Choice Chamber Virtual Lab: Taxis, Kinesis and Chi-Squared

This choice chamber virtual lab runs the classic animal behavior practical without collecting a single woodlouse. Students release 10 woodlice into a chamber with a dry half (silica gel) and a humid half (water), count them for 10 minutes, swap the sides and repeat. The mean speed and turning rate on each side show that woodlice gather in humid air by kinesis, not by heading for the water. A chi-squared test on single and pooled trials shows why sample size matters. Every value below comes from the simulation.

Curriculum links

• AQA A-level Biology 7402, 3.6.1.1 (Survival and response): taxes and kineses as simple responses that keep an organism in a favourable environment; required practical 10, the effect of an environmental variable on the movement of an animal using a choice chamber or a maze.
• AP Biology, topic 8.1 (Responses to the Environment): organisms respond to their environment through behavior, as in the fruit fly behavior investigation.

Simulic is not affiliated with or endorsed by the College Board or AQA.

Before the lab (5 min)

Ask students to commit to a prediction, on paper or as question 1 of the class link:

"Ten woodlice are released in the middle of a chamber with a dry half and a humid half. Where will most of them be after 10 minutes, and why?"

Many students think the woodlice sense the water and walk to it.

Method in the simulation

1. Keep Apparatus on Choice chamber, Animal on Woodlice, Set-up on Dry – humid, Model on As the real animal, Animals 10 and Duration 10 min. Type 2 in Seed before the first trial.
2. Press Release animals – trial 1, then Run to end. Before returning the animals, copy the final counts and the line "Mean speed (including stops) and sharp turns per minute".
3. Press Return animals to habitat, then Swap sides, and run trial 2. Return the animals, press Swap sides again and run trial 3.
4. Click the Σ row in the trials table to see the chi-squared working for the pooled trials.
5. Control: set Set-up to Same (control) and run one more trial.

Trial	Sides	Dry (end)	Humid (end)	χ²	Significant at p = 0.05?
1	normal
2	swapped
3	normal
Pooled

Ethics: in a real lab, use few animals, move them with a soft paintbrush and return them to damp leaf litter afterwards.

Expected results

With Seed 2 on a freshly opened page:

Trial	Sides	Dry	Humid	χ²	p
1	normal	4	6	0.40	≈ 0.53
2	swapped	2	8	3.60	≈ 0.06
3	normal	3	7	1.60	≈ 0.21
Pooled		9	21	4.80	≈ 0.03

• No single trial is significant, but the pooled χ² = 4.80 beats the critical value 3.84 (1 degree of freedom).
• Kinesis in trial 1: dry 7.3 mm/s and 11.5 sharp turns per minute; humid 1.9 mm/s and 2.9 turns per minute. Woodlice move about 3.8 times faster in dry air.
• Snapshot effect: in trial 1, 9 or 10 woodlice sat on the humid side at every count from 4:30 to 9:30, but only 6 at 10:00.
• Control (trial 4, both halves the same): Side A 4, Side B 6, χ² = 0.40.
• Seeds 1–300: trial 1 alone was significant 182 times, the pooled trials 299 times.

Questions for students

1. (Prediction, asked again after the lab) Where do most woodlice end up, and how?
2. Which variable must be kept the same on both halves?
3. What is χ² for your pooled trials 1–3?
4. How many times faster do woodlice move on the dry side than on the humid side?
5. Why is the pooled result significant when trial 1 is not, and why swap the sides?

Answers for teachers: (1) On the humid side, by kinesis: they move faster and turn more in dry air. (2) Light (keep the whole chamber dark). (3) 4.80 (accept 4.75–4.85). (4) Accept 3.4–4.7 (3.8 with Seed 2). (5) With 10 animals, chance easily hides a real preference; 30 animals are a more reliable sample. Swapping shows the preference follows humidity, not one side of the dish.

Common misconceptions

• "Kinesis means moving towards the stimulus." That is taxis. In kinesis the speed and turning rate change, not the direction.
• "Not significant means no preference." Trial 1 was not significant, yet the pooled data were. It means there is not enough evidence yet.
• "The final count tells the whole story." One snapshot can mislead; a mean of several counts is better.

Extension

• Set Model to Taxis only, then Kinesis only, and tick Show tracks: taxis tracks head straight to one side, kinesis tracks wander.
• Choose Maggots (blowfly larvae) with Light – dark to see strong negative phototaxis.

FAQ

Can the whole class get the same numbers?

Yes. In the link's starting values, pin Random seed (the same seed gives the same results) at 2 and keep Animals per trial at 10. The same seed and trial number give the same result, so students start from trial 1 on a freshly opened page.

Why use 10 animals if 10 is too few?

It matches a typical school chamber and makes the sample-size point: ten animals give an expected value of 5, the smallest the test allows.

Do I need a chi-squared table?

No. The simulation gives the critical value (3.84) and p. Ask students to calculate χ² first, then check it against the working.

Related simulations and guides

Plant tropisms: phototropism, hydrotropism, gravitropism Reaction time – the ruler drop test

For another chi-squared practical, see the mitotic index virtual lab. For more topics, see interactive biology lesson ideas.