The apoplastic route is blocked by the casparian strip. The symplastic route involves special openings between adjacent cell walls called plasmodesmata . Paths that solutions can take through plant cells Symplastic vs Apoplastic paths Transpiration and photosynthesis - a compromise An actively photosynthesizing plant has an insatiable need for water. This is the purpose of the spongy mesophyll which is honeycombed with air sacs. The spongy mesophyll has 10 to 30 times more surface area than the corresponding external surface of a leaf.
Photosynthesis is limited by available water which can be swiftly depleted by transpiration.
It has been estimated that for every gram of CO 2 fixed by the Calvin cycle, anywhere from 300 to 600 grams of water escape through transpiration. The humidity of rainforests is due in large part to this vast cycling of water from root to leaf to atmosphere and back to the soil. A stoma is a physical gap between two special epidermal cells called guard cells. If the plant experiences water deprivation it will wilt. To compensate the guard cells become flaccid and the stoma is closed.