7.2.9

Translocation

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Translocation

Translocation is the process where sugars produced in photosynthesis are transported from the leaves to other parts of a plant. The steps involved are:

1) Active transport of sucrose

1) Active transport of sucrose

  • Sucrose is produced during photosynthesis in the leaves.
    • The leaves are called the source.
  • Sucrose is actively transported into the companion cells in the phloem.
  • Energy is provided for active transport from mitochondria in the companion cells.
  • This process involves H+ ions being actively transported out of companion cells.
  • The H+ ions then diffuse back into the companion cells with sucrose. This is known as co-transport.
2) Diffusion of sucrose

2) Diffusion of sucrose

  • The loading of sucrose into the phloem causes the concentration of sucrose to increase.
  • Sucrose diffuses from the companion cells into the sieve tube elements.
3) Osmosis

3) Osmosis

  • The increase in the concentration of sucrose in the phloem causes water potential in the phloem to decrease.
  • There is a water potential gradient between the outside of the phloem and the inside.
  • Water diffuses into the phloem by osmosis.
4) Unloading of sucrose

4) Unloading of sucrose

  • At the bottom of the phloem, sucrose concentration is low because it is being used up in the cells.
    • The cells at the bottom of the phloem are called the sink.
  • Sucrose diffuses out of the phloem and into the sink cells.
  • This lowers the water potential of the sink cells.
5) Osmosis

5) Osmosis

  • Water diffuses down its water potential gradient out of the phloem by osmosis.
  • The diffusion of water into the phloem at the source and out of the phloem at the sink creates a hydrostatic pressure gradient.
  • The hydrostatic pressure gradient allows mass transport of sucrose from source to sink.
    • This is called mass flow.
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Practice questions on Translocation

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    Which of the following statements about translocation are true?True / false
  2. 2
    During translocation, what type of cell is sucrose co-transported into?Multiple choice
  3. 3
    Steps Involved in TranslocationPut in order
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Phloem Structure

Skeletal Muscle