Test what seedlings need

How can we test light and water one factor at a time?

Submit: Two investigation plans, dated observation records and qualified conclusions.

Related lesson: Plant and Animal Habitats

This is a teacher-led extension beyond the short lesson. The task supplies a performance opportunity; completion alone does not certify mastery, full NGSS coverage or state alignment.

Build the idea

To investigate a plant need, compare similar plants while changing one condition. Changing both water and light in the same comparison leaves the cause unclear. Seeds may sprout using stored food, so use established seedlings and observe continuing growth, leaf color and condition—not just whether a seed first sprouts.

Evidence and model inputs

Planning pairs: light test — similar seedlings receive the same appropriate watering, with one group in suitable light and one in darkness for a limited comparison. Water test — similar seedlings receive the same suitable light, with one group watered appropriately and one group not watered during the comparison. The adult sets a humane stopping point and restores care. No universal daily cup amount is prescribed.

Keep actual observations, published findings and invented model cases labeled separately. If a source or required equipment is unavailable, pause that part with a teacher; do not invent results.

Materials and preparation

Established seedlings, labels, matching containers and growing medium, ruler, watering supplies and adult-managed light locations. No sealed hot boxes or unsafe electrical setups.

Grade-level scope

Assess one variable at a time; the learner must actually plan and conduct the investigation rather than merely repeat an expected answer.

Do the work

1. With an adult, select several established seedlings of the same kind and similar starting condition for each treatment.
2. Draw two separate plans. Name the single factor changed in each comparison and what stays similar.
3. Randomly assign seedlings where practical. Record starting height, leaf color and condition; label every plant.
4. Observe on the same schedule. Measure height consistently and record all plants, including unexpected results.
5. Compare the groups within each test. Use several observations to discuss light and water; do not treat height alone as health because a dark-grown plant may become tall and pale.
6. Explain limitations and restore appropriate care promptly.

Learner worksheet

Write on paper or type here and print. Entries stay in this page’s memory and are lost when you leave or reload; they are not saved or submitted.

Check your reasoning

1. Why avoid changing water and light together?
2. Can a seed sprout without light?
3. Is a tall pale seedling necessarily healthiest?
4. What if seedlings differ before the test?

Teacher review guide

Review the actual deliverable and discuss the reasoning. For each criterion, use 0 when evidence is absent or fundamentally incorrect, 1 when partly supported with a material error or omission, and 2 when accurate, supported and complete for the stated task. Maximum 8 points is a task score, not a proficiency certification. Give feedback and allow revision.

1. Plans two comparisons with one changed factor each.
2. Records repeated observations of multiple comparable seedlings.
3. Uses actual results to discuss the roles of light and water.
4. Recognizes confounds and distinguishes sprouting from continuing healthy growth.

Sources and standard reference

• Official NGSS 2-LS2-1 performance expectation — inspect the practice, core idea, crosscutting concept and assessment boundary.

Instructional text and hypothetical cases are original. Linked source readings supply published evidence where specified. Teachers should judge fit with their course and state requirements.