Estimate salicylic acid in two samples with an iron(III) chloride colour key, graph salicylic acid in urine over time, then plan wrapped leaves, draw epidermal cells and measure a ratio. Paper 3 is done at the bench, so this page gives you a realistic set of readings for each experiment. Process them part by part, see how many of the 40 marks you would earn, then compare with a full-mark worked answer.
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The independent and dependent variables as they apply here, the standardised variables with how each is controlled, a control, and steps someone else could follow.
A table with headings and units, raw readings to a consistent precision, processed values such as rates or percentage changes, means of replicates.
Axes with labels and units, points plotted accurately, a line or curve that fits the data, and a conclusion that quotes the data.
Clear, sharp, unshaded drawings in proportion with ruled label lines; sources of error and improvements that fit this investigation; a risk assessment.
The questions on this page are rephrased from a Cambridge International past paper for teaching. The readings, figures, wording of the workout and the worked answers are our own; the marking follows the published mark scheme. The original question paper is available from Cambridge.