structure of vessels within plants

• What are the three main reasons why multicellular plants need transport systems?

  • To meet metabolic demands
  • Plants can be very large
  • Plants have a small SA:V ratio- cannot rely on diffusion alone
• What are dicotyledonous plants?

  • Plants producing seeds that contain two cotyledons
  • Cotyledons- act as food stores for developing embryo and form the first leaves when the seed germinates
• Where are the vascular bundles in the stem of a plant?

  Around the edge to provide strength and support. POXI- phloem on outside and xylem on inside

  
• Where are the vascular bundles in the root of a plant?

  In the middle, to help the plant withstand the tugging strains that result as the stems and leaves are blown in the wind- POXI

  
• Where are the vascular bundles in the leaves of a plant?

  The midrib- helps to support the structure if the leaf - POXI doesn't apply here

  
• What are the functions of the xylem?

  • Transport of water and mineral ions
  • Support
• Describe the structure of the xylem

  • Made up of dead cells
  • Xylem vessels are the main structures in the xylem
  • Xylem vessels are long and hollow, made by columns of cells fusing together end to end
  • xylem parenchyma- stores food and contains tannin deposits
  • Xylem cells are long
  • walls are lignified- lignin provides mechanical strength
  • unlignified bordered pits- so water can move out from the xylem to other cells
• How can lignin be arranged in the walls of xylem vessels?

  • Rings
  • Spirals
  • Solid tubes with unlignified areas called bordered pits- where water leaves the xylem and moves into the other cells of the plants
• What is translocation

  The movement or transport of assimilates around a plant from source to sink
• Why are sugars transported as sucrose in the phloem

  Because glucose is broken down easy by respiration
• What is the process by which sucrose molecules are loaded into the phloem?

  Phloem loading, happens in the apoplast pathway
• State what is meant by transpiration

  Loss of water vapour by evaporation through the stomata
• What is meant by the transpiration pull?

  Movement of water and mineral ions up the xylem from the roots
• What is the transpiration stream?

  Movement or pull of water through a plant to replace water lost by transpiration
• describe the structure of the phloem

  • sieve tube elements- transporting vessels of the phloem
  • cells join end to end to form a long hollow structure
  • in areas between the cells, the walls become perforated to form sieve plates, allowing the phloem's contents to flow through
  • companion cells- linked by many plasmodesmata, which links the cytoplasm of adjacent cells
  • companion cells maintain their nuclei and organelles as they are active cells, life support systems for phloem and provide energy for mass flow