AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
Required practical 10: Investigation into the effect of an environmental…
Full specification wording
Survival and response (A-level only): Required practical 10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze.
A choice chamber offers contrasting conditions, like damp and dry, where animals are introduced and allowed to distribute.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 6 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A choice chamber offers contrasting conditions, like damp and dry, where animals are introduced and allowed to distribute. The independent variable is the environmental condition. The dependent variable is the number of animals per compartment, or in a maze, the time taken. Distribution is recorded at fixed intervals after a settling period, as counting immediately records placement, not response. Confounding variables must be controlled: species, size, temperature, and time of day. The chamber is rotated between runs so external light or draughts do not skew results. For categorical count data in a choice chamber, a chi-squared test compares observed and expected frequencies; for continuous data like time in a maze, a t-test is used.
What earns the marks
- Identifying the independent variable as the environmental condition and the dependent variable as the number or position of animals.
- Allowing a settling period and then recording at set time intervals.
- Naming a controlled variable, such as temperature, number of animals, species or time of day.
- Repeating the investigation and calculating a mean, or rotating the apparatus to control the direction of light.
- Selecting a suitable statistical test, such as chi-squared for comparing observed with expected categorical distributions in a choice chamber, or a t-test for continuous maze time data.
Common mistakes and how to put them right
Counting the animals immediately after adding them, which records where they were placed rather than their response.
Changing two conditions at once, for example humidity and light, so the cause of the distribution is unknown.
Using different numbers of animals in different runs, so the counts cannot be compared.
Ignoring an external light source or a warm bench acting on the chamber from one side.
Concluding that a small difference in numbers is meaningful without a statistical test.
Exam tips
- Name the independent, dependent and at least two controlled variables explicitly when describing the method.
- Chi-squared is the test for counts of animals in categories, and the null hypothesis is an equal distribution between compartments.
- Consider adding a sentence on the ethical treatment of the animals, ensuring they are returned to their natural habitat unharmed.
Try the lesson
The start of the Survival and response (A-level only): Required practical 10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze. lesson, made from checked teaching notes for this specification point.
Have a go first
When using a choice chamber to investigate the effect of humidity on woodlice, which step improves the validity of the results?
Listen
A choice chamber offers contrasting conditions, like damp and dry, where animals are introduced and allowed to distribute. The independent variable is the environmental condition. The dependent variable is the number of animals per compartment, or in a maze, the time taken. Distribution is recorded at fixed intervals after a settling period, as counting immediately records placement, not response. Confounding variables must be controlled: species, size, temperature, and time of day. The chamber is rotated between runs so external light or draughts do not skew results. For categorical count data in a choice chamber, a chi-squared test compares observed and expected frequencies; for continuous data like time in a maze, a t-test is used. A strong answer earns marks for these points. identifying the independent variable as the environmental condition and the dependent variable as the number or position of animals. allowing a settling period and then recording at set time intervals. naming a controlled variable, such as temperature, number of animals, species or time of day. repeating the investigation and calculating a mean, or rotating the apparatus to control the direction of light. Exam tip: Name the independent, dependent and at least two controlled variables explicitly when describing the method.
Key words
Say what each word means before you turn the card.
choice chamber
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independent and dependent variables
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controlled variables
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chi-squared test
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See every definition
- choice chamber
- Offers contrasting conditions, like damp and dry, where animals are introduced and allowed to distribute.
- independent and dependent variables
- The environmental condition is the independent variable; the number of animals per compartment, or time taken in a maze, is the dependent variable.
- controlled variables
- Confounding variables that must be controlled, such as species, size, temperature, and time of day.
- chi-squared test
- For categorical count data in a choice chamber, compares observed and expected frequencies.
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