AQA Biology 4.2.3.2
Translocation
Sugars made in the leaves travel to every part that needs them. Send sugar to a root, a fruit and a growing tip, then compare phloem with xylem.
Triple Science · Higher tier
Start here
A sack of potatoes.
Potatoes and carrots are stores of food, and they grow underground. The leaves of the same plants are up in the light.
If you had to guess, is the food made in the leaves, or in the roots?
Where the sugar goes
Leaves to the rest of the plant, up or down.
Phloem tissue transports dissolved sugars from the leaves to the rest of the plant, for immediate use or storage. The movement of food molecules through phloem is called translocation. The leaves are the source; anywhere the sugar is used or stored is a sink. Send the sugar somewhere.
Pick where the sugar should go. Xylem, in blue, carries water up from the roots.
Phloem and xylem
Two tubes, built for two jobs.
Cut open a stem and the two tissues sit side by side. Their structure fits what they carry.
| Phloem | Xylem | |
|---|---|---|
| Carries | dissolved sugars | water and mineral ions |
| Direction | from the leaves, up or down | up, from the roots to the stems and leaves |
| Cells | tubes of elongated living cells | hollow tubes of dead cells |
| Adapted by | pores in the end walls let cell sap move from cell to cell | walls strengthened by lignin |
Water rising in the xylem is the transpiration stream: in Transpiration.
Think again · only down to the roots?
“Sugar only travels down, to the roots.”
Your call
ChooseA shoot tip above the leaves is growing fast. How does it get sugar?
Sort
Phloem or xylem?
Place each statement.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Compare
- Phloem and xylem: what, which way, what cells.
- Explain how
- A structure fits its job: “so that…”.
- Describe
- Where sugar goes after it is made.
Key fact
Translocation is the movement of dissolved sugars through the phloem, from the leaves to the rest of the plant for immediate use or storage.
Key note · AQA 4.2.3.2
Translocation
- Translocation is the movement of dissolved sugars through phloem, from the leaves to the rest of the plant for immediate use or storage.
- Phloem can move sugars up or down: to growing tips, fruits and roots.
- Phloem is tubes of elongated living cells; cell sap moves between them through pores in the end walls.
- Xylem is hollow tubes of dead cells strengthened by lignin, carrying water and mineral ions up from the roots.
- Source: where sugars are made (leaves). Sink: where they are used or stored.
Photograph this card. Tomorrow, cover it and say each line first.
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Not sure which tube carries what?
Plant and tissue drawings are schematic and not to scale.