15. CAM plants must close their stomata during the day and open them only at night because:

If the stoma are open during the day, the CAM plant will transpire too much water and it will wilt or photosynthesis will slow down markedly. It opens the stoma only at night to let oxygen diffuse out, to let carbon dioxide diffuse in, and then fix carbon dioxide into a 4-carbon carrier molecule that can give up its carbon dioxide during the day when needed.

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