ESAT 2017: 80 questions decoded out of 85, 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.

• 55Oxygen debt is the extra oxygen above rest taken in during recoveryKey methodBiologyAnimal Physiology: Systems, Homeostasis & Disease1 other sitting

  Same method, other sittings

  2019

  Worked solutionOpen the method
• 56Most mutations are neutral, of the rest most are harmful and beneficial ones are rarePavlovBiologyInheritance, Variation & Evolutiononly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 57Ecological 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

  20182019202020212022

  Worked solutionOpen the method
• 58Mitosis keeps the chromosome number and makes two cells, meiosis halves it and makes fourEvery body cell shares one genome, and the male gamete fixes the sexRead a stem cell division by counting what the two daughters areKey methodBiologyMembrane Transport, Cell Division & Reproduction6 other sittings

  Same method, other sittings

  201620182020202120222023

  Worked solutionOpen the method

  AlsoEvery body cell shares one genome, and the male gamete fixes the sexRead a stem cell division by counting what the two daughters are
• 59Weigh the modal word: always or must needs certainty, could or may needs only one plausible mechanismKey methodBiologyEcology & Plant Physiology3 other sittings

  Same method, other sittings

  202020212022

  Worked solutionOpen the method
• 60Prokaryote versus eukaryote: the defining feature contrast (wall, nucleus, mitochondria, chloroplasts)Animal cells never have a cell wall or chloroplasts: use it as an instant eliminatorPavlovBiologyCells6 other sittings

  Same method, other sittings

  201620182019202020212023

  Worked solutionOpen the method

  AlsoAnimal cells never have a cell wall or chloroplasts: use it as an instant eliminator
• 61Energy through trophic levels: about ten per cent passes on, step by step, and efficiency is out over inTunnelBiologyEcology & Plant Physiology1 other sitting

  Same method, other sittings

  2023

  Worked solutionOpen the method
• 62Bacterial binary fission is not mitosis, and the population doubles each divisionPavlovBiologyMembrane Transport, Cell Division & Reproduction1 other sitting

  Same method, other sittings

  2019

  Worked solutionOpen the method
• 63Trace the auxin: shoots bend to light, roots to gravity, driven by uneven hormone from an intact tipPavlovBiologyEcology & Plant Physiology2 other sittings

  Same method, other sittings

  20162018

  Worked solutionOpen the method
• 64Monohybrid cross Aa x Aa gives a 1:2:1 genotype ratio and a 3:1 phenotype ratioProbability of a specific sex and a specific genotype: multiply the two independent chancesTunnelBiologyInheritance, Variation & Evolution5 other sittings

  Same method, other sittings

  20162018202120222023

  Worked solutionOpen the method

  AlsoProbability of a specific sex and a specific genotype: multiply the two independent chances
• 65Osmosis moves water toward the more concentrated solutionPavlovBiologyMembrane Transport, Cell Division & Reproduction6 other sittings

  Same method, other sittings

  201620182020202120222023

  Worked solutionOpen the method
• 66Mitosis keeps the chromosome number and makes two cells, meiosis halves it and makes fourKey methodBiologyMembrane Transport, Cell Division & Reproduction6 other sittings

  Same method, other sittings

  201620182020202120222023

  Worked solutionOpen the method
• 67Read 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

  20192022

  Worked solutionOpen the method
• 68Could versus must: separate what the data proves from what it only allowsKey methodBiologyEnzymes2 other sittings

  Same method, other sittings

  20192020

  Worked solutionOpen the method
• 69Trace the auxin: shoots bend to light, roots to gravity, driven by uneven hormone from an intact tipPavlovBiologyEcology & Plant Physiology2 other sittings

  Same method, other sittings

  20162018

  Worked solutionOpen the method
• 70Could, may or might means find one valid scenario, not prove it always holdsRead a coding strand in non-overlapping triplets from the left and translate with the tableThe genetic code is degenerate: a base change need not change the amino acid or the phenotypeSubstitution hits one codon; an insertion or deletion reframes everything downstreamKey methodBiologyDNA, Protein Synthesis & Gene Technology4 other sittings

  Same method, other sittings

  2016201920202023

  Worked solutionOpen the method

  AlsoRead a coding strand in non-overlapping triplets from the left and translate with the tableThe genetic code is degenerate: a base change need not change the amino acid or the phenotypeSubstitution hits one codon; an insertion or deletion reframes everything downstream
• 71Oxygen sag below organic pollution: bacteria strip the oxygen, and indicator species track the curveKey methodBiologyEcology & Plant Physiology3 other sittings

  Same method, other sittings

  201620182020

  Worked solutionOpen the method
• 72A lethal or non-surviving genotype: delete it and re-read the ratio among survivorsKey methodBiologyInheritance, Variation & Evolution2 other sittings

  Same method, other sittings

  20212022

  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.

• 37Read a nuclide symbol into protons, neutrons and electronsIsoelectronic species share an electron count but differ in protonsPavlovChemistryAtomic Structure, Bonding & the Periodic Table5 other sittings

  Same method, other sittings

  20162018201920212023

  Worked solutionOpen the method

  AlsoIsoelectronic species share an electron count but differ in protons
• 38Judge 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

  20162018201920222023

  Worked solutionOpen the method

  AlsoElectron direction in a half-equation: left means reduction, right means oxidation
• 39Strong versus weak acid: only the hydrogen ion properties differ, not the amount of acidKey methodChemistryChemical Reactions, Acids, Bases & Redox2 other sittings

  Same method, other sittings

  20162023

  Worked solutionOpen the method
• 40Screen an equilibrium with the three Le Chatelier leversKey methodChemistryRates of Reaction & Energetics2 other sittings

  Same method, other sittings

  20162018

  Worked solutionOpen the method
• 41Rf equals spot distance over solvent-front distanceInterpreting a chromatogram: purity, identity, mobility and phasesPavlovChemistryOrganic Chemistry, Separation & Analysis6 other sittings

  Same method, other sittings

  201620182019202020212022

  Worked solutionOpen the method

  AlsoInterpreting a chromatogram: purity, identity, mobility and phases
• 42Electron configuration gives the Period, the Group and the elementOxide formula and acid-base character straight from the groupPavlovChemistryAtomic Structure, Bonding & the Periodic Table3 other sittings

  Same method, other sittings

  201820222023

  Worked solutionOpen the method

  AlsoOxide formula and acid-base character straight from the group
• 43An ionic formula must be charge neutral: cross the ion chargesIonic equations keep only the ions that change; spectators do not affect mass or ratePavlovChemistryChemical Reactions, Acids, Bases & Redox2 other sittings

  Same method, other sittings

  20202023

  Worked solutionOpen the method

  AlsoIonic equations keep only the ions that change; spectators do not affect mass or rate
• 44Recall Group 1 and Group 17 trends whole, without deriving themPavlovChemistryAtomic Structure, Bonding & the Periodic Table3 other sittings

  Same method, other sittings

  201820202021

  Worked solutionOpen the method
• 45Aqueous electrolysis discharge rules: below hydrogen deposits, halide gives the halogenCathode is reduction, anode is oxidation, and electrons flow from plus to minus outsideKey methodChemistryElectrolysis & Metals5 other sittings

  Same method, other sittings

  20162018201920202022

  Worked solutionOpen the method

  AlsoCathode is reduction, anode is oxidation, and electrons flow from plus to minus outside
• 46Empirical formula: masses to moles to the simplest whole number ratioTunnelChemistryQuantitative Chemistry3 other sittings

  Same method, other sittings

  201620192022

  Worked solutionOpen the method
• 47Read the balanced equation directly in gas volumes, and track the change in the number of gas moleculesKey methodChemistryQuantitative Chemistry3 other sittings

  Same method, other sittings

  201820202021

  Worked solutionOpen the method
• 48Read a rate-time curve as two separate things: plateau and steepnessKey methodChemistryRates of Reaction & Energetics4 other sittings

  Same method, other sittings

  2016201920202022

  Worked solutionOpen the method
• 49Bond-energy balance: broken minus formed, counting every bondTunnelChemistryRates of Reaction & Energetics4 other sittings

  Same method, other sittings

  2016201920212023

  Worked solutionOpen the method
• 50Electron accounting: turn charge into moles, then read every amount off the half-equationsCathode is reduction, anode is oxidation, and electrons flow from plus to minus outsideMolten electrolysis always splits the compound into its two elementsTunnelChemistryElectrolysis & Metals5 other sittings

  Same method, other sittings

  20162018201920202021

  Worked solutionOpen the method

  AlsoCathode is reduction, anode is oxidation, and electrons flow from plus to minus outsideMolten electrolysis always splits the compound into its two elements
• 51Limiting reagent by moles over coefficient, and the graph plateau marks the exact stoichiometric pointTunnelChemistryQuantitative Chemistry2 other sittings

  Same method, other sittings

  20182021

  Worked solutionOpen the method
• 52Relative atomic mass as an abundance-weighted mean, forwards or reversedBound the relative atomic mass between the isotope masses to eliminate optionsTunnelChemistryAtomic Structure, Bonding & the Periodic Table6 other sittings

  Same method, other sittings

  201620182020202120222023

  Worked solutionOpen the method

  AlsoBound the relative atomic mass between the isotope masses to eliminate options
• 53Read a rate-time curve as two separate things: plateau and steepnessKey methodChemistryRates of Reaction & Energetics4 other sittings

  Same method, other sittings

  2016201920202022

  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.

• 1Factor out surds before expanding or rationalisingExploit algebraic identities to skip expanding surdsKey methodPureNumber & Units3 other sittings

  Same method, other sittings

  201920222023

  Worked solutionOpen the method

  AlsoExploit algebraic identities to skip expanding surds
• 2Polynomial InequalitiesTunnelPureAlgebra, Functions & Graphs2 other sittings

  Same method, other sittings

  20162019

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

  Same method, other sittings

  2019

  Worked solutionOpen the method
• 4Simultaneous Linear Equations by EliminationTunnelPureAlgebra, Functions & Graphs2 other sittings

  Same method, other sittings

  20192020

  Worked solutionOpen the method
• 5Setting up the proportionality constantTunnelPureRatio & Proportion5 other sittings

  Same method, other sittings

  20162018202020222023

  Worked solutionOpen the method
• 6Polynomial InequalitiesTunnelPureSequences & Series2 other sittings

  Same method, other sittings

  20162019

  Worked solutionOpen the method
• 7Algebraic Fraction SimplificationPavlovPureAlgebra, Functions & Graphs6 other sittings

  Same method, other sittings

  201620192020202120222023

  Worked solutionOpen the method
• 8Parallelogram missing vertex: equate opposite vectorsPavlovPureCoordinate Geometryonly this sitting

  Same method, other sittings

  This one has only struck here so far.

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

  Same method, other sittings

  201620192023

  Worked solutionOpen the method
• 10Fill the two-way table for overlapping categoriesTunnelProb & StatsProbability & Statistics2 other sittings

  Same method, other sittings

  20162018

  Worked solutionOpen the method
• 11Regular polygons: work with exterior angles, not interiorPavlovPureGeometry3 other sittings

  Same method, other sittings

  201620182022

  Worked solutionOpen the method
• 12Bearings: use back-bearings and subtraction to find anglesPavlovPureGeometry3 other sittings

  Same method, other sittings

  201620182019

  Worked solutionOpen the method
• 14Scaling laws for similar figures and solidsPavlovPureRatio & Proportion4 other sittings

  Same method, other sittings

  2018201920222023

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

  Same method, other sittings

  2016201920212023

  Worked solutionOpen the method
• 16Overlay a coordinate system for complex intersecting shapesKey methodPureGeometry5 other sittings

  Same method, other sittings

  20192020202120222023

  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.

• 35Sector and Segment MechanicsTunnelPureTrigonometry2 other sittings

  Same method, other sittings

  20182021

  Worked solutionOpen the method
• 37Common-Base ConversionKey methodPureExponentials & Logarithms1 other sitting

  Same method, other sittings

  2022

  Worked solutionOpen the method
• 41Geometry Optimisation via QuadraticsTunnelPureTrigonometry1 other sitting

  Same method, other sittings

  2022

  Worked solutionOpen the method
• 51Sequential Curve TransformationsTunnelPureAlgebra, Functions & Graphs1 other sitting

  Same method, other sittings

  2016

  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.

• 73Rationalise the denominator using the conjugateTunnelPureNumber & Units2 other sittings

  Same method, other sittings

  20192021

  Worked solutionOpen the method
• 75Intersection of Solution SetsPavlovPureTrigonometryonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 77Substitute to a Polynomial (Exponentials & Logs)Work Backwards from Logarithmic OptionsTunnelPureExponentials & Logarithms3 other sittings

  Same method, other sittings

  201920202022

  Worked solutionOpen the method

  AlsoWork Backwards from Logarithmic Options
• 79Coefficient Matching from Turning PointsKey methodPureDifferentiation1 other sitting

  Same method, other sittings

  2019

  Worked solutionOpen the method
• 81Look Ahead in Binomial ExpansionsKey methodPureSequences & Series2 other sittings

  Same method, other sittings

  20182023

  Worked solutionOpen the method
• 85Factor and Remainder TheoremPavlovPureSequences & Series3 other sittings

  Same method, other sittings

  201620202023

  Worked solutionOpen the method
• 87Factor and Remainder TheoremPolynomial InequalitiesPavlovPureAlgebra, Functions & Graphs4 other sittings

  Same method, other sittings

  2016201920202023

  Worked solutionOpen the method

  AlsoPolynomial Inequalities
• 89Perpendicular lines: the product of their gradients is -1PavlovPureCoordinate Geometry2 other sittings

  Same method, other sittings

  20162021

  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.

• 19Read a motion graph by gradient and area, one phase at a timeAnswer only the phase the question names: every other phase area is an offered optionTunnelPhysicsKinematics & Forces4 other sittings

  Same method, other sittings

  2016201820192020

  Worked solutionOpen the method

  AlsoAnswer only the phase the question names: every other phase area is an offered option
• 20Sort the three transfer modes by what each one actually requiresPavlovPhysicsThermal Physics2 other sittings

  Same method, other sittings

  20162020

  Worked solutionOpen the method
• 21Classify a wave on the spectrum by converting band edges with the wave equationTunnelPhysicsWaves, Sound & the Electromagnetic Spectrum3 other sittings

  Same method, other sittings

  201820202021

  Worked solutionOpen the method
• 22Find the current first: it is the hub of every electrical chainPavlovPhysicsElectricity & Magnetism4 other sittings

  Same method, other sittings

  2016202120222023

  Worked solutionOpen the method
• 23Energy lost, wasted or done against drag is the input total minus the useful totalKey methodPhysicsEnergy, Work & Momentum3 other sittings

  Same method, other sittings

  202020212022

  Worked solutionOpen the method
• 24Turn measured times into distances with the right geometric factor for reflected or multi-speed signalsKey methodPhysicsWaves, Sound & the Electromagnetic Spectrum3 other sittings

  Same method, other sittings

  201620212022

  Worked solutionOpen the method
• 25Nuclear reactions: balance nucleon number and proton number across the arrowTunnelPhysicsRadioactivity2 other sittings

  Same method, other sittings

  20162018

  Worked solutionOpen the method
• 26Power is energy per second: convert the time first, and use force times velocity at constant speedEfficiency chain: multiply going out, divide coming back, never add the lossesPavlovPhysicsEnergy, Work & Momentum2 other sittings

  Same method, other sittings

  20182019

  Worked solutionOpen the method

  AlsoEfficiency chain: multiply going out, divide coming back, never add the losses
• 27Alpha and beta decay bookkeeping: fix the alpha count from the mass number firstTunnelPhysicsRadioactivity5 other sittings

  Same method, other sittings

  20162018201920202023

  Worked solutionOpen the method
• 28When only a ratio is asked, form the ratio and let the unknowns cancelDecide the direction of the change first, then read the spread of the optionsKey methodPhysicsMatter4 other sittings

  Same method, other sittings

  2016202020212022

  Worked solutionOpen the method

  AlsoDecide the direction of the change first, then read the spread of the options
• 29Read the period and wavelength off wave graphs as half-cycle steps and reduce fractional periodsKey methodPhysicsWaves, Sound & the Electromagnetic Spectrum2 other sittings

  Same method, other sittings

  20202022

  Worked solutionOpen the method
• 30Find the current first: it is the hub of every electrical chainRead the option spread before computing: the distractors name the slipPavlovPhysicsElectricity & Magnetism6 other sittings

  Same method, other sittings

  201620192020202120222023

  Worked solutionOpen the method

  AlsoRead the option spread before computing: the distractors name the slip
• 31In a collision momentum carries signs and kinetic energy does notKey methodPhysicsEnergy, Work & Momentum2 other sittings

  Same method, other sittings

  20192020

  Worked solutionOpen the method
• 32Let the option list choose your units, and kill options by dimensionsKey methodPhysicsMatter3 other sittings

  Same method, other sittings

  201620212023

  Worked solutionOpen the method
• 33Power 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

  201620182019

  Worked solutionOpen the method

  AlsoCompound option tables: settle the cheapest quantity first and strike out
• 34Half-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

  201620192020202120222023

  Worked solutionOpen the method

  AlsoDecay conserves atoms one for one: daughter equals initial daughter plus parent decayed
• 35Two scenarios compared: take the ratio, never recompute either oneKey methodPhysicsEnergy, Work & Momentum1 other sitting

  Same method, other sittings

  2022

  Worked solutionOpen the method
• 36Label the circuit with the two invariants, then carry the one given number acrossChoose the power formula by the shared quantity, then split power as R or as one over RTunnelPhysicsElectricity & Magnetism5 other sittings

  Same method, other sittings

  20162018201920222023

  Worked solutionOpen the method

  AlsoChoose the power formula by the shared quantity, then split power as R or as one over R