Cross Section of a Leaf

Stoma Open vs. Closed Open – w/light & when guard cells filled

with water

Closed – w/o light & when guard cells lacking water (dehydrated)

Why is it important to have stomata open?

Closed vs. Open

Stomata Open vs. Closed Water No Water

Light Dark

How many stomata?

High light: more stomataLow light: less stomata (less photosynthesis)

Dicots (Webbed veins) more stomata lower leafMonocots (Parallel veins) same amount both sidesWater plants: none on bottom, always openDesert: limited stomata, open at night (adaptation)

Why is it important to have stomata open? GAS EXCHANGE for photosynthesis!

Capillarity Action/Transpiration Cohesion &adhesion

draw water - capillary action.

Water travels from roots, up stem & throughout leaves via xylem

Water enters the guard cells (Ψ)

Water evaporates to atmosphere (transpiration)

How Does Osmosis determine if the Stomata are open or

closed?

Osmosis due to hypertonic and hypotonic environments!

Guard Cells/Stomata