Question

CAM plants keep stomata closed in daytime, thus reducing loss of water. They can do this because they

• A. fix CO2 into organic acids during the night.
• B. fix CO2 into sugars in the bundle-sheath cells.
• C. fix CO2 into pyruvate in the mesophyll cells.
• D. use the enzyme phosphofructokinase, which outcompetes rubisco for CO2.

Answer 1

The correct option is A

fix CO2 into organic acids during the night.

In CAM plants, the stomata in the leaves remain shut during the day to reduce transpiration through evaporation, but open at night to collect carbon dioxide (CO₂). The CO₂ is stored as the four-carbon acid malate in vacuoles at night. During daytime, the malate is transported to chloroplasts where it is converted back to CO₂, which is then used during photosynthesis. The pre-collected CO₂ is concentrated around the enzyme RuBisCO, thus increasing the photosynthetic efficiency.