IB Biology HL Theme D: Continuity and change questions

Using Figure 1, state which of A and B is synthesized continuously and which is synthesized discontinuously. Name the short DNA pieces on B.

Explain, using the strand orientations in Figure 1, why A requires one RNA primer whereas B requires repeated RNA primers.

A newly synthesized lagging-strand region is 2.4 kb long. The mean length of an Okazaki fragment is 200 nucleotides. For this calculation, use 1 kb = 1000 nucleotides. Estimate the number of Okazaki fragments and the number of RNA primers required.

In four separate bacterial preparations, the replication fork has already formed and exactly one enzyme is selectively inactivated. All other replication components remain active.

For each preparation, identify the inactive enzyme and explain how its normal function accounts for the observation.

Identify the exon present in the mRNA from cell type X but absent from the mRNA from cell type Y.

State the two exons present in both mRNAs.

Using the table, explain how this gene can code for different polypeptides.

For P, Q and R, state the codon and nucleotide substitution. Explain why these differences are SNPs.

For each variant, state the amino acid encoded at the changed codon and whether this amino acid differs from that in the reference sequence.

Explain why the substitution in P does not change the amino acid.

A student concludes that variants Q and R must produce a different phenotype from the reference individuals. Evaluate this conclusion using the information given.

State the number of chromosomes and the number of chromatids in the replicated parent nucleus in Figure 1.

Using Figure 1, compare the number of nuclei formed and the chromosome number per nucleus after mitosis and meiosis.

Explain the role of DNA replication before mitosis and meiosis, referring to chromatids and their separation during these processes.

Explain two processes by which meiosis can generate genetically different nuclei. Explain why nuclear division should be completed before cytokinesis.

State which plant’s pollen could be transferred to a receptive stigma on day 1.

Explain how the different maturation times and one feature of an insect-pollinated flower promote cross-pollination between the plants.

State the genotype of the F₁ beetle and the arrangement of its alleles on its homologous chromosomes.

Assuming the genes assort independently, determine the gamete types produced by the F₁ beetle and the expected offspring genotypes and phenotypes from the testcross. State the expected phenotypic ratio.

Using the observed offspring, identify the recombinant gamete types from the F₁ beetle and their corresponding offspring genotypes and phenotypes.

Identify the parental offspring phenotype and genotype classes. Compare the observed results with the expected outcome if the genes assort independently, and infer whether the genes are linked.

Calculate the percentage decrease in osmotic concentration at the inner medulla when transport is reduced compared with normal transport.

Compare the osmotic concentration profiles and collecting-duct outcomes in the three conditions.

Explain how active sodium-ion transport in the ascending limb can affect water reabsorption from the collecting ducts and urine flow.

In a separate test, collecting-duct segments with identical water permeability were used. The osmotic concentration of the fluid inside each segment was 300 units. The surrounding solution had the concentration shown below; its solute could not cross the duct wall. The percentage of the initial water volume inside the segment that crossed out after 10 minutes was measured.

Deduce what this test adds to the interpretation of the first experiment.

A researcher concludes: “These results establish that active sodium-ion transport in the ascending limb is the only factor controlling water reabsorption from the collecting ducts.” Evaluate this conclusion using both experiments.

State what p and q represent for this gene and give their relationship.

Calculate p and q for generation 1, and the expected frequencies of BB, Bb and bb.

Calculate the observed genotype frequencies in generation 2. Determine whether they fit the Hardy–Weinberg equation for the allele frequencies given.

Explain how the mating pattern could account for the genotype frequencies in generation 2.

State three conditions, other than random mating, required for a population to remain in genetic equilibrium.

Describe the patterns in the sea otter, sea urchin and kelp data between 2018 and 2024.

Using the data and feeding relationships, explain how a decline in sea otters could affect ecosystem stability and support identifying sea otters as a keystone species.

Calculate the percentage of annual replacement harvested for each resource. Show your working.

Using your results from (c), assess whether harvesting meets the sustainability criterion for each resource in the year shown.

Explain why the results for one year cannot by themselves establish whether each harvest is sustainable over the long term.

Calculate the percentage decrease in mean calcification rate when CO₂ is elevated at 27 °C.

Compare the effects of elevated CO₂ and increased temperature on calcification and bleaching.

A separate survey was carried out at one reef in Year 0 and again in Year 12. No comparison reef was surveyed. Fish species were grouped as those recorded using living coral for shelter and those not recorded doing so; the two groups together make up total fish species richness.

Compare the changes in the two fish groups from Year 0 to Year 12, using data.

Evaluate the claim that rising CO₂ and water temperature could cause coral loss and lead to collapse of the reef ecosystem. Use evidence from both studies and give one limitation of the evidence.