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 enzymeProteins that act as biological catalysts, meaning they speed up reactions without being used up themselves..