Drawing a Graph for Enzyme Rate Experiments (AQA AS Biology): Revision Note

Drawing a graph for enzyme rate experiments

• Enzyme rate experiments are experiments that are carried out to determine the effect of changing a particular factor on the rate of a reaction that is catalysed by an enzyme

• Factors that can be changed include:

  • temperature

  • pH

  • enzyme concentration

  • substrate concentration

• How the reaction rate can be measured includes:

  • measuring how much of a product is made in a given time period (e.g. using a gas cylinder to collect the oxygen produced from the breakdown of hydrogen peroxide by catalase)

  • measuring how much a substrate is broken down in a given time period (e.g. using iodine to determine how quickly starch is broken down into maltose by amylase)

Line graphs

• Line graphs should be used to present the results of enzyme rate experiments

  • The data should be plotted with the independent variable on the x-axis and the dependent variable on the y-axis

  • If a trend can be identified, a line of best fit (straight or curved) should be added to the graph

  • The line of best fit can be used to interpolate or extrapolate data

Tips for plotting line graphs

• When plotting line graphs for enzyme rate experiments, remember the following:

  • Plot data points accurately

  • Use appropriate linear scales on axes

  • Choose scales that enable all data points to be plotted within the graph area

  • Label axes, with units included

  • Construct graphs that fill the space the exam paper allows

  • Draw a line (or curve) of best fit to identify trends. The line must be smooth and have a balance of data points above and below the line

  • In some cases, the line of best fit should be drawn through the origin, for example, for rate-concentration graphs (the reaction cannot occur if the concentration of enzyme or substrate is 0). The line of best fit should only go through the origin if the data and trend allow it