CAM Flashcards
What does CAM stand for?
Crassulacean Acid Metabolism
Where is the CAM pathway seen?
Mostly in desert xerophytes
Why do CAM plants tend to be slow growing?
CAM is less efficient as carbon fixation is temporally separated. CAM is less efficient than constant photosynthesis.
Why is CAM necessary for desert plants but not for tropical plants?
CAM increases water resistance - desert plants experience more water stress than tropical plants as they live in arid conditions.
What is the effect of closing the stomata during the day?
Less water loss, but also stops gas exchange - there is no carbon dioxide entering.
When is carbon dioxide fixed during CAM metabolism?
Fixed overnight, ready for use during the day.
How is fixed carbon dioxide stored overnight in CAM metabolism and where is it stored?
Stored as malic acid - in vacuoles.
Why is there a circadian pattern of pH change during CAM metabolism?
Leaves are more acidic at night due to storage of malic acid. pH starts to rise throughout the day as malate is broken down.
How is carbon dioxide fixed during CAM metabolism?
Using the C4 pathway
Describe what happens during the day.
Stomata close. Malic enzyme stored in vacuoles overnight is released as malate. This is broken down into pyruvate and carbon dioxide. Carbon dioxide is fed into the Calvin cycle.
Describe what happens at night.
Stomata open, allowing carbon dioxide uptake. PEP is carboxylated to oxaloacetate, using carbon dioxide. Oxaloacetate is then reduced to give malate, using NADH. Malate is stored as malic acid in vacuoles.
What is the role of NADP malic enzyme?
Breaks malate down to give pyruvate and carbon dioxide during the day.
What happens to the pyruvate released by NADP malic enzyme?
Forms triose sugars which form starch stores in the chloroplasts.
What happens to the carbon dioxide released by NADP malic enzyme?
It moves from the cytoplasm to the chloroplasts, where it is fed into the Calvin cycle.
How is PEP generated at night?
Starch stores are broken down to give triose sugars which are then phosphorylated to give PEP.
