Which of the following actions occurs in many plants when CO2 concentrations are high?
A. Calcium ions are transported faster through the phloem.
B. Guard cells lose turgor, and the stomata close.
C. CAM photosynthesis fixes CO2 at night.
D. Water evaporates at a higher rate than usual.
E. Oxygen is used by plants for photosynthesis.
Answer: B
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