ESAT 2019: 82 questions decoded out of 82, by method and by chapter.

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 55Prokaryote versus eukaryote: the defining feature contrast (wall, nucleus, mitochondria, chloroplasts)Animal cells never have a cell wall or chloroplasts: use it as an instant eliminatorStructure implies function: name the cell or tissue from what it is shown doing, then read off its propertiesOne person, one genome: division type, stem cells, and same DNA but different proteinsPavlovBiologyCells6 other sittings

  Same method, other sittings

  201620172018202020212023

  Worked solutionOpen the method

  AlsoAnimal cells never have a cell wall or chloroplasts: use it as an instant eliminatorStructure implies function: name the cell or tissue from what it is shown doing, then read off its propertiesOne person, one genome: division type, stem cells, and same DNA but different proteins
• 56Structure implies function: name the cell or tissue from what it is shown doing, then read off its propertiesThe biological organisation ladder: check every noun sits at the level (cell, tissue, organ) the option claimsOne person, one genome: division type, stem cells, and same DNA but different proteinsKey methodBiologyCells3 other sittings

  Same method, other sittings

  201820212022

  Worked solutionOpen the method

  AlsoThe biological organisation ladder: check every noun sits at the level (cell, tissue, organ) the option claimsOne person, one genome: division type, stem cells, and same DNA but different proteins
• 57DNA structure recall: a nucleotide is phosphate plus sugar plus base, and the backbone alternates sugar and phosphatePavlovBiologyDNA, Protein Synthesis & Gene Technology1 other sitting

  Same method, other sittings

  2023

  Worked solutionOpen the method
• 58Population curves and extinction risk: a plateau is a limiting factor, and small plus narrow plus restricted is fragilePavlovBiologyEcology & Plant Physiology1 other sitting

  Same method, other sittings

  2022

  Worked solutionOpen the method
• 59Ecological abundance: frequency is presence in quadrats, density is count per area, and both need a random sampleKey methodBiologyEcology & Plant Physiology5 other sittings

  Same method, other sittings

  20172018202020212022

  Worked solutionOpen the method
• 60Structure implies function: name the cell or tissue from what it is shown doing, then read off its propertiesThe biological organisation ladder: check every noun sits at the level (cell, tissue, organ) the option claimsKey methodBiologyCells2 other sittings

  Same method, other sittings

  20182022

  Worked solutionOpen the method

  AlsoThe biological organisation ladder: check every noun sits at the level (cell, tissue, organ) the option claims
• 61Rate of diffusion or osmosis is set by the steepness of the gradientKey methodBiologyMembrane Transport, Cell Division & Reproduction2 other sittings

  Same method, other sittings

  20182023

  Worked solutionOpen the method
• 62Copy-number reflex: a diploid body cell has two copies of each gene, a plasmid or gamete one, a protein nonePavlovBiologyDNA, Protein Synthesis & Gene Technologyonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 63Read what actually measures a rate: quantity against time, and equal steps give rate proportional to one over timeKey methodBiologyEcology & Plant Physiology2 other sittings

  Same method, other sittings

  20172022

  Worked solutionOpen the method
• 64Bacterial binary fission is not mitosis, and the population doubles each divisionMutation is the exception that breaks any absolute genetic claimPavlovBiologyMembrane Transport, Cell Division & Reproduction2 other sittings

  Same method, other sittings

  20172021

  Worked solutionOpen the method

  AlsoMutation is the exception that breaks any absolute genetic claim
• 65Could, may or might means find one valid scenario, not prove it always holdsThe genetic code is degenerate: a base change need not change the amino acid or the phenotypeSomatic changes are not inherited; only gamete (germline) changes reach offspringKey methodBiologyDNA, Protein Synthesis & Gene Technology3 other sittings

  Same method, other sittings

  201720202023

  Worked solutionOpen the method

  AlsoThe genetic code is degenerate: a base change need not change the amino acid or the phenotypeSomatic changes are not inherited; only gamete (germline) changes reach offspring
• 66A mutation present in every cell must have arisen in a gamete or the fertilised eggKey methodBiologyInheritance, Variation & Evolution1 other sitting

  Same method, other sittings

  2018

  Worked solutionOpen the method
• 67Denaturation is loss of the active-site shape, caused by heat, extreme pH or boilingFollow the product to fix the pH direction and read the indicatorCould versus must: separate what the data proves from what it only allowsKey methodBiologyEnzymes6 other sittings

  Same method, other sittings

  201620172018202020222023

  Worked solutionOpen the method

  AlsoFollow the product to fix the pH direction and read the indicatorCould versus must: separate what the data proves from what it only allows
• 68Counting alleles across a pedigree: body cells are diploid, mind the sex chromosomesTunnelBiologyInheritance, Variation & Evolution2 other sittings

  Same method, other sittings

  20162023

  Worked solutionOpen the method
• 69Oxygen debt is the extra oxygen above rest taken in during recoveryKey methodBiologyAnimal Physiology: Systems, Homeostasis & Disease1 other sitting

  Same method, other sittings

  2017

  Worked solutionOpen the method
• 70Phenotype comes from genotype and environment together, beware the alone trapKey methodBiologyInheritance, Variation & Evolution2 other sittings

  Same method, other sittings

  20202022

  Worked solutionOpen the method
• 71A rise-then-plateau curve means a factor is now limiting; plateau height is set by total substrateBiology arithmetic reflexes: percentage over the original, rate as amount over time, area as radius squaredKey methodBiologyEnzymes5 other sittings

  Same method, other sittings

  20162020202120222023

  Worked solutionOpen the method

  AlsoBiology arithmetic reflexes: percentage over the original, rate as amount over time, area as radius squared
• 72Read a coding strand in non-overlapping triplets from the left and translate with the tableTunnelBiologyDNA, Protein Synthesis & Gene Technology2 other sittings

  Same method, other sittings

  20162017

  Worked solutionOpen the method

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 37Alkene addition: one atom to each double-bond carbon, one molecule per bondClassic organic-product distractors the examiner offersPavlovChemistryOrganic Chemistry, Separation & Analysis3 other sittings

  Same method, other sittings

  202120222023

  Worked solutionOpen the method

  AlsoClassic organic-product distractors the examiner offers
• 38Classify the structure and bonding, then read off the propertyKey methodChemistryAtomic Structure, Bonding & the Periodic Table6 other sittings

  Same method, other sittings

  201620182020202120222023

  Worked solutionOpen the method
• 39Rf equals spot distance over solvent-front distanceInterpreting a chromatogram: purity, identity, mobility and phasesPavlovChemistryOrganic Chemistry, Separation & Analysis6 other sittings

  Same method, other sittings

  201620172018202020212022

  Worked solutionOpen the method

  AlsoInterpreting a chromatogram: purity, identity, mobility and phases
• 40Largest or smallest possible mass: take the extreme isotope of every atom and ignore abundancesKey methodChemistryAtomic Structure, Bonding & the Periodic Tableonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 41Read the reactivity order off the behaviour, do not recall a fixed listKey methodChemistryElectrolysis & Metals2 other sittings

  Same method, other sittings

  20212023

  Worked solutionOpen the method
• 42Read a nuclide symbol into protons, neutrons and electronsPavlovChemistryAtomic Structure, Bonding & the Periodic Table5 other sittings

  Same method, other sittings

  20162017201820212023

  Worked solutionOpen the method
• 43Empirical formula: masses to moles to the simplest whole number ratioTunnelChemistryQuantitative Chemistry3 other sittings

  Same method, other sittings

  201620172022

  Worked solutionOpen the method
• 44Judge a reaction as redox from its type before assigning oxidation numbersElectron direction in a half-equation: left means reduction, right means oxidationKey methodChemistryChemical Reactions, Acids, Bases & Redox5 other sittings

  Same method, other sittings

  20162017201820222023

  Worked solutionOpen the method

  AlsoElectron direction in a half-equation: left means reduction, right means oxidation
• 45Standard qualitative tests to identify ionsPavlovChemistryOrganic Chemistry, Separation & Analysis2 other sittings

  Same method, other sittings

  20202021

  Worked solutionOpen the method
• 46Electron accounting: turn charge into moles, then read every amount off the half-equationsIn amount MCQs the wrong options are the electron-count and diatomic-gas slipsTunnelChemistryElectrolysis & Metals4 other sittings

  Same method, other sittings

  2016201720202021

  Worked solutionOpen the method

  AlsoIn amount MCQs the wrong options are the electron-count and diatomic-gas slips
• 47Precipitation gravimetry: only the ion that forms the solid counts, ignore the spectatorsKey methodChemistryQuantitative Chemistry1 other sitting

  Same method, other sittings

  2021

  Worked solutionOpen the method
• 48Balance a skeleton equation one element at a time, most constrained firstTunnelChemistryChemical Reactions, Acids, Bases & Redox3 other sittings

  Same method, other sittings

  201820202021

  Worked solutionOpen the method
• 49Read a rate-time curve as two separate things: plateau and steepnessKey methodChemistryRates of Reaction & Energetics4 other sittings

  Same method, other sittings

  2016201720202022

  Worked solutionOpen the method
• 50Pick the separation technique from the property that differsKey methodChemistryOrganic Chemistry, Separation & Analysis2 other sittings

  Same method, other sittings

  20182020

  Worked solutionOpen the method
• 51Reactivity series reflex: a metal below hydrogen gives no reaction with dilute acid, a more reactive metal displaces a less reactive onePavlovChemistryQuantitative Chemistry1 other sitting

  Same method, other sittings

  2023

  Worked solutionOpen the method
• 52Purity and hydration are just multiplying factors: scale in the right direction and the pre-scaled value is the trapKey methodChemistryQuantitative Chemistry2 other sittings

  Same method, other sittings

  20182023

  Worked solutionOpen the method
• 53Bond-energy balance: broken minus formed, counting every bondExploit the bond-energy option list: sign, factor and phantom bondsTunnelChemistryRates of Reaction & Energetics4 other sittings

  Same method, other sittings

  2016201720212023

  Worked solutionOpen the method

  AlsoExploit the bond-energy option list: sign, factor and phantom bonds
• 54Cathode is reduction, anode is oxidation, and electrons flow from plus to minus outsideMolten electrolysis always splits the compound into its two elementsPavlovChemistryElectrolysis & Metals3 other sittings

  Same method, other sittings

  201620172018

  Worked solutionOpen the method

  AlsoMolten electrolysis always splits the compound into its two elements

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 1Exploit algebraic identities to skip expanding surdsKey methodPureNumber & Units1 other sitting

  Same method, other sittings

  2017

  Worked solutionOpen the method
• 2Rearranging Complex FormulasPavlovPureAlgebra, Functions & Graphs4 other sittings

  Same method, other sittings

  2016202120222023

  Worked solutionOpen the method
• 3Unwrapping Squared FormulasPavlovPureAlgebra, Functions & Graphs1 other sitting

  Same method, other sittings

  2017

  Worked solutionOpen the method
• 4Successive percentage changes as a product of decimal multipliersPavlovPureRatio & Proportion5 other sittings

  Same method, other sittings

  20162018202020212022

  Worked solutionOpen the method
• 5Simultaneous Linear Equations by EliminationTunnelPureAlgebra, Functions & Graphs2 other sittings

  Same method, other sittings

  20172020

  Worked solutionOpen the method
• 6Algebraic Fraction SimplificationPavlovPureAlgebra, Functions & Graphs6 other sittings

  Same method, other sittings

  201620172020202120222023

  Worked solutionOpen the method
• 7Scaling laws for similar figures and solidsPavlovPureRatio & Proportion4 other sittings

  Same method, other sittings

  2017201820222023

  Worked solutionOpen the method
• 8The solving for x multiple-choice trapKey methodPureGeometry2 other sittings

  Same method, other sittings

  20162022

  Worked solutionOpen the method
• 9Reduce exponential equations to a single prime basePavlovPureNumber & Units3 other sittings

  Same method, other sittings

  201620172023

  Worked solutionOpen the method
• 10The solving for x multiple-choice trapRhombus area from diagonalsKey methodPureGeometry2 other sittings

  Same method, other sittings

  20162022

  Worked solutionOpen the method

  AlsoRhombus area from diagonals
• 11Overlay a coordinate system for complex intersecting shapesKey methodPureGeometry5 other sittings

  Same method, other sittings

  20172020202120222023

  Worked solutionOpen the method
• 12Chaining ratios by scaling the common termPavlovPureRatio & Proportion2 other sittings

  Same method, other sittings

  20162020

  Worked solutionOpen the method
• 13Implicit line equations: isolate y to find the gradient safelyPavlovPureCoordinate Geometry3 other sittings

  Same method, other sittings

  201820202023

  Worked solutionOpen the method
• 14Coordinate transformations algebraicallyKey methodPureGeometry3 other sittings

  Same method, other sittings

  202020222023

  Worked solutionOpen the method
• 15Set up algebraic probability treesTunnelProb & StatsProbability & Statistics4 other sittings

  Same method, other sittings

  2016201720212023

  Worked solutionOpen the method
• 16Bearings: use back-bearings and subtraction to find anglesPavlovPureGeometry3 other sittings

  Same method, other sittings

  201620172018

  Worked solutionOpen the method
• 17Test abstract statistics with extreme or simple listsKey methodProb & StatsProbability & Statisticsonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 183D solids: equating volumes and surface areas algebraicallyTunnelPureGeometry5 other sittings

  Same method, other sittings

  20182020202120222023

  Worked solutionOpen the method

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 25Rationalise the denominator using the conjugateTunnelPureNumber & Units2 other sittings

  Same method, other sittings

  20172021

  Worked solutionOpen the method

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 73Areas bounded by intersecting lines: use an axis as the baseKey methodPureCoordinate Geometry3 other sittings

  Same method, other sittings

  201820202022

  Worked solutionOpen the method
• 75Coefficient Matching from Turning PointsKey methodPureDifferentiation1 other sitting

  Same method, other sittings

  2017

  Worked solutionOpen the method
• 77Pythagorean Substitution to QuadraticKey methodPureTrigonometry2 other sittings

  Same method, other sittings

  20162020

  Worked solutionOpen the method
• 79Shaded areas by structural subtractionPavlovPureGeometry2 other sittings

  Same method, other sittings

  20162020

  Worked solutionOpen the method
• 81Substitute to a Polynomial (Exponentials & Logs)Work Backwards from Logarithmic OptionsTunnelPureExponentials & Logarithms3 other sittings

  Same method, other sittings

  201720202022

  Worked solutionOpen the method

  AlsoWork Backwards from Logarithmic Options
• 83Integrals as Linear UnknownsKey methodPureIntegrationonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 85Differentiating to Find an Integral's ExpansionKey methodPureIntegrationonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 87Hidden Triangle Constraints (The Obtuse Trap)PavlovPureTrigonometryonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 89Polynomial InequalitiesTunnelPureAlgebra, Functions & Graphs2 other sittings

  Same method, other sittings

  20162017

  Worked solutionOpen the method

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 19Total path of an oscillating particle is four times the amplitude per cycleKey methodPhysicsWaves, Sound & the Electromagnetic Spectrum3 other sittings

  Same method, other sittings

  201620182023

  Worked solutionOpen the method
• 20Power is energy per second: convert the time first, and use force times velocity at constant speedCompound option tables: settle the cheapest quantity first and strike outPavlovPhysicsEnergy, Work & Momentum3 other sittings

  Same method, other sittings

  201620172018

  Worked solutionOpen the method

  AlsoCompound option tables: settle the cheapest quantity first and strike out
• 21Label the circuit with the two invariants, then carry the one given number acrossRead the option spread before computing: the distractors name the slipFor a non ohmic component the graph is its Ohm law: the circuit picks the axisTunnelPhysicsElectricity & Magnetism6 other sittings

  Same method, other sittings

  201720182020202120222023

  Worked solutionOpen the method

  AlsoRead the option spread before computing: the distractors name the slipFor a non ohmic component the graph is its Ohm law: the circuit picks the axis
• 22In a vacuum every electromagnetic wave shares one speed, so frequency and wavelength are strictly inversePavlovPhysicsWaves, Sound & the Electromagnetic Spectrum2 other sittings

  Same method, other sittings

  20162021

  Worked solutionOpen the method
• 23Energy audit on a heated body: supplied, stored, lostThe option list holds your intermediate results: never stop one step earlyTunnelPhysicsThermal Physics2 other sittings

  Same method, other sittings

  20202021

  Worked solutionOpen the method

  AlsoThe option list holds your intermediate results: never stop one step early
• 24Numbered statements: check what each quantity is proportional to, and who each force acts onKey methodPhysicsKinematics & Forcesonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 25Trapped gas: build the absolute pressure first, then apply Boyle's lawLiquid pressure counts only what lies above the point, layer by layerTunnelPhysicsMatter3 other sittings

  Same method, other sittings

  202120222023

  Worked solutionOpen the method

  AlsoLiquid pressure counts only what lies above the point, layer by layer
• 26Transformers: voltage by turns ratio, current by power, never turns ratio for a non ideal currentTunnelPhysicsElectricity & Magnetism3 other sittings

  Same method, other sittings

  202020212023

  Worked solutionOpen the method
• 27Energy audit on a heated body: supplied, stored, lostThe option list holds your intermediate results: never stop one step earlyTunnelPhysicsThermal Physics2 other sittings

  Same method, other sittings

  20202021

  Worked solutionOpen the method

  AlsoThe option list holds your intermediate results: never stop one step early
• 28Heat transfer is driven by the temperature difference alone, never by the individual temperaturesConduction along a bar: rate is proportional to area times temperature difference, divided by lengthScale by the exponents: multiply the factor changes, never recompute the quantityKey methodPhysicsThermal Physics3 other sittings

  Same method, other sittings

  201620182022

  Worked solutionOpen the method

  AlsoConduction along a bar: rate is proportional to area times temperature difference, divided by lengthScale by the exponents: multiply the factor changes, never recompute the quantity
• 29Force on a current: the work is deciding what B, I and L really areKey methodPhysicsElectricity & Magnetism4 other sittings

  Same method, other sittings

  2020202120222023

  Worked solutionOpen the method
• 30Alpha and beta decay bookkeeping: fix the alpha count from the mass number firstTunnelPhysicsRadioactivity5 other sittings

  Same method, other sittings

  20162017201820202023

  Worked solutionOpen the method
• 31Force from a momentum change: divide by the contact time, and double the speed for a bounceThe bridge between momentum and kinetic energyTunnelPhysicsEnergy, Work & Momentum4 other sittings

  Same method, other sittings

  2016201820212022

  Worked solutionOpen the method

  AlsoThe bridge between momentum and kinetic energy
• 32Label the circuit with the two invariants, then carry the one given number acrossWhen the resistances are identical or never given, call each one R and let it cancelTunnelPhysicsElectricity & Magnetism5 other sittings

  Same method, other sittings

  20172018202120222023

  Worked solutionOpen the method

  AlsoWhen the resistances are identical or never given, call each one R and let it cancel
• 33Compound option tables: settle the cheapest quantity first and strike outIn a collision momentum carries signs and kinetic energy does notKey methodPhysicsEnergy, Work & Momentum3 other sittings

  Same method, other sittings

  201620172020

  Worked solutionOpen the method

  AlsoIn a collision momentum carries signs and kinetic energy does not
• 34Read a motion graph by gradient and area, one phase at a timeDistance, displacement and average speed are three different readings of the same motionAnswer only the phase the question names: every other phase area is an offered optionTunnelPhysicsKinematics & Forces5 other sittings

  Same method, other sittings

  20162017201820202023

  Worked solutionOpen the method

  AlsoDistance, displacement and average speed are three different readings of the same motionAnswer only the phase the question names: every other phase area is an offered option
• 35Prism with a hole: subtract in the cross-section, multiply by the length onceTunnelPhysicsMatter2 other sittings

  Same method, other sittings

  20162020

  Worked solutionOpen the method
• 36Half-life arithmetic: work in powers of one-half, never in logarithmsDecay conserves atoms one for one: daughter equals initial daughter plus parent decayedPavlovPhysicsRadioactivity6 other sittings

  Same method, other sittings

  201620172020202120222023

  Worked solutionOpen the method

  AlsoDecay conserves atoms one for one: daughter equals initial daughter plus parent decayed