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Getting started: variables, fair tests and means
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GCSE Biology has required practicals, and exam questions ask you to plan, spot variables and process results. These skills start at KS3.
Three kinds of variable
Independent variable: the one you change.
Dependent variable: the one you measure.
Control variables: everything you keep the same, so it is a fair test.
A variable can be categoric (named groups, such as colour of light) or continuous (any number, such as temperature).
Dependent variable: the one you measure.
Control variables: everything you keep the same, so it is a fair test.
A variable can be categoric (named groups, such as colour of light) or continuous (any number, such as temperature).
An example
Investigation: how does light intensity affect the rate of photosynthesis in pondweed?
Repeats, means and anomalies
Repeat each measurement (usually three times). This lets you check the results are repeatable and spot anomalies: results that do not fit the pattern.
mean = total of the results ÷ number of results
Leave anomalies out of the mean.
mean = total of the results ÷ number of results
Leave anomalies out of the mean.
A student counts the bubbles from pondweed in one minute, three times: 21, 23 and 22. Find the mean.
- Total = 21 + 23 + 22 = 66
- Mean = 66 ÷ 3
Answer: 22 bubbles per minute
Independent: you change it. Dependent: you measure it. Control: you keep it the same. Repeat, leave out anomalies and calculate a mean.
The interactive lesson includes the diagrams for this topic.
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