Investigating Science 11–12 · Year 11

Slaters in a damp and dry choice chamber, with a chi-square test

Module 1: Cause and Effect – Observing

PracticalLow risk

The idea

Counting where animals settle turns a behaviour into quantitative data, and a statistical test shows whether a small sample is enough to support the pattern the eye sees.

What you need

10 slaters (woodlice) collected from under damp logs or bark, kept in a damp container
a choice chamber: a large Petri dish or shallow plastic box divided in half, damp paper towel under one half and dry paper under the other, with a clear lid
black card to cover half the lid for the light and dark test, soft paintbrush for moving the animals, stopwatch

How to do it

Set up the damp and dry halves and place all 10 slaters in the centre with the paintbrush; replace the lid.
Count the slaters on each side every minute for 10 minutes and record every count.
Repeat with a fresh set-up with the damp side swapped to the other end, to rule out a preference for one end of the dish.
Pool the 10-minute counts from every group in the class.
Calculate χ² = Σ (O − E)² / E against an even split for your group and for the pooled class data, and compare with 3.84 (1 degree of freedom, p = 0.05).
Repeat with both halves damp and half the lid blacked out to test light against dark.
Return the slaters to the place they were collected within the lesson.

What you should see

Slaters are land crustaceans that lose water readily, so the hypothesis is that they accumulate on the damp side, moving about on the dry side and slowing once they reach damp conditions. The statistics are fixed by arithmetic: with 10 animals an 8 : 2 split gives χ² = 3.6, below the 3.84 critical value, so it is not significant at p = 0.05, while 9 : 1 gives χ² = 6.4; a pooled class of 60 splitting 45 : 15 gives χ² = 15.0 and 40 : 20 gives 6.7. The learner reports the minute-by-minute counts, the pooled χ², and whether the swap of ends changed the result.

What changes

What you change: moisture of the substrate (damp or dry), then light or dark
What you measure: number of slaters on each side at 10 minutes
What you keep the same: same number of slaters
same chamber and paper
same temperature and room light
ends swapped between runs

Common misconceptions

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

Slaters are insects (they are crustaceans with seven pairs of legs).
The animals decide where to go, rather than changing how fast they move.
Ten animals are enough to be sure of a pattern.

Safety card

Low riskLearners carry it out

Hazards

soil micro-organisms on hands
harm to the animals from drying out or rough handling

Controls

move animals only with a paintbrush
keep the holding container damp and shaded
wash hands after the activity
return animals to the collection site the same day

Note

No chemicals or heat. Live animals are handled: follow the NSW Department of Education Animals in Schools requirements and record the activity in the school’s RiskAssess risk assessment.

Curriculum references

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

Investigating Science Stage 6 Syllabus (2017), NESA; currentINS11-8 INS11/12-1 INS11/12-3 INS11/12-4
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

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