Lesson 9 of 9 / Nutrition and transport in flowering plants
Translocation: moving sugars in plants
How can sugars travel down to roots and up to growing shoots?
In this lesson: Define translocation as food transport, mainly sucrose, through phloem.
About 4 min
The key ideaTranslocation moves food, mainly sucrose, through phloem from sources to sinks. Its direction depends on where food is supplied and used or stored.
Explore the idea
Where can the leaf send 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
Name the cargo
Food, mainly sucrose.
- 2
Name the tissue
Phloem carries this food.
- 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.
Is this true? "Translocation means water evaporating from a leaf."
That is part of transpiration. Translocation is the movement of food, mainly sucrose, through phloem.