Transport Systems in Plants

  • Created by: cfear
  • Created on: 31-10-18 09:51
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  • Transport Systems in Plants
    • Substances that are transported in plants
      • Plants make glucose (a simple sugar) by photosynthesis in the leaves and other green parts.  This glucose is needed all over the plant.
      • Similarly, water and mineral ions move into the plant from the soil through the roots, but they are needed in every cell of the plant
      • Plants have two separate transport systems to move substances around the whole plant
    • Transport in phloem and xylem tissue
      • Phloem - moving food
        • The phloem tissue transports the sugars made by photosynthesis from the leaves to the rest of the plant. 
          • This includes transport to the growing areas of the stems and roots where the dissolved sugars are needed for making new plant cells
        • Food is also transported to the storage organs where it provides an energy store for the winter.
        • Phloem is a living tissue — the phloem cells are alive. The movement of dissolved sugars from the leaves to the rest of the plant is called translocation.
        • Greenfly and other aphids are plant pests. They push their sharp mouthparts right into the phloem and feed on the sugary fluid.
          • If too many of them attack a plant, they can kill it by taking all of its food.
      • Xylem — moving water and mineral ions
        • The xylem tissue is the other transport tissue in plants. It carries water and mineral ions from the soil around the plant to the stem and the leaves.  Mature xylem cells are dead.
        • In woody plants like trees, the xylem makes up the bulk of the wood and the phloem is found in a ring just underneath the bark.
        • This makes young trees particularly vulnerable to damage by animals — if a complete ring of bark is eaten, transport in the phloem stops and the tree will die.
    • Why is transport so important?
      • It is vital to move the food made by photosynthesis around the plant - all the cells need sugars for respiration as well as for providing materials for growth.
      • The movement of water and dissolved mineral ions from the roots is equally important — the mineral ions are needed for the production of proteins and other molecules within the cells.  
        • The plant needs water for photosynthesis, the process in which carbon dioxide and water combine to make glucose (plus oxygen).
      • The plant also needs water to hold itself upright. When a cell has plenty of water inside it, the vacuole presses the cytoplasm against the cell walls.
        • This pressure of the cytoplasm against the cell walls gives support for young plants and for the structure of the leaves. For young plants and soft stem plants (although not trees) this is the main method of support.

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