Answer:
Carbon dioxide and oxygen cannot pass through the cuticle, but move in and out of leaves through openings called stomata (stoma = "hole"). Guard cells control the opening and closing of stomata. When stomata are open to allow gases to cross the leaf surface, the plant loses water vapor to the atmosphere. Photosynthesis also removes CO2 from the atmosphere and replaces it with O2. Respiration takes O2 from the atmosphere and replaces it with CO2.