Exchanging substances: diffusion due to surface of leaves

• 1. CO2 diffuses into the air spaces within the leaf, then it diffuses into the cells where photosynthesis happens
• 2. underneath the leaf is an exchange surface - covered in little holes called stomata which the CO2 diffuses through
• 3. oxygen and water vapour diffuse out the stomata
• 4. size of stomata is controlled by guard cells. They close the stomata if the plant is losing water faster than it is being replaced by the roots. Without these guard cells the plant would soon be wilt
• 5. fattened shape of leaf increases area of this exchange surface so that it's more effective
• 6. walls of the cells inside the leaf form another exchange surface. The air spaces inside the leaf increases the area of theirs surface so there's more chance for carbon dioxide to get into the cells
• 7. the water vapour evaporates from the cells inside the leaf. Then it escapes by diffusion beacuse there's a lot of it inside the leaf and less of it in the air outside