Translocation

• What is responsible for pulling water up the xylem?

  Transpiration
• What pushes water up from the roots?

  Root pressure
• How does evaporation from the leaves affect the pressure in the xylem?

  It creates negative pressure in the xylem
• What word describes how water molecules are attracted to the walls of a container?

  Adhesion
• What feature suits a root hair cell in absorbing mineral ions?

  Lots of mitochondria
• How are xylem adapted to cope with tension during transpiration?

  Strengthened with lignin
• What is translocation in plants?

  • Transport of sucrose and amino acids
  • From one part of the plant to another
  • Mainly involves sucrose
  • Occurs in phloem tubes
• What is the main form of sugar transported in plants?

  Sucrose
• What are the two main sites involved in translocation?

  Source and sink
• What is the mass flow theory in translocation?

  It explains rapid transport in phloem
• What are the stages of translocation via mass flow theory?

  1. Sucrose into the sieve element
  2. Mass flow of sucrose towards the sink
  3. Transfer of sucrose into sink cells
• How is sucrose loaded into sieve tube elements?

  By active transport with proton ions
• What happens to sucrose in sink cells?

  Converted to glucose or starch
• What effect does sucrose conversion have on sink cells?

  Reduces sucrose concentration
• What occurs when sucrose reaches the sieve tube element near the sink?

  It diffuses out along a concentration gradient
• How does water potential change near the sink during translocation?

  It lowers, causing water to leave
• What creates low pressure near the sink for continued mass flow?

  Water leaving the sieve cell via osmosis
• What evidence supports the mass flow theory?

  • Ringing experiments show sugar accumulation
  • Tracer experiments with C14 demonstrate sugar movement
• What happens in ringing experiments?

  Phloem is removed, causing swelling above
• What do tracer experiments reveal about sugar transport?

  Phloem transports sugars, not xylem
• What is the role of companion cells in phloem?

  Carry out active and co-transport
• What is the significance of sieve plates in phloem?

  Allow substances to pass without crossing membranes
• How does the structure of sieve tubes facilitate transport?

  Less cytoplasm and fewer organelles
• What is the function of the large central vacuole in sieve tubes?

  Facilitates easier movement of cell sap
• What is the role of mitochondria in companion cells?

  Produce ATP for active transport
• What is the relationship between transpiration and root pressure?

  Transpiration creates negative pressure, aiding root pressure
• How does osmosis relate to water movement in plants?

  Water moves from high to low potential
• What is the significance of the concentration gradient in translocation?

  It drives the movement of sucrose
• What is the role of H+ ions in sucrose transport?

  They create a concentration gradient for co-transport
• How does the structure of phloem contribute to its function?

  Specialized cells facilitate rapid transport
• What happens to the pressure in the phloem during sucrose loading?

  Pressure increases due to water influx
• What is the effect of sucrose on water potential in phloem?

  It lowers water potential, causing water to enter
• How does the mass flow of sucrose occur in phloem?

  Along a pressure gradient from high to low
• What is the relationship between sucrose concentration and hydrostatic pressure?

  Higher sucrose concentration increases hydrostatic pressure
• What is the role of osmosis in the movement of water in phloem?

  Water moves into phloem due to low potential
• How does the conversion of sucrose in sink cells affect translocation?

  It maintains the concentration gradient for continued flow
• What is the significance of the companion cells in the phloem structure?

  They support active transport of substances
• What is the role of the sieve plates in phloem transport?

  Facilitate movement of substances between cells
• How does the structure of sieve tubes enhance their function?

  Less cytoplasm allows easier sap movement
• What is the importance of the large central vacuole in sieve tubes?

  Facilitates easier movement of cell sap