Back to Biology
Biology · Plant transport · Potometer
Measuring transpiration rate with a potometer
A leafy shoot is sealed into a water-filled capillary tube with an air bubble. As the leaves lose water by transpiration, the bubble moves along the capillary. Distance ÷ time = rate of water uptake — a good proxy for transpiration rate.
t = 0.00 min · d = 0 mm
WHY: Baseline
Results (5-min run)
| Condition | d (mm) | rate (mm/min) |
|---|---|---|
| Still air | — | — |
| Fan on (wind) | — | — |
| Bright light | — | — |
| Polythene bag | — | — |
| Heated to 30 °C | — | — |
Exam-style questions
1. Which condition gave the fastest rate?
2. Why does WIND increase transpiration rate?
3. Why does a POLYTHENE BAG DECREASE the rate?
4. The bubble moves AWAY from the cut shoot. What does this indicate?