Edexcel IGCSE Biology Ratios and Percentages
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.
1C Ratios, fractions, percentages, powers and roots 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.
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 = \%
All question bank results loaded