what is translocation

• translocation is the movement of dissolved substances (e.g. like sucrose and amino acids) to where they're needed in a plant
• dissolved substances are sometimes called assimilates
• translocation is an energy requiring process that occurs in the phloem
• translocation moves substances from "sources" to "sinks"
• the source of a substance is where its made ( its at a high concentration there)
• the sink of a substance is the area where the substance is used up so is at a lower concentration
• e.g. the source for sucrose is the leaves (where its made following photosynthesis) and the sinks are the other parts of the plant e.g. food storage organs and meristems ( areas of growth ) in the roots, stem and leaves
• some parts of a plant can be both a sink and a source

  • sucrose can be stored in the roots. during the growing season, sucrose is transported from the roots to the leaves to provide the leaves with energy for growth. in this case roots are the source and leaves are the sink
• enzymes maintain a concentration gradient from the source to the sink by changing the dissolved substances at the sink (e.g. by breaking them down or making them into something else) this makes sure there's always a lower concentration at the sink than at the source
• enzymes maintain a concentration gradient from the source to the sink so there's always a lower concentration of sucrose inside the sink then inside the phloem

  • e.g. in potatoes, sucrose is converted to starch in the sink areas, so there's always a lower concentration of sucrose at the sink than in the phloem which makes sure a constant supply of sucrose reaches the sink from the phloem
  • in other sinks, enzymes such as invertase break down sucrose into glucose for use by the plant - makes sure there's a lower concentration of sucrose at the sink