Osmosis in potato and enzyme activity are the two investigations that turn up most in IGCSE Biology practical papers. Weigh the cylinders, time the starch digestion with iodine, calculate, plot and explain. Fresh results every time.
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Masses recorded to the precision of the balance, and times read from the iodine tests.
Percentage change = (final − initial) ÷ initial × 100, with a minus sign for a loss; rate = 1 ÷ time.
A best-fit line through the points, and readings taken from the line.
Osmosis is the movement of water; enzymes are denatured above the optimum, never “killed”.
Control variables named, such as volume, concentration and cylinder size, with water baths for temperature.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.