February 17, 2026 • By KayScience
The enzyme required practical GCSE Biology is one of the most common sources of lost marks in AQA, Edexcel and OCR exams. Students often understand what enzymes do, but struggle to explain the method clearly or evaluate results at GCSE level. This article focuses on how to answer exam questions on the required practical with examiner precision.
Across AQA, Edexcel and OCR, the required practical usually investigates how pH affects the rate of amylase breaking down starch.
You must understand:
The independent variable (pH)
The dependent variable (time taken for starch to break down)
Control variables (temperature, enzyme concentration, volume)
Examiners are not testing whether you can memorise a method. They are testing whether you understand why each step matters.
For example, mentioning a water bath at 37°C is not enough. You must explain it is used to control temperature because temperature also affects enzyme activity.
Students often describe steps without linking them to enzyme theory.
Weak answer:
“Add amylase and starch, test with iodine every 30 seconds.”
Stronger GCSE-level answer:
“Mix amylase and starch at a set pH and measure the time taken for iodine to remain brown. The shorter the time, the faster the reaction rate because starch has been broken down into sugars.”
Notice the link between observation and biological explanation. This is where marks are awarded.
When calculating rate, many students forget:
Rate = 1 ÷ time
This is frequently required in GCSE osmosis method-style calculation questions as well as enzyme questions.
For more exam-style practice, see Past Papers and Exam practice.
Question (6 marks)
A student investigates the effect of pH on amylase. Describe how they would carry out this investigation and how they would ensure the results are valid.
To access full walkthrough answers, KayScience.com to access videos.
Top-grade answers include evaluation.
You should mention:
Repeat trials and calculate a mean
Use a water bath to control temperature
Use a buffer solution to maintain pH
Identify the optimum pH where the reaction rate is highest
Many students forget to state that extreme pH changes the shape of the enzyme’s active site (denature). Without this, you cap your marks.
Always link method → variable → enzyme theory.
If you state a control variable, explain why it must be controlled.
If you describe a result, link it to enzyme structure.
This structured approach consistently reaches Level 3 on AQA-style mark schemes.
If your child is losing marks on 4- and 6-mark biology questions, structured exam practice makes the difference. Explore our Tuition Timetable for guided support and examiner-led walkthroughs.
Check out our blog for more exam tips on Osmosis - Osmosis Practical
