WJEC A-Level Biology Unit 1 Revision Tools

Track your confidence with our interactive RAG checklist covering all 130 learning objectives, and analyse 7 years of past paper topics to focus your revision where it matters most.

WJEC Unit 1 AS and A-Level Free Tools

Last updated: February 2026 – Includes papers up to 2024

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130 Learning Objectives

7 Years of Past Papers

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Created by WJEC Examiner

Learning Objectives Checklist (RAG Rating)

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Unit 1: Basic Biochemistry and Cell Organisation covers six main topics from the WJEC specification, plus essential mathematical and practical skills. Rate your confidence on every learning objective using the traffic light system below.

Red – Need to learn

Amber – Understand but need practice

Green – Confident and exam-ready

Tip: Click any learning objective to see the exact terminology the mark scheme demands and the common mistakes that lose students marks. Your ratings save automatically in your browser.

1.1 Biological Molecules

0/38 rated

1.2 Cell Structure and Organisation

0/11 rated

1.3 Cell Membranes and Transport

0/16 rated

1.4 Enzymes and Biological Reactions

0/12 rated

1.5 Nucleic Acids and Their Functions

0/19 rated

1.6 Cell Division

0/14 rated

Mathematical Skills

0/10 rated

Required Practical Skills

0/10 rated

Inorganic Ions [Spec 1.1(a)]

1 State the four inorganic ions required by living organisms and describe the specific role of each: Mg²⁺ in chlorophyll, Fe²⁺ in haemoglobin, Ca²⁺ in cell walls and bones, PO₄³^– in nucleic acids, ATP and phospholipids?

Required Terminology: Mg²⁺, Fe²⁺, Ca²⁺, PO₄³^–, chlorophyll, haemoglobin, nucleic acids, ATP, phospholipids

Common Mistakes: REJECT ‘chloroplast’ – must say chlorophyll. REJECT vague roles like ‘needed for growth’. Must name the SPECIFIC molecule each ion is part of.

Depth: 3 marks in 2017. Name all four ions with specific molecules.

Water [Spec 1.1(b)]

2 Explain why water is described as a polar molecule, using δ⁺ and δ^– notation to show the partial charges on hydrogen and oxygen?

Required Terminology: polar, δ⁺ (hydrogen), δ^– (oxygen), covalent bond, electronegative, partial charge

Common Mistakes: REJECT using just + and – symbols. Must use DELTA notation (δ⁺/δ^–). 2024 Q4ci penalised students who used +/- instead.

Depth: 1 mark. Must annotate diagram correctly.

3 Describe how hydrogen bonds form between water molecules and explain why water’s polarity is the basis for ALL of its biological properties?

Required Terminology: hydrogen bond, δ⁺ hydrogen, δ^– oxygen, intermolecular, attraction

Common Mistakes: REJECT ‘strong bonds’ – hydrogen bonds are WEAK individually but collectively significant. REJECT ‘ionic bonds’.

Depth: QER 2019. Foundation for all water properties.

4 Explain why water is an excellent solvent for ionic and polar substances, and give named biological examples of substances dissolved in water?

Required Terminology: solvent, polar, ionic, dissolves, hydroxyl groups, hydrogen bonds with water

Common Mistakes: REJECT ‘dissolves everything’. Water only dissolves POLAR and IONIC substances, NOT lipids. 2024 Q4cii: sugars dissolve because OH groups H-bond with water.

Depth: 2 marks. Name substances: glucose, amino acids, salts, ions.

5 Explain the importance of water’s high specific heat capacity and high latent heat of vaporisation for living organisms?

Required Terminology: specific heat capacity, latent heat of vaporisation, thermal buffer, evaporative cooling

Common Mistakes: REJECT mentioning only one thermal property – Teachers’ Guide explicitly requires BOTH specific heat capacity AND latent heat of vaporisation.

Depth: QER 2019. Two separate properties, two separate explanations.

6 Describe water’s role as a metabolite, naming specific reactions where water is a reactant AND specific reactions where water is a product?

Required Terminology: metabolite, hydrolysis (reactant), photosynthesis (reactant), condensation (product), aerobic respiration (product)

Common Mistakes: REJECT ‘water is used in reactions’ without naming the reactions. Must give specific named reactions for each role.

Depth: QER 2019. At least 2 examples each side.

7 Explain cohesion and surface tension in water and link these to biological functions such as transport in xylem?

Required Terminology: cohesion, surface tension, hydrogen bonds, transpiration pull, xylem

Common Mistakes: REJECT confusing cohesion (water-water) with adhesion (water-surface).

Depth: 1-2 marks. Brief explanation + biological context.

8 Explain why ice floats and why this is biologically important?

Required Terminology: less dense, open lattice, hydrogen bonds, insulates, aquatic habitats

Common Mistakes: REJECT ‘ice is lighter’ – must say ‘less dense’. Explain the open lattice structure.

Depth: QER 2019. Brief – 1 mark point in extended answer.

Carbohydrates [Spec 1.1(c)(d)(e)]

9 Classify monosaccharides by the number of carbon atoms and name examples of each: triose (glyceraldehyde), pentose (ribose, deoxyribose), hexose (α-glucose, β-glucose, fructose, galactose)?

Required Terminology: triose, pentose, hexose, C_n(H₂O)_n, glyceraldehyde, ribose, deoxyribose, α-glucose, β-glucose, fructose, galactose

Common Mistakes: Teachers’ Guide names ALL these examples. Know all of them.

Depth: 1-2 marks. Recall and classify.

10 Define the term ‘structural isomer’ and explain how α-glucose and β-glucose differ, identifying them from structural formulae?

Required Terminology: structural isomer, same molecular formula, different structural formula, C1, OH group position

Common Mistakes: REJECT defining isomers with only half the definition – must state BOTH ‘same formula’ AND ‘different structure’. 2016 + 2024 both require this.

Depth: 1 mark for definition. Must identify from diagrams: α = OH below on C1, β = OH above on C1.

11 Describe a condensation reaction between two monosaccharides and draw a labelled diagram showing water removal and glycosidic bond formation?

Required Terminology: condensation, glycosidic bond, water removed, covalent bond

Common Mistakes: REJECT calling it a ‘dehydration reaction’. Must show water molecule being released in diagram.

Depth: 2 marks. Must be able to DRAW it with annotations.

12 Describe hydrolysis as the reverse of condensation: the addition of water to break a glycosidic bond, and draw a labelled diagram?

Required Terminology: hydrolysis, water added, glycosidic bond broken, monosaccharides released

Common Mistakes: REJECT ‘water breaks down the molecule’ – must say water is ADDED across the bond. 2016 Q4ai, 2024 Q4aiii.

Depth: 2 marks. Must be able to DRAW it with annotations.

13 Name the three disaccharides and their component monosaccharides: maltose (α-glucose + α-glucose), sucrose (glucose + fructose), lactose (glucose + galactose)?

Required Terminology: maltose, sucrose, lactose, α-glucose, fructose, galactose

Common Mistakes: REJECT confusing composition. Must know ALL three precisely.

Depth: 1-2 marks. Recall.

14 Describe the structure of amylose: unbranched polymer of α-glucose, α-1,4 glycosidic bonds only, forming a helical/coiled chain?

Required Terminology: amylose, α-glucose, α-1,4 glycosidic bonds, unbranched, helical, coiled

Common Mistakes: REJECT ‘straight chain’ for amylose – it is HELICAL. Straight chains are cellulose.

Depth: QER 2018, 2024 Q4aii (6 marks). Must distinguish from amylopectin.

15 Describe the structure of amylopectin: branched polymer of α-glucose, α-1,4 glycosidic bonds in main chain AND α-1,6 glycosidic bonds at branch points?

Required Terminology: amylopectin, α-glucose, α-1,4, α-1,6, branched, branch points

Common Mistakes: REJECT ‘just like amylose but branched’. Must name BOTH bond types. 2023 Q4aii: more branches = more ends = faster hydrolysis.

Depth: 3 marks in 2023. Know why branching matters.

16 Explain why starch (amylose + amylopectin) is a good storage molecule: insoluble (no osmotic effect), compact (helical), easily hydrolysed to release glucose?

Required Terminology: insoluble, compact, no osmotic effect, easily hydrolysed, energy storage

Common Mistakes: REJECT ‘good for energy’. Must explain WHY – insolubility prevents osmotic effects. 2018 QER.

Depth: QER 2018. Link structure > property > function.

17 Describe the structure of cellulose: β-glucose monomers with alternate molecules rotated 180°, forming long straight chains; hydrogen bonds between adjacent chains form microfibrils?

Required Terminology: β-glucose, rotated 180°, straight chains, hydrogen bonds, microfibrils, tensile strength

Common Mistakes: REJECT ‘helical’ for cellulose – that’s amylose. Cellulose = STRAIGHT. REJECT ‘strong bonds’ – the H-bonds are individually weak but collectively strong as microfibrils.

Depth: 4-6 marks across papers. HIGH VALUE. Must connect: β-glucose > 180° rotation > straight > H-bonds > microfibrils > strength > prevents lysis.

18 Explain how cellulose prevents osmotic lysis in plant cells, linking its structural strength to resisting the pressure of water entering by osmosis?

Required Terminology: microfibrils, tensile strength, osmotic lysis, turgid, cell wall, pressure potential

Common Mistakes: REJECT answers that don’t link structure to function. 2016 Q3c, 2019 Q2c.

Depth: 4 marks. The CHAIN of reasoning is what earns marks.

19 Describe the structure of chitin and compare it to cellulose?

Required Terminology: chitin, β monomers, acetylamine groups, nitrogen-containing, fungal cell walls, arthropod exoskeleton

Common Mistakes: Teachers’ Guide: ‘similar to cellulose but some OH groups replaced by nitrogen-containing acetylamine groups’. In spec but rarely tested.

Depth: Low frequency. Know it exists and basic structure.

20 Describe the structure of glycogen and explain how it differs from starch?

Required Terminology: glycogen, α-glucose, highly branched, more branches than amylopectin, animal/fungi storage

Common Mistakes: More branched = more ends = even faster glucose release. Animal equivalent of starch.

Depth: 1-2 marks. Compare with starch.

21 Name the three enzymes involved in starch digestion and state the specific role of each: amylase (starch > maltose), maltase (maltose > glucose), isomaltase (hydrolyses 1,6 bonds at branch points)?

Required Terminology: amylase, maltase, isomaltase, maltose, glucose, 1-6 glycosidic bonds, branch points

Common Mistakes: 2023 Q4bii (3 marks). All three enzymes needed. REJECT ‘amylase breaks starch into glucose’ – amylase produces MALTOSE.

Depth: 3 marks. Three enzymes, three specific actions.

Food Tests [Spec 1.1 Practical]

22 Describe and perform the iodine test for starch, stating the colour change?

Required Terminology: iodine-potassium iodide, brown/yellow > blue-black

Common Mistakes: REJECT ‘black’ alone – must say blue-black. 2023 Q4biv: negative = stays brown.

Depth: 1-2 marks. Method + result.

23 Describe the Benedict’s test for reducing sugars: add reagent, heat in water bath at 70-90°C, observe colour change from blue > green > yellow > orange > brick red?

Required Terminology: Benedict’s reagent, water bath, 70-90°C, blue > brick red, precipitate, semi-quantitative

Common Mistakes: REJECT ‘boil’ – must say ‘heat in water bath’. REJECT ‘red’ – say ‘brick red precipitate’. Know colour progression = semi-quantitative.

Depth: 2 marks. Method + precise colour change.

24 Describe the complete method for testing for non-reducing sugars: negative Benedict’s test first, then add dilute HCl and heat, neutralise with NaOH/sodium bicarbonate, THEN repeat Benedict’s test?

Required Terminology: dilute HCl, hydrolysis, neutralise, NaOH, repeat Benedict’s, brick red

Common Mistakes: REJECT missing the neutralisation step. REJECT adding HCl to Benedict’s directly. 2019 Q5aiii: NOT reference to HCl in reducing sugar test.

Depth: 3 marks. Full multi-step method required.

25 Describe the Biuret test for proteins: add Biuret reagent (NaOH then CuSO₄), observe colour change from blue > lilac/purple?

Required Terminology: Biuret reagent, NaOH, CuSO₄, blue > lilac/purple

Common Mistakes: REJECT ‘violet’ or ‘pink’ – say LILAC or purple. REJECT heating – Biuret test does NOT require heat. 2016 Q4aiv.

Depth: 1-2 marks.

26 Describe the emulsion test for lipids: dissolve in ethanol (absolute alcohol), pour into cold water, positive = cloudy white emulsion?

Required Terminology: ethanol, absolute alcohol, cold water, cloudy white emulsion

Common Mistakes: Ethanol must be ABSOLUTE (not dilute). Spec requires this test.

Depth: 1-2 marks.

Lipids [Spec 1.1(f)(g)]

27 Describe the structure of a triglyceride: one glycerol + three fatty acids joined by three ester bonds via condensation reactions?

Required Terminology: triglyceride, glycerol, three fatty acids, ester bond, condensation

Common Mistakes: REJECT ‘peptide bond’ or ‘glycosidic bond’. Lipid bond = ESTER bond. QER 2018.

Depth: QER 2018. Draw and label.

28 Compare saturated fatty acids (only single C-C bonds, straight chains, pack closely, solid at room temp) with unsaturated fatty acids (one or more C=C double bonds, kinks in chain, cannot pack closely, liquid at room temp)?

Required Terminology: saturated, unsaturated, C=C double bond, kink, packing, mono-unsaturated, poly-unsaturated

Common Mistakes: REJECT ‘unsaturated = double bond’ without explaining the KINK and its consequences. 2017 Q5bii: kinks > less packing > more fluid.

Depth: 3-4 marks. Must explain physical consequences.

29 Describe the structure of a phospholipid and compare it with a triglyceride: phospholipid = glycerol + 2 fatty acid tails (hydrophobic) + 1 phosphate head (hydrophilic)?

Required Terminology: phospholipid, glycerol, two fatty acids, phosphate head, hydrophilic, hydrophobic, amphipathic

Common Mistakes: REJECT not distinguishing from triglyceride. Phospholipid = 2 tails + phosphate. Triglyceride = 3 tails, no phosphate.

Depth: 2 marks. Know the difference.

30 Explain how unsaturated fatty acids in phospholipids affect membrane fluidity: C=C double bonds cause kinks > phospholipids cannot pack as closely > membrane is more fluid > lower transition temperature?

Required Terminology: C=C double bond, kink, packing, fluidity, transition temperature

Common Mistakes: REJECT answers that stop at ‘kinks’. Must complete the chain: kinks > gaps > fluid > lower transition temp. 2017 Q5bii (4 marks).

Depth: 4 marks. Full chain of reasoning.

31 State the functions of lipids: energy storage (more energy per gram than carbohydrate), insulation, waterproofing, protection, component of cell membranes?

Required Terminology: energy storage, insulation, waterproofing, protection

Common Mistakes: Teachers’ Guide lists multiple functions.

Depth: 1-2 marks. State at least three.

32 Explain how a high intake of saturated fat can lead to coronary heart disease: raises LDL cholesterol > atheroma builds up in coronary arteries > restricts blood flow > CHD?

Required Terminology: saturated fat, LDL cholesterol, atheroma, coronary arteries, CHD

Common Mistakes: REJECT detailed atheroma formation – ‘detailed knowledge not expected’ (Teachers’ Guide). But must name LDL and atheroma. 2017 Q5biv.

Depth: 2 marks. Short chain: saturated fat > increasesLDL > atheroma > CHD.

Proteins [Spec 1.1(h)(i)(j)]

33 Draw the general structure of an amino acid labelling: amino group (NH₂), carboxyl group (COOH), R group (variable side chain), hydrogen atom, central carbon?

Required Terminology: amino group, carboxyl group, R group, central carbon, 20 different amino acids

Common Mistakes: REJECT unlabelled diagrams. Must identify all functional groups. Teachers’ Guide: ‘draw the general formula’.

Depth: 2 marks. Draw AND label.

34 Explain that R groups can be polar (hydrophilic), non-polar (hydrophobic), acidic or basic, and that R group properties determine how the protein folds and functions?

Required Terminology: R group, polar, non-polar, hydrophilic, hydrophobic, folding

Common Mistakes: 2019 Q4e (sickle cell): polar > non-polar R group change affects haemoglobin structure and function.

Depth: 2-3 marks in application questions.

35 Draw a condensation reaction between two amino acids showing peptide bond formation and water release?

Required Terminology: condensation, peptide bond, dipeptide, water released

Common Mistakes: REJECT showing water ADDED – that’s hydrolysis. Condensation = water REMOVED. 2018 Q4ai.

Depth: 2 marks. Draw with annotations.

36 Define and describe ALL four levels of protein structure: primary (sequence of amino acids, peptide bonds), secondary (α-helix or β-pleated sheet, hydrogen bonds), tertiary (3D folding, H-bonds + ionic bonds + disulfide bonds + hydrophobic interactions), quaternary (2+ polypeptide chains)?

Required Terminology: primary, sequence, peptide bonds, secondary, α-helix, β-pleated sheet, hydrogen bonds, tertiary, disulfide bonds, ionic bonds, hydrophobic interactions, quaternary

Common Mistakes: REJECT naming bonds at wrong level. H-bonds = secondary. ALL bond types = tertiary. REJECT ‘strong bonds’ for secondary – say ‘hydrogen bonds’. 2018 Q4bii: identify from ribbon diagrams.

Depth: 2-4 marks per question. High frequency.

37 Compare globular proteins (roughly spherical, soluble, metabolic function, e.g. enzymes, haemoglobin) with fibrous proteins (long/elongated, insoluble, structural function, e.g. collagen, keratin)?

Required Terminology: globular, fibrous, soluble, insoluble, metabolic, structural, haemoglobin, collagen, keratin

Common Mistakes: 2022 Q6b: fibrinogen (globular, soluble) > fibrin (fibrous, insoluble). Must know named examples.

Depth: 2 marks. Comparative.

38 Describe post-translational modification of polypeptides: addition of carbohydrates (glycosylation), lipids, or phosphate groups; assembly of quaternary structures; modification occurs in the Golgi body?

Required Terminology: post-translational modification, glycosylation, glycoprotein, Golgi body, quaternary assembly

Common Mistakes: 2022 Q6aiii. Often missed by students. Must name specific modifications.

Depth: 2 marks.

Organelles [Spec 1.2(a)]

39 Identify ALL the following organelles from electron micrographs AND diagrams, and state the function of each: nucleus, nucleolus, nuclear envelope, nuclear pores, mitochondria, RER, SER, ribosomes, Golgi body, lysosomes, centrioles, chloroplasts, vacuole, plasmodesmata?

Required Terminology: All organelle names, cristae, thylakoids, grana, stroma, cisternae

Common Mistakes: REJECT identifying by name only – must also know EM APPEARANCE. Tested EVERY paper.

Depth: 2-3 marks. Core knowledge.

40 Explain how organelles work together in the synthesis and secretion of proteins (glycoprotein pathway): DNA transcribed in nucleus > mRNA exits through nuclear pores > translation on RER ribosomes > protein enters RER > vesicle buds off > Golgi modifies/glycosylates/packages > secretory vesicle > exocytosis?

Required Terminology: transcription, mRNA, nuclear pores, translation, RER, vesicle, Golgi, glycosylation, exocytosis

Common Mistakes: REJECT missing steps. 2018 Q1b (8 marks total). Must describe EVERY step in sequence. REJECT ‘sent to Golgi’ without describing vesicle transport.

Depth: 6-8 marks. Full pathway in detail.

41 Explain why mitochondria are important for active processes, always naming the specific process requiring ATP (e.g. active transport, protein synthesis, exocytosis)?

Required Terminology: mitochondria, ATP, aerobic respiration, cristae, surface area

Common Mistakes: REJECT ‘mitochondria provide energy’ alone. Must say: mitochondria > ATP > named specific process. 2018 Q1biii.

Depth: 2 marks every time. Always the same structure.

42 Explain why cristae in mitochondria increase the rate of ATP production?

Required Terminology: cristae, inner membrane, folded, increased surface area, respiratory enzymes, ATP

Common Mistakes: REJECT ‘bigger surface area’ without saying for WHAT. Must say: cristae > increasesSA for respiratory enzymes > increasesATP. 2017 Q1biii.

Depth: 2 marks.

Prokaryotic Cells, Viruses and Cell Theory [Spec 1.2(b)(c)]

43 Compare eukaryotic and prokaryotic cells in a table format, giving at least 5 differences?

Required Terminology: eukaryotic, prokaryotic, membrane-bound organelles, linear DNA, circular DNA, 80S, 70S, histones, murein/peptidoglycan, mesosome, plasmids

Common Mistakes: REJECT non-comparative answers – must state BOTH sides. REJECT ‘bigger ribosomes’ – say 80S vs 70S. 2016 Q3d, 2019 Q2d.

Depth: 3 marks. Must be comparative.

44 Explain why viruses cannot reproduce independently, naming SPECIFIC organelles they lack and the consequence of each?

Required Terminology: ribosomes (no translation), mitochondria (no ATP), acellular, protein coat/capsid, nucleic acid

Common Mistakes: REJECT ‘no organelles’ unqualified – 2016 MS explicitly rejects this. MUST name ribosomes AND mitochondria specifically and state why each matters.

Depth: 2 marks. 2016, 2024.

45 Explain why bacterial cell division (binary fission) is NOT mitosis, giving at least two reasons?

Required Terminology: binary fission, no spindle, no centrioles, circular DNA, no nucleus, no histones

Common Mistakes: 2024 Q6c (2 marks). Three possible reasons: no spindle, circular DNA not chromosomes, no nuclear membrane.

Depth: 2 marks. Name specific structures bacteria lack.

Microscopy [Spec 1.2 Practical]

46 Calculate magnification, actual size, and image size using M = I/A, converting between units (1 mm = 1000 μm = 1,000,000 nm)?

Required Terminology: magnification, image size, actual size, mm, μm, nm

Common Mistakes: REJECT not showing working. REJECT wrong units. REJECT forgetting to convert. Most common error: measuring in mm but not converting to μm.

Depth: 2-3 marks per question. Tested 6/7 papers.

47 Calculate magnification from a scale bar on an image: measure the bar in mm, convert to μm, divide by stated value?

Required Terminology: scale bar, measure, convert, divide

Common Mistakes: Must PHYSICALLY MEASURE the bar. 2022, 2023, 2024.

Depth: 2 marks.

Tissues and Organs [Spec 1.2(d)]

48 Define a tissue (group of similar cells working together for one function), an organ (different tissues working together), and an organ system?

Required Terminology: tissue, organ, organ system, similar cells, specific function

Common Mistakes: 2017 Q1aii: ‘only one type of cell/tissue, so cannot be an organ’. Precise definitions.

Depth: 1-2 marks.

49 Recognise and describe tissue types: squamous epithelium (flat/thin, short diffusion distance), ciliated epithelium (cilia sweep mucus), columnar epithelium (tall, absorption), striated/smooth/cardiac muscle, connective tissue?

Required Terminology: squamous, ciliated, columnar, striated, smooth, cardiac, connective tissue

Common Mistakes: 2022 Q1: squamous adaptation = thin = short diffusion distance. Teachers’ Guide lists ALL these types.

Depth: 2-3 marks.

Membrane Structure [Spec 1.3(a)]

50 Draw and label a diagram of the Fluid Mosaic Model: phospholipid bilayer, intrinsic (transmembrane) proteins, extrinsic proteins, glycoproteins, glycolipids, cholesterol?

Required Terminology: phospholipid bilayer, intrinsic/extrinsic proteins, glycoprotein, glycolipid, cholesterol, glycocalyx, fluid mosaic model

Common Mistakes: Must know ALL components. Glycoproteins form the glycocalyx on extracellular surface.

Depth: 2-3 marks. Must be able to DRAW.

51 Compare the Davson-Danielli model with the Fluid Mosaic model, identifying key differences?

Required Terminology: Davson-Danielli: proteins coat surface. Fluid Mosaic: proteins EMBEDDED in bilayer, plus glycocalyx and cholesterol

Common Mistakes: 2017 Q5a. Key difference = protein POSITION. D-D: on surface. FM: embedded/spanning.

Depth: 4 marks.

52 State the function of each membrane component: phospholipids (barrier), cholesterol (regulates fluidity), channel proteins (passive transport of ions), carrier proteins (facilitated diffusion/active transport), glycoproteins (cell recognition)?

Required Terminology: phospholipid barrier, cholesterol fluidity, channel proteins, carrier proteins, cell recognition

Common Mistakes: 2024 Q1ci (3 marks). Must link component > function.

Depth: 3 marks.

Membrane Permeability [Spec 1.3(b)]

53 Explain the effect of increasing temperature on membrane permeability: at moderate increases, phospholipids gain kinetic energy, membrane more fluid; above ~40°C proteins begin to DENATURE; above ~60-70°C membrane destroyed, all contents leak?

Required Terminology: kinetic energy, fluidity, protein denaturation, tertiary structure, bonds broken

Common Mistakes: NEVER say ‘phospholipids denature’ – 2022 MS explicitly REJECTS this. Only PROTEINS denature. Phospholipids become more fluid/form gaps.

Depth: 2-3 marks. Critical distinction.

54 Explain the effect of organic solvents (ethanol) and acids on membrane permeability?

Required Terminology: ethanol dissolves phospholipids, acid denatures proteins, tertiary structure disrupted

Common Mistakes: 2022 Q4bi: ethanol > dissolves LIPIDS. Acid > denatures PROTEINS. Two DIFFERENT mechanisms.

Depth: 3 marks.

55 Describe the beetroot membrane permeability experiment: method, variables, use of colorimeter (blue/green filter, 530 nm), measuring absorbance?

Required Terminology: betalain pigment, colorimeter, 530 nm, absorbance, blue/green filter, temperature/ethanol/pH

Common Mistakes: Must know: wash beetroot first (remove pigment from cut cells). Equilibrate water bath. Measure absorbance.

Depth: 3-5 marks in practical questions.

Transport Mechanisms [Spec 1.3(c)]

56 Describe simple diffusion: net movement from high > low concentration, through phospholipid bilayer, no energy required; and state the factors affecting rate: concentration gradient, temperature, SA, membrane thickness, size and lipid solubility?

Required Terminology: diffusion, concentration gradient, phospholipid bilayer, no ATP, non-polar, lipid-soluble, linear graph

Common Mistakes: 2016 Q5a: O₂ = non-polar = through bilayer = simple diffusion. REJECT ‘active transport’ for channel proteins allowing O₂ through.

Depth: 2-3 marks.

57 Describe facilitated diffusion: passive movement of polar/charged molecules through channel or carrier proteins, down the concentration gradient; explain why the graph plateaus (limited number of protein channels/carriers = saturation)?

Required Terminology: facilitated diffusion, channel proteins, carrier proteins, polar, charged, no ATP, saturation, plateau

Common Mistakes: 2023 Q3aii (4 marks): MUST explain why rate plateaus – limited number of proteins. REJECT ‘runs out of substrate’.

Depth: 4 marks. Explain plateau.

58 Describe active transport: movement against the concentration gradient (low > high), through carrier proteins, requiring ATP from respiration; explain the effect of cyanide (inhibits respiration > no ATP > active transport stops)?

Required Terminology: active transport, against gradient, carrier proteins, ATP, cyanide, respiration inhibited

Common Mistakes: 2017 Q6bi: if concentration HIGHER inside than outside = active transport. Must QUOTE DATA as evidence. 2017 Q6bii: no O₂ > no ATP > no active transport > stunted growth.

Depth: 3-4 marks.

59 Define osmosis using water potential: net movement of water from higher (less negative) water potential to lower (more negative) water potential through a partially permeable membrane?

Required Terminology: osmosis, water potential, higher to lower, partially permeable membrane

Common Mistakes: REJECT ‘water concentration’ – 2024 QER MS explicitly REJECTS this. Must say WATER POTENTIAL. Tested 6/7 papers.

Depth: Core definition. 1-2 marks.

60 Define water potential (ψ), solute potential (ψs) and pressure potential (ψp); use the equation ψ = ψs + ψp; state that pure water has ψ = 0 and all solutions have negative ψs values?

Required Terminology: ψ, ψs, ψp, ψ = ψs + ψp, negative values

Common Mistakes: Must use correct symbols. Know: ψs is ALWAYS negative. More concentrated = more negative ψs.

Depth: 2-3 marks.

61 Describe osmosis in plant cells: hypotonic solution > water enters > turgid; hypertonic solution > water leaves > plasmolysed; at incipient plasmolysis (50% cells plasmolysed) > ψp = 0 > ψ = ψs?

Required Terminology: turgid, plasmolysed, incipient plasmolysis, ψp = 0, ψ = ψs

Common Mistakes: 2023 Q6aiiiII (2 marks): at 50% plasmolysis, pressure potential = 0, so water potential = solute potential. Critical relationship.

Depth: 2-4 marks.

62 Describe osmosis in animal cells: hypotonic solution > water enters > osmotic lysis (burst); hypertonic solution > water leaves > crenation (shrinks); isotonic > no net change?

Required Terminology: osmotic lysis, crenation, haemolysis, isotonic, hypotonic, hypertonic

Common Mistakes: 2024 QER: must predict what happens to animal tissue – no cell wall so cells BURST (lysis) or SHRINK (crenation). Not just ‘change shape’.

Depth: QER 2024. 3+ marks in QER context.

63 Explain why percentage change in mass is used in osmosis experiments, not absolute change?

Required Terminology: percentage change, fair comparison, initial masses differ

Common Mistakes: 2018 Q5a: initial masses of potato cylinders differ, so % change allows FAIR COMPARISON.

Depth: 2 marks.

64 Calculate solute potential from a plasmolysis experiment: plot % plasmolysed vs concentration, read concentration at 50% plasmolysis, use ψs = -(concentration x constant)?

Required Terminology: 50% plasmolysis, incipient plasmolysis, ψs, negative value, graph reading

Common Mistakes: 2023 Q6aiiiI: read from graph, multiply by constant, answer MUST be negative.

Depth: 2 marks. Calculation.

65 Describe endocytosis (phagocytosis and pinocytosis): membrane invaginates to engulf material, forming a vesicle; and exocytosis: vesicle fuses with membrane to release contents; explain how these change cell surface area?

Required Terminology: endocytosis, phagocytosis, pinocytosis, exocytosis, vesicle, membrane surface area

Common Mistakes: 2024 Q5bii: endocytosis = membrane ADDED to inside (SA decreases). Exocytosis = membrane ADDED to surface (SA increases). Or think of it as: endocytosis removes surface membrane, exocytosis adds to it.

Depth: 2 marks.

Enzyme Structure and Function [Spec 1.4(a)-(f)]

66 Define metabolism as the sum of all enzyme-controlled reactions: anabolic (building up, e.g. protein synthesis) and catabolic (breaking down, e.g. digestion)?

Required Terminology: metabolism, anabolic, catabolic, enzyme-controlled

Common Mistakes: Teachers’ Guide defines both terms.

Depth: 1 mark.

67 Distinguish between intracellular enzymes (work inside the cell, e.g. catalase) and extracellular enzymes (secreted, work outside the cell, e.g. digestive enzymes)?

Required Terminology: intracellular, extracellular

Common Mistakes: 2017 Q4a (1 mark). Simple recall.

Depth: 1 mark.

68 Describe the lock-and-key model AND the induced fit model: in induced fit, the active site changes shape slightly as the substrate enters, bringing reactive groups closer together and weakening bonds in the substrate?

Required Terminology: lock and key, induced fit, active site, complementary, enzyme-substrate complex (ESC), reactive groups

Common Mistakes: REJECT ‘the substrate changes shape to fit’ – in induced fit, the ENZYME/ACTIVE SITE changes shape. 2023 Q1aiv. REJECT ‘same shape’ – say COMPLEMENTARY.

Depth: 3-4 marks in QER context.

69 Define activation energy and explain how enzymes lower it; draw an energy profile diagram showing both catalysed and uncatalysed reactions (same start/end energy levels, lower peak with enzyme)?

Required Terminology: activation energy, lower, energy profile, catalysed, uncatalysed

Common Mistakes: 2018 Q6aii: draw enzyme curve with LOWER peak but SAME start and end energy levels. REJECT ‘enzymes provide energy’.

Depth: 2 marks.

Factors Affecting Enzyme Activity [Spec 1.4(g)]

70 Describe and explain the FULL effect of temperature on enzyme activity: increasing temp > increaseskinetic energy > more collisions > increasesrate; above optimum > H-bonds/ionic bonds in tertiary structure break > active site changes shape (denatured) > no ESC > rate drops to zero?

Required Terminology: kinetic energy, collisions, enzyme-substrate complex, optimum, hydrogen bonds, ionic bonds, tertiary structure, denatured, active site shape

Common Mistakes: REJECT ‘enzymes die’ or ‘enzymes killed’ – enzymes are not alive, they are DENATURED. REJECT ‘bonds in the active site break’ without naming the bond types.

Depth: 4-5 marks when fully tested.

71 Describe and explain the effect of substrate concentration: low [S] > substrate is limiting factor > rate increases; high [S] > all active sites occupied > enzyme is limiting factor > rate plateaus?

Required Terminology: substrate concentration, limiting factor, active sites occupied/saturated, plateau

Common Mistakes: 2024 Q3biii (3 marks). Must explain BOTH phases: increasing AND plateau. REJECT ‘no more substrate’ – substrate is still present, active sites are just full.

Depth: 3 marks.

72 Explain the importance of buffers in enzyme experiments: maintain constant pH, preventing changes that would alter tertiary structure and reduce activity; pH is a controlled variable?

Required Terminology: buffer, constant pH, controlled variable, prevent denaturation

Common Mistakes: 2019 Q3aiI. Also 2017 Q4biii: buffer CANNOT be used if the experiment RELIES on pH change (e.g. with pH indicator).

Depth: 2-3 marks.

Inhibition [Spec 1.4(h)]

73 Describe competitive inhibition: inhibitor has a SIMILAR shape to the substrate; competes for the active site; fewer ESCs formed; rate decreases; effect overcome by increasing substrate concentration; Vmax CAN be reached at high [S]?

Required Terminology: competitive, SIMILAR shape, active site, competes, fewer ESCs, overcome by increasing [S], Vmax reached

Common Mistakes: REJECT ‘SAME shape’ – 2019 MS explicitly rejects this. Must say SIMILAR. REJECT ‘blocks the active site permanently’ – usually reversible. QER 2016, 2018, 2019, 2022.

Depth: 5+ marks across papers. Extremely high frequency.

74 Describe non-competitive inhibition: inhibitor binds to allosteric site (NOT the active site); changes the shape of the active site; substrate can no longer bind; increasing [S] CANNOT overcome the effect; Vmax CANNOT be reached?

Required Terminology: non-competitive, allosteric site, changes active site shape, cannot overcome, Vmax not reached

Common Mistakes: REJECT ‘binds to active site’ – that’s competitive. Non-competitive = ALLOSTERIC site. 2024 Q3bv: draw graph with same shape but lower Vmax.

Depth: QER 2016, 2024. 3+ marks.

Immobilised Enzymes [Spec 1.4(i)]

75 State advantages of immobilised enzymes (fixed to insoluble support): reusable, product not contaminated, improved thermal stability?

Required Terminology: immobilised, alginate beads, reusable, not contaminated, thermal stability

Common Mistakes: 2022 Q5ciII: immobilised enzymes are MORE active at high temps because support STABILISES tertiary structure, preventing denaturation.

Depth: 3 marks.

76 State that biosensors use immobilised enzymes (e.g. glucose oxidase in glucose biosensors) – detailed knowledge not required?

Required Terminology: biosensor, immobilised enzyme, glucose oxidase

Common Mistakes: 2019 Q5b: competitive inhibitor of glucose oxidase = similar shape to glucose.

Depth: Application context.

Calculations [Spec 1.4 Maths]

77 Calculate rate of reaction: rate = 1/time, OR rate = volume/time, OR rate = gradient (Δy/Δx from a tangent)? Express in standard form when required?

Required Terminology: rate, 1/time, gradient, tangent, standard form, correct units

Common Mistakes: 2017 Q4ci: 1/18 = 5.56×10^–². MUST use standard form for full marks. MUST include units. REJECT wrong standard form.

Depth: 3 marks.

Nucleotides and ATP [Spec 1.5(a)-(d)]

78 Describe the structure of a nucleotide: pentose sugar + phosphate group + organic/nitrogenous base?

Required Terminology: pentose sugar, phosphate group, organic/nitrogenous base

Common Mistakes: REJECT naming a specific base unless asked – 2017 Q3ai says ‘NOT named base’. Just say ‘organic base’.

Depth: 1 mark.

79 State the structural differences between DNA, RNA and ATP nucleotides?

Required Terminology: DNA: deoxyribose, thymine. RNA: ribose, uracil. ATP: ribose, adenine, THREE phosphates

Common Mistakes: 2024 Q2aii: compare all three types.

Depth: 2 marks.

80 Describe the structure of ATP (adenine + ribose + 3 phosphates) and explain its role: energy released (30.6 kJ mol^–¹) when terminal phosphate hydrolysed (exergonic); ATP reformed from ADP + Pi using energy from respiration (endergonic)?

Required Terminology: ATP, adenine, ribose, three phosphates, 30.6 kJ mol^–¹, hydrolysis, exergonic, endergonic, ADP, Pi

Common Mistakes: REJECT ‘energy PRODUCED’ – 2017 MS explicitly rejects this. Must say ‘energy RELEASED’. Know the value: 30.6 kJ mol^–¹.

Depth: 3 marks.

81 Explain why ATP is called the ‘universal energy currency’ – it is the energy source used in ALL cells in ALL organisms?

Required Terminology: universal energy currency, all cells, all organisms, hydrolysis, ADP + Pi

Common Mistakes: 2024 Q2c (3 marks): three aspects – energy released on hydrolysis + energy stored as ADP > ATP + universal.

Depth: 3 marks.

82 Describe the role of creatine phosphate in muscle: stores phosphate during rest; donates phosphate to ADP during exercise for rapid ATP regeneration?

Required Terminology: creatine phosphate, ADP, rapid, phosphate transfer, regeneration

Common Mistakes: 2017 Q3c (4 marks). CP = short-term emergency phosphate supply for muscle.

Depth: 4 marks.

DNA and RNA Structure [Spec 1.5(e)(f)]

83 Describe DNA structure: two antiparallel polynucleotide strands (5′ > 3′ and 3′ > 5′) in a double helix; complementary base pairing (A-T via 2 H-bonds, C-G via 3 H-bonds); sugar-phosphate backbone on outside?

Required Terminology: double helix, antiparallel, 5′ to 3′, complementary base pairing, A-T (2 H-bonds), C-G (3 H-bonds), sugar-phosphate backbone

Common Mistakes: REJECT ‘bases on the outside’ – bases are on the INSIDE. Teachers’ Guide specifies 5′ > 3′ direction.

Depth: 2-3 marks.

84 Classify bases as purines (adenine, guanine – double ring, larger) and pyrimidines (cytosine, thymine/uracil – single ring, smaller)?

Required Terminology: purine, pyrimidine, adenine, guanine, cytosine, thymine, uracil

Common Mistakes: Teachers’ Guide: ‘differentiate between purine and pyrimidine bases when given structural formulae’.

Depth: 1 mark.

85 Explain Chargaff’s rules (Aapprox. T%, Capprox. G%) and how this provides evidence for complementary base pairing?

Required Terminology: Chargaff’s rules, A=T, C=G, complementary base pairing, evidence

Common Mistakes: 2023 Q5aiiiII: must use DATA to support. Say: ‘small variation from exact match is due to experimental error’.

Depth: 3 marks.

86 Compare DNA and RNA in a table format: DNA (double stranded, deoxyribose, thymine, larger) vs RNA (usually single stranded, ribose, uracil, smaller)?

Required Terminology: double stranded, single stranded, deoxyribose, ribose, thymine, uracil

Common Mistakes: 2016 Q2a: answers MUST be comparative – state both sides.

Depth: 4 marks.

87 Describe the structure of tRNA (clover-leaf, anticodon at one end, amino acid attachment at other) and name three types of RNA: mRNA, rRNA, tRNA with their roles?

Required Terminology: tRNA, clover-leaf, anticodon, amino acid attachment, mRNA (code carrier), rRNA (ribosome), tRNA (amino acid carrier)

Common Mistakes: 2024 Q1ai: tRNA = transfer RNA, NOT transport RNA. 2023 QER: must name ALL THREE types with location AND function.

Depth: QER 2023.

DNA Replication [Spec 1.5(g)(h)]

88 Describe semi-conservative replication step by step: helicase breaks H-bonds > strands separate > each strand acts as template > free nucleotides align by complementary base pairing > DNA polymerase forms phosphodiester bonds > ligase joins fragments?

Required Terminology: semi-conservative, helicase, template, complementary base pairing, DNA polymerase, ligase, phosphodiester bonds

Common Mistakes: 2017 Q2biv: name AND describe ALL three enzymes: helicase (unzips/breaks H-bonds), polymerase (adds nucleotides), ligase (joins fragments).

Depth: 3-4 marks.

89 Describe and interpret the Meselson-Stahl experiment: heavy (¹⁵N) and light (¹⁴N) isotopes, density gradient centrifugation; predict results for generations 0 (all heavy), 1 (all hybrid), 2 (50% hybrid, 50% light), 3 (25% hybrid, 75% light)?

Required Terminology: Meselson-Stahl, ¹⁵N, ¹⁴N, density gradient, centrifugation, heavy, hybrid, light, template

Common Mistakes: 2022 Q3aii: must PREDICT later generations. Gen 3 = 1:3 ratio. 2017 Q2b: explain that each molecule = one old + one new strand.

Depth: 3-4 marks.

Genetic Code and Protein Synthesis [Spec 1.5(i)-(o)]

90 Describe the genetic code as: triplet (3 bases = 1 codon), non-overlapping, degenerate (64 codons for 20 amino acids, so most amino acids have multiple codons), universal, with start and stop codons?

Required Terminology: triplet, codon, non-overlapping, degenerate, universal, 64 codons, 20 amino acids

Common Mistakes: 2019 Q4bii: why 3? Because 4¹=4, 4²=16, 4³=64. Only 64 is enough for 20 amino acids.

Depth: 2 marks.

91 Define exons (coding regions) and introns (non-coding regions); state that eukaryotic genes contain both (discontinuous) while prokaryotic genes are usually continuous (no introns)?

Required Terminology: exons, introns, discontinuous, continuous, pre-mRNA, splicing

Common Mistakes: 2018 Q4cii: pre-mRNA contains both introns and exons > introns REMOVED by splicing > mature mRNA is shorter/lighter.

Depth: 5 marks.

92 Describe transcription in full: DNA helicase unwinds > RNA polymerase binds to template strand > free RNA nucleotides align by complementary base pairing (A:U, C:G) > pre-mRNA produced > introns removed (splicing) > mature mRNA exits through nuclear pores?

Required Terminology: transcription, DNA helicase, RNA polymerase, template strand, A:U, C:G, pre-mRNA, splicing, nuclear pores

Common Mistakes: REJECT DNA base pairing rules in RNA context – must say A:U not A:T. Teachers’ Guide requires full detail including stop sequence.

Depth: 4-5 marks.

93 Describe translation in full: mRNA attaches to small ribosome subunit > tRNA carries specific amino acid > anticodon matches codon by complementary base pairing > ribosome has 2 tRNA binding sites > peptide bond forms (condensation) > ribosome moves one codon > repeats until stop codon > polypeptide released?

Required Terminology: translation, ribosome, tRNA, amino acid, codon, anticodon, complementary base pairing, peptide bond, condensation, stop codon

Common Mistakes: 2016 Q2biii, 2019 Q4c: must describe in SEQUENCE. All 8 steps above are mark points. REJECT ‘tRNA matches mRNA’ without saying codon-anticodon.

Depth: 5 marks.

94 Describe tRNA activation: ATP provides energy > amino acid reacts with ATP > two phosphate groups released > activated amino acid transferred to specific tRNA?

Required Terminology: tRNA activation, ATP, activated amino acid, aminoacyl-tRNA synthetase

Common Mistakes: 2023 QER: tRNA activation mechanism was part of top-band answer.

Depth: QER 2023.

95 State the ‘one gene, one polypeptide’ hypothesis: each gene codes for one specific polypeptide?

Required Terminology: one gene one polypeptide

Common Mistakes: 2024 Q5ai: use this to calculate minimum genes from number of proteins. HIV has 3 proteins > minimum 3 genes.

Depth: 1-3 marks in application.

96 Describe post-translational modification: addition of carbohydrates/lipids/phosphate; assembly of quaternary structures; occurs in Golgi?

Required Terminology: post-translational modification, glycosylation, Golgi, quaternary structure

Common Mistakes: Spec 1.5(o). 2022 Q6aiii.

Depth: 1-2 marks.

Cell Cycle and Mitosis [Spec 1.6(a)(b)(c)]

97 Describe ALL phases of interphase: G1 (cell growth, organelle replication, protein synthesis), S phase (DNA replication), G2 (continued growth, preparation for division)?

Required Terminology: interphase, G1, S phase, G2, DNA replication, organelle replication, protein synthesis, ATP

Common Mistakes: 2022 QER: interphase is where MOST of the cell cycle occurs. Must know what happens in EACH sub-phase. Not just ‘the cell grows’.

Depth: QER 2022. 3+ marks.

98 Describe the events at each stage of mitosis: Prophase (chromatin condenses > chromosomes visible, each = 2 chromatids at centromere; nuclear envelope breaks down; spindle forms from centrioles). Metaphase (chromosomes align on equator; spindle fibres attach to centromeres). Anaphase (centromeres split; chromatids pulled to opposite poles by shortening spindle fibres). Telophase (chromatids reach poles; nuclear envelope reforms; chromosomes decondense; spindle disassembles)?

Required Terminology: prophase, metaphase, anaphase, telophase, chromatids, centromere, spindle, equator, condense, decondense

Common Mistakes: REJECT confusing chromatids with chromosomes. A replicated chromosome = 2 chromatids joined at centromere. 2016 Q1, 2024 Q6aii.

Depth: 4-6 marks.

99 Identify cells at each stage of mitosis from micrographs and diagrams?

Required Terminology: –

Common Mistakes: 2016 Q1ai: Telophase=chromosomes at poles. Metaphase=chromosomes on equator. REJECT meiosis terminology (penalised in 2016 MS).

Depth: 2 marks.

100 Describe cytokinesis in animal cells (cleavage furrow) and plant cells (cell plate)?

Required Terminology: cytokinesis, cleavage furrow, cell plate

Common Mistakes: Different mechanisms. 2017 QER includes cytokinesis.

Depth: 1 mark.

101 Explain the significance of mitosis: growth (new cells for growth), repair (damaged tissue), replacement (worn-out cells); distinguish young organisms (growth + repair) from older organisms (repair only)?

Required Terminology: growth, repair, replacement, genetically identical, diploid

Common Mistakes: 2018 Q3cii: young = growth + repair. Old = repair only.

Depth: 2 marks.

102 Explain how cyclins control the cell cycle; explain that uncontrolled cyclin levels lead to continuous mitosis > tumour formation > cancer?

Required Terminology: cyclin, cell cycle control, uncontrolled division, tumour, cancer

Common Mistakes: 2022 QER: too much cyclin B > cells keep dividing > cancer. No knowledge of oncogenes required (Teachers’ Guide).

Depth: QER 2022.

103 Define mitotic index (dividing cells / total cells) and explain why rapidly renewing tissues (skin, gut lining, bone marrow) have higher mitotic indices?

Required Terminology: mitotic index, dividing cells, total cells, renewal, skin, gut, bone marrow

Common Mistakes: 2022 QER: tissues where cells are constantly replaced have high mitotic index. Cancer tissues have abnormally high MI.

Depth: QER 2022.

Meiosis [Spec 1.6(d)(e)]

104 Describe meiosis I: Prophase I (homologous chromosomes pair = bivalents/synapsis; crossing over at chiasmata). Metaphase I (bivalents line up randomly = independent assortment). Anaphase I (homologous chromosomes separate; centromeres do NOT split). Telophase I + cytokinesis (two haploid cells)?

Required Terminology: bivalents, synapsis, crossing over, chiasmata, independent assortment, homologous chromosomes separate, centromeres intact

Common Mistakes: REJECT ‘chromatids separate’ in meiosis I – chromatids separate in meiosis II. In meiosis I, WHOLE chromosomes separate. 2019 Q1biii.

Depth: 3-4 marks.

105 Describe meiosis II: similar to mitosis. Metaphase II (chromosomes line up). Anaphase II (centromeres split, chromatids pulled to poles). Result: four genetically different haploid cells?

Required Terminology: chromatids separate, centromeres split, haploid, four cells, genetically different

Common Mistakes: 2019 Q1biii: key comparison – Anaphase I = homologous chromosomes separate (centromeres intact). Anaphase II = chromatids separate (centromeres split).

Depth: 2 marks.

106 Explain the two sources of genetic variation in meiosis: (1) crossing over in prophase I (exchange of alleles between non-sister chromatids) and (2) independent assortment in metaphase I (random orientation of bivalents)?

Required Terminology: crossing over, independent assortment, genetic variation, non-sister chromatids, random orientation

Common Mistakes: 2019 Q1biv: must name BOTH sources. REJECT ‘organisms adapt’ – say ‘variation allows natural selection’. REJECT ‘meiosis causes mutation’.

Depth: 3 marks.

107 Compare mitosis and meiosis in a table: mitosis (1 division, 2 diploid identical cells, no crossing over, no pairing) vs meiosis (2 divisions, 4 haploid different cells, crossing over, bivalent formation)?

Required Terminology: mitosis, meiosis, diploid, haploid, genetically identical, genetically different, one division, two divisions

Common Mistakes: 2023 Q2aii: two key differences – genetic identity AND chromosome number.

Depth: 2-3 marks.

108 State where meiosis occurs: in plants = anthers (pollen) and ovaries (ovules); in animals = testes and ovaries?

Required Terminology: anthers, ovaries, testes, pollen, ovules, gametes

Common Mistakes: 2019 Q1bi.

Depth: 1 mark.

Cell Division Practicals [Spec 1.6 Practical]

109 Describe the root tip squash technique: cut tip > stain with acetic/propionic orcein (stains DNA) > macerate with HCl (separates cells) > squash under coverslip > observe stages of mitosis?

Required Terminology: root tip, acetic orcein, HCl, macerate, squash, apical meristem

Common Mistakes: 2023 Q2ciii: cells from root tip because it’s the apical meristem = region of active growth/division.

Depth: 2 marks.

110 Draw scientific diagrams of cells at each stage of mitosis and meiosis from slides, calculating magnification?

Required Terminology: scientific drawing, unbroken lines, proportions, labels, magnification

Common Mistakes: Must follow drawing rules: no shading, clear lines, correct proportions, ruled label lines.

Depth: Practical skill.

Core Maths Skills [Average 10 marks per paper]

M1 Calculate magnification = image size / actual size, and rearrange for actual size?

Required Terminology: magnification, image size, actual size, μm

Common Mistakes: Not converting mm > μm. Not showing working. No units on answer.

Depth: Frequency: 6/7

M2 Use a scale bar to calculate magnification (measure bar, convert, divide)?

Required Terminology: scale bar, mm > μm

Common Mistakes: Not physically measuring the bar. Using stated magnification instead.

Depth: Frequency: 5/7

M3 Calculate percentages and percentage change [(final-initial)/initial x 100]?

Required Terminology: percentage, percentage change

Common Mistakes: Forgetting x100. Using final/initial instead of change/initial.

Depth: Frequency: 6/7

M4 Plot graphs correctly: labelled axes with units, linear scales using >=1/2 paper, accurate plots (±1/2 small square), appropriate line, NO extrapolation?

Required Terminology: axes, labels, units, linear scale, ±1/2 square, no extrapolation

Common Mistakes: No units on axes. Non-linear scales. Extrapolating beyond data. Dot-to-dot when curve needed.

Depth: Frequency: 7/7

M5 Draw range bars on graphs (minimum to maximum at each data point)?

Required Terminology: range bars, minimum, maximum

Common Mistakes: Confusing range bars with error bars. Drawing from mean±1 instead of min to max.

Depth: Frequency: 3/7

M6 Calculate rate: 1/time, OR volume/time, OR gradient (Δy/Δx)?

Required Terminology: rate, 1/time, gradient, tangent

Common Mistakes: Not including units. Not using standard form when asked.

Depth: Frequency: 5/7

M7 Use and convert standard form (a x 10ⁿ)?

Required Terminology: standard form, a x 10ⁿ (1<=a<10)

Common Mistakes: Incorrect rounding. Forgetting to express in standard form when required (loses marks).

Depth: Frequency: 3/7

M8 Read values from graphs and calibration curves?

Required Terminology: calibration curve, interpolation

Common Mistakes: Not using a ruler. Not accounting for dilution factors.

Depth: Frequency: 5/7

M9 Calculate surface area of a sphere: SA = 4πr² (use radius NOT diameter)?

Required Terminology: 4πr², radius, diameter

Common Mistakes: Using DIAMETER instead of RADIUS (must divide by 2 first).

Depth: Frequency: 1/7

M10 Calculate amino acids from base number: bases / 3 (triplet code)?

Required Terminology: triplet code

Common Mistakes: Forgetting to divide by 3. Confusing bases with nucleotides.

Depth: Frequency: 2/7

Specified Practicals [Average 16 marks per paper]

P1 Describe the method, reagent, conditions and colour change for ALL five food tests (starch, reducing sugar, non-reducing sugar, protein, lipid)?

Common Mistakes: Saying ‘boil’ instead of ‘heat in water bath’. Forgetting neutralisation in non-reducing sugar test. Saying ‘purple’ instead of ‘lilac’ for Biuret.

Depth: Practical: Food Tests [1.1]

P2 Calibrate using eyepiece graticule and stage micrometer? Calculate actual size and magnification of drawings?

Common Mistakes: Working in fractions of eyepiece units. Not converting units. Not showing formula.

Depth: Practical: Microscope Calibration [1.2]

P3 Design and carry out an osmosis experiment (potato cylinders in different concentrations)? Calculate % change? Plot graph? Read x-intercept to find water potential?

Common Mistakes: Using absolute change instead of %. Not blotting cylinders. Not leaving long enough to equilibrate.

Depth: Practical: Water Potential [1.3]

P4 Count plasmolysed/turgid cells? Calculate %? Plot graph? Read concentration at 50% plasmolysis? Calculate ψs = -(conc x constant)?

Common Mistakes: Counting same cell twice. Not using consistent scoring for partially visible cells. Forgetting the negative sign on ψs.

Depth: Practical: Solute Potential by Plasmolysis [1.3]

P5 Describe the beetroot experiment? Use a colorimeter (530 nm, blue/green filter)? Explain results in terms of protein denaturation and phospholipid fluidity?

Common Mistakes: Saying ‘phospholipids denature’. Not washing beetroot to remove cut-cell pigment. Not controlling volume of water.

Depth: Practical: Beetroot Permeability [1.3]

P6 Investigate enzyme activity vs temperature or pH? Use equilibration? Identify all variables? Calculate rate? Plot and explain results?

Common Mistakes: Not equilibrating before mixing. Not using buffer when investigating temperature. Using buffer when investigating pH change with indicator.

Depth: Practical: Enzyme Temp/pH [1.4]

P7 Investigate concentration effects? Prepare serial dilutions? Explain plateau in substrate conc graph? Suggest improvements?

Common Mistakes: Saying ‘accurate’ when meaning ‘reliable’. Not suggesting intermediate values to refine optimum.

Depth: Practical: Enzyme/Substrate Conc [1.4]

P8 Describe the method? Stain with acetic orcein? Identify stages of mitosis from your slide?

Common Mistakes: Looking at wrong region (xylem instead of meristem). Not squashing enough.

Depth: Practical: Root Tip Squash [1.6]

P9 Observe prepared slides of anthers? Identify stages of meiosis? Draw cells?

Common Mistakes: Confusing meiosis I with meiosis II stages.

Depth: Practical: Anther Meiosis Slides [1.6]

P10 Describe the method: crush, detergent (disrupts membranes), salt (clumps DNA), filter, cold ethanol (precipitates DNA)?

Common Mistakes: Not understanding role of each chemical. Not using cold ethanol.

Depth: Practical: DNA Extraction [1.5]

Past Paper Topic Analysis (2016-2024)

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A detailed analysis of every WJEC Unit 1 exam paper from 2016 to 2024, showing which topics are tested most frequently, how many marks they are worth, and the exact terminology the mark scheme requires.

Examiner tip: Cross-reference your RAG checklist with the frequency data below. Topics that are both high-frequency AND rated red or amber on your checklist should be your top revision priority.

Specification: WJEC GCE AS Biology 2015 onwards – Unit 1

Exam Papers Analysed: 2016, 2017, 2018, 2019, 2022, 2023, 2024 (7 papers)

Sources: Official specification, Teachers’ Guide, all question papers and mark schemes

Exam: 1 hour 30 minutes – 80 marks – 20% of A-Level (50% of AS)

Summary

Comprehensive analysis of 7 years of Unit 1 papers (560 total marks) showing exactly what gets tested, how often, and the precise terminology needed to score marks.

Papers Analysed

560

Total Marks Reviewed

35%

Avg AO1 (Knowledge)

45%

Avg AO2 (Application)

20%

Avg AO3 (Analysis)

Avg Maths Marks

2024 Year tested

AO1 Knowledge & recall

AO2 Application

AO3 Analysis & evaluation

Inorganic Ions (Mg²⁺, Fe²⁺, Ca²⁺, PO₄³⁻)

Spec 1.1(a): The key elements present as inorganic ions in living organisms: Mg²⁺, Fe²⁺, Ca²⁺, PO₄³⁻.

Exam Appearances

2019 QER (9 marks) – Water properties AND chemical elements (phosphorus for phospholipids/nucleotides/ATP; sulfur for amino acids/methionine/cysteine)

2023 Phosphate and nitrate ions needed by plants (1 mark)

Teachers’ Guide requires knowledge of:

Mg²⁺ – component of chlorophyll
Fe²⁺ – component of haemoglobin
PO₄³⁻ – component of nucleic acids, phospholipids, ATP
Ca²⁺ – strengthening tissues (bones/teeth in animals, cell walls in plants)

Mark Scheme Terminology

Phosphorus: “required to synthesise phospholipids / nucleotides / ATP / DNA / RNA”
Sulfur: “required to synthesise some amino acids / methionine / cysteine / proteins”
Iron: component of haemoglobin (prosthetic group)
Magnesium: component of chlorophyll

Water Properties

Spec 1.1(b): The importance of water in terms of its polarity, ability to form hydrogen bonds, surface tension, as a solvent, thermal properties, as a metabolite.

Exam Appearances

2019 QER (9 marks) – Structure of water AND properties essential to supporting life

2022 Osmosis – water potential concepts applied to protoctistans (4 marks)

Required properties (from 2019 mark scheme):

Property	Biological Importance
Dipole / polar	Allows hydrogen bonding between molecules
Polar solvent	All chemical reactions occur in aqueous solutions; polar molecules and ions dissolve and are transported
High specific heat capacity	Requires a lot of energy to heat up/cool down – creates thermostable environments
Cohesive / hydrogen bonds	Allows movement of water (e.g. in xylem); surface tension
Ice less dense than water	Ice floats, insulating water below, allowing organisms to survive
Metabolite	Reactant in photosynthesis & hydrolysis; product of respiration & condensation

Mark Scheme Terminology

“Dipole”: oxygen has slight negative charge (δ-), hydrogen has slight positive charge (δ+)
“Hydrogen bonds”: intermolecular bonds between water molecules
“Thermostable”: environments that resist temperature change
TG also requires: understanding of high latent heat of vaporisation; water provides support and buoyancy

Carbohydrates

Spec 1.1(c)-(e): Monosaccharides (triose, pentose, hexose); disaccharides (sucrose, lactose, maltose); polysaccharides (starch, glycogen, cellulose, chitin). Alpha and beta isomerism. Chemical and physical properties related to function.

Exam Frequency – CRITICAL

Tested in: 2016 2017 2018 2019 2022 2023 2024

Common question types:

Hydrolysis diagrams – showing bond breaking with addition of water (2017, 2022)
Identifying monosaccharide products of disaccharide hydrolysis, e.g. lactose > galactose + glucose (2022)
Structure of cellulose: β-glucose, 180° rotation, hydrogen bonds between chains, microfibrils (2017, 2019)
Comparing starch (amylose + amylopectin) and glycogen structure for storage function (2018 QER)
Using calibration curves with a colorimeter to determine unknown glucose concentration (2016, 2022)

Mark Scheme Terminology

Starch: “polymer of α-glucose; composed of amylose (1,4 glycosidic bonds, helical) and amylopectin (1,4 and 1,6 glycosidic bonds, branched)”
Glycogen: “polymer of α-glucose; more highly branched than starch”
Cellulose: “polymer of β-glucose; adjacent monomers twisted 180°; hydrogen bonds between chains forming microfibrils”
Chitin: “polymer of β monomers with -OH groups replaced by nitrogen-containing acetylamine groups”
Hydrolysis: “water added; glycosidic bond broken; two monosaccharides released”
Condensation: “water removed; glycosidic bond formed”
Storage properties: “insoluble so osmotically inert; compact; readily hydrolysed to glucose for respiration”

Exam Tip

The 2018 QER (9 marks) asked students to describe starch AND triglyceride structure and relate these to their function as energy stores in a seed. Students needed detailed structural knowledge of both molecules to score highly.

Lipids & Phospholipids

Spec 1.1(f)-(g): Structure, properties and functions of triglycerides and phospholipids. Implications of saturated and unsaturated fat on human health.

Exam Appearances

2018 QER (9 marks) – Triglyceride structure and function in seed energy storage

2019 Phospholipid structure in cell membranes (linked to membrane questions)

2022 Mammary epithelial cells producing lipid – organelle function (2 marks)

2024 HIV viral envelope contains phospholipid bilayer (context for virus questions)

Required detail:

Triglyceride = glycerol + 3 fatty acids, joined by ester bonds
Saturated: single C-C bonds only; Unsaturated: at least one C=C double bond
Phospholipid = glycerol + 2 fatty acids + phosphate group
Hydrophilic head (phosphate) and hydrophobic tails (fatty acids)

Mark Scheme Terminology

Ester bond: bond joining glycerol to fatty acids (formed by condensation)
Saturated fat & health: “raises LDL cholesterol; increases incidence of atheromas in coronary arteries”
Triglyceride energy storage: “many high-energy bonds; provides approximately twice the energy of carbohydrate”
Functions of lipids: insulation, energy storage, protection, waterproofing

Amino Acids & Proteins

Spec 1.1(h)-(j): Structure and role of amino acids and proteins. Primary, secondary, tertiary, quaternary structure. Fibrous vs globular proteins.

Exam Frequency – CRITICAL

Tested in: 2016 2017 2018 2019 2022 2023 2024

Common question types:

Protein synthesis pathway through organelles: Nucleus > RER > Golgi > Vesicles > Exocytosis (2018, 2022)
Quaternary structure – assembly of polypeptide subunits (2022: fibrinogen > fibrin)
Identifying bonds at each structural level: peptide, hydrogen, disulfide, ionic, hydrophobic interactions (2022, 2023)
Fibrous vs globular: fibrous proteins (e.g. keratin) = structural; globular proteins (e.g. enzymes) = metabolic (2022)
Post-translational modification: addition of carbohydrate/glycosylation in Golgi body (2022)

Mark Scheme Terminology

Peptide bond: bond joining amino acids (formed by condensation between amino and carboxyl groups)
Primary: “sequence of amino acids”
Secondary: “α-helices and β-pleated sheets” (held by hydrogen bonds)
Tertiary: “further folding of the polypeptide chain” (held by disulfide, ionic, hydrogen bonds, hydrophobic interactions)
Quaternary: “more than one polypeptide chain bonded together”
Golgi body: “assembly of polypeptides / addition of carbohydrate / glycosylation / packaged into vesicles”

Food Tests (Specified Practical)

Specified Practical: Iodine/KI for starch; Benedict’s for reducing & non-reducing sugars; Biuret for protein; Emulsion test for fats/oils.

Exam Appearances

2016 Calibration curve with colorimeter for reducing sugar concentration (3 marks)

2022 Benedict’s test on hydrolysed disaccharide (linked to lactose hydrolysis)

Non-reducing sugar test requires: boil with HCl first, neutralise with NaOH, then add Benedict’s

Organelle Structure & Function

Spec 1.2(a): Structure and function of: mitochondria, ER (rough & smooth), ribosomes, Golgi body, lysosomes, centrioles, chloroplasts, vacuoles, nucleus, chromatin, nuclear envelope, nucleolus, plasmodesmata.

Exam Frequency – CRITICAL

Tested in: 2016 2017 2018 2019 2022 2023 2024

Common question types:

Identifying organelles from electron micrographs or diagrams (every year)
Protein secretion pathway: DNA in nucleus > mRNA > ribosome on RER > Golgi body > vesicles > exocytosis (2018: 10 marks; 2022: 5 marks)
Role of mitochondria providing ATP for specific processes (2018, 2022, 2023, 2024)
Why mature red blood cells cannot make haemoglobin: no DNA/genes, no ribosomes, no Golgi body (2023: 4 marks)
Organelles working together to carry out functions (TG emphasis)

Mark Scheme Terminology

RER: “transports proteins through the cell / to Golgi body / packages proteins into vesicles”
Golgi body: “packaging / modification of protein / activation of enzyme / addition of carbohydrate / glycosylation”
Mitochondria: “provides ATP for synthesis of lipid/protein/lactose / for exocytosis / active transport”
Lysosomes: contain hydrolytic/digestive enzymes; break down worn-out organelles or pathogens
Nucleolus: makes rRNA / ribosome assembly

Prokaryotic Cells & Viruses

Spec 1.2(b)-(c): Structure of prokaryotic cells and viruses. Cell theory. Similarities and differences: eukaryotes (animal & plant), prokaryotes, viruses.

Exam Frequency – HIGH

2016 Influenza virus structure & replication (16 marks – 20% of entire paper!)

2017 Why bacteria don’t undergo mitosis (2 marks); prokaryote vs eukaryote comparison (3 marks)

2022 Prokaryote vs eukaryote comparison table (3 marks)

2023 Ribosome size/location comparison (2 marks); cell size comparison (2 marks)

2024 HIV structure, replication, surface area calculations (9 marks); binary fission vs mitosis (2 marks)

Prokaryote vs Eukaryote comparison (frequently tested):

Feature	Eukaryote	Prokaryote
Membrane-bound organelles	Present	Absent
DNA location	Enclosed in nuclear membrane	Free in cytoplasm
DNA structure	Linear, associated with histones	Circular loop (+ plasmids)
Ribosomes	80S (larger)	70S (smaller)
Respiration site	Mitochondria	Mesosomes / cell membrane
Cell wall	Cellulose (plants) / absent (animals)	Peptidoglycan / murein

Mark Scheme Terminology – Viruses

Virus structure: “protein capsid surrounds genetic material (DNA or RNA)”
Why viruses need host cells: “no ribosomes for protein synthesis; no mitochondria to produce ATP; need raw materials (nucleotides, amino acids)”
Viral RNA replication (2016 MS): “RNA acts as template; complementary base pairs attach (A:U, C:G); RNA polymerase catalyses formation; sugar-phosphate backbone forms”
One gene one polypeptide (2024 MS): minimum number of genes = number of different proteins (e.g. HIV: glycoprotein + capsid + reverse transcriptase = 3 genes)

Levels of Organisation – Tissues, Organs, Systems

Spec 1.2(d): Aggregation of cells into tissues, tissues into organs, organs into systems. Examination of epithelia, muscle and connective tissue.

Exam Appearances

2017 Identifying ciliated epithelium from micrograph; tissue vs organ distinction (3 marks)

2019 Identifying organelles in Chlorella and Amoeba from diagrams (1 mark)

TG requires recognition of: ciliated, columnar and squamous epithelia; striated, smooth and cardiac muscle; connective tissue.

Mark Scheme Terminology

Tissue: “group of similar cells working together to perform a particular function”
Organ: “group of different tissues working together to perform a particular function”
Tissue vs organ: a tissue is composed of ONE type of cell; an organ contains DIFFERENT types of tissue

Fluid Mosaic Model

Spec 1.3(a): Principal components of the plasma membrane and the fluid-mosaic model.

Exam Appearances

2016 Identifying phospholipids and intrinsic proteins from diagram; stating their functions (3 marks)

2019 Membrane structure linked to osmosis in protoctistans (context)

2022 Membrane permeability – beetroot experiment; effect of temperature on membrane (4 marks)

2023 Identifying membrane components from diagram; phospholipid bilayer as barrier (3 marks)

Components to know: phospholipid bilayer, intrinsic (channel & carrier) proteins, extrinsic proteins, glycoproteins, cholesterol (in animal cells)

Mark Scheme Terminology

Phospholipid bilayer: “physical barrier / controls diffusion/transport of small/non-polar molecules”
Intrinsic proteins: “channel proteins and carrier proteins; facilitate transport of large/polar molecules/ions”
Fluid: phospholipids and proteins can move laterally within the membrane
Mosaic: proteins are scattered throughout the phospholipid bilayer like tiles in a mosaic

Factors Affecting Membrane Permeability

Spec 1.3(b): Factors affecting permeability including temperature and organic solvents.

Exam Appearances

2022 Beetroot membrane permeability experiment – effect of temperature on pigment leakage; colorimeter readings (6 marks)

How temperature affects membranes:

Low temperatures: phospholipids less fluid; membrane more rigid; less permeable
High temperatures: proteins denature; phospholipids move more; membrane becomes more permeable; pigment/contents leak out

Transport Mechanisms

Spec 1.3(c): Diffusion, osmosis & water potential, pinocytosis, facilitated diffusion, phagocytosis, exocytosis, active transport & the influence of cyanide.

Exam Frequency – CRITICAL

Tested in: 2016 2017 2018 2019 2022 2023 2024

Transport mechanisms comparison (tested every year):

Mechanism	Requires ATP?	Requires Proteins?	Direction
Diffusion	No	No	Down concentration gradient
Facilitated diffusion	No	Yes (channel/carrier)	Down concentration gradient
Active transport	Yes	Yes (carrier)	Against concentration gradient
Osmosis	No	No	Down water potential gradient
Endocytosis (phago/pino)	Yes	N/A (membrane engulfs)	Into cell
Exocytosis	Yes	N/A (vesicle fuses)	Out of cell

Key exam contexts:

Oxygen diffuses through phospholipid bilayer (non-polar) – linear relationship with concentration (2023)
Glucose uses channel/carrier proteins (polar) – rate limited by number of proteins = saturation effect (2023)
Osmosis in protoctistans: contractile vacuoles in freshwater organisms (2019: 4 marks)
Endocytosis & exocytosis change membrane surface area (2024: 2 marks)
Co-transport: two substances transported simultaneously by a carrier protein (TG requirement)
Cyanide inhibits active transport by blocking ATP production in mitochondria (spec requirement)

Mark Scheme Terminology

Diffusion (O₂): “passes through phospholipid bilayer because it is non-polar”
Facilitated diffusion: “through channel/carrier/intrinsic/transmembrane proteins”
Active transport: “requires ATP; against concentration gradient; uses carrier proteins”
Saturation effect: “rate is eventually limited by the number of channel/carrier proteins”
Osmosis: “net movement of water from a region of higher water potential to lower water potential through a selectively permeable membrane”
Endocytosis: “membrane lost / surface area decreases”; Exocytosis: “membrane added / surface area increases” (or ORA)

Enzyme Structure, Active Sites & Induced Fit

Spec 1.4(a)-(f): Metabolism. Protein nature. Intra/extracellular enzymes. Active sites & 3D structure. Induced fit (lysozyme). Catalysis & lowering activation energy.

Exam Frequency – HIGH

2016 QER (9 marks) – Pyrophosphatase enzyme specificity, competitive & non-competitive inhibition

2018 Activation energy diagram; enzyme-substrate complex formation (alcohol dehydrogenase) (5 marks)

2022 Thrombin specificity – complementary active site to specific peptide bond (2 marks)

2023 Lysozyme – induced fit model; pH effects on tertiary structure (4 marks)

Key concepts always required:

Enzyme has specific shaped active site / specific tertiary structure
Substrate has complementary shape (NOT “same shape”)
Enzyme-substrate complex forms
Induced fit: active site changes shape slightly to fit substrate more closely, weakening bonds
Activation energy is lowered

Mark Scheme Terminology

“Specific shaped active site” – NEVER say “same shape”; always “complementary”
“Enzyme-substrate complex” – required for full marks in most enzyme questions
Induced fit: “changes of shape of both active site and substrate bring reactive groups close together, weakening bonds in the substrate”
Activation energy: “the minimum energy required for a reaction to take place”

Factors Affecting Enzyme Activity

Spec 1.4(g): Influence of temperature, pH, substrate and enzyme concentration. Inactivation and denaturation. Importance of buffers.

Exam Appearances

2018 Rate of reaction graph with two regions (P & Q) – identifying limiting factors; gradient calculation (6 marks)

2023 Effect of pH on lysozyme activity; denaturation explanation (3 marks)

2022 Temperature effect on beetroot membrane proteins (linked to membrane topic)

MS requires precise distinction between:

Inactivation: temporary loss of activity (can be reversed)
Denaturation: permanent change to tertiary structure; active site no longer complementary to substrate

Mark Scheme Terminology

Temperature too high: “bonds in tertiary structure broken; active site changes shape; substrate no longer complementary; fewer enzyme-substrate complexes form”
Substrate concentration: “at high [S], all active sites occupied; enzyme concentration becomes the limiting factor”
Enzyme concentration: “more active sites available; more enzyme-substrate complexes per unit time”
Rate calculation: rate = change in product (or substrate) ÷ time

Competitive & Non-Competitive Inhibition

Spec 1.4(h): Principles of competitive and non-competitive inhibition.

Exam Appearances

2016 QER (9 marks) – Pyrophosphatase inhibited by phosphate (competitive) AND phenylalanine (non-competitive)

2017 Inhibition of ATP synthesis by cyanide (context question)

This table is essential for exams:

Feature	Competitive Inhibitor	Non-Competitive Inhibitor
Shape	Similar to substrate	Different to substrate
Binding site	Active site	Allosteric site (away from active site)
Mechanism	Competes with substrate for active site	Changes shape of active site
Effect of increasing [S]	V_max CAN be reached	V_max CANNOT be reached
Reversibility	Can be reversible or irreversible	Can be reversible or irreversible

Mark Scheme Terminology (from 2016 QER)

Competitive: “similar shape to substrate; binds to/competes for active site; prevents substrate binding; fewer E-S complexes; V_max can be reached at higher [S]”
Non-competitive: “binds to allosteric site; causes change in shape of active site; substrate no longer complementary; fewer E-S complexes; V_max cannot be reached at any [S]”

Immobilised Enzymes

Spec 1.4(i): Importance of immobilised enzymes; industrial reuse and improved stability. (TG: detailed biosensor knowledge NOT expected.)

Exam Appearances

Rarely tested directly in recent papers. When it does appear, it is typically 1-2 marks on advantages of immobilisation.

Key advantages: enzyme can be reused; product not contaminated with enzyme; enzyme more stable at higher temperatures

Nucleotide Structure

Spec 1.5(a): Structure of nucleotides (pentose sugar, phosphate, organic base).

Exam Appearances

2017 Components of a nucleotide (1 mark); drawing a nucleotide (1 mark)

2022 Nucleotide base sequence determines mRNA codons which determine amino acid sequence (3 marks)

2023 Components of a nucleotide; structural differences between ATP and RNA nucleotide (3 marks)

Three components: pentose sugar + phosphate group + organic/nitrogenous base

ATP – Structure & Function

Spec 1.5(b)-(d): Importance of chemical energy. Central role of ATP as energy carrier. Structure of ATP.

Exam Frequency – HIGH

2017 Universal energy currency; exergonic reaction; creatine phosphate as ATP buffer (10 marks)

2018 Labelling ATP structure (adenine, ribose, phosphate); uses of ATP in plant cells; calculating % efficiency of respiration using 30.6 kJ mol-¹ (6 marks)

2023 ATP structure differences from RNA nucleotide; function of nucleic acids in protein synthesis (QER, 9 marks)

Must know:

ATP = adenine + ribose + 3 phosphate groups
Energy released by hydrolysis of ATP > ADP + P_i
Energy stored when ADP + P_i > ATP
Universal energy currency: source of energy in all cells/organisms
Structural difference: ATP has 3 phosphates vs RNA nucleotide has 1

Mark Scheme Terminology

ATP hydrolysis: “energy is released when ATP is hydrolysed/broken down to ADP and P_i“
ATP synthesis: “energy is stored when ADP and phosphate are joined”
Universal energy currency: “source of energy in all cells/reactions in all organisms”
Uses in plant cells (2018): active transport, DNA replication, protein synthesis, cell division
Exergonic: “energy released/given out” (NOT produced)

DNA Structure & Base Pairing

Spec 1.5(e)-(f): DNA bases (purines: A & G; pyrimidines: C & T). Complementary base pairing. Hydrogen bonding. Double helix. Antiparallel strands. RNA vs DNA differences.

Exam Appearances

2016 DNA vs RNA comparison in context of virus (4 marks)

2022 Complementary base pairing; nucleotide sequence changes affecting protein (3 marks)

2023 Chargaff’s ratios – calculating % bases; explaining complementary base pairing evidence (4 marks)

2024 Ribosome location & size comparison between bacterial and animal cells (2 marks)

DNA vs RNA (frequently tested):

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, T, C, G	A, U, C, G
Strands	Double-stranded / double helix	Single-stranded
Size	Larger / longer molecule	Smaller / shorter molecule

DNA Replication & Meselson-Stahl

Spec 1.5(g)-(h): Two major functions of DNA. Semi-conservative replication. Roles of DNA polymerase and helicase. Meselson & Stahl experiments.

Exam Frequency – CRITICAL

2017 Meselson & Stahl – interpreting density gradient results; drawing graph of DNA distribution after 2 generations (13 marks!)

2022 Meselson & Stahl – semi-conservative replication evidence; enzyme functions (11 marks)

2023 Semi-conservative replication – template and new strand (2 marks)

This topic is worth a LOT of marks when it appears.

Mark Scheme Terminology

Semi-conservative: “each strand acts as a template for a new strand; newly synthesised DNA contains one old strand and one new strand”
DNA helicase: “breaks hydrogen bonds between bases; unwinds/unzips the double helix; exposes unpaired bases”
DNA polymerase: “joins/bonds adjacent nucleotides in the new strand; forms phosphodiester bonds”
Free nucleotides: “attach to exposed bases by complementary base pairing”
Meselson & Stahl (2017 MS): after 1 generation = 1 band (intermediate density); after 2 generations = 2 bands (one intermediate, one light); ratio 1:1

Exam Tip

Meselson & Stahl questions often require you to draw a graph showing DNA density distribution. Practise drawing peaks at correct positions with correct relative heights (e.g. after 2 generations: 2 peaks in ratio 3:1 or 1:1 depending on what generation the question asks about).

Genetic Code, Exons & Introns

Spec 1.5(i)-(k): The genetic code. Triplet code for amino acids. Exons (coding) and introns (non-coding).

Exam Appearances

2022 How a changed nucleotide sequence affects protein structure and function (3 marks)

2023 Post-translational modification of mRNA – removing introns, splicing exons

Properties of the genetic code: linear, triplet, non-overlapping, degenerate, unambiguous, universal

Transcription & Translation

Spec 1.5(l)-(n): Transcription of DNA to mRNA. Translation of mRNA into polypeptide. One gene, one polypeptide hypothesis.

Exam Frequency – CRITICAL

2016 Viral protein synthesis using host ribosomes (5 marks)

2022 Changed base sequence > different mRNA > different amino acid > changed protein function (3 marks)

2023 QER (9 marks) – Functions of DNA, mRNA, rRNA, tRNA in protein synthesis AND role of ATP in tRNA activation

2024 One gene one polypeptide applied to HIV (3 marks)

Mark Scheme Terminology (from 2023 QER)

Nucleic Acid	Role	Location
DNA	Provides the genetic code/template for mRNA production	Nucleus
mRNA	Produced in transcription; carries genetic code from nucleus to ribosomes	Cytoplasm / ribosomes
rRNA	Forms ribosomes / site of translation	Cytoplasm / rough ER
tRNA	Delivers amino acids to the site of protein synthesis	Cytoplasm

tRNA activation (2023 QER): “ATP provides energy; two phosphates released; amino acid reacts with ATP to form activated amino acid; amino acid transferred to tRNA”

Cell Cycle & Mitosis

Spec 1.6(a)-(c): Interphase and stages of mitosis. Significance: identical copies of genes, cytokinesis. Damage repair, healing, cancerous growth.

Exam Frequency – HIGH

2017 QER (9 marks) – Interpreting DNA mass and cell mass graphs during cell cycle; explaining changes at each stage

2018 Identifying stages of mitosis from microscope images (2 marks)

2019 Cell cycle – interphase function; chromosome behaviour (3 marks)

2022 Mitosis stages identification; significance of mitosis (4 marks)

2023 Identifying metaphase cells from images; mitosis vs meiosis comparison table (4 marks)

2024 Binary fission vs mitosis in prokaryotes and eukaryotes (2 marks)

Mark Scheme Terminology (from 2017 QER)

Interphase: “DNA replicates; DNA mass doubles; organelles replicate; cell grows; mass of cell increases”
After interphase: “DNA present as chromosomes / two chromatids joined at centromere”
Telophase/Cytokinesis: “mass of DNA halves; nuclear membrane reforms; cell divides; mass of cell halves”
Significance of mitosis: growth, repair, asexual reproduction; daughter cells genetically identical to parent cell
Cancer: unrestricted/uncontrolled cell division

Meiosis

Spec 1.6(d)-(e): Main stages of meiosis and cytokinesis. Differences between mitosis and meiosis; meiosis produces non-identical daughter cells.

Exam Appearances

2017 Meselson & Stahl graph interpretation (context of DNA replication before division)

2019 Identifying meiotic stages from images (2 marks)

2022 Comparing mitosis and meiosis outcomes (3 marks)

2023 Identifying metaphase of mitosis, meiosis I, meiosis II from chromosome diagrams (2 marks); differences in daughter cells (2 marks)

Mitosis vs Meiosis comparison (frequently tested):

Feature	Mitosis	Meiosis
Number of divisions	1	2
Daughter cells produced	2	4
Ploidy of daughter cells	Diploid (2n)	Haploid (n)
Genetic variation	Genetically identical (clones)	Genetically different
Crossing over	No	Yes (prophase I)
Independent assortment	No	Yes (metaphase I)
Homologous pairing	No	Yes (bivalents form)

Mark Scheme Terminology

Sources of genetic variation in meiosis: crossing over (prophase I) and independent assortment (metaphase I)
Haploid: one set of chromosomes (n); Diploid: two sets (2n)
Why bacteria don’t do mitosis (2017): “no spindle/centrioles; circular DNA; no chromosomes/histones; no nucleus; divide by binary fission”

AO Distribution Across All Papers

The AO split is fixed by WJEC at AO1: 35% AO2: 45% AO3: 20%. This means nearly half the marks require you to apply your knowledge to unfamiliar situations, not just recall facts.

Year	AO1	AO2	AO3	Total	Maths	Practical
2016	28 (35%)	36 (45%)	16 (20%)	80	11 (14%)	15 (19%)
2017	28 (35%)	36 (45%)	16 (20%)	80	8 (10%)	12 (15%)
2018	28 (35%)	36 (45%)	16 (20%)	80	9 (11%)	15 (19%)
2019	28 (35%)	36 (45%)	16 (20%)	80	8 (10%)	12 (15%)
2022	28 (35%)	36 (45%)	16 (20%)	80	9 (11%)	18 (23%)
2023	28 (35%)	36 (45%)	16 (20%)	80	15 (19%)	20 (25%)
2024	28 (35%)	36 (45%)	16 (20%)	80	10 (13%)	14 (18%)

What This Means For Your Revision

AO1 (35%): Learn definitions, structures, processes and terminology precisely
AO2 (45%): Practise applying knowledge to NEW contexts – this is where most marks are. Use past papers!
AO3 (20%): Practise interpreting data, graphs, and experimental results
Maths (10-19%): Practise calculations – percentages, ratios, gradients, surface area
Practical (15-25%): Know your specified practicals inside out – method, variables, results interpretation

Topics by Exam Frequency (2016-2024)

Use this table to prioritise your revision. Red = Critical (appears almost every year), Amber = High (appears regularly), Green = Medium (appears occasionally but can carry high marks).

Topic	Years Tested	Frequency	Priority
Protein structure & function (amino acids, levels of structure, bonds)	2016, 2017, 2018, 2019, 2022, 2023, 2024	7/7	Critical
Organelle structure & function (identifying, protein pathway)	2016, 2017, 2018, 2019, 2022, 2023, 2024	7/7	Critical
Transport mechanisms (diffusion, facilitated, active, osmosis)	2016, 2017, 2018, 2019, 2022, 2023, 2024	7/7	Critical
Carbohydrate structure (starch, cellulose, hydrolysis/condensation)	2016, 2017, 2018, 2019, 2022, 2023, 2024	7/7	Critical
Cell cycle, mitosis & meiosis	2017, 2018, 2019, 2022, 2023, 2024	6/7	Critical
DNA structure, replication & Meselson-Stahl	2016, 2017, 2022, 2023, 2024	5/7	Critical
Prokaryote vs eukaryote comparison	2016, 2017, 2022, 2023, 2024	5/7	Critical
Enzyme specificity, induced fit & inhibition	2016, 2018, 2022, 2023	4/7	Critical (often QER / high marks)
Protein synthesis (transcription & translation)	2016, 2022, 2023, 2024	4/7	Critical
Fluid mosaic model & membrane components	2016, 2019, 2022, 2023	4/7	High
Lipid & phospholipid structure	2018, 2019, 2022, 2024	4/7	High
ATP structure & function	2017, 2018, 2023	3/7	High
Viruses – structure & replication	2016, 2024	2/7	High (very high marks when tested: 16 & 9 marks)
Water properties	2019, 2022	2/7	High (QER when tested: 9 marks)
Inorganic ions (Mg, Fe, Ca, PO₄)	2019, 2023	2/7	High (part of QER)
Food tests (Benedict’s, biuret, iodine, emulsion)	2016, 2022	2/7	High (specified practical)
Factors affecting enzyme rate (temp, pH, [S], [E])	2018, 2023	2/7	High
Membrane permeability (beetroot experiment)	2022	1/7	High (6 marks when tested)
Genetic code properties (triplet, degenerate, non-overlapping)	2022, 2023	2/7	Medium
Tissues, organs, systems	2017, 2019	2/7	Medium
Immobilised enzymes	Rarely tested	<1/7	Medium (low priority)
Saturated fat & health	Rarely tested directly	<1/7	Medium (low priority)

Extended Response Questions by Year

Every paper has one 9-mark QER question (Quality of Extended Response). You need to cover three distinct content areas in detail, using correct scientific terminology throughout.

Year	Topic	Required Content Areas
2016	Enzyme inhibition (pyrophosphatase)	Enzyme specificity & E-S complex; competitive inhibition by phosphate; non-competitive inhibition by phenylalanine
2017	Cell cycle (DNA mass & cell mass graphs)	DNA replication during interphase; DNA mass changes during mitosis; cell mass changes during cell cycle
2018	Starch & triglyceride structure as energy stores	Structure of starch (amylose & amylopectin); structure of triglycerides (glycerol + fatty acids); how properties relate to function in seed storage
2019	Water & chemical elements	Structure of water (dipole, hydrogen bonds); properties supporting life (solvent, thermal, metabolite); roles of phosphorus & sulfur in biological molecules
2022	Meselson & Stahl / DNA replication	Evidence from density gradient centrifugation; semi-conservative mechanism; enzyme roles (helicase & polymerase)
2023	Nucleic acids in protein synthesis & tRNA activation	Functions of DNA, mRNA, rRNA, tRNA and their locations; role of ATP in tRNA activation process
2024	Cellulose structure & function	β-glucose monomers; 1,4 glycosidic bonds with 180° rotation; hydrogen bonds between chains forming microfibrils; structural function in cell walls

QER Preparation Tips

QER questions always require linking three distinct areas. To score 7-9 marks you must demonstrate:

Detailed coverage of all three areas (not just two!)
An articulate, integrated account with sequential reasoning
Appropriate scientific vocabulary used accurately throughout
No irrelevant inclusions or significant omissions

QER Topic Patterns:

Topics 1.1 (Biological molecules) and 1.5 (Nucleic acids) dominate – 5 out of 7 years
Topic 1.4 (Enzymes) appeared as QER in 2016
Topic 1.6 (Cell division) appeared as QER in 2017
Topics 1.2 (Cell structure) and 1.3 (Membranes) have NEVER been the QER topic

How to Get the Most from These Tools

Start with the Checklist

Go through every learning objective and rate yourself honestly. Don't worry about having lots of reds - that's completely normal and tells you exactly where to focus.

Cross-Reference with Past Papers

Check which of your red/amber topics are also high-frequency in the past paper analysis. These are your highest-priority revision targets.

Revise and Update

After each revision session, come back and update your RAG ratings. Watch your progress improve over time - it's genuinely motivating to see red turn to amber and amber turn to green.

Practice Past Papers

Once your checklist is mostly green, start working through past papers under timed conditions. Use the topic analysis to identify which questions to attempt first.

Unit 1 Topics at a Glance

Unit 1: Basic Biochemistry and Cell Organisation is the foundation of A-Level Biology. Here is what each topic covers:

Topic	Content	Spec Ref
1. Chemical Elements and Biological Compounds	Carbohydrates, lipids, proteins, water, inorganic ions, biochemical tests	1.1
2. Cell Structure and Organisation	Eukaryotic and prokaryotic cells, organelles, electron microscopy, tissues	1.2
3. Cell Membranes and Transport	Fluid mosaic model, diffusion, osmosis, active transport, water potential	1.3
4. Enzymes	Kinetics, inhibition, immobilised enzymes, commercial applications	1.4
5. Nucleic Acids and Their Functions	DNA and RNA structure, replication, protein synthesis, genetic code	1.5
6. Cell Division	Cell cycle, mitosis, meiosis, significance of each type	1.6

Unit 1 Exam Information

Detail	Information
Exam Length	1 hour 30 minutes
Raw Marks	80
UMS Marks	100
A-Level Weighting	20% of A-Level (40% of AS)
Question Types	Short answer, structured, data analysis, extended response (QER)
Assessment Objectives	AO1 (knowledge), AO2 (application), AO3 (analysis and evaluation)

Official resources: Download the full WJEC Biology specification, past papers and mark schemes from wjec.co.uk

Frequently Asked Questions

What topics are covered in WJEC Biology Unit 1?▼

Unit 1: Basic Biochemistry and Cell Organisation covers six main topics: (1) Chemical Elements and Biological Compounds - carbohydrates, lipids, proteins, water and biochemical tests; (2) Cell Structure and Organisation - eukaryotic and prokaryotic cells, organelles and tissues; (3) Cell Membranes and Transport - the fluid mosaic model, diffusion, osmosis and active transport; (4) Enzymes - kinetics, inhibition and immobilised enzymes; (5) Nucleic Acids - DNA, RNA, replication and protein synthesis; (6) Cell Division - mitosis, meiosis and the cell cycle.

How many marks is WJEC Biology Unit 1 worth?▼

Unit 1 is worth 80 raw marks, converted to 100 UMS. It contributes 20% of the full A-Level qualification or 40% of the AS qualification. The exam is 1 hour 30 minutes long and includes a mix of short answer, structured and extended response (QER) questions.

What are the most commonly examined topics in Unit 1?▼

Based on analysis of every exam paper from 2016 to 2024, the most frequently examined topics include enzyme kinetics and inhibition, membrane transport mechanisms, DNA replication (including the Meselson-Stahl experiment), protein structure from primary to quaternary level, comparing mitosis and meiosis, and water potential calculations. Use the past paper analysis tool above to see the full frequency breakdown.

How should I use the RAG checklist for revision?▼

Work through each learning objective and rate your confidence honestly. Red means you need to learn the topic from scratch, amber means you understand it but need more practice, and green means you are confident and exam-ready. Focus your revision time on red and amber topics first, then cross-reference with the past paper analysis to prioritise high-frequency topics. Come back regularly to update your ratings as your confidence grows.

Does my RAG checklist progress get saved?▼

Yes - your progress saves automatically in your browser. You can close the page and come back later, and your RAG ratings will still be there. Note that your progress is saved on this specific browser and device. You can also reset individual topic sections or your entire progress if you want to start fresh.

Can I get help with topics I have rated red or amber?▼

Absolutely. I offer one-to-one and group online A-Level Biology tuition, and I have been teaching the WJEC specification for over 13 years. As a former WJEC examiner, I can show you exactly what examiners are looking for in each topic area. Book a free 20-minute consultation to discuss how I can help.

About This Resource

These revision tools were created by an experienced A-Level Biology teacher and former WJEC examiner who knows exactly what the examiners are looking for.

Tyrone John

Chartered Biologist (CBiol MRSB) • Former WJEC/Eduqas & Edexcel Examiner

With 25+ years of teaching experience including 13+ years on the WJEC specification, I have created these tools based on real examiner insight. I hold a BSc in Immunology from King's College London, a Research Degree in Molecular Pharmacology, and a PGCE.

Learn more about Tyrone →

Disclaimer: The information provided on this page is intended for educational guidance only. While every effort has been made to ensure accuracy, Biology Education and its author accept no responsibility for individual exam outcomes. Students are advised to consult their own teachers, tutors, and official WJEC resources as part of their revision.

Copyright Acknowledgement: WJEC and CBAC are registered trademarks of WJEC CBAC Ltd. Past paper questions and mark scheme content referenced on this page are copyright WJEC CBAC Ltd and are used here solely for non-commercial educational purposes. Biology Education is not affiliated with or endorsed by WJEC CBAC Ltd. For official past papers and mark schemes, visit wjec.co.uk.