6.4 gas exchange in the leaf of a plant

leaf structure

-epidermal tide covers plants and protects them

• palisade mesophyll contains chloroplasts for photosynthesis

• spongy mesophyll contain chloroplasts but mainly have air spaces between them for diffusion

• waxy cuticle prevents water loss

what is a dicotyledonous leaf?

a leaf of a dicot plant that has a midrib and branching veins

What is a xerophyte?

a plant that can live in dry conditions because of its additional adaptations

Adaptations of the leaf and its structure

• no living cell is far from the external air

• diffusion takes place as a gas which is quicker

• thin so there is a short diffusion pathway

• flat so there is a large sa:vol ratio

• lots of stomata and lots of air spaces

Adaptations for xerophytes (limiting water loss)

• controlled opening and closing of stomata stomata sunk in pits or grooves which trap moist air next to the leaf and reduce water potential gradient

• curled leaves with stomata inside them which traps moist air again reducing the gradient, and meaning that the stomata are protected from wind

• layer of hair in epidermis to trap moist air close to the stomata

• reduced number of stomata in given area

• thick and waxy cuticle smaller sa to volume ratio eg having leaves that are small and circular like pine needles