Labs / Biology
Transpiration Stream
Water evaporates from the leaves and drags a continuous chain of water up the xylem, all the way from the roots. Drag the sun, tap the leaves to open or close the stomata, and change the weather — then watch how fast the stream flows and whether the plant can drink quickly enough to stay turgid.
E 0Uptake 0VPD 0Leaf turgid
What to try
- Close the stomata. Where does the water stream go, and what happens to the transpiration rate?
- Crank up the heat and drop the humidity. Why does the vapour-pressure deficit (VPD) climb, and how does the leaf respond?
- Add wind on a dry day. Why would a breeze pull water out of a leaf faster than still air?
- Push transpiration higher than the roots can supply. How long before the leaves start to wilt — and can you reverse it?
- Dim the light to nearly nothing. What do the guard cells do, and why might a plant close up when it is dark?