When designing an experiment to test the effect of factors affecting enzyme activity, the three key decisions to be made are:

1. Which specific enzyme / substrate reaction to investigate
   

2. Which experimental factor to manipulate (i.e. the independent variable)
   

3. How to measure the enzyme activity (i.e. the dependent variable)
   

The rate of an enzyme-catalysed reaction can be calculated and plotted according to the time taken for the reaction to proceed

• The time taken can be measured according to either the amount of product formed or the amount of substrate consumed
  

• Reaction rate is the inverse of time taken, meaning that the reaction rate is higher when less time is taken (and vice versa)
  

The rate of reaction can be calculated according to the following formula:

• Rate of reaction (s–1) = 1 ÷ time taken (s)