How does the leaf get carbon dioxide for photosynthesis?
Carbon dioxide enter the leaf through stomata from the atmosphere.
Plants need carbon dioxide for photosynthesis. Carbon dioxide is converted into glucose during dark reaction of photosynthesis.
Plants consume oxygen during cellular respiration just like all living organisms and carbon dioxide is released.
During day time when photosynthesis is occuring, carbon dioxide produced in respiration is not released into the atmosphere but is used in photosynthesis.
Carbon dioxide produced in respiration does not meet the complete requirement of plants for photosynthesis. So more carbon dioxide enters the leaf through stomata, which are meant for gaseous exchange and transpiration.