Illustration of leaf cell
The under side of the leaf is the exchange surface, this part of the leaf has
and pores called stomata which allow substances to pass through the cell
Water and oxygen diffuses out of the cell and carbon dioxide will diffuse into cell.
The stomata are controlled by guard cells which control when substance enter
and leave the cell.
The flattened shape of the leaf increases the area of exchange, which makes
it more efficient.
There are air spaces within the leaf which allow the substances to exchange.
The water is evaporate as soon as it leaves the cell which keeps the
concentration gradient high, this is best in hot dry windy conditions where
more water can be evaporated quickly.