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.
Reading it isn't running it.
Collect the apparatus, build the setup and take your own readings — as many times as it takes.