Biology HL
Theme D: Continuity and change (HL) — Theme D HL
- 1.
Outline the role of the enzyme DNA helicase and the enzyme DNA polymerase during DNA replication.
[3 marks] · no calculator - 2.
Marking analysis: A learner attempts the following task: “Outline the role of the enzyme DNA helicase and the enzyme DNA polymerase during DNA replication.” Their response addresses only this point: “States that DNA helicase unwinds the double helix and separates the two strands by breaking the hydrogen bonds between complementary base pairs.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 3.
Explain the role of DNA ligase in joining Okazaki fragments on the lagging strand during replication.
[2 marks] · no calculator - 4.
Marking analysis: A learner attempts the following task: “Explain the role of DNA ligase in joining Okazaki fragments on the lagging strand during replication.” Their response addresses only this point: “States that the lagging strand is synthesized discontinuously as a series of short Okazaki fragments, each begun from a separate primer.” Evaluate the response against the complete 2-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[2 marks] · no calculator - 5.
Outline the process of post-transcriptional modification of pre-mRNA in eukaryotic cells, including splicing.
[3 marks] · no calculator - 6.
Marking analysis: A learner attempts the following task: “Outline the process of post-transcriptional modification of pre-mRNA in eukaryotic cells, including splicing.” Their response addresses only this point: “States that many eukaryotic pre-mRNAs contain introns and exons; exons are retained in mature mRNA and can include untranslated regions as well as protein-coding sequence.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 7.
Explain how alternative splicing of the same pre-mRNA transcript can produce different protein products.
[3 marks] · no calculator - 8.
Marking analysis: A learner attempts the following task: “Explain how alternative splicing of the same pre-mRNA transcript can produce different protein products.” Their response addresses only this point: “States that alternative splicing means different combinations of exons can be joined together (or some exons excluded) from the same pre-mRNA transcript.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 9.
Outline the role of transcription factors in controlling gene expression in eukaryotic cells.
[3 marks] · no calculator - 10.
Marking analysis: A learner attempts the following task: “Outline the role of transcription factors in controlling gene expression in eukaryotic cells.” Their response addresses only this point: “States that transcription factors are proteins that bind to specific regulatory DNA sequences (e.g. promoters or enhancers) near a gene.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 11.
Outline how DNA replication is described as a semi-conservative and bidirectional process at a replication origin.
[2 marks] · no calculator - 12.
Marking analysis: A learner attempts the following task: “Outline how DNA replication is described as a semi-conservative and bidirectional process at a replication origin.” Their response addresses only this point: “Explains that semi-conservative replication produces daughter DNA molecules each containing one parental strand and one newly synthesised strand; replication is initiated at an origin.” Evaluate the response against the complete 2-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[2 marks] · no calculator - 13.
Explain why a single-base substitution within an intron, away from splice sites and known regulatory sequences, may be less likely to alter a protein's amino acid sequence than a substitution in its protein-coding sequence.
[3 marks] · no calculator - 14.
Marking analysis: A learner attempts the following task: “Explain why a single-base substitution within an intron, away from splice sites and known regulatory sequences, may be less likely to alter a protein's amino acid sequence than a substitution in its protein-coding sequence.” Their response addresses only this point: “States that introns are removed from the pre-mRNA during splicing and are not present in the mature mRNA that is translated.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 15.
Outline the role of proofreading by DNA polymerase in maintaining the accuracy of DNA replication.
[2 marks] · no calculator - 16.
Marking analysis: A learner attempts the following task: “Outline the role of proofreading by DNA polymerase in maintaining the accuracy of DNA replication.” Their response addresses only this point: “States that DNA polymerase can detect when an incorrectly paired (mismatched) nucleotide has been added to the new strand.” Evaluate the response against the complete 2-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[2 marks] · no calculator - 17.
Outline how the enzyme reverse transcriptase is used in genetic engineering to produce complementary DNA (cDNA) from an mRNA template.
[3 marks] · no calculator - 18.
Marking analysis: A learner attempts the following task: “Outline how the enzyme reverse transcriptase is used in genetic engineering to produce complementary DNA (cDNA) from an mRNA template.” Their response addresses only this point: “States that reverse transcriptase is an enzyme that synthesizes a strand of DNA using an RNA molecule (e.g. mRNA) as its template.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 19.
Distinguish between the structure and role of stamens and carpels in a flowering plant.
[4 marks] · no calculator - 20.
Marking analysis: A learner attempts the following task: “Distinguish between the structure and role of stamens and carpels in a flowering plant.” Their response addresses only this point: “States that a stamen consists of an anther (which produces pollen containing the male gametes) supported on a filament.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 21.
Explain two ways in which meiosis generates genetic variation among gametes.
[4 marks] · no calculator - 22.
Marking analysis: A learner attempts the following task: “Explain two ways in which meiosis generates genetic variation among gametes.” Their response addresses only this point: “States that crossing over exchanges corresponding DNA segments between non-sister chromatids of homologous chromosomes during prophase I.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 23.
In a hypothetical sweet-pea cross, purple flower colour P is completely dominant to red p, and long pollen L to round l. The loci are linked. Assume a 10% recombination frequency, approximately 10 map units. A PL/pl plant is test-crossed with pl/pl, with equal viability of offspring classes. State the expected phenotype proportions and explain why they differ from the 1:1:1:1 ratio for an independently assorting dihybrid test cross.
[5 marks] - 24.
Marking analysis: A learner attempts the following task: “In a hypothetical sweet-pea cross, purple flower colour P is completely dominant to red p, and long pollen L to round l. The loci are linked. Assume a 10% recombination frequency, approximately 10 map units. A PL/pl plant is test-crossed with pl/pl, with equal viability of offspring classes. State the expected phenotype proportions and explain why they differ from the 1:1:1:1 ratio for an independently assorting dihybrid test cross.” Their response addresses only this point: “States that the loci are linked and do not show the independent assortment that would give 1:1:1:1 in this test cross.” Evaluate the response against the complete 5-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[5 marks] - 25.
Distinguish between polygenic inheritance and epistasis, each with a brief example.
[4 marks] · no calculator - 26.
Marking analysis: A learner attempts the following task: “Distinguish between polygenic inheritance and epistasis, each with a brief example.” Their response addresses only this point: “States that polygenic inheritance involves two or more loci contributing to one trait, often modelled with additive effects, although interactions between loci can also occur.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 27.
A population of 500 beetles is in Hardy-Weinberg equilibrium for a gene with two alleles, A (dominant) and a (recessive). 180 beetles show the recessive phenotype. Calculate the allele frequencies of A and a, and the number of heterozygous beetles.
[5 marks] - 28.
Marking analysis: A learner attempts the following task: “A population of 500 beetles is in Hardy-Weinberg equilibrium for a gene with two alleles, A (dominant) and a (recessive). 180 beetles show the recessive phenotype. Calculate the allele frequencies of A and a, and the number of heterozygous beetles.” Their response addresses only this point: “Calculates q² = 180/500 = 0.36.” Evaluate the response against the complete 5-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[5 marks] - 29.
In fruit flies, the genes for body colour and wing length are found to be linked, with a recombination frequency of 18%. Explain what this recombination frequency indicates about the relative positions of the two genes.
[3 marks] · no calculator - 30.
Marking analysis: A learner attempts the following task: “In fruit flies, the genes for body colour and wing length are found to be linked, with a recombination frequency of 18%. Explain what this recombination frequency indicates about the relative positions of the two genes.” Their response addresses only this point: “States that 18% recombinant offspring give an approximate two-point map distance of 18 map units under the simple short-interval approximation.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 31.
Explain the role of non-disjunction during meiosis I in causing Down syndrome (trisomy 21).
[4 marks] · no calculator - 32.
Marking analysis: A learner attempts the following task: “Explain the role of non-disjunction during meiosis I in causing Down syndrome (trisomy 21).” Their response addresses only this point: “States that non-disjunction is the failure of homologous chromosomes (chromosome 21) to separate properly during anaphase I.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 33.
Explain how directional selection can change the allele frequencies of a population over time, using antibiotic resistance in bacteria as an example.
[4 marks] · no calculator - 34.
Marking analysis: A learner attempts the following task: “Explain how directional selection can change the allele frequencies of a population over time, using antibiotic resistance in bacteria as an example.” Their response addresses only this point: “States that within a bacterial population there is already variation, with a small number of individuals carrying a resistance allele (e.g. due to a pre-existing mutation).” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 35.
Distinguish between a gene pool and a gene, and explain how genetic drift can reduce genetic diversity in a small population.
[4 marks] · no calculator - 36.
Marking analysis: A learner attempts the following task: “Distinguish between a gene pool and a gene, and explain how genetic drift can reduce genetic diversity in a small population.” Their response addresses only this point: “States that a gene is a heritable factor at a specific locus that controls a characteristic, while a gene pool is the complete set of all alleles of all genes present in a population.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 37.
Explain how the loop of Henle establishes a concentration gradient in the medulla that enables the kidney to produce concentrated urine.
[5 marks] · no calculator - 38.
Marking analysis: A learner attempts the following task: “Explain how the loop of Henle establishes a concentration gradient in the medulla that enables the kidney to produce concentrated urine.” Their response addresses only this point: “States that the ascending limb is relatively impermeable to water; its thick portion reabsorbs NaCl using energy-dependent transport, whereas the thin ascending limb transports salt passively.” Evaluate the response against the complete 5-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[5 marks] · no calculator - 39.
Explain the role of antidiuretic hormone (ADH) in regulating the water permeability of the collecting duct, and predict the effect of dehydration on ADH secretion.
[4 marks] · no calculator - 40.
Marking analysis: A learner attempts the following task: “Explain the role of antidiuretic hormone (ADH) in regulating the water permeability of the collecting duct, and predict the effect of dehydration on ADH secretion.” Their response addresses only this point: “States that ADH is released from the posterior pituitary gland and travels in the blood to the kidney.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 41.
Outline the roles of follicle-stimulating hormone (FSH) and luteinising hormone (LH) in controlling the menstrual cycle.
[4 marks] · no calculator - 42.
Marking analysis: A learner attempts the following task: “Outline the roles of follicle-stimulating hormone (FSH) and luteinising hormone (LH) in controlling the menstrual cycle.” Their response addresses only this point: “States that FSH, secreted by the pituitary gland, stimulates the growth and development of ovarian follicles.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 43.
Explain the hormonal changes that occur if fertilisation does not take place, leading to menstruation.
[3 marks] · no calculator - 44.
Marking analysis: A learner attempts the following task: “Explain the hormonal changes that occur if fertilisation does not take place, leading to menstruation.” Their response addresses only this point: “States that if fertilisation does not occur, the corpus luteum degenerates towards the end of the cycle.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 45.
A woman takes a combined oral contraceptive containing an oestrogen and a progestogen as prescribed. Explain how suppression of ovulation reduces the chance of pregnancy.
[3 marks] · no calculator - 46.
Marking analysis: A learner attempts the following task: “A woman takes a combined oral contraceptive containing an oestrogen and a progestogen as prescribed. Explain how suppression of ovulation reduces the chance of pregnancy.” Their response addresses only this point: “States that the supplied oestrogen and progestogen exert negative feedback on the hypothalamic-pituitary-ovarian axis.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator