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