Paper V — Biology
33 QUESTIONS
Paper V covers biology from the molecular to the evolutionary scale. Its questions examine the genome and the gene itself, heritability and its misuse, the units and levels of selection, neutral theory, the error threshold, the genetic code and its departures from universality, epistasis and the genotype–phenotype map; the physics of the living cell as an open system far from equilibrium, replication fidelity, ribosomal speed against accuracy, the thermodynamic cost of biological information processing, and the limits of biological imaging; and the developmental and organismal questions of robustness, plasticity, allometric scaling, ageing, cancer as an evolutionary process, and convergence as evidence of constraint. Three later questions treat cochlear mechanics, the independent evolution of vocal learning, and the species–area relationship.
The paper examines mechanism and inference together. A candidate is expected to give a physical or chemical account where one exists — why replication is as accurate as it is, why folding is hard given the sequence, what a signalling network has that a reaction network lacks — and to be equally exact about what evolutionary reasoning can and cannot establish, including whether natural selection is a law, a tautology or a mechanism, and whether the species concept survives contemporary molecular biology. Questions about the origin of life ask not for speculation but for criteria: what would count as a second, independent origin, and which single measurement would most constrain the theories. Precision about levels of explanation is expected throughout, and rewarded.
Conduct of the response
Answer in the idiom of the college: provocations invite a disciplined essay; technical problems require correct, quantitative reasoning; interdisciplinary questions require two fields to be brought together. A response is an argument, not a survey; where the question admits a position, one is to be taken at the outset and defended. It must be exactly as technical as the question requires, and no more, and its course must remain followable by the educated layman. It may not exceed three thousand words, exclusive of equations, figures, tables, and references; the limit is a ceiling, not a target, and of two answers of equal force the shorter is judged the better. The full statement of the response required is given on the Responses page.
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1.
Is the genome a program, a blueprint, or neither? Defend your choice mechanistically.
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2.
What does it mean for a trait to be heritable, and why is heritability so often misunderstood?
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3.
Explain the thermodynamics of the living cell as an open system far from equilibrium.
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4.
Is natural selection a law, a tautology, or a mechanism?
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5.
What is a gene? Give a definition that survives contemporary molecular biology.
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6.
Account for the maintenance of sexual reproduction despite its twofold cost.
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7.
Why is the protein-folding problem hard even given the sequence?
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8.
What does information theory legitimately contribute to molecular biology?
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9.
Is there a unit of selection? Defend a level.
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10.
Explain the error threshold and its relevance to the origin of replication.
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11.
What distinguishes a signalling network from a mere chemical reaction network?
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12.
Why is convergent evolution evidence about constraint rather than chance?
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13.
What is the physical basis of the fidelity of DNA replication?
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14.
Explain how a developmental program can be robust to noise yet evolvable.
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15.
Is ageing selected for, tolerated, or a physical inevitability?
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16.
What does "junk DNA" mean now, and was the concept a mistake?
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17.
Account for allometric scaling laws in metabolism.
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18.
Explain why the neutral theory of molecular evolution was necessary.
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19.
Is the species concept salvageable, and does biology need it?
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20.
What is the thermodynamic cost of biological information processing?
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21.
How does a ribosome achieve both speed and accuracy?
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22.
Explain epistasis and why it complicates the genotype–phenotype map.
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23.
What would count as a second, independent origin of life, and how would we recognise it?
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24.
Why is cancer better understood as an evolutionary process than as a single disease?
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25.
Explain how phenotypic plasticity relates to, and differs from, evolution.
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26.
What sets the fundamental limits on the resolution of biological imaging?
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27.
Is the brain a computer? Answer with reference to what computation requires.
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28.
Account for the origin of the genetic code's near-universality and its departures.
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29.
What is the role of stochasticity in gene expression, and is it a bug or a feature?
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30.
Which single measurement would most constrain theories of the origin of life?
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31.
How does the cochlea achieve its frequency selectivity? Give the mechanics of the travelling wave, and say what the active process adds that passive filtering cannot.
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32.
Vocal learning has evolved independently in songbirds, cetaceans, and humans. State what the capacity requires neurally, and decide whether the convergence is evidence of one solution or of three.
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33.
State the species–area relationship, and decide whether island biogeography theory explains it or merely fits it.
Questions added by Examination Expansion v5.0, which extended the examination to music and geography. All earlier questions stand verbatim and unrenumbered.