Translocation

• What is the term used for the movement of sugars and other chemicals in plants?

  Translocation
• What does translocation involve in plants?

  It involves the transport of assimilates through the phloem tissue.
• What are assimilates in the context of translocation?

  Products produced by the incorporation of carbon into organic substances during photosynthesis.
• What is the role of a source in translocation?

  A source releases sucrose into the phloem.
• What is the role of a sink in translocation?

  A sink removes sucrose from the phloem.
• How is sucrose moved into the phloem from the source?

  Through an active process using ATP to pump H+ ions into surrounding tissue.
• What do companion cells use to facilitate the movement of sucrose into the phloem?

  ATP
• What happens to the water potential in the sieve tube when sucrose enters?

  The water potential in the tube decreases.
• What process causes more water to enter the sieve tube after sucrose enters?

  Osmosis
• What effect does the entry of sucrose have on hydrostatic pressure in the sieve tube?

  It increases the hydrostatic pressure in the sieve tube element.
• How is sucrose utilized by cells surrounding the phloem?

  In respiration or stored as starch.
• What happens to the sucrose concentration in cells surrounding the phloem?

  It reduces as sucrose is used or stored.
• How does sucrose move into surrounding cells from the phloem?

  Via diffusion or active transport.
• What happens to the water potential in the sieve tubes as sucrose moves into surrounding cells?

  The water potential becomes higher in the sieve tubes.
• What causes water to move into surrounding cells from the sieve tubes?

  Osmosis
• What effect does the movement of water have on hydrostatic pressure in the phloem at the sink?

  It reduces the hydrostatic pressure in the phloem at the sink.
• What causes the flow in the phloem?

  The difference in hydrostatic pressure at the source and sink.
• What is the term used for the movement of assimilates in the phloem flow?

  Mass flow
• Can mass flow occur in one direction only?

  No, it can flow up or down depending on where sugars are needed.
• What can affect the direction of assimilate flow in the phloem?

  The presence and absence of sugars, which affect hydrostatic pressure.
• What evidence supports the process of translocation in plants?

  • Labelled carbon experiments
  • Ringing experiments
  • Aphid studies
  • Mitochondria activity
  • Speed of diffusion
  • pH of companion cells
  • Concentration of sucrose at source and sink
• What is the function of sieve plates in the phloem?

  They facilitate the flow of sap through the phloem.
• What are the limitations of the translocation process?

  • Not all solutes move at the same rate
  • Sucrose moves to all parts of the plant at the same rate