Use a simple choice chamber constructed from plastic petri dishes
with a perforated zinc floor.

Seal the edges of the chamber to the zinc floor using plasticene.

Task 1. Test the response of slaters to light and dark

Arrange for one side of the chamber to be completely darkened.
Add 5 animals to each compartment through the holes in the lid.
Seal the holes with sticky tape.
After 10 minutes, count the number of animals in each compartment.
Repeat this procedure several times, using fresh slaters for each trial.

Questions to think about

In which compartment do the animals collect ?
What do we call this behavioural response ?
How might this behaviour influence survival in the wild ?

Further analysis

In experiments like this, using choice chambers and limited numbers of animals, we are unlikely to have "perfect" results (i.e. 100% of the animals in one side or the other). To help us decide if our results are significant we can use simple statistics.
e.g. In the example we have studied, we can test the null hypothesis (H₀) "that slaters show no preference for light or dark" (if this is true, we would expect 50% in each side after a large number of trials)

The alternative hypothesis (H_A) is that they do show a preference for one condition.

The test we use is called the X₂ test. (Chi squared)

The formula is

This can be written more fully for our experiment as

To find out if our result is significantly different from the null hypothesis, we use the X₂ tables to give us the probability that H₀ is correct.

In biological work we usually accept a 5% (or less) probability level as indicating that the results are significantly different from H₀.
In other words if X₂ => 3.84 we can reject H₀ and accept H_A.

Set out your written record of this experiment as follows:

AIM
NULL HYPOTHESIS
METHOD
OBSERVATIONS
STATISTICAL ANALYSIS
INTERPRETATION

Task 2. Test the response of slaters to different humidities.

Use the choice chamber.
Both compartments should be in equal subdued lighting.
Place wet cotton wool under one compartment and anhydrous
calcium chloride CaCl₂ under the other. Carry out the experiment, analyse the results and present a written account.