transport in plants

• meristem : a layer of dividing cells, in stems and roots is called pericycle
• phloem : transports dissolved assimilates
• vascular tissue : consists of cells specialised for transporting fluids by mass flow
• xylem : transports water and minerals
• The vascular tissues

  • water and soluble mineral ions travel upwards in xylem tissue
  • assimilates, such as sugars, travel up or down in phloem tissues

  both xylem and phloem are highly specialised to carry out their transport function. But, unlike animals, there is no pump, and respiratory gases are not carried by these tissues
• Distribution of vascular tissues

  Dicotyledonous plants are those that have two seed leaves.

  • they also have a characteristic distribution of vascular tissue
  • the vascular tissue is distributed throughout the plant; the xylem and phloem are found together in vascular bundles
  • these bundles may also contain other types of tissues (collenchyma and sclerenchyma) that gives the bundle some strength and help support the plant
• Xylem and phloem in young root

  the vascular bundle is found at the centre of a young root (centre core of xylem is X-shaped in roots)

  • phloem is found in between the arms of the X-shaped xylem tissue

  →this arrangement provides strength to withstand pulling forces to which roots are exposed

  • around vascular bundle is a special sheath of cells called the endodermis

  →this has a key role in getting water into xylem vessels

  inside the the endodermis is a layer of meristem cells called the pericycle
• Xylem and phloem in stem

  The vascular bundles are found in the outer edge of the stem

  • in non- woody plants the bundles are separate and discrete
  • in woody plants, the bundles are separate in young stems, but become a continuous ring in older stems

  →this means there is a complete ring of vascular tissue just under the bark of a tree

  this arrangement provides strength and flexibility to withstand the bending forces to which stems and branched are exposed
• Xylem and phloem in stem 2

  • the xylem is found towards inside of each vascular bundle and the phloem towards the outside
  • in between xylem + phloem is a layer of cambium

  →layer of meristem cells that divide to produce new xylem + phloem