Magnification
M = image size / actual size Edexcel International A Level XBI11/YBI11
🧬 Edexcel International A Level Biology Formula Sheet 2026
Quantitative relationships for microscopy, transport, genetics, ecology and statistics — organised for Edexcel XBI11/YBI11 papers.
Microscopy Transport Genetics Ecology
Our formula sheets are free to download — save this one as PDF for offline revision.
Aligned with the latest 2026 syllabus and board specifications. This sheet is prepared to match your exam board’s official specifications for the 2026 exam series.
Handle Biology Calculations with Confidence
Although Biology is concept-based, Cambridge exams expect precise quantitative work. Use this formula sheet to keep magnification calculations, water potential, genetic ratios and statistical tests at your fingertips.
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Microscopy & cell measurement calculations
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Water potential and gas exchange relationships
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Population genetics and inheritance maths
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Ecological diversity and productivity formulas
Magnification & microscopy
Light and electron microscopy calculations.
Actual size
actual = image / M Resolution
Minimum distance two points can be distinguished.
λ shorter or NA higher → better resolution (Rayleigh criterion in context).
Topic Focus
Units
- Convert µm ↔ nm consistently before dividing.
- Electron microscopes: higher resolution than light for ultrastructure.
Cell biology & biochemistry
Membranes, enzymes, and respiration/photosynthesis quant links.
Enzyme rate
V depends on [S], temperature, pH.
Michaelis–Menten: V = V_max [S] / (K_m + [S]) Respiration (summary)
ATP yield depends on pathway; use exam values.
Aerobic vs anaerobic efficiency context.
Photosynthesis efficiency
Energy capture vs incident light (qualitative + % calculations if given data).
Efficiency ≈ (energy stored chemically / incident light energy) × 100% Topic Focus
Practicals
- Control variables for enzyme assays: pH, temperature, substrate concentration.
- Use repeats and means; identify anomalies.
Genetics & evolution
Mendelian ratios, Hardy–Weinberg, and selection.
Hardy–Weinberg
p + q = 1; p² + 2pq + q² = 1 for two alleles.
p² = freq(hom dom) 2pq = freq(hetero) q² = freq(hom rec) Selection coefficient
s relative fitness reduction.
w = 1 − s (relative fitness) Topic Focus
Assumptions
- Hardy–Weinberg: random mating, no selection/mutation/migration, large population.
- Use HW to estimate carriers from allele frequencies.
Ecology & sampling
Populations, energy transfer, and statistics.
Lincoln index
M marked first sample, C second capture, R marked in second.
N ≈ (M × C) / R Simpson’s index of diversity
n total individuals, n_i in category i.
D = 1 − Σ (n_i / n)² Net primary production
Energy available to consumers.
NPP = GPP − R_plant Energy transfer efficiency
efficiency = (energy at trophic level n+1) / (energy at trophic level n) × 100% Topic Focus
Fieldwork
- Random coordinates reduce bias; systematic for transects along gradients.
- Abiotic factors correlate with distribution (pH, light, moisture).
Physiology
Cardiac, ventilation, and kidney quantitative ideas.
Cardiac output
CO = SV × HR Ventilation rate
Per minute.
pulmonary ventilation = tidal volume × respiratory rate Filtration rate idea
Kidney.
GFR links plasma flow and filtration pressure (qualitative + given data calculations) Topic Focus
Homeostasis
- Negative feedback opposes change; compare set point vs receptor/controller/effector.
- Exercise shifts CO₂, temperature, and lactate — link to compensation.
Statistics (biology context)
Tests commonly used in practical papers.
Standard deviation (sample)
s = √( Σ(x − x̄)² / (n − 1) ) Standard error
SE = s / √n 95% CI (large n, normal approx.)
≈ mean ± 1.96 SE Chi-squared
Goodness of fit / contingency.
χ² = Σ (O − E)² / E Spearman’s rank
Correlation on ranks.
Use when data not linear or ordinal.
Topic Focus
Hypothesis testing
- State null/alternative; choose test by data type and design.
- Compare test statistic to critical value at chosen significance level.
How to Use This Formula Sheet
Boost your Cambridge exam confidence with these proven study strategies from our tutoring experts.
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Quote Formula + Units
Write the relevant formula before substitution and track units carefully — especially for water potential and gas calculations.
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Support Conclusions with Stats
When presenting practical conclusions, use calculated means, standard deviations and χ² to justify claims.
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Check Biological Plausibility
Sense-check your final values against typical biological ranges (e.g., realistic cell sizes, population counts).
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Link Numbers to Processes
After calculations, explain the biological mechanism behind the result to collect explanation marks.
Formula sheet FAQ
Quick answers about this free PDF, how to use it for exam revision, and how it relates to your official syllabus.
Is the Edexcel International A Level Biology Formula Sheet 2026 free to download as a PDF?
Yes. This Tutopiya formula sheet is free to use and you can download it as a PDF from this page for offline revision. There is no payment or account required for the PDF download.
What Biology topics and equations does this formula sheet cover?
This page groups key Biology formulas in one place for revision. Edexcel International A Level Biology (XBI11/YBI11) formula sheet for 2026 covering magnification, water potential, population genetics, statistics and ecology calculations. Always cross-check with your official syllabus and past papers for your exam session.
Can I use this instead of the official exam formula booklet in the exam?
No. In the exam you must follow only what your exam board allows in the hall—usually the official formula booklet or data sheet where provided. This page is a revision and teaching aid, not a replacement for board-issued materials.
Who is this formula sheet for (Upper Secondary)?
It is written for students preparing for assessments at Upper Secondary in Biology, including classroom revision, homework support, and independent study. Teachers and tutors can also share it as a quick reference.
How should I revise with this formula sheet?
Work through past paper questions, quote the correct formula before substituting values, and check units and notation every time. Pair this sheet with timed practice and mark schemes so you see how examiners expect working to be set out.
Where can I get more help with Biology revision?
Explore Tutopiya’s study tools, past paper finder, and revision checklists linked from our tools hub, or book a trial lesson with a subject specialist for personalised support alongside this formula reference.
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Matches the quantitative requirements of Edexcel International AS & A Level Biology (XBI11/YBI11), including practical assessment expectations.
Always specify significant figures based on instrument precision and indicate biological context in written answers.