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Edexcel IGCSE Biology 1c Ratios Fractions Percentages Powers and Roots Questions

Practise Edexcel IGCSE Biology ratios, fractions and percentages by calculating RDA, rate changes, stomatal density and communication-speed ratios.

Syllabus
Issue 3 (2024)
Course
Biology 4BI1

Exam points

  • Calculate percentage increases or percentage changes from biological time and rate data.
  • Use ratios and scaling to compare nutrients, communication speeds or population data.
  • Convert areas or serving sizes to estimate stomatal density or food mass.

Edexcel IGCSE Biology 1c Ratios Fractions Percentages Powers and Roots Questions question 1

[Maximum number: 2]

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.

Figure for Question Edexcel IGCSE Biology 1c Ratios Fractions Percentages Powers and Roots Questions question 1 — Edexcel IGCSE Biology

Calculate the percentage increase in time taken for the apple pulp to turn brown at pH 11 compared with the time taken at pH 7.
percentage increase = \%

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