Membrane permeability is a classic 9700 Paper 3 investigation. By hand, make six colour standards with two syringes, bore and cut 10 mm pieces of beetroot, rinse them, set the water baths and time 20 minutes on the stopwatch. Then match each solution to your standards by eye, plot your own results, and explain and evaluate them. Every attempt shifts the temperature at which the membranes fail. Allow about 40 minutes.
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The volumes of extract and water for each standard by proportional dilution, and six standards made accurately to 10 cm³ with the syringes.
Headings with units, temperatures recorded as read from the thermometers, at least five temperatures in ascending order across the steep rise, colours matched to your own standards, and the controlled method: equal rinsed pieces and 20 minutes in every bath.
Temperature on the x-axis and concentration of dye on the y-axis, the points joined by ruled lines or a smooth curve, and a reading taken from your own line.
The pattern described in two stages, the steep rise explained by denatured membrane proteins, and the route of betalain across the tonoplast and the cell surface membrane.
Subjective colour matching as the main error, a colorimeter as the improvement, surface area as the standardised variable, why the pieces are rinsed, and a sensible safety precaution.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.