Microscopy · cell structure
Magnification and image size
Calculate magnification, actual size and image size, then practise using a scale bar. Get new values, clues and worked solutions.
Maths and data practice
Cell sizes · osmosis · measurements
Units and standard form
Practise mm, μm and nm conversions, standard form and percentage changes using biological measurements. Check each answer and see the working.
Enzymes · photosynthesis · practical data
Rates and graph gradients
Practise mean rates, reciprocal time and tangent gradients with enzyme and photosynthesis contexts. Use original labelled graphs and worked solutions.
Inheritance · ecology · comparing treatments
Statistical tests and conclusions
Choose chi-squared, Spearman’s rank or a t-test for suitable data. Interpret supplied critical values, null hypotheses and statistical significance.
Exchange surfaces · cell size
Surface area to volume ratio
Calculate surface area, volume and surface area to volume ratios for cubes and spheres. Practise rearranging a ratio into x:1.
Glucose standards · practical preparation
Dilutions and solution concentrations
Practise stock volumes, final concentrations and serial dilutions. Use C₁V₁ = C₂V₂ and keep track of the final volume.
Replicates · microscopy · data interpretation
Averages, spread and mitotic index
Calculate means, medians, ranges and mitotic index. Interpret supplied standard deviations, with sample standard-deviation calculation in OCR mode.
Apparatus readings · practical evaluation
Measurement uncertainty
Convert a supplied absolute uncertainty into a percentage and combine uncertainties for the difference between two readings.
Quadrats · population estimates
Ecological sampling calculations
Estimate abundance from quadrats, calculate species frequency and use a simple mark–release–recapture estimate with its assumptions stated.
Species counts · richness and evenness
Biodiversity index calculations
Calculate biodiversity indices from original species-count data, using the stated AQA or OCR formula. Compare values calculated with the same formula.
Ecosystems · trophic levels
Energy transfers and productivity
Calculate net primary production, consumer production, transfer efficiency and production per unit area from biological energy budgets.
Gas exchange · respirometer data
Respiration measurements and RQ
Calculate respiratory quotient, volume changes in a capillary and respiration rates per gram from supplied measurements and assumptions.
Genetic diagrams · independent outcomes
Inheritance probabilities and genetic ratios
Use Punnett tables, independent dihybrid probabilities, sex-linked reference groups and expected phenotype counts. Each question states its genetic assumptions.
Alleles · genotype frequencies · populations
Hardy–Weinberg calculations
Calculate allele frequencies, heterozygote frequencies and expected genotype counts from a stated two-allele Hardy–Weinberg model.
Observed counts · expected ratios · goodness of fit
Chi-squared calculations
Calculate chi-squared contributions and total goodness-of-fit statistics from original count tables, then choose degrees of freedom for a fully specified ratio.
Pigment separation · distances · ratios
Chromatography and Rf calculations
Calculate Rf, pigment spot distance and solvent-front distance. Use matching units and distances measured from the same origin.
Microbial growth · doubling time · logarithmic axes
Exponential growth and logarithmic scales
Calculate populations, generations and doubling times. Read base-ten logarithmic scales and explain why exponential growth can appear as a straight line.
Apply a skill to OCR A questions
Use an official H420 paper after a short practice session. The maths tools are shared with AQA; the separate topic question bank covers AQA.
OCR H420 papers, mark schemes and examiner reports
A useful revision routine
- Try five skill questions.
- Review your mistakes and write out the method once.
- Attempt a related textbook or past-paper question without the answer open.
- Check your working against the publisher answer or official mark scheme.
This page brings together the resources currently available. For the complete course requirements, use the official OCR A specification.