Redox indicators are on the 9700 practical list. By hand, set five water baths and read their thermometers, put yeast suspension and glucose into tubes with syringes, let them reach temperature, add methylene blue, invert each tube once and time how long the blue takes to go against a colour standard. A boiled-yeast control shows what the enzymes do. Then tabulate, calculate rates, plot rate against temperature, and explain and evaluate. Every attempt moves the optimum and the times. Allow about 40 minutes.
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Marked from your bench: at least five temperatures across a wide range, the same volumes of yeast, glucose and methylene blue in every tube, each tube at the bath temperature before the indicator goes in, each tube inverted once only, and a colour standard and a boiled-yeast control made like the test tubes.
Headings with units, temperatures as read from the thermometers in ascending order, times in whole seconds that match your stopwatch, timing started at mixing and stopped at the colour standard, and rate = 1 / time to the right number of significant figures.
Temperature on the x-axis and rate on the y-axis, the points joined by ruled lines or a smooth curve without extrapolating, and the optimum read from your own line.
The rise and fall described, the indicator reduced by hydrogen removed by dehydrogenases, and the shape explained by kinetic energy below the optimum and denatured enzymes above it.
Why the colour standard and the control are used, the variables kept constant, why a tube is never shaken again, the subjective end point, a colorimeter, replicates and a risk assessment.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.