Enzyme investigations are a 9700 Paper 3 favourite. By hand, plan and make a proportional dilution of hydrogen peroxide with two syringes, soak filter-paper discs in yeast suspension with forceps, drop each one into a tube and time it rising to the surface. Then work out means and rates, plot your own graph, explain the shape with active sites and evaluate the method. Every attempt uses a different batch of yeast. Allow about 40 minutes.
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At least five concentrations with the same total volume, each concentration worked out from the volumes, and tubes on the bench that really hold the volumes in your table.
Headings with units, every time to the same sensible precision, times that match your stopwatch, at least two replicates per concentration, correct means and rates with the right significant figures, and good timing technique.
Concentration on the x-axis and rate on the y-axis, points joined by ruled lines or a smooth curve with no extrapolation, and a value read correctly from your own line.
The trend described in full, the rise explained by more enzyme-substrate complexes per second, and the levelling off explained by saturated active sites.
A boiled-enzyme control, a standardised variable with a method, the most significant source of error with a matching improvement, and a hazard and risk assessment.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.