Dye uptake in celery: does warmer water speed up the xylem stream?
Stand a dyed celery stalk in ice-cold water and its twin in warm water, then cut both into 5 mm cross-sections to see how far the dye actually travelled — and why warmth wins.
WHAT YOU'LL LEARN
- ✓The transpiration stream: how water (and dissolved dye) moves up through xylem vessels
- ✓Why this is bulk flow driven by evaporation and temperature, not osmosis
- ✓Reading a thermometer to 1 °C and a stop-clock for a fixed timed period
- ✓Turning a count of stained cross-sections into a distance, and a distance into a rate
ON YOUR BENCH
- □2 celery stalks (leaves removed, ~10 cm), pre-soaked in dye
- □2 beakers of dark food dye, ~1 cm depth
- □250 cm³ beaker C — ice-cold water, ~2 cm depth
- □250 cm³ beaker W — warm water (40–50 °C), ~2 cm depth
- □Thermometer, −10 °C to +110 °C
- □Stop-clock
- □Knife or scalpel
- □Hand lens (×6 or better)
- □30 cm ruler with a mm scale
- □White tile
- □Paper towels
- □Eye protection and gloves
The protocol, step by step
The same guide is printed and waiting at your bench.
- 01
Start with pre-dyed stalks
Both celery stalks have already stood in dye long enough for it to enter the base of the xylem — that soak isn't timed in this experiment, only what happens next is.
- 02
Transfer to the water baths and record starting temperatures
Stand one stalk in beaker C (ice-cold water) and the other in beaker W (warm water, 40–50 °C). Read and record both starting temperatures before you do anything else.
- 03
Stand for a fixed 3 minutes
Start the stop-clock the moment both stalks are in their baths. Don't disturb them — the whole comparison depends on both getting exactly the same amount of time.
- 04
Record final temperatures
The instant the 3 minutes are up, read and record both final temperatures. Cold water tends to warm slightly; warm water tends to cool — that drift is real and worth recording, not an error to hide.
- 05
Cut cross-sections from the base
Working on the white tile, cut each stalk into 5 mm cross-sections starting at the base. After each cut, use the hand lens to check whether the xylem still shows dye. Stop counting the moment a section shows none.
- 06
Calculate distance and rate
Distance moved = number of stained sections × 5 mm. For beaker W, rate = distance ÷ 3 minutes, in mm per minute.
What you should see
- →The dye travels further up the stalk that stood in warm water than the one in ice-cold water, over the identical 3-minute period.
- →This is the transpiration stream, not osmosis: water and dissolved dye are pulled up hollow xylem vessels as bulk flow, and warmth speeds up both evaporation and molecular movement.
- →A single run can throw up an anomaly — a stalk that clogged unusually early, or ran unusually far. That's exactly why the investigation is worth repeating rather than trusting one pair of stalks.
- →The cold beaker often warms a little and the warm beaker often cools a little over 3 minutes in an uncontrolled water bath — a real limitation the mark scheme rewards you for noticing.
| Beaker C (cold) | Beaker W (warm) | |
|---|---|---|
| Starting temperature /°C | 3 | 45 |
| Final temperature /°C | 6 | 39 |
| Sections showing dye | 1 | 4 |
| Distance moved /mm | 5 | 20 |
| Rate /mm per min | — | 6.7 |
⚠ BEFORE YOU START
- •No hazards are flagged for this practical beyond normal lab care — celery, food dye and water only.
- •Wear eye protection and gloves while cutting the stalks, and handle the knife or scalpel with the blade always pointing away from your hand.
- •Warm water is hot enough to scald — don't dip fingers into beaker W to test the temperature; read it with the thermometer.
Try it, then run it for real.
Practise the whole thing on the virtual bench, then book real lab time and do it with your own hands.