candidates, however, plotted their graphs in their answer books instead of on the graph paper.
Some left out the unit (i.e. minutes) for the time interval,
This part was satisfactory, but the following errors were frequently made:
Some candidates did not understand that the slope of the curve represented the reaction rate. They equated the
volume of gas collected with the reaction rate. Consequently, they wrongly stated that the reaction rate increased
with time as more and more gas was collected.
Some candidates were able to state that the reaction rate decreased with time, but gave the wrong explanation, e.g.
that the decrease in reaction rate was due to a drop in the amount of catalase. This reflected the fact that they held
the serious misconception that enzyme molecules were used up during a reaction.
Most candidates could not relate the decrease in reaction rate to the reduced chance of collision between the
substrate and enzyme molecules as the concentration of the substrate molecules decreased .