O-Level Biological Molecules: worked solution

Question

Using the data in Table 24.1 (enzyme activity at 0-50 degC), plot rate of enzyme activity against temperature and draw a best-fit curve.

Step 1 - decide which variable goes on which axis. Temperature is the variable the experimenter changed, so it goes on the x-axis, running from 0 °C to 50 °C. Rate of enzyme activity is what was measured, so it goes on the y-axis. Step 2 - choose the scales. Find the largest value in Table 24.1 and choose a scale in easy steps (1, 2, 5 or 10 units per square) so the plotted points cover more than half the grid both across and up. Points squashed into one corner lose the scale mark. Step 3 - label the axes. Copy the headings from Table 24.1, giving the quantity and its unit, for example 'temperature / °C' across and 'rate of enzyme activity / units' up. Step 4 - plot the points. Mark each pair of readings from the table with a neat cross or an encircled dot, accurate to within half a small square. Step 5 - draw the best-fit curve. Draw one smooth freehand curve that passes through or between the points; do not join them with a ruler, and do not extend the curve past the first and last readings. The expected shape is a curve rising as temperature increases (the molecules gain kinetic energy, so there are more successful collisions between enzyme and substrate), reaching a peak at the optimum temperature of about 35-40 °C, then falling steeply towards zero as the enzyme's active site is denatured by the heat.