Translocation of sucrose

• What are organic substances moved around in plants?

  Sugars like glucose
• What is the key function of leaves in plants?

  Photosynthesis
• What is the basic word equation for photosynthesis?

  Carbon dioxide + water → glucose + oxygen
• Why are glucose and other sugars considered organic substances?

  They contain carbon
• What is the role of phloem in plants?

  Transporting organic substances
• What are the two key cells in phloem tissue?

  Sieve tube elements and companion cells
• What is a feature of sieve tube element cells?

  They have perforated end walls
• Why do sieve tube elements lack a nucleus?

  To maximize flow of sugar solution
• What is required for active transport in translocation?

  ATP from companion cells
• What is the mass flow hypothesis related to?

  Transport from source to sink
• What is the source in the mass flow hypothesis?

  Leaves during photosynthesis
• What is the sink in the mass flow hypothesis?

  Respiring cells
• How does osmosis affect the source cell during translocation?

  Water moves into the source cell
• What happens to hydrostatic pressure in the source cell?

  It increases due to water influx
• How does sucrose move from the companion cell to the sieve tube elements?

  By co-transport with hydrogen ions
• What effect does sucrose transport have on water potential?

  It lowers the water potential in phloem
• What happens to water in the sink cell during respiration?

  It moves out by osmosis
• What is the result of sucrose leaving the sieve tube elements?

  Lower hydrostatic pressure in phloem
• What is the purpose of tracer experiments?

  To track the movement of sugars
• How does radioactive carbon help in tracing sugars?

  It labels sugars for detection
• What happens in ringing experiments?

  Phloem is removed to observe swelling
• What is the conclusion from ringing experiments?

  Phloem transports sugars in plants
• What is translocation in plants?

  • Mass transport of organic substances
  • Primarily sucrose and glucose
  • From source (leaves) to sink (respiring cells)
  • Driven by hydrostatic pressure changes
• What are the steps involved in translocation?

  1. Sucrose produced in leaves
  2. Sucrose enters companion cells by facilitated diffusion
  3. Active transport of hydrogen ions creates a gradient
  4. Co-transport of sucrose into sieve tube elements
  5. Water enters sieve tubes by osmosis
  6. High hydrostatic pressure pushes solution to sink
  7. Sucrose actively transported into sink cells
  8. Water moves out of sieve tubes by osmosis
• What are the methods to investigate translocation?

  • Tracer experiments using radioactive carbon
  • Ringing experiments to observe swelling
  • Testing liquid for sugar presence