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Gas Exchange in Plants Photosynthesis and Respiration Photosynthesis, green plants need a supply of carbon dioxide and a means of disposing of oxygen In order to carry on cellular respiration, plant cells need oxygen and a means of disposing of carbon dioxide (jus...

Gas Exchange in Plants Photosynthesis and Respiration Photosynthesis, green plants need a supply of carbon dioxide and a means of disposing of oxygen In order to carry on cellular respiration, plant cells need oxygen and a means of disposing of carbon dioxide (just as animal cells do). Photosynthesis: Carbon dioxide + Water = oxygen + energy Respiration: glucose + oxygen= carbon dioxide + water Photosynthesis and Respiration Plants have no specialised organs for gas exchange Gas exchange takes place in the leaf, stem and root Preventing Water Loss Plants have adaptations to promote gas exchange at the same time as preventing water loss. - Water proof covering; cuticle and bark. - Under surface of leaves with gaps that allow gas exchange; stomata and lenticels The Leaf Gas exchange takes place in the leaf The plant consist of many leaves with large surface area for gas exchange Leaf consist of an epidermal layer of clear cells covered in a waxy cuticle, which prevents water loss Stomata are pores in the cuticles for gas exchange Beneath the epidermal layer are palisade cells which are packed with chlorophyll Leaf Continued Plants green color (chlorophyll) They are close to the surface to absorb light they use for photosynthesis The next layer is the spongy mesophyll below this is another layer of epidermal cells Stomata There are lots of them on any plant surface The exchange of oxygen and carbon dioxide in the leaf (as well as the loss of water vapor in transpiration) occurs through pores called stomata (singular = stoma) When they need CO2 for photosynthesis, the guard cells around each stoma swell with water and pull back, opening the passageway. Stomata Continued The concentration of CO2 is higher outside of the leaf than inside, it diffuses into the leaf along a concentration gradient In order to conserve water, the guard cells are able to close around the stoma, preventing water loss Stomata are found underneath the leaf to prevent water evaporation from direct sunlight Grasses and algae have stomata on both sides Guard Cells Guard cells open and close in response to a variety of internal and external stimuli Light Low carbon dioxide levels An internal clock Water deficiency High temperatures Gas Exchange in Stems Lenticels are pores in the woody stems of plants Gases needed for respiration by the cells of the stem are exchanged by diffusion