Plant Transport
Year 9 ๐ฌ Cell Biology & Biochemistry Xylem, phloem, transpiration, and water uptake.
๐ฑ Xylem and Phloem
Plants have two separate transport tissues with different roles and structures.
| Feature | Xylem | Phloem |
|---|---|---|
| Substance transported | Water + dissolved mineral ions | Sucrose (sugars) + amino acids |
| Direction | Upward only (root โ leaf) | Both up and down |
| Cell type | Dead, hollow vessels with lignified walls | Living sieve tube cells + companion cells |
| Energy required? | No (passive: transpiration pull) | Yes (active loading of sucrose) |
| Process | Transpiration stream | Translocation |
๐ฑ Transpiration
Transpiration is the loss of water vapour from leaves, mainly through stomata. It creates the transpiration pull that moves water up the xylem.
Cohesion-Tension Theory
Water evaporates from leaves โ tension (negative pressure) created โ water pulled up xylem as a continuous column (cohesion = water molecules hydrogen-bond to each other)- Factors increasing transpiration rate: higher temperature, lower humidity, higher wind speed, higher light intensity (stomata open wider)
- Stomatal control: Guard cells take up Kโบ ions in light โ water enters by osmosis โ guard cells become turgid โ stomata open
Ready to test yourself? Click the Quiz tab above!
Interactive Demo โ Plant Transport
Transpiration Rate Calculator
Calculate transpiration rate from potometer data.