Science 7–10 · Year 7

Seed germination and abiotic factors: temperature, water and salt

Science understanding: Biological sciences (the need for water to germinate is Year 6 content in ACARA v9, AC9S6U01, so the ACARA side is coded to Year 7 science inquiry only; NSW Stage 4 focus area Living systems, interactions of biotic and abiotic factors)

PracticalLow risk

The idea

Germination needs water and a suitable temperature but not light for many species, and each factor can be tested one at a time with a controlled comparison.

What you need

Cress seeds, or white mustard seeds which SAPS suggests as a cheaper alternative, 20 per dish, from a garden supplier
Petri dishes lined with filter paper, labels, 10 mL syringe
Fridge at 4 °C, a room or incubator at 20 to 25 °C, a dark cupboard, a windowsill
Salt solutions at 0, 5, 10 and 20 g/L (0, 1.0, 2.0 and 4.0 g of table salt in 200 mL of water)

How to do it

Place 20 seeds on filter paper in each dish, and add 5 mL of water or salt solution to every dish except the dry dish of the water test, which gets none.
Temperature test: one dish in the fridge, one at 20 to 25 °C, both dark. Light test: one dish in the dark cupboard, one on the windowsill, both at room temperature. Water test: one dish dry, one damp. Salt test: the four salt concentrations at room temperature.
Check daily for seven days; a seed has germinated when the root (radicle) has emerged. Keep the papers damp with the same solution, and keep the dry dish dry.
Record the number germinated each day and calculate germination percentage = germinated divided by 20 times 100.
Plot germination percentage against day for each condition; plot final percentage against salt concentration.
Pool the class results for each condition.

What you should see

Cress, which SAPS describes as quick and reliable to germinate, shows emerged roots within a few days on damp paper at 20 to 25 °C. The dry dish shows none. The fridge dish is expected to show fewer or slower germination within the week. The dark dish germinates as well as the windowsill dish, because these seeds do not need light to germinate (SAPS advises keeping cress seeds dark until after germination), though the seedlings differ later: pale and tall in the dark. Germination percentage is expected to fall as salt concentration rises. The learner knows it worked when the two dishes in each pair differ in only one factor and the pooled class percentages show the same order.

What changes

What you change: One abiotic factor per test: temperature, light, water, salt concentration
What you measure: Germination percentage by day
What you keep the same: Seed type and number (20)
Volume of liquid (5 mL)
Dish and paper
All other factors held equal within a pair

Common misconceptions

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

Seeds need light to germinate.
Seeds need soil to germinate.
A cold seed is dead rather than dormant.

Safety card

Low riskLearners carry it out

Hazards

Mould on old dishes

Controls

Discard dishes after seven days; wash hands

Note

No hazardous chemicals; record a RiskAssess risk assessment for the activity as school procedure requires.

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 7–10 Syllabus (2023)SC4-LIV-01 SC4-WS-03 SC4-WS-04 SC4-WS-05
Australian Curriculum v9AC9S7I02AC9S7I04

Sources

The pages the author read to write this activity.

All Concept Studio activities