8.4 Translocation

2026 Syllabus Objectives

  1. Describe translocation as the movement of sucrose and amino acids in phloem from sources to sinks
  2. Describe:
    • (a) sources as the parts of plants that release sucrose or amino acids
    • (b) sinks as the parts of plants that use or store sucrose or amino acids
  3. Explain why some parts of a plant may act as a source and a sink at different times

What is Translocation? 🌿

Translocation is the movement of sucrose and amino acids in phloem from sources to sinks.

Leaves are the primary sites of photosynthesis, where carbohydrates are produced. These carbohydrates, along with other organic substances, need to be distributed to other parts of the plant. Some key substances made in leaves include:

  • Sucrose (the main transported sugar)
  • Amino acids (building blocks of proteins)
  • Proteins
  • Fats and oils
  • Other organic substances

Key Point: Translocation specifically refers to the transport of sucrose and amino acids through the phloem tissue.


Sources and Sinks 📍

What is a Source?

A source is the part of a plant that releases sucrose or amino acids to be transported to other parts.

Characteristics of sources:

  • Produce or release organic substances (particularly sucrose and amino acids)
  • Export materials to other parts of the plant
  • During active growth, leaves are typically the major sources
  • Storage organs can become sources when stores are mobilized

What is a Sink?

A sink is the part of a plant to which sucrose or amino acids are being transported, and where they are used or stored.

Characteristics of sinks:

  • Receive organic substances from sources
  • Either use the materials immediately or store them for later use
  • Examples include roots, flowers, fruits, and storage organs

Common sinks and their functions:

SinkFunction
RootsConvert sucrose to starch for storage
FlowersUse sucrose to make fructose for nectar
FruitsUse sucrose to produce sweet, juicy fruits to attract animals
Growing budsUse sucrose for growth and development
Storage organsStore materials as starch or other compounds

Sign in to view full notes