Enzymes can be investigated by measuring how fast a reaction goes. With amylase, starch is broken down into sugars. Iodine solution turns blue-black when starch is present, so samples are tested with iodine at intervals. The reaction is finished when the iodine no longer turns blue-black. The time taken is measured, and rate = 1 divided by time. For example, starch taking 50 s at 30 °C and 25 s at 40 °C means the time halved, so the rate doubled.
With catalase, hydrogen peroxide is broken down into water and oxygen. The oxygen can be collected in a gas syringe, and the rate is the volume of oxygen divided by the time taken.
To make the test fair, only one factor is changed. This is the independent variable, such as temperature. The measured result is the dependent variable. Other factors are kept the same: a water bath controls temperature, a buffer solution keeps pH constant, and the same volumes and concentrations are used. The experiment is repeated so a mean can be calculated, and the results are plotted on a graph. Wear eye protection, because iodine stains and hydrogen peroxide is an irritant.