chimichurri
C4 plants separate the initial carbon fixation stage and the rest of the Calvin cycle over space. In the mesophyll cells, a 4-carbon molecule called oxaloacetate is produced via the help of the enzyme PEP carboxylase. Oxaloacetate is then converted into another 4-carbon molecule called malate. Malate is then transported to the bundle-sheath cells and is broken down to release carbon dioxide, which can then enter the Calvin cycle in a similar manner to C3 photosynthesis light-independent processes. Therefore, C4 plants are more efficient than C3 plants in dry conditions because they can capture more CO2 in less time and the stomata can stay closed for longer to reduce water loss. PEP carboxylase also prevents photorespiration occurring as it has no affinity for binding with oxygen.
CAM plants separate the initial carbon fixation stage and the rest of the Calvin cycle over time. The stomata opens at night to bring in CO2. PEP carboxylase fixes the CO2 to form oxaloacetate, which is then converted into malate or another organic molecule. The molecule is then stored in the vacuoles until daytime. Once it is daytime, the stomata does not open (prevents water loss) but the plant can still photosynthesise by using the malate/organic molecule that has been transported out of the vacuole, which breaks down to release CO2. This CO2 then enter the Calvin cycle in a similar manner to C3 photosynthesis light-independent processes. Therefore, CAM plants are also more efficient than C3 plants in dry conditions because they can capture more CO2 in less time, and allow the stomata to open for effective exchange over night whilst ensuring that water is not lost during the day (due to increased temperatures during the day causing more water loss). PEP carboxylase also prevents photorespiration occurring as it has no affinity for binding with oxygen.
Why is water loss a problem? The stomata closes, meaning CO2 cannot enter and O2 cannot exit, causing photorespiration to increase. This is a problem for C3 plants who have no mechanisms to prevent this. C4 plants prevent this by capturing more CO2 in less time and therefore closing their stomata for longer (of course, stomata will still open to release O2, but since more CO2 is present anyway in comparison to O2, the rate of photorespiration will still decrease). CAM plants open their stomata at night to reduce water loss.
Not sure if this will be helpful because it's quite in depth. In summary, both C4 and CAM plants aim to prevent water loss by either separating carbon fixation and the rest of photosynthesis over space or time. This is to increase the amount of CO2 present, reduce water loss, and reduce the amount of O2 present (to therefore reduce photorespiration).
