Plant growth and light lab
01 // Question
How are three daily light environments associated with bean seedling growth over two weeks?
Compare dark, partial-light, and brighter-light environments. Record both hours and how bright each location is; this setup does not isolate duration from intensity.
02 // Variables
Independent
Assigned daily light environment- Dark setting (~0 h), partial-light schedule (about 4–6 h/day), or brighter-light schedule (about 8+ h/day)
- Log actual exposure hours, observed brightness, and temperature; groups also differ by location
Dependent
Growth and visible condition- Height of each of 9 seedlings every 2 days
- Day-14 leaf count; color and posture notes
03 // Hypothesis
IF matched bean seedlings are placed in different daily light environments, THEN their height trends and visible condition may differ over 14 days, BECAUSE light relates to plant development, while the assigned environments may also differ in brightness, temperature, and other local conditions.
04 // Procedure
1. Match nine seedlings
Choose nine similar bean seedlings from one seed batch and starting stage. Put three in matching pots for each light environment; keep each trio together in one assigned location.
2. Log each light environment
Use a dark, ventilated location (~0 h), a partial-light schedule (about 4–6 h/day), and a brighter-light schedule (about 8+ h/day). Record actual hours, how brightness was judged, and temperature; these location-based settings combine more than one light property.
3. Water on a schedule
Water every pot with the same amount on the same schedule, regardless of light group.
4. Measure all nine plants
At Days 0, 2, 4, 6, 8, 10, 12 and 14, measure each plant from the soil line to its tip at the same time of day. Note color, posture, and the direction of any lean at each check; count leaves on Day 14.
5. Add a labeled growth sketch
On Day 0 and Day 14, draw one representative seedling from each environment using clear biological-drawing lines. Label the shoot, leaves, and light direction where it is known; use the height table for measurement rather than estimating size from a sketch.
6. Show variation
Keep each plant's measurements. Plot individual lines or a treatment mean with the individual values visible; summarize Day-14 height with a mean and range.
Materials // Prepare the bench
- Nine similar bean seedlings from one seed batch (three per environment)
- nine matching pots and equal soil amounts
- a dark but ventilated, partial-light, and brighter-light location
- measured water
- ruler and individual log
- labels
- thermometer if available
- tray
05 // Data table
| Condition / plant | Day 0 (cm) | Day 2 (cm) | Day 4 (cm) | Day 6 (cm) | Day 8 (cm) | Day 10 (cm) | Day 12 (cm) | Day 14 (cm) | Leaves D14 | Color / posture |
|---|---|---|---|---|---|---|---|---|---|---|
| Dark A | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ |
| Dark B | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ |
| Dark C | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ |
| Partial A | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ |
| Partial B | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ |
| Partial C | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ |
| Brighter A | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ |
| Brighter B | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ |
| Brighter C | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ | ____ |
Summarize each treatment without hiding spread
| Environment | Mean D14 height (cm) | D14 height range (cm) | Mean leaves (D14) | Color / posture pattern |
|---|---|---|---|---|
| Dark | ____ | ____ | ____ | ____ |
| Partial | ____ | ____ | ____ | ____ |
| Brighter | ____ | ____ | ____ | ____ |
06 // What to expect
The three assigned environments may show different height trends or visible condition, but this small classroom comparison does not guarantee which group will be tallest or have the most leaves.
A dark-grown seedling can elongate while remaining pale or weak, so height alone does not show health. Treat the three plants in one shared location as subsamples of that environment, not three independent light-environment replications.
07 // Lab notes
- Measure at the same time of day each check, since some seedlings droop slightly overnight and stand straighter after a few hours of light.
- A closet or windowsill can also change temperature. Check that groups stay at similar temperatures and record any differences instead of attributing every result to light.
- Use a ruler with millimeter marks for more precise height readings on young seedlings.
08 // Remember
More light does not guarantee proportionally more growth. Compare height, leaves and plant condition; write down how each light group was set up.
09 // Compare light environments and log what differs
Use nine similar bean seedlings from one seed batch, with three seedlings assigned to each of three environments: dark but ventilated, partial light, and brighter light. Put each trio in matching pots with equal soil and keep the three pots together in one assigned location. Record actual exposure hours, how brightness was judged, and temperature at that location. These three environments can differ in both duration and intensity, so this is a comparison of combined settings, not a test that isolates hours or brightness.
Measure each plant from the soil line to its tip at the same time on Days 0, 2, 4, 6, 8, 10, 12, and 14. Keep the nine individual records, note color and posture, and count leaves on Day 14. Three plants sharing one light location are subsamples within that setup, not three independent replications of the treatment; stronger treatment replication needs multiple independently arranged enclosures per condition.
10 // Interpret growth without confusing it with health
Plants use light energy in photosynthesis, but height alone is not a complete measure of plant health. A dark-grown seedling can elongate while remaining pale or weak. Record leaf color, leaf count, and stem posture alongside height, and do not assume the tallest plant is healthiest.
Plot each individual time series or show individual traces beside a treatment mean. Summarize Day-14 height with both the mean and range so a single unusual plant does not disappear inside an average. Record water and light schedules; if a plant wilts, note it and check moisture rather than silently giving one treatment extra water. Conclusions apply to this species, these combined locations, and this two-week sample.
11 // Keep the plant study healthy and repeatable
Use a timer or written schedule to apply light consistently, and make sure the grow light is set up safely away from water. Do not place lamps where they can overheat leaves or start a fire. Keep cords dry and secured. If natural light is used, rotate or randomize pot positions when appropriate so one edge of the windowsill does not receive a consistent advantage.
For a more controlled follow-up, use the same grow-light type, brightness and distance for every group, then change only its daily operating time with timers. Check temperature because lamps can warm nearby plants. To replicate the treatment itself, arrange multiple independent enclosures per condition; plants sharing one enclosure are subsamples. Photograph the setup at the start so another class can repeat it.
12 // Summarize each plant without hiding variation
For each light environment, calculate the Day-14 mean height and range from its three individual seedlings. Keep the raw measurements and show the individual lines beside any mean line; these plants share one location, so the spread describes plant-to-plant variation within that setup rather than independent treatment replication.
If comparing average height change per day, calculate (Day 14 height − Day 0 height) ÷ 14 for each plant first, then report the three rates and their spread. Graph the full time series before reducing it to a single number. Record germination separately and state how a seed that failed to sprout is handled; summarize leaf count as its own outcome rather than combining it with height. For a qualitative record, make a clear labeled biological drawing at Day 0 and Day 14, and add an arrow showing the light direction when it is known. Keep that sketch separate from ruler measurements; it can show posture or bending, but it is not a height scale.
13 // Questions people ask
Why can height alone be misleading in a plant growth experiment?
A seedling under limited light may stretch taller while developing a thinner stem and paler leaves. Record leaf count and condition as well as height so you do not treat every increase in length as healthier growth.
What is the independent variable in this plant growth experiment?
The assigned light environment is the planned comparison. Because the dark, partial, and brighter locations may differ in both duration and intensity, record the actual conditions and do not claim this setup isolates one light property.
Why measure several seedlings in each light environment?
Individual plants vary. Keeping three plant records per environment lets students show the mean and range instead of letting one seedling represent the group. Since the three share one location, they are subsamples, not independent replications of the light treatment.
Does a longer light period always make a plant grow more?
This comparison cannot answer that by itself because duration and brightness are combined. A duration test would use the same lamp, distance, and intensity while changing only hours with timers, and should use several independently set up replicates per schedule.
14 // Keep going
Can you explain the investigation?
Plant growth and light lab · Student Data Sheet
Question: How are three daily light environments associated with bean seedling growth over two weeks?
Hypothesis: If matched bean seedlings are placed in different daily light environments, then their height trends and visible condition may differ over 14 days, because light relates to plant development, while the assigned environments may also differ in brightness, temperature, and other local conditions.
Materials
- Nine similar bean seedlings from one seed batch (three per environment)
- nine matching pots and equal soil amounts
- a dark but ventilated, partial-light, and brighter-light location
- measured water
- ruler and individual log
- labels
- thermometer if available
- tray
Safety before starting
- If using a lamp, have an adult place it securely and keep water, damp soil, and hands away from plugs and electrical connections. Use a cool-running light and allow it to cool before moving.
- Wash hands after handling potting mix or seedlings, and do not eat experimental plants.
Lab notes
- Measure at the same time of day each check, since some seedlings droop slightly overnight and stand straighter after a few hours of light.
- A closet or windowsill can also change temperature. Check that groups stay at similar temperatures and record any differences instead of attributing every result to light.
- Use a ruler with millimeter marks for more precise height readings on young seedlings.
Variables
Independent: Assigned daily light environment · Dependent: Growth and visible condition
Keep constant: same seed batch · starting size · pot and soil · measured water · observation time · similar temperature
Procedure
- Match nine seedlings: Choose nine similar bean seedlings from one seed batch and starting stage. Put three in matching pots for each light environment; keep each trio together in one assigned location.
- Log each light environment: Use a dark, ventilated location (~0 h), a partial-light schedule (about 4–6 h/day), and a brighter-light schedule (about 8+ h/day). Record actual hours, how brightness was judged, and temperature; these location-based settings combine more than one light property.
- Water on a schedule: Water every pot with the same amount on the same schedule, regardless of light group.
- Measure all nine plants: At Days 0, 2, 4, 6, 8, 10, 12 and 14, measure each plant from the soil line to its tip at the same time of day. Note color, posture, and the direction of any lean at each check; count leaves on Day 14.
- Add a labeled growth sketch: On Day 0 and Day 14, draw one representative seedling from each environment using clear biological-drawing lines. Label the shoot, leaves, and light direction where it is known; use the height table for measurement rather than estimating size from a sketch.
- Show variation: Keep each plant's measurements. Plot individual lines or a treatment mean with the individual values visible; summarize Day-14 height with a mean and range.
Record your observations
| Condition / plant | Day 0 (cm) | Day 2 (cm) | Day 4 (cm) | Day 6 (cm) | Day 8 (cm) | Day 10 (cm) | Day 12 (cm) | Day 14 (cm) | Leaves D14 | Color / posture |
|---|---|---|---|---|---|---|---|---|---|---|
Summarize each treatment without hiding spread
| Environment | Mean D14 height (cm) | D14 height range (cm) | Mean leaves (D14) | Color / posture pattern |
|---|---|---|---|---|
Answer key and expected pattern
The three assigned environments may show different height trends or visible condition, but this small classroom comparison does not guarantee which group will be tallest or have the most leaves.
A dark-grown seedling can elongate while remaining pale or weak, so height alone does not show health. Treat the three plants in one shared location as subsamples of that environment, not three independent light-environment replications.
Remember: More light does not guarantee proportionally more growth. Compare height, leaves and plant condition; write down how each light group was set up.