K327 / K328 / 2027

Lesson 12 of 12 / Nutrition and transport in flowering plants

Translocation: moving sugars in plants

How can sugars travel down to roots and up to growing shoots?

I can define translocation as food transport, mainly sucrose, through phloem.

  • I can define translocation as food transport, mainly sucrose, in phloem.Syllabus

    Syllabus K327 / K328, Topic 8(l). Define translocation as food transport, mainly sucrose, in phloem.

About 4 min

Make a guess. You are not marked.

A leaf makes sugar. A fruit growing above that leaf needs it. Can sugar move upwards in a plant?

  1. Yes. The xylem carries it up with the water.
  2. Yes. Phloem carries it from source to sink.
  3. No. Food moves down to the roots to be stored.
Show the answer

Yes. Phloem carries it from source to sink.

Sugar moves from where it is made to where it is used or stored, upwards or downwards.

The key idea

Translocation moves food, mainly sucrose, through phloem from sources to sinks. Its direction depends on where food is supplied and used or stored.

Where is the food source, and where is the sink?

Explore the idea

Where can the leaf send sucrose?

Mature leafPhloemcarries sucrose

Translocation carries food, mainly sucrose, in phloem. The growing root receives food for respiration and growth even though it does not photosynthesise. Food does not always move downwards.

The highlighted arrow follows one food route. Other phloem pathways can supply other destinations at the same time.

Explanation

Translocation is the transport of food, mainly sucrose, in phloem tissue. A mature photosynthesising leaf supplies sugars, while growing tissues and storage organs need a supply for use or storage.

Food can move towards growing shoots above a leaf and towards roots below it in different phloem pathways. Its destination is determined by where food is supplied and where it is needed, rather than by a rule that it always moves downwards.

Translocation differs from transpiration. Translocation moves food within phloem, whereas transpiration is water-vapour loss from stomata. Xylem supplies water and mineral ions; phloem supplies organic food.

A growing root can receive sucrose for respiration and growth even though it does not photosynthesise. The plant therefore depends on connections between its photosynthetic and non-photosynthetic parts. The transport tissue and its cargo should both appear in a precise definition.

Step by step
  1. 1

    Name the cargo

    Food, mainly sucrose.

  2. 2

    Name the tissue

    Phloem carries this food.

  3. 3

    Name a destination

    For example, a growing root, shoot or storage organ.

Worked example

Feeding a non-green root

How can a growing root obtain food made in a leaf? Name the process, main sugar and tissue.

One way to explain it

Sucrose is transported from the leaf to the growing root by translocation in phloem.

Why this answer works
  • The root needs organic food for respiration and growth.
  • Sucrose is the main transported food named here.
  • Distinguish the phloem route from water flow in xylem.

Watch out for this

A student says: "Translocation means water evaporating from a leaf." What is wrong with this?

Show the answer

That is part of transpiration. Translocation is the movement of food, mainly sucrose, through phloem.

Check your understanding

Which correctly defines translocation?

  1. Transport of food, mainly sucrose, in phloem.
  2. Transport of only mineral ions through xylem.
  3. Loss of water vapour through stomata.
Show the answer

Transport of food, mainly sucrose, in phloem.

Include both the transported material and the tissue.

Quick recall

Card 1 of 3. Answer in your head, then check.

How can sugars travel down to roots and up to growing shoots?

You can return to this lesson any time.