Science and Technology K–6 · Years 1–2

What do plants need: seedlings with and without water and light

Living World (NSW 2017); Science understanding, Biological sciences (ACARA v9)

PracticalLow risk

The idea

Plants need water and light, and a fair test that removes one need at a time shows what each one does.

What you need

Four punnets of bean or pea seedlings of the same age and size, one per condition
Labels: water and light; water and dark; no water and light; no water and dark
A cardboard carton to make dark, with air holes cut low on two opposite sides and a card baffle taped over each hole so air moves through but no light gets in; a sunny windowsill for light; a 100 mL measuring cup
A ruler and a paddle-pop stick per punnet marked with the height each Monday, Wednesday and Friday for two weeks

How to do it

Predict what each punnet will look like after two weeks.
On day 1 water all four punnets with 50 mL each and let them drain, so every punnet starts equally damp. Measure and record the height of the tallest seedling in each punnet.
Place the two light punnets on the windowsill and the two dark punnets under the vented carton on the bench beside the window, out of direct sun so the air inside stays near room temperature.
Every Monday, Wednesday and Friday give the two water punnets 50 mL each; give the no-water punnets nothing.
Before watering, measure the tallest seedling in each punnet and note the leaf colour (green, pale, yellow) and whether the stem stands or droops.
After two weeks compare the four rows in the table with the prediction, say which need mattered most, and write one sentence about it.

What you should see

After two weeks only the water-and-light punnet is green and upright. The water-and-dark seedlings are pale or yellow with thin, weak stems; they are often taller than the lit seedlings because they stretch in the dark, so height alone does not show health. The no-water punnets wilt, droop and dry, in light or dark; the one under the carton usually takes longer, because taking the light away also takes away the sun's warmth on the soil, so that punnet loses water more slowly. That is the one thing this test cannot hold the same, and it is worth saying aloud to the class; the day each punnet first wilts is the class's record. Growth in millimetres is the class measurement; the pattern (green and upright only with both water and light) is the result. The learner knows it worked when both no-water punnets wilt (limp leaves, dry soil) while both watered punnets still have firm leaves, and the day each one first wilted is recorded.

What changes

What you change: water (given or withheld) and light (window or box), one at a time across four punnets
What you measure: height of the tallest seedling (mm); leaf colour; stem standing or drooping
What you keep the same: same seedlings and punnets
all four watered with 50 mL on day 1
same room, with the dark carton vented and standing out of direct sun
50 mL per watering
measured on the same days

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Plants get their food from the soil, so light is only for warmth.
A plant in the dark will not grow at all (it grows tall and pale, then dies).
More water is always better.

Safety card

Low riskLearners carry it out

Hazards

Mould in the dark, wet punnet; potting mix and soil can carry Legionella bacteria (NSW Health)

Controls

Punnets checked by the adult; the punnets come already planted and the mix is kept damp, so no dry potting mix is opened in class
Where potting mix is opened, NSW Health advises wetting it down and wearing gloves and a mask, if possible a P2 or N95 mask, and the adult does that away from faces; learners wear gloves when handling the punnets and soil; hands washed after handling soil

Note

No chemicals or heat. Record the activity on the school's risk assessment (Primary School RiskAssess, Ecosolve Australia, riskassess.com.au).

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science and Technology K-6 Syllabus (2017), NESA. Current syllabus; NESA's timeline is 2026 plan and prepare, 2027 start teaching the 2024 syllabus. Code read from the official syllabus document on 2026-09-22.ST1-4LW-S ST1-1WS-S
Science and Technology K-6 Syllabus (2024), NESA. Implementation from 2027, so this code describes the future syllabus. Code read from the outcomes page on 2026-09-22.ST1-SCI-01 ST1-PQU-01 ST1-DAT-01
Australian Curriculum v9AC9S1U01AC9S1I01AC9S1I02AC9S1I03AC9S1I04AC9S1I05AC9S1I06

Sources

The pages the author read to write this activity.

All Concept Studio activities