This experiment involved the chosen enzyme, B-Galactosidase, to be tested with a substrate called o-nitrophenol-B-D-galactopyranoside (ONPG). The purpose was to determine over time the effects the enzyme had on the substrate concentration, as well as to examine the effect of lactose, a disaccharide on the formation of o-nitrophenol. The experiment utilized a spectrophotometer to determine at which the rate that the enzyme catalyzes, by timing the change in absorbance every 15 seconds, as well as observing any colour change. The amount of enzyme added to the B-Galactosidase is increased over time, and the ONPG is set to a constant value each trial. It was determined that through the trials of testing the absorbance of the enzyme, the faster