A-level Biology Exam Study Guide (2027)
Everything the A-level Biology Exam tests, topic by topic: what each section covers, the facts that come up most, and how to study it. Pair it with the free 15-question practice test.
The exam at a glance
| Questions | AQA: 3 written papers of 91, 91 and 78 marks (260 marks in total), including a 25-mark essay on Paper 3. OCR Biology A: 100, 100 and 70 marks |
|---|---|
| Time | AQA: 6 hours in total (3 × 2 hours). OCR Biology A: 2 hours 15 minutes, 2 hours 15 minutes and 1 hour 30 minutes |
| Grades and pass mark | Grades run from A* to E, and grade E is a pass. Boundaries are set after every exam series, so aim for 70% in practice |
| Format | Written exams, calculator allowed, no tiers. The practical endorsement (12 required practicals with AQA) is assessed by your teachers and reported separately as Pass or Not classified |
| Exam boards | AQA, OCR and Pearson Edexcel |
| Test provider | At your school or college, or as a private candidate at an exam centre that accepts them |
Mind map: the whole exam on one screen
Read the complete A-level Biology study notes for “Biological Molecules”
Our first full set of comprehensive notes, about 20 minutes of reading: Monomers, polymers and the two key reactions · Carbohydrates · Lipids · Proteins and enzymes · Nucleic acids and DNA replication · ATP, water and inorganic ions · Biochemical tests, a worked exam example, the traps examiners use and a one-minute recap. Create a free account to read it and see how premium notes work before you decide.
1. Biological Molecules
AQA topic 1 (Papers 1 and 3). Monomers and polymers, carbohydrates, lipids, proteins and enzymes, nucleic acids and DNA replication, ATP, water and inorganic ions, and the biochemical tests.
Key facts
- Condensation reactions join monomers with a chemical bond and release water; hydrolysis breaks the bond using water. Glycosidic bonds join monosaccharides, peptide bonds join amino acids, ester bonds join fatty acids to glycerol, and phosphodiester bonds join nucleotides.
- α-glucose and β-glucose are isomers. Maltose = glucose + glucose, sucrose = glucose + fructose, lactose = glucose + galactose. Starch (amylose and amylopectin) and glycogen are α-glucose energy stores; cellulose is made of β-glucose, with alternate molecules inverted, forming straight chains held by hydrogen bonds into microfibrils.
- A triglyceride is one glycerol plus three fatty acids joined by ester bonds: a compact, insoluble energy store. In a phospholipid one fatty acid is replaced by a phosphate group, giving a hydrophilic head and hydrophobic tails that form bilayers. Saturated fatty acids have no C=C double bonds.
- Protein structure: primary (sequence of amino acids), secondary (α-helix or β-pleated sheet held by hydrogen bonds), tertiary (3D folding held by hydrogen, ionic and disulfide bonds) and quaternary (more than one polypeptide, sometimes with prosthetic groups).
- Enzymes lower the activation energy. In the induced-fit model the active site changes shape slightly as the substrate binds, putting strain on bonds. Competitive inhibitors bind to the active site; non-competitive inhibitors bind elsewhere and change the shape of the active site. Rate depends on temperature, pH, enzyme concentration and substrate concentration.
- DNA nucleotides contain deoxyribose, a phosphate group and a base (A, T, C or G); two antiparallel strands are joined by hydrogen bonds between complementary bases. RNA has ribose and uracil and is usually single-stranded. Semi-conservative replication: DNA helicase separates the strands, free nucleotides pair with exposed bases, DNA polymerase joins them. Meselson and Stahl's experiment supported this model.
- ATP is adenine + ribose + three phosphates. ATP hydrolase releases energy in small, manageable amounts and the Pi can phosphorylate other compounds; ATP synthase reforms ATP by condensation. Water is a metabolite, a solvent, has a high specific heat capacity and a large latent heat of vaporisation, and shows strong cohesion. Inorganic ions: H⁺ (pH), Fe²⁺ (haemoglobin), Na⁺ (co-transport) and PO₄³⁻ (DNA, ATP).
- Tests: Benedict's reagent heated gives a brick red precipitate with reducing sugars; for non-reducing sugars, boil with dilute acid, neutralise, then repeat the Benedict's test; iodine turns blue-black with starch; ethanol then water gives a white emulsion with lipids; biuret turns purple with protein.
Flashcards
Exam tip: Always name both the reaction (condensation or hydrolysis) and the bond. Mark schemes rarely accept 'a bond is formed'.
2. Cells
AQA topic 2 (Paper 1). Eukaryotic and prokaryotic cells and viruses, microscopy and cell fractionation, the cell cycle and mitosis, membranes and transport, and the immune response including vaccines, HIV and monoclonal antibodies.
Key facts
- Eukaryotic organelles: nucleus, mitochondria, chloroplasts (plants and algae), Golgi apparatus and vesicles, lysosomes, ribosomes (80S), rough and smooth endoplasmic reticulum, cell wall (cellulose in plants, chitin in fungi) and vacuole. Specialised cells form tissues, organs and organ systems.
- Prokaryotes have no membrane-bound organelles, smaller 70S ribosomes, a murein cell wall and circular DNA not associated with histones; they may have plasmids, a capsule and flagella. Viruses are acellular and non-living: nucleic acid, a capsid and attachment proteins.
- magnification = image size ÷ actual size. Resolution is the minimum distance apart two objects can be and still be seen as separate. TEMs give the highest resolution but need thin specimens in a vacuum; SEMs give 3D surface images. Cell fractionation uses a cold, isotonic, buffered solution, homogenisation, filtration and ultracentrifugation (nuclei sediment first).
- The cell cycle: interphase (DNA replication and growth), mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis. Mitotic index = number of cells in mitosis ÷ total number of cells. Uncontrolled mitosis can lead to tumours. Prokaryotes divide by binary fission; viruses replicate only inside host cells.
- Fluid mosaic model: a phospholipid bilayer with intrinsic and extrinsic proteins, glycoproteins, glycolipids and cholesterol (which restricts movement of phospholipids). Transport: simple diffusion, facilitated diffusion (channel and carrier proteins), osmosis, active transport (carrier proteins and ATP) and co-transport (sodium-glucose in the ileum).
- Osmosis is the net movement of water from a higher (less negative) water potential to a lower (more negative) water potential across a partially permeable membrane. Pure water has ψ = 0 kPa. Diffusion rate depends on surface area, concentration gradient and diffusion distance.
- Immunity: phagocytes engulf pathogens and present antigens. T cells (cell-mediated response) and B cells (humoral response) are activated; clonal selection and expansion produce plasma cells that secrete antibodies and memory cells for the secondary response. Antibodies are quaternary proteins whose variable regions bind specific antigens, forming antigen-antibody complexes and causing agglutination.
- Active immunity (infection or vaccination) produces memory cells; passive immunity (antibodies given, as via the placenta or breast milk) is immediate but short-lived. Herd immunity, antigenic variability, HIV structure and how HIV destroys helper T cells, and uses of monoclonal antibodies including the ELISA test and targeted drugs.
Flashcards
Exam tip: Water potential answers must say water moves from a higher (less negative) to a lower (more negative) water potential. Avoid 'water concentration' at A-level.
3. Exchange and Transport
AQA topic 3 (Paper 1). Surface area to volume ratio, gas exchange in insects, fish, plants and humans, digestion and absorption, haemoglobin, the circulatory system and heart, tissue fluid, and mass transport in plants.
Key facts
- Smaller organisms have a larger surface area to volume ratio. Larger organisms need specialised exchange surfaces with a large surface area, a short diffusion distance and a steep concentration gradient maintained by ventilation and circulation.
- Insects use spiracles, tracheae and tracheoles; fish gills have filaments and lamellae with countercurrent flow, which keeps a diffusion gradient along the whole lamella. Leaves exchange gases through stomata and air spaces in the spongy mesophyll. Xerophytes reduce water loss with thick cuticles, rolled leaves, sunken stomata and hairs.
- Human lungs: alveoli with thin walls and a rich capillary network. Inspiration: external intercostal muscles and the diaphragm contract, volume increases, pressure falls below atmospheric, air moves in. Pulmonary ventilation = tidal volume × ventilation rate. Lung diseases such as fibrosis, asthma and emphysema reduce gas exchange.
- Digestion: amylase hydrolyses starch to maltose; membrane-bound disaccharidases (maltase, sucrase, lactase) finish carbohydrate digestion. Endopeptidases, exopeptidases and membrane-bound dipeptidases digest proteins. Lipase and bile salts produce monoglycerides and fatty acids that form micelles. Glucose and amino acids are absorbed by co-transport with sodium ions; lipids are re-formed into triglycerides and leave as chylomicrons.
- Haemoglobin is a quaternary protein with four haem groups. It loads oxygen where the partial pressure is high (lungs) and unloads it where it is low (respiring tissues). The oxyhaemoglobin dissociation curve is S-shaped (cooperative binding). Higher CO₂ shifts it to the right (Bohr effect), so more oxygen is unloaded.
- The mammalian circulation is double. Cardiac cycle: atrial systole, ventricular systole, diastole; valves open and close because of pressure differences. Cardiac output = stroke volume × heart rate. Arteries have thick elastic and muscular walls, veins have valves, capillaries have walls one cell thick.
- Tissue fluid forms at the arteriole end of capillaries because hydrostatic pressure is higher than the pull of water potential; at the venule end water returns by osmosis because plasma proteins lower the water potential in the capillary. Excess tissue fluid drains into the lymph.
- Xylem: the cohesion-tension theory. Water evaporates from leaves (transpiration), creating tension that pulls a continuous column of water held by cohesion and adhesion. A potometer measures water uptake. Phloem: the mass flow hypothesis, with sucrose actively loaded at the source, water entering by osmosis and pressure pushing sap to the sink. Ringing and tracer experiments provide evidence.
Flashcards
Exam tip: For oxygen dissociation curves, always link the curve position to affinity, then to loading or unloading, then to the organism's oxygen needs.
Test yourself on these topics
Take the free 15-question A-level Biology test, then save your results to unlock your Readiness Score and the mistakes bank.
4. Genetic Information, Variation and Relationships
AQA topic 4 (Paper 1). Genes and chromosomes, the genetic code, transcription and translation, mutations and meiosis, genetic diversity and natural selection, species and taxonomy, and biodiversity.
Key facts
- A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or for a functional RNA; it occupies a fixed locus. Eukaryotic nuclear DNA is long, linear and wound around histones; prokaryotic, mitochondrial and chloroplast DNA is short, circular and not associated with histones. Eukaryotic genes contain introns (non-coding) and exons.
- The genetic code is a triplet code, universal, non-overlapping and degenerate. The genome is the complete set of genes in a cell; the proteome is the full range of proteins the cell can produce.
Flashcards
Exam tip: When asked how a mutation affects a protein, follow the chain: base sequence, codon, amino acid, primary structure, tertiary structure (hydrogen, ionic, disulfide bonds), shape of the active site or binding site.
5. Energy Transfers
AQA topic 5 (Paper 2). Photosynthesis (light-dependent and light-independent reactions), respiration (glycolysis, link reaction, Krebs cycle, oxidative phosphorylation, anaerobic pathways), energy transfer in ecosystems and nutrient cycles.
Key facts
- Light-dependent reaction in the thylakoid membranes: light causes photoionisation of chlorophyll; electrons pass along an electron transfer chain, releasing energy that pumps protons; ATP is made by chemiosmosis through ATP synthase; NADP is reduced; photolysis of water produces protons, electrons and oxygen.
- Light-independent reaction (Calvin cycle) in the stroma: rubisco catalyses CO₂ + RuBP → two molecules of glycerate 3-phosphate (GP); GP is reduced to triose phosphate (TP) using ATP and reduced NADP; some TP makes hexose sugars, most regenerates RuBP using ATP.
Flashcards
Exam tip: Keep a one-page map of where each stage happens and what goes in and out. Most Paper 2 marks on this topic come from inputs, outputs and locations.
6. Responding to Change
AQA topic 6 (Paper 2). Tropisms and taxes, receptors, control of heart rate, nerve impulses and synapses, skeletal muscle contraction, homeostasis, blood glucose control and osmoregulation.
Key facts
- In flowering plants IAA controls tropisms: in shoots it moves to the shaded side and stimulates cell elongation, so the shoot bends towards light; in roots it inhibits elongation. Taxis is directional movement in response to a stimulus; kinesis is a non-directional change in speed or turning rate.
- The Pacinian corpuscle responds to pressure: deformation opens stretch-mediated sodium channels, producing a generator potential. Rods contain rhodopsin and give high sensitivity through summation (several rods to one bipolar neurone) but low visual acuity; cones give colour vision and high acuity.
Flashcards
Exam tip: In action potential questions, always name the ion, the channel and the direction of diffusion: 'voltage-gated Na⁺ channels open and Na⁺ diffuses in'.
7. Genetics, Populations, Evolution and Ecosystems
AQA topic 7 (Paper 2). Inheritance (monohybrid, dihybrid, codominance, multiple alleles, sex linkage, autosomal linkage, epistasis), chi-squared, the Hardy-Weinberg principle, evolution and speciation, populations, sampling and succession.
Key facts
- Genotype is the genetic constitution; phenotype is the expression of the genotype and its interaction with the environment. Alleles can be dominant, recessive or codominant; some genes have multiple alleles (such as human ABO blood groups).
- A dihybrid cross between two double heterozygotes gives a 9:3:3:1 ratio if the genes are on different chromosomes. Autosomal linkage gives more parental-type offspring and fewer recombinants. Sex-linked genes are on the X chromosome, so males (XY) express recessive X-linked alleles more often. Epistasis gives modified ratios such as 9:3:4.
Flashcards
Exam tip: In Hardy-Weinberg questions, start from q² (the recessive phenotype frequency) and square root it. Never start from the dominant phenotype, which is p² + 2pq.
8. Control of Gene Expression
AQA topic 8 (Paper 2). Gene mutations, stem cells, transcription factors and oestrogen, epigenetics, RNA interference, cancer, genome projects and recombinant DNA technology, including PCR, gene probes and genetic fingerprinting.
Key facts
- Gene mutations: addition, deletion, substitution, inversion, duplication and translocation of bases. Additions and deletions cause a frameshift. Mutagenic agents such as ionising radiation and some chemicals increase the mutation rate.
- Stem cells: totipotent (early embryo, any cell including placenta), pluripotent (embryonic, most cell types), multipotent (adult, a limited range) and unipotent (one type, such as cardiomyocytes). Induced pluripotent stem cells are made from adult cells using transcription factors.
Flashcards
Exam tip: For epigenetics and transcription questions, link every change to whether transcription factors and RNA polymerase can access the promoter.
How to pass
- AQA Papers 1 and 2 are 91 marks in 120 minutes, about 1.3 minutes per mark. Paper 3 is 78 marks, but the essay deserves about 35 to 40 minutes of it.
- The Paper 3 essay rewards accurate, relevant A-level content drawn from across the specification. Plan five or six paragraphs from different topics, each linking a precise piece of biology to the title.
- Use exact A-level vocabulary: 'water potential' not 'water concentration', 'complementary shape' for enzymes and antibodies, 'reduced NADP' not 'NADPH'.
- Required practical questions ask you to evaluate methods. Learn the variables, controls and sources of error for all 12, and know how to calculate rates, standard deviation and percentage change.
- Statistics carry marks: know when to use chi-squared, Spearman's rank or a t-test, how to write a null hypothesis, and how to use a critical value at p = 0.05.
Frequently asked questions
How long should I study for the A-level Biology exam?
Most students do best starting 10 to 12 weeks before the first paper, with 30 to 45 minutes a day per subject. You're ready once your Readiness Score has stayed at 80 or higher for about a week.
Can I take the A-level Biology exam online?
No. A-level Biology is a written exam sat in person at your school, college or an approved exam centre. Format: written exams, calculator allowed, no tiers. The practical endorsement (12 required practicals with AQA) is assessed by your teachers and reported separately as Pass or Not classified. Check your exam board's timetable for dates.
What score do I need to pass the A-level Biology exam?
Grades run from A* to E, and grade E is a pass. Boundaries are set after every exam series, so aim for 70% in practice. The exam has aqa: 3 written papers of 91, 91 and 78 marks (260 marks in total), including a 25-mark essay on paper 3. ocr biology a: 100, 100 and 70 marks and a time limit of aqa: 6 hours in total (3 × 2 hours). ocr biology a: 2 hours 15 minutes, 2 hours 15 minutes and 1 hour 30 minutes.
What are the most tested topics?
The outline covers biological molecules, cells, exchange and transport, genetic information, variation and relationships, energy transfers, responding to change, genetics, populations, evolution and ecosystems, control of gene expression. Use the free practice test to see which ones you need most.
The premium A-level Biology study path
Premium A-level Biology prep is studied one topic at a time. Each step starts with that topic's key notes and flashcard deck, then its own question sets of 25, so you master one topic before you move to the next. When every topic is strong, the 6 full mock exams show you're ready.
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- 1Biological Molecules8 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25Notes free with an account
- 2Cells8 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25Premium
- 3Exchange and Transport8 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25Premium
- 4Genetic Information, Variation and Relationships8 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25Premium
- 5Energy Transfers7 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25Premium
- 6Responding to Change7 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25Premium
- 7Genetics, Populations, Evolution and Ecosystems7 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25Premium
- 8Control of Gene Expression7 key notes, 100 flashcards, then 375 practice questions in 15 sets of 25Premium
- Final step: 6 full mock exams50 questions each, timed like exam day. Hit your target on them before your first paper.Premium
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Summarised from the exam boards' published specifications and the rules cited, checked November 2026. Confirm current requirements with AQA, OCR and Pearson Edexcel.