OCR A-Level Biology data sheet: Formulae and definitions explained

OCR A-Level Biology A (H420) sets out exactly which formulae you need to recall from memory and which the paper will provide. If you've gone looking for a downloadable 'OCR Biology data sheet' PDF, you won't find a separate booklet. Instead the specification publishes a two-column table in Section 5d listing every formula with its status, and the paper itself prints the provided formulae on the questions where they're used.

This guide covers OCR A (H420). If you're sitting OCR Biology B Advancing Biology (H422), the formulae list is different, so check your spec code on your timetable before using this.

OCR Biology's data provision is the most generous of the three major English A-Level boards: a longer recall list (check Section 5d of the H420 spec for the current list), two biological formulae provided, and a stats-tests list that includes paired and unpaired t-tests, Spearman's rank, chi-squared, and standard deviation. The piece below maps the main items in the recall list, groups them by use case, and flags the ones that look obscure but genuinely do come up.

OCR splits its biology formulae into four groups: biological formulae to recall, biological formulae provided, mathematical formulae to recall (GCSE 9-1 Higher content), and mathematical formulae provided (including every stats test). The tables below work through each group.

A few of these look obscure but genuinely come up. The 'proportion of polymorphic gene loci' formula tests genetic biodiversity measurement and shows up on Paper 2 questions about population genetics. Q₁₀ appears in enzyme-rate questions where you've got two rates measured 10°C apart. RQ is the respiration-topic quick win: an RQ of 1 means pure carbohydrate respiration, around 0.7 means lipid, around 0.9 means protein. Learning these three alongside the obvious ones (magnification, rate, SA:V) picks up marks that other candidates leave on the table.

OCR expects you to recall all the GCSE 9-1 Higher Tier maths content for A-Level Biology calculations. The key ones that show up in biology contexts are:

• Circumference of a circle: 2πr
• Area of a circle: πr² (used for microbiology inhibition zones and quadrat corrections)
• Surface area of a cuboid: 2(bh + bl + hl)
• Volume of a cuboid: hbl
• Mean: x̄ = Σx / n
• Percentage change: ((new - original) / original) × 100
• Percentage yield: (actual / theoretical) × 100
• Percentage error (uncertainty): (2 × absolute uncertainty / quantity measured) × 100% (OCR's listed form, for an instrument read twice). OCR Biology A Section 5d (shown here in the AS H020 spec)

The percentage-error calculation is one students most often forget to drill. OCR's listed form assumes an instrument read twice (initial and final), such as a burette or a thermometer at the start and end of a reaction, so the single-reading uncertainty is doubled before dividing. For a single-reading instrument (balance, measuring cylinder), use the uncertainty once and drop the factor of 2. OCR flags percentage error as a required calculation skill, and burettes come up a lot in OCR practicals.

OCR Biology is unusual in providing BOTH paired and unpaired t-test formulae. AQA and Edexcel don't always list both forms explicitly. The practical implication is that OCR students need to be able to recognise which version of the t-test applies to a given dataset.

Use the paired t-test when the same individuals are measured twice (before and after a treatment, say). Use the unpaired t-test when you're comparing two independent groups. Picking the wrong one is a common error even when the formula is in front of you.

Standard-deviation calculation IS examinable at OCR. This is different from AQA, which rules out standard-deviation calculation on written papers. On OCR you can be set a mechanical calculation; the formula is provided, but you need to apply it under time pressure. The critical-values tables for every stats test are provided on the paper alongside the formula.

The three major boards all use embedded formulae rather than a separate downloadable booklet, but the details differ enough to matter.

OCR Biology has the most generous data provision of the three. Its recall list in Section 5d of the H420 spec is the longest, with two biological formulae provided on the paper (Hardy-Weinberg and Simpson's). It provides paired AND unpaired t-test formulae, plus standard deviation, Spearman's and chi-squared.

AQA's recall list is shorter (magnification, cardiac output, 2ⁿ, NPP = GPP - R, N = I - (F + R), plus Hardy-Weinberg, which spec section 3.7.2 treats as content you must use rather than guaranteeing it's printed). AQA provides Simpson's (in two forms across different sections of the spec), chi-squared, t-test, Spearman's and the Lincoln index in the question stem when needed. AQA explicitly rules out standard-deviation calculation on written papers (section 3.4.7). See our AQA A-Level Biology data sheet guide for the full AQA split.

Edexcel Spec B names two biological formulae as exemplar recall items in Appendix 6: magnification (A.1.8) and cardiac output (stroke volume × heart rate, A.2.4), plus Hardy-Weinberg from Topic 8, which Pearson doesn't guarantee will be printed in the stem. It provides index of diversity, chi-squared, t-test (of difference), and Spearman's in the question stem when needed. See our Edexcel A-Level Biology data sheet guide for the Spec B specifics.

Simpson's index comes in different forms across boards. OCR uses only D = 1 - Σ(n/N)². AQA uses both D = 1 - Σ(n/N)² and d = N(N-1) / Σn(n-1) in different sections of the spec. Edexcel Spec B uses D = N(N-1) / Σn(n-1) as its Appendix 6 exemplar. If you've been working with cross-board past papers, read the question carefully to see which form is given before plugging in numbers.

Mark-release-recapture via the Lincoln index is explicitly surfaced in AQA Biology (section 3.7.4) and is provided when needed. It isn't surfaced in OCR's formulae list, so don't claim it as a provided OCR formula.

The students who pick up marks on OCR Biology calculations tend to drill the recall list to automatic, then focus their revision time on applying the provided formulae under time pressure. Our wider A-Level revision techniques guide covers the general approach, but a few OCR-specific habits make a real difference.

For the recall list, build a one-page summary and write it from memory each weekend during the exam run-up. The Section 5d biological list runs to around 10 formulae plus the GCSE maths staples. That sounds like a lot, but most are short. The ones candidates most often forget (polymorphic loci, Q₁₀, RQ, biomass transfer efficiency) are worth drilling specifically.

For magnification, drill the unit conversions. The algebra is trivial once units are right; the mark scheme punishes the wrong unit. 1 mm = 1000 μm, 1 μm = 1000 nm.

For the stats tests, practise picking the right test for the dataset. Chi-squared when you've got observed and expected counts. Spearman's for correlation between two ranked variables. Paired t-test when the same individuals are measured twice. Unpaired t-test when you've got two independent groups. Standard deviation when the question asks for a measure of spread. OCR often tells you which test to apply, but Paper 3 'Unified biology' leaves the choice to you.

For each stats test, time yourself on past-paper questions with the formula in front of you. A chi-squared on three or four categories should take three to four minutes. A t-test is longer because of the arithmetic. Spearman's drags most students because of the rank-assignment step: tied values take the average of the ranks they would have occupied. Drill that specifically.

For the Hardy-Weinberg questions, run through our worked examples on the Hardy-Weinberg equation for A-Level Biology page. The two directions (allele frequency to genotype frequency, and genotype count back to allele frequency) are the ones most commonly asked.

Finally, cross-check against mark schemes. OCR mark schemes are tight on significant figures and on which value you took from the data. A calculated answer that's off by a factor of ten usually means a unit-conversion slip rather than a formula error.

Cognito's OCR A-Level Biology course covers every topic that uses the OCR formula list, with worked-example videos on magnification, Hardy-Weinberg, Simpson's index, chi-squared genetic-ratio tests, Spearman's rank correlation, and both paired and unpaired t-tests. If you also want to compare how different boards structure their data provision, our guides to the AQA A-Level Biology data sheet and the Edexcel A-Level Biology data sheet walk through the differences in detail.