When do desert plants typically take up carbon dioxide?
I. During the day
II. During the night
Show answer & explanation
Correct answer: B
Explanation
Xerophytes, such as cacti, use a special type of adaptation to survive in desert conditions. This is called the CAM (Crassulacean Acid Metabolism) pathway.
Deserts experience very high daytime temperatures. If these plants opened their stomata during the day to take in carbon dioxide (CO2), they would lose a lot of water through transpiration.
To avoid this:
During the night: These plants open their stomata at night when temperatures are lower. They take in CO2 at night and store it as an intermediate product (malic acid).
During the day: The stomata remain closed during the day to conserve water. The CO2 stored at night is used to complete photosynthesis during the day in the presence of sunlight.