Plants form and function (part 3)

Question 1

Water / mineral transportation

Answer 1

• Enters plants through roots
• Transported from cell to cell via three routes
  1. Apoplastic route: within cell wall or intercellular space (or through dead cells)
  2. Symplastic route: through cells via plasmodesmata
  3. Transmembrane route: through cells with repeated crossing of cell membranes
  *Both symplastic and transmembrane minerals are screened

Question 2

Water / mineral transportation (more details)

Answer 2

• water/minerals enter xylem sap
• Bulk flow of sap upwards is possible with a
  process called transpiration: loss of water vapour from leaves
• Cohesion-tension hypothesis:
  Transpiration provides the pull for the ascent of water
• Cohesion of water molecules transmits this pull along the entire length of the xylem
• Adhesion of water molecules to cell walls
  prevents water from moving back to roots and provides the force to pull water up the sides of the xylem

Question 3

Sugar transportation

Answer 3

• Translocation: transport of the products of
  photosynthesis (sugars)
• Sugars move from sites of production to sites of use/storage
• The pressure due to water/ sugar is relieved when sugar is unloaded and water is lost, water is recycled into xylem