Transport system in multicellular plants (A level Bio)

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Plants have two transport systems. These are called xylem and phloem. The xylem transports water up the plant and the phloem transports soluble organic substances up and down the plant. Oxygen and carbondioxide enter and leave the plant through diffusion. Water enters the plant at its roots because of the water potential gradient. Once it has entered the root it either travels to the xylem through the cell wall (the apoplast pathway) or through the cytoplasm and vacuole (the symplast pathway). Water is lost by transpiration. This is when water leaves the plant through tiny holes on the bottom of the leaf called stomata. When transpiration occurs more water enters the plant at the roots to replace it. You can measure rates of transpiration using a potometer. There are many different factors that effect the rate of transpiration, e.g. light intensity and wind speed. Moving onto phloem. There are sieve elements found in phloem tissue which actually transport the substances around the plant. The plant needs energy for them to do so. This energy is produced in photosynthesis. Transport of minerals in the phloem is known as Translocation.

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