LF-21 · TEACHER LESSON PLAN

Plant growth and light lab

Compare three light environments with repeated seedling measurements

BiologyGrades 4–810–14 days · checked every 2 daysHazard low; soil and lamp safetyNGSS MS-LS1-5

01 //

Driving question

START THE LESSON WITH THISHow are three daily light environments associated with bean seedling growth across two weeks?

02 //

Learning objectives

Students measure the height of nine matched seedlings from soil line to tip on eight shared dates across three light environments.
Students graph individual height traces and a treatment summary while keeping plant-to-plant spread visible.
Students explain a pattern in height and day-14 leaves while distinguishing subsamples in one location from independent treatment replication.

03 //

Standards

Dimension	Alignment
Performance expectation	MS-LS1-5Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms. (Partial alignment: students vary one environmental factor (light) for one kind of plant and cannot separate genetic factors; the assessment boundary excludes genetic mechanisms and biochemical processes.)
Practices	SEP 4Analyze and interpret data.
Core idea	LS1.BGenetic factors as well as local conditions affect the growth of the adult plant.
Crosscutting	Cause and effectCause and effect relationships are routinely identified, tested, and used to explain change.

Standards text paraphrased from nextgenscience.org. Alignment is partial; this hands-on activity does not cover every part of the performance expectation. The CCC connection is conceptual: students identify an association between assigned light conditions and observed growth, while other causes may remain.

03A //

State standards crosswalk

Use the row as a planning crosswalk, then confirm local district pacing and grade placement. “Partial” labels describe a skill connection, not full mastery of the complete standard.

State	Verified standard	How this lesson aligns	Official source
California	CA NGSS MS-LS1-5	Partial. Students use evidence to explain how light as one local condition relates to growth, but the plan does not compare genetic factors or multiple plant varieties.	Open standard ↗
Texas	Science.7.1(B)	Practice connection. Students plan and conduct a comparative investigation; this expectation is a science practice, not a plant-growth content standard.	Open standard ↗
Florida	SC.7.L.17.3	Limited. The activity tests light with seedlings but does not investigate ecosystem limiting factors or effects on native populations.	Open standard ↗
New York	MS-LS1-5	Partial. Students use repeated height and leaf observations to explain a light-related pattern, but do not test genetic differences.	Open standard ↗
Pennsylvania	3.1.6-8.E	Partial. The light comparison addresses an environmental factor with evidence; the activity does not address genetic factors or multiple varieties.	Open standard ↗

04 //

Materials and prep timeline

PER GROUP

9 matched, pre-started bean seedlings from one seed batch (3 per condition)
9 matching pots with 250 mL equal potting soil each
Labels for three dark, three partial-light and three brighter-light seedlings
Ruler marked in millimeters or centimeters
Water measure and observation log for 8 check-ins
Thermometer if available; tray

TEACHER ONLY

Prepare one dark but ventilated location (~0 h), one partial-light schedule (about 4–6 h/day), and one brighter-light schedule (about 8+ h/day); log actual hours, brightness description and temperature.
Keep temperature as similar as practical and check all pots for water at the same time. Three seedlings in one location are subsamples, not independent treatment replicates.
If using a lamp, secure a cool-running lamp away from water and plugs; provide one student sheet per student.

CLASS-SIZE KIT PLANNER

One per-group kit contains every item in the team materials list above. Groups are balanced around the listed 3–4 students target.

Students	Groups	Per-group kits	Student sheets	Suggested group split
20	6	6 complete kits	20 copies	2 groups of 4 and 4 groups of 3
25	7	7 complete kits	25 copies	4 groups of 4 and 3 groups of 3
30	8	8 complete kits	30 copies	6 groups of 4 and 2 groups of 3

DAY 0 · 15 MINMatch and assign

Choose similar seedlings from one seed batch, label each light condition, measure starting height and record the actual daily light schedule.

DAYS 2, 4, 6, 8, 10, 12 · 5 MIN/CHECKMeasure all nine plants

At the same time of day, record each soil-to-tip height and note color or leaning. Water equally as needed and log changes.

DAY 14 · 15 MINFinish and compare

Measure all nine plants, count each plant's leaves, make a labeled biological drawing of a representative seedling from each environment, graph individual trends, and summarize each environment with a mean and range.

04A //

Lab figures and data visuals

Reviewed article images support the lesson flow. Use the tables and student sheet to record actual observations; pictured patterns are not target results.

Three matched groups of bean seedlings sit in a ventilated dark enclosure, partial daylight, and brighter daylight beside blank observation journals. — **Log light hours and the setting itself.**The three locations can differ in both duration and brightness. Record what each setup actually provides instead of treating the labels as one isolated light variable.

A holographic biology illustration contrasts a green photosynthesizing leaf with pale elongated seedlings showing etiolation in darkness. — **Taller does not always mean healthier.**Leaves use light energy to build plant tissue; seedlings in darkness may stretch and become pale as they use stored energy.

Three bean seedling groups are observed over time while a hand measures one plant from the soil line with a ruler; blank journals contain no results. — **Measure each plant on the same two-day schedule.**Record all nine seedlings at Days 0, 2, 4, 6, 8, 10, 12 and 14; preserve individual readings before calculating group summaries.

04B //

Printable shopping list

TEACHER PREP · Plant growth and light lab

Shopping and staging checklist

Multiply the per-group kit contents by the class-size planner. The teacher section includes teacher-provided materials and setup or safety notes.

PER-GROUP KITS

9 matched, pre-started bean seedlings from one seed batch (3 per condition)
9 matching pots with 250 mL equal potting soil each
Labels for three dark, three partial-light and three brighter-light seedlings
Ruler marked in millimeters or centimeters
Water measure and observation log for 8 check-ins
Thermometer if available; tray

TEACHER-PROVIDED MATERIALS + SETUP RULES

Prepare one dark but ventilated location (~0 h), one partial-light schedule (about 4–6 h/day), and one brighter-light schedule (about 8+ h/day); log actual hours, brightness description and temperature.
Keep temperature as similar as practical and check all pots for water at the same time. Three seedlings in one location are subsamples, not independent treatment replicates.
If using a lamp, secure a cool-running lamp away from water and plugs; provide one student sheet per student.

QUANTITIES BY CLASS SIZE

Material	Per group kit	20 students	25 students	30 students
Matched bean seedlings, three per light environment	9 seedlings	54 seedlings	63 seedlings	72 seedlings
Matching pots and labels	9 pots + 9 labels	54 + 54	63 + 63	72 + 72
Potting soil, equal fill	2.25 L total	13.5 L	15.75 L	18 L
Rulers, water measures, and trays	1 of each	6 of each	7 of each	8 of each
Student observation sheets	1 per student	20 copies	25 copies	30 copies

Prepare 6 kits for 20 · 7 kits for 25 · 8 kits for 30 students.

05 //

Lesson flow

Minutes	What happens
Day 0 · 0–5	Engage Predict how light exposure could relate to growth, while distinguishing height from overall health.
Day 0 · 5–15	Explore Assign three matched seedlings to each of three environments: dark, partial (about 4–6 hours) and brighter (about 8+ hours). Log actual hours, observed brightness, temperature and starting heights.
Days 2–12	Measure all nine plants from soil line to tip at the same time every two days. Note color and leaning; keep soil, pots and watering matched.
Day 14 · 0–8	Explain Plot individual height lines across all check-in days. Summarize Day-14 height by environment with mean and range; count leaves separately and draw one representative plant with clear labeled lines and an arrow for known light direction.
Day 14 · 8–15	Evaluate Compare final leaf counts and appearance with height. The three plants in one location are subsamples; independent treatment replication would require separate enclosures per environment.

06 //

Discussion questions

1. Why measure on the same days and at the same time?

SAMPLE ANSWERA shared schedule makes the three environments comparable. Measure each individual seedling at every check-in so both the time trend and plant-to-plant spread remain visible.

2. Does a taller seedling always mean it grew better?

SAMPLE ANSWERNo. A low-light seedling may stretch taller while becoming thin or pale. Compare height with leaves, color and posture rather than treating height as health by itself.

3. What light conditions were actually compared?

SAMPLE ANSWERUse the recorded hours and descriptions for dark, partial and brighter light. The labels alone do not say exactly how much light reached a plant.

4. What can this class investigation say about cause and effect?

SAMPLE ANSWERIt can describe a pattern associated with these assigned environments. Because each environment uses one shared location, light duration and brightness may both differ; the three plants there are subsamples, not independent treatment replications.

07 //

Common misconceptions

STUDENTS OFTEN SAY“The tallest plant is automatically the healthiest.”

BETTER IDEALow-light seedlings may stretch. Compare height with leaf number, color and posture to describe growth more fully.

STUDENTS OFTEN SAY“Every plant grows at the same rate each day.”

BETTER IDEAGrowth can speed up, slow down or pause; repeated measurements show the trend instead of assuming a straight line.

STUDENTS OFTEN SAY“The light condition is the only difference between these plants.”

BETTER IDEAThe plan controls seed batch, pot, soil and watering, but small differences in seedling genetics, temperature and actual light can remain.

08 //

Differentiation

SUPPORT

Provide a calendar with check-in dates (Day 0, 2, 4, 6, 8, 10, 12 and 14) and assign a recorder for each check.
Mark where the ruler begins at the soil line and show how to read millimeters before the first measurement.
Offer frames: “From Day __ to Day __, the ___-light group changed from __ to __ cm.”

EXTEND

Calculate average height change per day from Day 0 to Day 14, then compare it with the line graph.
Run more seedlings per condition and graph each plant alongside its group mean to show variation.
Plan a follow-up that measures light intensity while keeping temperature and water as similar as possible.

09 //

Assessment rubric

Criterion	Beginning	Developing	Secure
Consistent measurement	Measurements omit dates or use different starting points.	Most heights use the soil line but one or more check-ins are missing.	Records soil-to-tip height on the shared two-day schedule with units.
Time-series graph	Does not graph height against time.	Graphs some days but omits a condition or mislabels an axis.	Shows each light condition across check-in days with day and height axes labeled.
Pattern and evidence	Claims a result without using recorded data.	Uses a final value but overlooks the trend or observations.	Compares time trends and supports a statement with measurements plus leaves, color or posture.
Limits	Says height proves health or light is the only cause.	Names one limitation without connecting it to the conclusion.	Explains that height is not health and mentions genetics or local conditions such as temperature/light variation.

10 //

Vocabulary

Seedling – A young plant that has recently sprouted.
Environmental factor – A condition around an organism, such as light, water or temperature.
Time series – Measurements of the same kind collected at multiple times.

Growth rate – Change in a measurement divided by the time over which it changed.
Control variable – A condition kept as similar as practical while testing a planned factor.
Trend – A general pattern across measurements, which may include pauses or variation.

11 //

Safety, cleanup and troubleshooting

BEFORE STUDENTS TOUCH ANYTHING

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.

Troubleshooting: If a seedling leans, record the direction and do not rotate only one pot. If a lamp warms one group, increase distance or use a cooler light with adult help and record the change. Do not move wet pots near plugs.