Magnification
All measurements in same units (mm or μm). Rearrange to find actual size: actual = image ÷ magnification.
Magnification = image size / actual size Cambridge O Level 5090
🧬 O Level Biology Formula Sheet 2026
Key formulas, calculations and definitions for Cambridge O Level Biology (5090) — organised by topic for quick exam revision.
Cells Nutrition Transport Respiration 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.
O Level Biology Calculations and Key Relationships
Cambridge O Level Biology (5090) includes quantitative questions on magnification, osmosis, photosynthesis, genetics and ecology. This reference sheet brings together all the key formulas and structures you need for Papers 1 and 2.
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Microscopy and magnification calculations
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Osmosis and water potential
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Photosynthesis and respiration equations
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Genetics and inheritance ratios
Cell Biology — Microscopy
Unit Conversions
Always convert to the same unit before using the magnification formula.
1 mm = 1000 μm
1 μm = 1000 nm
1 cm = 10 mm
Nutrition and Photosynthesis
Photosynthesis Word Equation
Light energy required. Chlorophyll is the photosynthetic pigment.
Carbon dioxide + Water → Glucose + Oxygen Photosynthesis Symbol Equation
Balanced equation. Light energy absorbed by chlorophyll.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ Testing for Starch
Iodine solution: brown → blue-black in presence of starch.
Testing for Glucose (Reducing Sugar)
Benedict's solution: blue → brick red precipitate when heated with reducing sugar.
Testing for Protein
Biuret reagent: blue → purple/violet in presence of protein.
Testing for Fat
Ethanol emulsion test: white emulsion forms when fat is present.
Transport — Osmosis and Diffusion
Osmosis Definition
Net movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane.
Diffusion Definition
Net movement of particles from a region of higher concentration to a region of lower concentration.
Factors Affecting Rate of Diffusion
Surface area ↑ → faster. Concentration gradient ↑ → faster. Diffusion distance ↓ → faster. Temperature ↑ → faster.
Turgid vs Plasmolysed Cell
Turgid: water enters by osmosis, vacuole fills, cell wall prevents bursting. Plasmolysed: water leaves by osmosis, cytoplasm shrinks, membrane pulls away from cell wall.
Respiration
Aerobic Respiration Word Equation
Releases maximum ATP. Takes place in mitochondria.
Glucose + Oxygen → Carbon dioxide + Water (+ energy) Aerobic Respiration Symbol Equation
Energy released as ATP.
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O Anaerobic Respiration (Yeast)
Fermentation. Less ATP than aerobic.
Glucose → Ethanol + Carbon dioxide (+ energy) Anaerobic Respiration (Muscle)
Lactic acid accumulates causing fatigue. Repaid as oxygen debt.
Glucose → Lactic acid (+ energy) Respiratory Quotient (RQ)
RQ = 1.0 for carbohydrates, ~0.7 for fats, ~0.8 for proteins.
RQ = CO₂ produced / O₂ consumed Genetics and Inheritance
Monohybrid Cross
Use Punnett square: P generation → gametes → F1 → F1 × F1 → F2. Show all genotypes and phenotypes.
Expected Ratios
Dominant × Dominant (both heterozygous): 3 dominant : 1 recessive
Dominant × Recessive (homozygous): 1 dominant : 1 recessive
2 heterozygous parents: 1 AA : 2 Aa : 1 aa
Codominance
Both alleles expressed equally. Use different capital letters (e.g. Cᴿ and Cᵂ). No dominant allele.
Sex Determination
Sex chromosomes. Eggs carry X; sperm carry X or Y. Expected ratio: 1 female : 1 male.
Female: XX | Male: XY Ecology
Population Size (Mark-Release-Recapture)
N = estimated population, n₁ = first sample size, n₂ = second sample size, m = number of marked individuals recaptured.
N = (n₁ × n₂) / m Energy Transfer
Typically 10% efficient. Most energy lost as heat, movement, undigested material.
Efficiency (%) = (energy at next trophic level / energy at previous level) × 100% Carbon Cycle Key Processes
Photosynthesis removes CO₂. Respiration and combustion add CO₂. Decomposition by bacteria/fungi releases CO₂.
How to Use This Formula Sheet
Boost your Cambridge exam confidence with these proven study strategies from our tutoring experts.
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Magnification: always show working
Write the formula first, substitute with correct units, calculate. Both image size and actual size must be in the same unit.
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Genetics: draw the Punnett square
Always draw the full Punnett square. State genotype and phenotype ratios. Name alleles (e.g. T = tall, t = short).
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Osmosis: direction of water movement
Water moves from HIGH water potential to LOW water potential. Dilute solution = higher water potential. Concentrated = lower.
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Equations must be balanced
Photosynthesis and respiration equations: check atoms balance on both sides. Examiners check stoichiometry.
Formula Sheet FAQ
Quick answers about this free PDF and how to use it for exam revision and active recall.
Is the Cambridge O 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. Complete formula reference for Cambridge O Level Biology (5090). Key calculations, definitions and relationships for cells, nutrition, transport, respiration, genetics and ecology with O Level exam tips. 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 (Secondary)?
It is written for students preparing for assessments at 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.
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