School / IB / BIOLOGY HL / Theme A: Unity and diversity (HL) Question practice
Theme A: Unity and diversity (HL) About this practice HL-only depth on nucleic acid structure and the mechanisms and evidence behind speciation.
Biology HL Theme A: Unity and diversity (HL)
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3 Outline how natural selection can lead to allopatric speciation. Medium 4 marks No calculator + 4 Marking analysis: A learner attempts the following task: “Outline how natural selection can lead to allopatric speciation.” Their response addresses only this point: “States that a geographic barrier (e.g. a river, mountain range or ocean) physically separates a population into two subpopulations, preventing gene flow between them.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks No calculator + 7 Describe the Meselson-Stahl experiment, and state what its results showed about the mechanism of DNA replication. Medium 4 marks No calculator + 8 Marking analysis: A learner attempts the following task: “Describe the Meselson-Stahl experiment, and state what its results showed about the mechanism of DNA replication.” Their response addresses only this point: “States that bacteria were grown in a medium containing heavy nitrogen (¹⁵N) for several generations, so all their DNA contained ¹⁵N.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks No calculator + 9 Outline the purpose of the polymerase chain reaction (PCR), and state the three main temperature-controlled steps involved in a single PCR cycle. Medium 4 marks No calculator + 10 Marking analysis: A learner attempts the following task: “Outline the purpose of the polymerase chain reaction (PCR), and state the three main temperature-controlled steps involved in a single PCR cycle.” Their response addresses only this point: “States that PCR is used to make many identical copies (amplify) of a specific, small sample of DNA very quickly.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks No calculator + 11 Describe how gel electrophoresis is used to separate fragments of DNA by size, and state one application of this technique. Medium 4 marks No calculator + 12 Marking analysis: A learner attempts the following task: “Describe how gel electrophoresis is used to separate fragments of DNA by size, and state one application of this technique.” Their response addresses only this point: “States that DNA samples are placed into wells at one end of a gel, and an electric current is applied across the gel.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks No calculator + 17 Distinguish between homologous structures and analogous structures, giving one example of each, and state what each provides evidence for. Medium 4 marks No calculator + 18 Marking analysis: A learner attempts the following task: “Distinguish between homologous structures and analogous structures, giving one example of each, and state what each provides evidence for.” Their response addresses only this point: “States that homologous structures have a similar underlying structure but may have different functions, because the species share a common ancestor, e.g. the forelimb bones of a human, bat and whale.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks No calculator + 27 In a population, the frequency of the recessive allele (q) for a particular gene is 0.2. Assuming the population is in Hardy-Weinberg equilibrium, calculate the frequency of the dominant allele (p), and the percentage of the population expected to be heterozygous. Medium 4 marks Calculator + 28 Marking analysis: A learner attempts the following task: “In a population, the frequency of the recessive allele (q) for a particular gene is 0.2. Assuming the population is in Hardy-Weinberg equilibrium, calculate the frequency of the dominant allele (p), and the percentage of the population expected to be heterozygous.” Their response addresses only this point: “States that p + q = 1, so p = 1 − 0.2.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks Calculator + Self-assessed Not marked yet
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