Describe CAM photosynthesis and its adaptation.

• A. Crassulacean acid metabolism; plants fix CO2 at night into malate (via oxaloacetate), store in vacuoles; during day CO2 is released for the Calvin cycle with stomata closed to conserve water.
• B. C4 photosynthesis using PEP carboxylase in mesophyll; stomata always open.
• C. It's the uptake of CO2 via roots; no stomata involvement.
• D. It involves chloroplasts in roots performing photosynthesis.

Answer: (A)

CAM photosynthesis is an adaptation that lets plants fix carbon dioxide at night and keep stomata closed during the hot day to save water. At night, the stomata open, and CO2 is fixed by the enzyme PEP carboxylase into oxaloacetate, which is quickly converted to malate and stored in vacuoles as malic acid. When daylight arrives, the stomata stay closed to reduce water loss, malate is decarboxylated to release CO2 inside the leaf, and this CO2 then enters the Calvin cycle with the energy from the light reactions. This temporal separation—CO2 uptake at night and CO2 release for the Calvin cycle during the day—gives CAM plants high water-use efficiency, a useful trait in arid environments. CAM is characteristic of many succulents, like cacti and pineapples. In contrast, other strategies differ: C4 uses a spatial separation with different cell types and can use stomata more flexibly; roots don’t perform photosynthesis, and CO2 uptake via roots isn’t how photosynthesis operates.