- Carbon dioxide diffuses into the air spaces within the leaf, then into cells - photosunthesis occurs. Leaf's structure is adapted.
- Underneath of leaf is an exchange surface - covered in stomata where carbon dioxide diffuses in through. Water vapour (partly lost through leaf's surface) and oxygen also diffuse out through the stomata.
- Size of stomata controlled by guard cells: they close if the plant is losing water faster than it is being replaced by the roots. Without the guard cells, plant would soon wilt.
- Flattened shape of leaf increases exchange surface area - more effective.
- Walls of cells inside leaf form another exchange surface - air spaces increase surface area so there's more chance carbon dioxide can diffuse into cells.
Water vapour escapes by diffusion - alot more of it inside than outside. This is transpiration; goes quicker in hot/dry/windy conditions.
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