translocation

• What process allows plants to transport solutes in the phloem?

  Translocation
• What are the two main processes involved in translocation?

  Active loading and mass flow
• What monosaccharide is produced during photosynthesis?

  Glucose
• What is glucose converted to for transport in plants?

  Sucrose
• Why is sucrose less reactive than glucose?

  It is a disaccharide
• What term is used for molecules made as a result of photosynthesis?

  Assimilate
• What are the two types of regions in plants related to assimilate transport?

  Sources and sinks
• What is an example of a source in plants?

  Photosynthesizing leaves
• What is an example of a sink in plants?

  Roots
• What is the role of storage organs in translocation?

  They can release carbohydrate stores
• How do companion cells contribute to sucrose transport?

  They actively load sucrose into the phloem
• What process is used to pump hydrogen ions out of the companion cell?

  Active transport
• What does the inward flow of hydrogen ions couple with?

  Inward flow of sucrose
• What do companion cells contain that provides ATP?

  Mitochondria
• What effect does high sucrose concentration have in companion cells?

  It allows sucrose to diffuse into sieve tube elements
• What happens to water potential in sieve tube elements when sucrose is loaded?

  It lowers the water potential
• How does water move into the sieve tube element?

  By osmosis from nearby tissues
• What is the bulk movement of phloem sap called?

  Mass flow
• What happens to sucrose at the sink?

  It is converted to glucose or starch
• What occurs to water potential in the sieve tube element when sucrose leaves?

  It increases the water potential
• What happens to some of the water that moves out of the sieve tube element?

  It joins the transpiration stream
• What evidence supports the active model of movement in the phloem?

  Rate of flow is faster than diffusion
• What happens if companion cell mitochondria are inhibited?

  Translocation stops