Biology 1 Diffusion
All plants require carbon dioxide and water for photosynthesis. The carbon dioxide is obtained via diffusion through the leaves. The flattened shape of the leaves increases the surface area for diffusion to take place across. Leaves are usually flat, too, so that the distance between the air and the photosynthesising cells is as short as possible. A problem is that water is always being lost by evaporation. So allowing carbon dioxide in will also lose water vapour. However, the plant does not need carbon dioxide all the time, because at night there is no sunlight – so photosynthesis cannot take place. So they have openings known as stomata which can open and close at specific times to allow carbon dioxide in and out. Another adaptation is that they have a waxy cuticle covering them, which is both gas-proof and waterproof. Roots have been adapted for uptake of water and mineral ions. Water is vital for shaping cells and for photosynthesis. Minerals are needed to make proteins and other chemicals. The roots themselves are thin and have a large surface area. The root hair cells have also adapted to increase surface area and increase efficiency of water uptake. The cell membranes of root hair cells have microvilli which further increase surface area for diffusion and osmosis. The distance between here and the xylem (transport tissue for the water) is minimal, also.