Amylase, starch and iodine on a spotting tile is the enzyme practical IGCSE Biology Paper 5 and Paper 6 keep coming back to. By hand, turn the water bath dial, stand the starch and amylase in the bath until they reach its temperature, sweep iodine across the tile, pour, start the stopwatch and carry a drop to the next well at every 30 second mark until the iodine stays orange-brown. Do it at five temperatures or more, then calculate the rates, plot your own graph and explain the shape with collisions and denaturation. Every attempt uses a different amylase. Allow about 35 minutes.
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Headings with quantity / unit, at least five temperatures spread over 30 °C or more, each time read from your own spotting tile (the first drop that stays orange-brown, or a tick if the starch was never digested), tubes at the bath temperature before mixing, and rate = 1 / time to a consistent 2 or 3 significant figures.
Axes labelled from your column headings, the smallest y-axis scale that fits your largest rate, every point within half a small square, and a smooth curve (or ruled point-to-point lines) with no extrapolation.
The optimum from your own results; the rate rises to the optimum and then falls steeply; more kinetic energy means more successful collisions and more enzyme-substrate complexes; above the optimum the amylase is denatured and the active site changes shape.
Why the solutions are warmed separately first, the control variables, the 30 s testing interval as the main limitation, an improvement (shorter intervals, more temperatures near the optimum, repeats) and a safety precaution.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.