Edexcel IGCSE Biology Accuracy and Validity

Edexcel IGCSE Biology Accuracy and Validity
Edexcel IGCSE Biology syllabusBiology 4BI1Issue 3 (2024)

Practise Edexcel IGCSE Biology accuracy and validity by explaining subjective observations, timing delays and limits in biological investigations.

How this is tested

  • 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.

Question 4(b)(ii)

[Maximum number: 2]

When potatoes are cut and exposed to the air, the cut surface turns brown.
Potato cells contain colourless chemicals called polyphenols and an enzyme called polyphenol oxidase.

When the polyphenols and polyphenol oxidase enzyme are exposed to oxygen in the air, a reaction occurs between the polyphenols and oxygen. This reaction produces brown-coloured chemicals.

A student uses this method to investigate the effect of changing pH on the time taken for potatoes to turn brown.
- cut three slices of potato and place them into a beaker
- cover the slices in a pH 7 buffer solution to maintain the pH
- after five minutes, remove the pH buffer solution so the potato slices are exposed to the air
- record the time taken for each of the potato slices to turn from white to brown and calculate the mean time

The student repeats the experiment using four different pH buffer solutions.
The table shows the student's results.

Table for Question 4(b)(ii) — Edexcel IGCSE Biology

Explain how the student could improve the accuracy of the investigation.