AP BIOLOGY

Detailed explanation-1: -Cacti store the carbon dioxide they take in during the night in their cells in the form a chemical called malic acid.

Detailed explanation-2: -In CAM plants there is temporal separation between initial carbon dioxide fixation and Calvin cycle. In these plants, during night time the stomata are open and atmospheric carbon dioxide is fixed into organic acids like malic acid. The organic acids are stored in cell vacuoles during night time.

Detailed explanation-3: -CAM plants close their stomata during the day and take up CO2 at night, when the air temperature is lower.

Detailed explanation-4: -CO2 is taken up at night-time and stored in the vacuole as malic acid, which is decarboxylated in the light behind closed stomata and CO2 is released for fixation by rubisco in the chloroplast. The closed stomata through the day help CAM plants to maintain water.