9700 · 7.1
Structure of transport tissues
Just like humans need blood vessels, plants need specialised tissues to move vital substances around. These are the xylem, which carries water and minerals from roots to leaves, and the phloem, which transports sugars (food) from leaves to where they're needed.
Need to know
What you need to know
- **Xylem** moves water and mineral ions by mass flow — a passive process driven by transpiration — in one direction, from the roots to the rest of the plant.
- **Phloem** moves assimilates (sucrose and amino acids) by mass flow from source to sink. Loading the sieve tubes is an active process, and translocation can run in either direction.
Explanation
Plant's Plumbing System
- Visualise xylem as continuous, hollow tubes.
- Understand why lignin is crucial for xylem function.
- Recall the key components of phloem: sieve tubes and companion cells.
- Link each structural feature to its specific role in transport.