vascular bundle (not mock)

• why do plants need transport systems?

  multicellular organisms = large size

  high metabolism = high metabolic demands --> can't rely on direct diffusion alone (too slow)

  small surface area : volume ratio
• plants that have specialised transport systems are known as vascular plants
• xylem tissue transports water and mineral ions in solution up the plant from the roots to the leaves --> passive process (osmosis) - transpiration
• phloem tissue mainly transports sugars (sucrose) and amino acids in solution both up and down the plant --> active process - translocation
• vascular tissue is made up of xylem and phloem tissue

  function: transport and structural support
• vascular bundle in roots:

  • makes a 'drill' like structure
  • the xylem is in the centre (it's the strongest) surrounded by the phloem to provide support for the root as it pushes through the soil
• vascular bundle in the leaf:

  • xylem and phloem make up a network of veins which support the thin leaves
  • xylem is on top of the phloem

  
• vascular bundle in stem:

  • xylem and phloem are near the outside
  • xylem is located on the inside in non-wooded plants
  • provides additional support to the stem and reduces bending
  • the cambium layer in the middle contains meristem cells