this is a slightly old thread, but there is a good khan academy page that explains C4 and CAM transpiration.
here is the link:
C3, C4, and CAM plants (article) |
Khan Academy
all you need to know is that the Calvin Cycle is the part of photosynthesis that actually produces sugar and does not require light to function (although most plants, ie C3 and C4 plants, do the Calvin cycle during the day anyway). The Calvin cycle uses an enzyme called rubisco, which binds to CO2 and incorporates it into sugars. The issue is that it can also bind with O2, and when the enzyme incorporates O2 into sugar, it creates the wrong type of molecule and it takes the plant lots of energy to undo that, which is wasteful. C4 and CAM prevent that.
the general idea is that C4 and CAM make CO2 uptake more efficient without opening the stomata (pores on the bottom of leaves that facilitate uptake/release of water, CO2, O2, etc) for too long, which would cause the plant to lose too much water.
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