Plants need specialised transport systems so water can travel up to the leaf cells from the roots, and sugar can pass from the leaves down to the roots.
Water in the xylem goes upwards.
Food in the phloem goes downwards.
Xylem - carries water and minerals.
pathway = upwards from the roots.
structure = non-living cells, no nucleus, end walls break down, side walls strengthened by lignin.
function = transport water and minerals and support.
Phloem - carries food in the form of sugar.
pathway = from the leaves to all parts of the plant.
structure = cells are living, have nucleus, 2 types of cell - sive tubes and companion cells.
function = transport sugar.
Stomata generally open in light and close in dark. When the stomata are open carbon dioxide diffuses into the leaf.