independent step occurs in the stroma where you get co2 fixation by rubisco, then you get reduction using nadph and atp. Finally regeneration of co2 acceptor. Produces 3c compound.