Answer
ATP must be used to return the three-carbon molecule from the bundle sheath cell and prepare it to take up another molecule of carbon dioxide from its surroundings. Since the mesophyll cells constantly pump carbon dioxide into neighboring bundle-sheath cells in the form of malate, a high carbon dioxide to oxygen ratio is maintained around the catalyst rubisco.
Work Step by Step
ATP must be used to return the three-carbon molecule from the bundle sheath cell and prepare it to take up another molecule of carbon dioxide from its surroundings. Since the mesophyll cells constantly pump carbon dioxide into neighboring bundle-sheath cells in the form of malate, a high carbon dioxide to oxygen ratio is maintained around the catalyst rubisco.