Biology- Plants

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Transport Systems- Phloem

  • Phloem tubes are made of columns of living cells with perforated end-plates to allow stuff to flow through.
  • Phloem tubes transport food substances (mainly sugars) both up and down the stem to growing and storage tissues.
  • This movement of food substances is known as translocation.
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Transport Systems- Xylem

  • Xylem vessels are made of dead cells joined end to end with no end walls between them and a lumen (hole) down the middle.
  • The thick side walls are made of cellulose: strong and stiff which gives the plant support.
  • Xylem vessels carry water and minerals from the roots up the shoot to the leaves in the transpiration stream.
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Transport Systems- Water flow through plants

  • The cells on plant roots grow into long hairs which stick out into the soil.
  • This gives the plant a big surface area for absorbing water from the soil.
  • There's usually a higher concentration of water in the soil than there is inside the plant so the water is drawn into the root hair cell by osmosis.


  • The loss of water from the plant.
  • Transpiration is caused by evaporation and diffusion of water vapour from inside the leaves.
  • This creates a slight shortage of water in the leaf so more water is drawn up from the rest of the plant through the xylem vessels.
  • This in turn means more water is drawn up from the roots so there's a constant transpiration stream of water through the plant. The constant stream helps to keep the plant cool and provides the plant with a constant supply of water for photosynthesis. 
  • Minerals needed by the plant can be bought in from the soil along with the water.
  • The water creates turgor pressure in the plant cells, this helps support the plant and stops it wilting.
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