Edexcel IGCSE Biology Accuracy and Validity
Practise Edexcel IGCSE Biology accuracy and validity by explaining subjective observations, timing delays and limits in biological investigations.
- Syllabus
- Issue 3 (2024)
- Course
- Biology 4BI1
Exam points
- Improve accuracy by using a colour chart, colorimeter, reference colour or second opinion.
- Explain why reaction time, decision making or synapse delays affect nerve impulse speed estimates.
- Evaluate conclusions by considering water loss, mineral transport, wilting and missing plant data.
Evaluate accuracy and validity question 1
Apples contain an enzyme called phenol oxidase.
When apple tissue is exposed to oxygen in the air, this enzyme turns the apple tissue brown.
A student uses this method to investigate the effect of pH on the time taken for apple tissue to turn brown.
- mash an apple to produce a pulp
- place 25 g of this pulp into a beaker
- mix a pH 7 buffer with the pulp to maintain the pH
- check the colour of the pulp every five minutes
- record the time when the pulp turns brown
The student repeats this method using pH buffers of 3, 5, 9, and 11.
The graph shows the student's results.
Explain how the student could modify this method to give a more accurate measure of the time taken for the apple pulp to turn brown.
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