Which plant type fixes carbon at night to reduce water loss?

• A. C3 plants
• B. CAM plants
• C. C4 plants
• D. All plants

Answer: (B)

CAM plants fix carbon at night to reduce water loss because they open their stomata after dark when temperatures are cooler and humidity is higher, which minimizes transpiration. The carbon dioxide is fixed into organic acids (like malic acid) and stored in vacuoles overnight. During the day, the stomata stay closed to conserve water, and the stored acids release CO2 for the Calvin cycle using the energy from daylight. This nocturnal carbon fixation is a key adaptation for surviving in dry, hot environments. In contrast, C3 plants fix CO2 directly during the day with more water loss, and C4 plants separate carbon fixation spatially to reduce photorespiration but still transpire mainly in daylight.