Celery and food coloring lab
01 // Question
How are different starting water temperatures associated with the time colored water first appears in celery leaves and the visible dye height after 24 hours?
This classroom comparison tests starting temperatures. Cups left on a bench may move toward room temperature, so it cannot show that one temperature was held constant for 24 hours.
02 // Variables
Independent
Starting water temperature- Cold starting water
- Room-temperature starting water
- Comfortably warm starting water
Dependent
Observed dye transport- Elapsed hours until color first appears in leaves; if absent, record not by 48 h
- Highest visible dye path at 24 hours (cm)
03 // Hypothesis
IF a celery stalk stands in warmer colored water, THEN the color may reach its leaves sooner in this setup, BECAUSE temperature could affect water movement, but leaf area, stalk freshness, light and other conditions can also change the visible result.
04 // Procedure
1. Make a fresh angled cut
Just before setup, an adult uses a sharp knife to trim about 1 cm from each base at about 45°. Avoid scissors, which can crush the vascular tissue.
2. Prepare nine matching cups
Make three labeled cups for each starting condition. Add 100 mL water and the same 10 drops of food coloring to every cup; use cold, room-temperature, or comfortably warm starting water.
3. Add nine matched stalks
Place one freshly cut, similar leafy stalk in each cup and start all nine together; each separate cup is one repeat.
4. Log temperature drift
Record each group's actual starting water temperature, then check it at 2, 4, and 24 hours. The cups are not temperature-controlled; describe the trial by starting temperature and report any drift.
5. Record and compare repeats
Check leaf color at consistent intervals through 48 hours. Record each observed arrival time; if color is absent at 48 hours, record ‘not by 48 h.’ At 24 hours, measure the highest visible dye path. Calculate arrival-time mean/range only if all three cups show color by 48 hours; otherwise report the non-arrival count and observed times without using 48 h as an arrival. Compare the three 24-hour heights with mean/range.
Materials // Prepare the bench
- Nine similar fresh celery stalks with leaves
- nine identical clear cups
- 900 mL water and 90 drops of the same food coloring
- thermometer, rulers, labels, timers
- covered tray and cleanup supplies; adult handles knife
05 // Data table
| Starting condition · cup | Start °C | 2 h °C | 4 h °C | 24 h °C | Leaf color first seen (h; or not by 48 h) | Visible path at 24 h (cm) |
|---|---|---|---|---|---|---|
| Cold · 1 | ____ | ____ | ____ | ____ | ____ | ____ |
| Cold · 2 | ____ | ____ | ____ | ____ | ____ | ____ |
| Cold · 3 | ____ | ____ | ____ | ____ | ____ | ____ |
| Room temperature · 1 | ____ | ____ | ____ | ____ | ____ | ____ |
| Room temperature · 2 | ____ | ____ | ____ | ____ | ____ | ____ |
| Room temperature · 3 | ____ | ____ | ____ | ____ | ____ | ____ |
| Comfortably warm · 1 | ____ | ____ | ____ | ____ | ____ | ____ |
| Comfortably warm · 2 | ____ | ____ | ____ | ____ | ____ | ____ |
| Comfortably warm · 3 | ____ | ____ | ____ | ____ | ____ | ____ |
Summarize each starting-temperature group
| Starting condition | Mean arrival (only if all arrive by 48 h) | Arrival range (only if all arrive) | Mean visible path at 24 h (cm) | Height range (cm) |
|---|---|---|---|---|
| Cold | ____ | ____ | ____ | ____ |
| Room temperature | ____ | ____ | ____ | ____ |
| Comfortably warm | ____ | ____ | ____ | ____ |
Formula For arrival time, calculate mean/range only when all three cups show color by 48 h; otherwise report how many did not and keep observed times without treating 48 h as an arrival. Calculate mean/range for all three 24-hour visible-path heights. Keep temperature readings separate from both outcomes.
06 // What to expect
The three repeats may differ, and starting temperatures may drift toward room temperature. Compare the recorded values and temperature logs; do not assume warmer water wins or claim that a temperature was maintained for 24 hours.
The color appears as thin lines running the length of the stalk rather than spreading evenly, because it's traveling through distinct bundles of vascular tissue rather than soaking through the stalk as a whole.
07 // Lab notes
- Use nine similar celery stalks with leafy tops, three per starting-temperature group, so within-group variation is visible.
- Cut a fresh slice off the bottom right before placing it in the water, since a stalk that's been sitting can have tubes partly blocked by air.
- Food coloring can stain hands and countertops — work on a covered surface.
08 // Remember
Celery has plumbing. Colored water traces visible water-conducting bundles in the cut stalk; it is a simplified model, not a rooted plant.
09 // Follow colored water through the stem
Use three separate cups for each starting condition—cold, room temperature, and comfortably warm—and put one similar fresh-cut celery stalk in each cup. Give all nine cups 100 mL water and 10 drops of the same food coloring. Immediately before setup, an adult cuts about 1 cm from each base at about 45° with a sharp knife on a stable board; do not use scissors, which can crush the stem. The three cups show how much individual stalks vary within a condition; they are more informative than one stalk per temperature, though they do not eliminate differences in stalk size or leaf area.
Record the actual starting temperature for each group, then measure again at 2, 4, and 24 hours. Cups sitting on a classroom bench exchange heat with the room, so their temperatures can converge quickly. This setup compares starting temperatures; it does not test water held cold, neutral, or warm for a full day. A stronger follow-up would use monitored, adult-supervised water baths that keep each cup at a safe target temperature.
10 // Record all nine stalks and compare the spread
Check for the first visible color in the leaves at consistent intervals and write a separate elapsed time for every cup. If color is still absent after 48 hours, record “not by 48 h” rather than inventing an arrival time. At exactly 24 hours, measure from the fresh cut base to the highest visible dye path in centimeters. A photograph against the same ruler and background can make thin streaks easier to compare.
For each starting condition, calculate the mean of its three arrival times and 24-hour heights, and report the range (highest minus lowest) too. Keep the raw cup readings beside those summaries: a mean alone hides stalk-to-stalk variation. Compare the temperature log before interpreting a pattern. Dye traces some water-conducting xylem pathways; visible height is not total water flow, and a cut stalk without roots is a simplified model rather than a whole living plant.
11 // Connect the color to xylem transport
Plants move water through xylem tissue from roots toward stems and leaves. The colored water is a tracer that makes some transport paths visible. Transpiration from leaf surfaces helps pull water upward through the plant, while adhesion and cohesion contribute to the movement of water in narrow vessels. The activity does not show the full living transport system, because a cut stalk in a cup has no roots and its normal conditions have been altered.
If comparing temperature or leaf area, change only one factor and measure it. Keep stalk variety, cut length, dye, water volume, and observation duration constant. A stalk with more leaves may lose water faster through transpiration, but it also differs in surface area and possibly size. State the specific comparison in the conclusion and avoid claiming that food coloring itself is a nutrient or that every colored vein represents a separate pipe.
12 // Improve the observation and cleanup
Use fresh celery from the same bunch when possible and keep the stems from drying before the test begins. If color does not move, check that the cut end is submerged and not sealed by a crushed section. A fresh angled cut made by an adult can expose tissue; keep knives under teacher control and avoid scissors, which can crush the stem. Food coloring may stain, so work on a tray and wash hands afterward.
An extension can compare celery with a white flower or test how a leaf covering changes the time to visible color. Use photos taken against the same background and lighting. Record qualitative observations such as leaf firmness separately from measured travel distance. Dispose of plant material and colored water according to classroom directions, and clean the cups before reusing them.
13 // Trace water movement with careful observation
Colored water can make transport through celery easier to see as liquid moves through vascular tissue. The color may travel at different rates depending on stalk size, leaf area, cut freshness, water level, and room conditions. Trim stalks consistently, place equal lengths in equal volumes, and photograph them at fixed times with the same lighting and background.
A visible color path shows where dye-containing water moved, but it is not a direct measurement of total water flow or proof that every plant transports water at the same rate. Measure a defined response, such as color height or mass change, and report any wilted or blocked stalk. Use food coloring approved for class and clean spills promptly.
14 // Questions people ask
Why does colored water travel up a celery stalk?
Celery, like other plants, has vascular tissue called xylem — narrow tubes that carry water and dissolved nutrients from the roots up to the leaves. A cut stalk standing in colored water pulls that water up through the same tubes, and the dye moves along with it, making the normally invisible tubes visible.
Why use three celery stalks for each starting temperature?
Separate cups show whether the same starting condition gives similar or variable results across stalks. Keep all three readings, then report the mean and range; one stalk per condition cannot show that within-group variation.
Why make a fresh angled cut with a knife?
A clean fresh cut exposes the stem's vascular tissue just before the test. Science Buddies recommends a fresh cut at about 45° and warns against scissors because they can crush the stem; an adult should cut on a stable board.
Does the water stay at its starting temperature for 24 hours?
Not in cups left on a bench. Measure the water at setup and at the planned checks because it may drift toward room temperature. Describe this activity as comparing starting temperatures; a maintained-temperature test needs monitored, safe water baths.
What if no color reaches a leaf within 48 hours?
Record ‘not by 48 h.’ Do not enter 48 hours as an observed arrival time. Report the number of cups without a visible arrival and summarize arrival times only if all three cups in that group show color by the 48-hour limit.
How is the celery experiment different from the walking water experiment?
Both involve water moving through narrow channels, but the walking water lab moves water through the physical gaps between paper towel fibers, while the celery lab moves water through a living plant's actual vascular tissue — the same biological structure a growing plant depends on.
Why does the color appear as thin lines instead of coloring the whole stalk?
The dye is traveling specifically through celery's vascular bundles, which run in distinct strands the length of the stalk rather than being spread evenly through all of its tissue. That's why the color shows up as visible streaks rather than an even tint.
15 // Keep going
Can you explain the investigation?
Celery and food coloring lab · Student Data Sheet
Question: How are different starting water temperatures associated with the time colored water first appears in celery leaves and the visible dye height after 24 hours?
Hypothesis: If a celery stalk stands in warmer colored water, then the color may reach its leaves sooner in this setup, because temperature could affect water movement, but leaf area, stalk freshness, light and other conditions can also change the visible result.
Materials
- Nine similar fresh celery stalks with leaves
- nine identical clear cups
- 900 mL water and 90 drops of the same food coloring
- thermometer, rulers, labels, timers
- covered tray and cleanup supplies; adult handles knife
Safety before starting
- Immediately before setup, an adult should cut about 1 cm from each stalk base at about 45° with a sharp knife on a stable cutting board; scissors can crush the stem. Students can place the prepared celery in the cups.
- Food coloring stains and the dyed celery is not food. Keep samples away from mouths, cover the bench, and wash hands after cleanup.
Lab notes
- Use nine similar celery stalks with leafy tops, three per starting-temperature group, so within-group variation is visible.
- Cut a fresh slice off the bottom right before placing it in the water, since a stalk that's been sitting can have tubes partly blocked by air.
- Food coloring can stain hands and countertops — work on a covered surface.
Variables
Independent: Starting water temperature · Dependent: Observed dye transport
Keep constant: three similar fresh-cut leafy stalks per starting condition · same food-coloring concentration, cup size, water volume, observation times, light, and location
Procedure
- Make a fresh angled cut: Just before setup, an adult uses a sharp knife to trim about 1 cm from each base at about 45°. Avoid scissors, which can crush the vascular tissue.
- Prepare nine matching cups: Make three labeled cups for each starting condition. Add 100 mL water and the same 10 drops of food coloring to every cup; use cold, room-temperature, or comfortably warm starting water.
- Add nine matched stalks: Place one freshly cut, similar leafy stalk in each cup and start all nine together; each separate cup is one repeat.
- Log temperature drift: Record each group's actual starting water temperature, then check it at 2, 4, and 24 hours. The cups are not temperature-controlled; describe the trial by starting temperature and report any drift.
- Record and compare repeats: Check leaf color at consistent intervals through 48 hours. Record each observed arrival time; if color is absent at 48 hours, record ‘not by 48 h.’ At 24 hours, measure the highest visible dye path. Calculate arrival-time mean/range only if all three cups show color by 48 hours; otherwise report the non-arrival count and observed times without using 48 h as an arrival. Compare the three 24-hour heights with mean/range.
Record your observations
| Starting condition · cup | Start °C | 2 h °C | 4 h °C | 24 h °C | Leaf color first seen (h; or not by 48 h) | Visible path at 24 h (cm) |
|---|---|---|---|---|---|---|
Summarize each starting-temperature group
| Starting condition | Mean arrival (only if all arrive by 48 h) | Arrival range (only if all arrive) | Mean visible path at 24 h (cm) | Height range (cm) |
|---|---|---|---|---|
Formula: For arrival time, calculate mean/range only when all three cups show color by 48 h; otherwise report how many did not and keep observed times without treating 48 h as an arrival. Calculate mean/range for all three 24-hour visible-path heights. Keep temperature readings separate from both outcomes.
Answer key and expected pattern
The three repeats may differ, and starting temperatures may drift toward room temperature. Compare the recorded values and temperature logs; do not assume warmer water wins or claim that a temperature was maintained for 24 hours.
The color appears as thin lines running the length of the stalk rather than spreading evenly, because it's traveling through distinct bundles of vascular tissue rather than soaking through the stalk as a whole.
Remember: Celery has plumbing. Colored water traces visible water-conducting bundles in the cut stalk; it is a simplified model, not a rooted plant.