stomata

how stomata open

the stomata open when guard cells become turgid and the pore opens, because the outer cell wall is thin and inner cell wall is thick

how stomata close

guard cells become flaccid and the pore closes, because the outer cell wall is thin and the inner cell wall is thick

mechanism for stomatal opening

• potassiam ions are actively transported from epidermal cells to the guard cells

• stored starch (insoluble) in the guard cells is converted to malate (soluble) by enzymes in the cytoplasm

• water potential in guard cell becomes lowered, so water moves in via osmosis

• guard cells become turgid and curve apart, because outer cell walls are thinner than the inner cell walls

stomatal activity

• opens during day to allow carbon dioxide to diffuse into leaf for photosynthesis

• at the same time oxygen produced by respiration and water vapour may diffuse out