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Identify the variables

Independent variable – the variable that is altered during a scientific experiment.

Dependent variable – the variable being tested or measured during a scientific experiment.

Controlled variable – a variable that is kept the same during a scientific experiment. Any change in a controlled variable would invalidate the results.

Example

Practical 1.4 - Investigating the effect of temperature on the action of an enzyme

• Independent variable – temperature.
• Dependent variable – time taken for starch to be digested.
• Controlled variables – pH, enzyme concentration and volume of enzyme.