Occurs in the leaves of plants.
LEAVES ARE ADDAPTED FOR EFFICIENCY:
Contains chlorophyll (which absorbs light) in millions of chloroplasts.
Is broad and flat to provide a huge surface area to absorb sunlight.
Is thin so that the gases (Carbon dioxide & Oxygen) only have a short distance to travel to and from the cells.
Has stomata on the underside of the leaf to prevent waterloss.
Carbon dioxide difuses in through the stomata.
Oxygen difuses out through the stomata.
Water is absorbed through the roots.
IN A TYPICAL LEAF:
Upper Epidermis --> Transparent --> To allow sunlight through to the layer below
Palisade Cells --> At the top of the leaf --> Are packed with chloroplasts so they can absorb the maximum amount of light
Spongy Mesophyll --> Contains Air Spaces --> To allow the optimum exchange of gases