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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
What this skill means
Mix amylase and starch under controlled conditions, sample at timed intervals into iodine and record when starch is no longer detected. Change one factor, repeat each value and calculate rate as 1 ÷ time.
The amylase investigation is a standard way to test temperature or pH effects. Its main challenges are defining the endpoint, keeping timing consistent and controlling all variables except the one being tested.
The iodine-sampling method
Place drops of iodine in a spotting tile. Equilibrate amylase and starch at the chosen condition, mix them and start the timer. At fixed intervals, transfer a sample to iodine. Record the time when iodine remains orange-brown, showing that starch is no longer detected.
Control the reaction conditions
If temperature is changed, keep pH constant with a buffer and use the same enzyme and substrate concentrations and volumes. If pH is changed, keep temperature constant with a water bath. Use fresh, clean equipment to avoid contamination.
Turn time into rate
When the same endpoint is used, rate can be estimated as 1 ÷ time. A shorter time therefore gives a greater rate. Repeat each condition, calculate a mean time and then calculate the rate consistently.
Limitations and improvements
Judging the exact colour endpoint is subjective and samples continue reacting during transfer. Sample at shorter intervals, use the same observer or a colorimeter where available, and keep transfer timing consistent. Pre-equilibrate solutions before mixing.
Use this before submitting your answer
A complete answer is specific enough for another person to repeat or assess.
✓Define the starch-disappearance endpoint.
✓Use fixed sampling intervals.
✓Control pH or temperature with buffer or water bath.
✓Keep volumes and concentrations constant.
✓Repeat and calculate a mean.
✓Calculate rate as 1 ÷ time where appropriate.
Try the skill in a question (2 marks)
At pH 6, starch disappears in 50 s. Calculate the reaction rate in s⁻¹.
Show the answer and marking guidance
Rate = 1 ÷ time.
Rate = 1 ÷ 50 = 0.020 s⁻¹.
Original practice content written for this site. It is not an official Cambridge question.