B3 -Gas and solute exchange

Substances move by diffusion, osmosis and active transport
Diffusion = particles move from an area of high concentration to an area of low concentration. Eg: a smell in a room.
1. Dissolved particles can diffuse in and out of smells through cell membranes
Gases/dissolved substances have to move through exchange surfaces. They allow enough of the necessary substance to pass through
1. They are adapted to maximise effectiveness, they are thin so substances have a short distance to diffuse, a large surface area to lots of substances can diffuse at once, lots of blood vessels to get stuff into/out the blood quickly,ventilated so air can move in and out
Co2 diffuses into air spaces within the leaf, then it diffuses into the cells where photosynthesis happens. Leafs are structured so this happens easily.
1. The underneath of the leaf is an exchange surface, covered in holes called stomata where the co2 diffuses through. O2 and water vapour diffuse out of it
  1. The size of the stomata is controlled by guard cells. They close it the plant is losing water quicker than being replaced. Without it the plant would wilt
The flattened shape of the leaf increases the area of the exchange surface so it's more effective
1. The walls of the cells inside the cell form another exchange surface. The air spaces inside increase the area of the surface so there's more chance for CO2 to get into cells

Resource summary

	Created by Lily O'Brien over 7 years ago