Why does CAM photosynthesis need 5 ATP per CO₂ while C3 needs only 3?

[Suraj M]

i was told that the ATP required to form 1/6 Glucose from 1 CO₂ in C4 cycle is just 3 but 5 in CAM plants...
dont both need 5 CO₂
and also why 5 CO₂??
3 for C3 cycle ..fine
one for regeneration of pyuruvic acid to PEP..fine
what about the other 1 ?

 

[Suraj M]

There isn't a way I can elaborate more on this!