Plant Tissues, Organs & Systems (AQA GCSE Biology): Revision Notes
Translocation
What is translocation?
Translocation is how plants move dissolved food substances through their bodies. It happens when sugars made in the leaves travel through special tubes called phloem tissue to reach other parts of the plant.
Think of phloem like the plant's food delivery system - it carries dissolved sugars from where they're made to where they're needed.
Key Definition: Translocation is the movement of dissolved food molecules through phloem tissue. This is essential for plant survival as it allows nutrients made in the leaves to reach all parts of the plant.
How phloem tissue works
Phloem tissue is made up of long, thin tubes that connect different parts of the plant. The transport process involves several key steps that work together to move nutrients throughout the plant.
Here's how it works:
- Sugar production: Leaves make glucose during photosynthesis, which gets converted to sucrose
- Transport route: The dissolved sucrose travels through phloem tubes from leaves to the rest of the plant
- Movement method: Cell sap (liquid inside plant cells) moves from one phloem cell to the next through tiny holes called pores in the cell walls
- Destinations: Sugars go to growing areas (like buds) and storage organs (like potatoes)
The movement of cell sap through pores is what makes translocation possible. Without these tiny connections between cells, sugars would be trapped in the leaves where they're made.
Where do the sugars go?
The dissolved sugars travel to two main places:
- Growing regions - Areas like buds that need energy to make new cells and grow
- Storage organs - Places like potato tubers where sugars get converted to starch and stored for later use
This means the plant can use its food immediately for growth or save it for when it's needed later.
Tracking sugar movement
Scientists can prove translocation happens by using radioactive carbon. This experimental approach provides clear evidence of how sugars move through plants.
Worked Example: Radioactive Carbon Tracking
Step 1: Give the plant carbon dioxide containing radioactive carbon atoms
Step 2: The leaf uses this radioactive carbon to make glucose during photosynthesis
Step 3: Some glucose gets converted to sucrose and travels through the phloem
Step 4: Later, scientists can detect radioactivity in the stem, proving that sugars have moved there
Result: This clever experiment shows that sugars really do travel from leaves to other plant parts.
Where does phloem come from?
Phloem tubes are made from special cells called meristem tissue. This tissue is found at the growing tips of shoots and roots.
Meristem cells are like stem cells - they can change into different types of specialised cells, including phloem and xylem cells. This process is called differentiation and is how plants create all their different tissue types.
Key Points to Remember:
- Translocation is the movement of dissolved sugars through phloem tissue
- Phloem acts like the plant's food delivery system, carrying sugars from leaves to other parts
- Sugars travel to growing regions for immediate use and storage organs for later use
- Cell sap moves through pores between phloem cells to transport the dissolved sugars
- Scientists can track sugar movement using radioactive carbon experiments