IB Biology SL Theme D: Continuity and change questions

PCR primers flank a 300 bp region of a DNA sample. After repeated temperature cycles, the products and a 600 bp DNA fragment are loaded into separate wells of the same gel. Which statement correctly links DNA synthesis in PCR to the relative movement of the fragments?

Figure 1 shows a stage in the elongation of a polypeptide during protein synthesis.

Two versions of a gene occur in a population. In version X, one nucleotide is replaced by another; in version Y, one nucleotide is inserted within the coding sequence, before its final codon. No other sequence changes are present. Which statements are correct?

I. Version X is a single-nucleotide polymorphism (SNP) resulting from a base substitution.
II. The replacement in X must change the amino acid encoded at that position.
III. The insertion in Y shifts the reading frame of subsequent codons, making it likely that the polypeptide ceases to function.

Phenylketonuria (PKU) is caused by the recessive mutated allele p. The allele P is dominant, and only individuals with genotype pp have PKU. Two unaffected parents both have genotype Pp.

Their daughter also has genotype Pp. As an adult, she develops a skin cancer. A mutation, T, in a gene involved in regulating cell division is detected in her tumour cells, but not in her non-tumour skin cells, blood cells or gametes.

Non-tumour skin cells and tumour cells from the daughter were cultured under the same conditions. The table shows the mean percentage of cells that underwent division in 48 hours, from three replicate cultures.

A nursery propagates a plant cultivar from stem cuttings, which reproduce asexually, and from seeds produced by sexual reproduction. Groups of 40 plants from each method were grown under two sets of conditions. The number of plants that met the nursery’s marketability standard is shown.

A mother with XX sex chromosomes and a father with XY sex chromosomes have a child. The father has allele R on his X chromosome, and R is absent from his Y chromosome. Which statement(s) are correct?

I. A sperm carrying Y results in an XY zygote, associated with certain male-typical physical characteristics.
II. A child with XY sex chromosomes inherits allele R from the father.
III. The X chromosome carries more genes than the Y chromosome.

After a meal, a patient’s blood glucose remains high even though the pancreas releases a normal amount of insulin. Which option identifies the likely type of diabetes and its relevant physiological change?

In a population of ground beetles, shell pattern is determined by one gene with two alleles, P and p. P is dominant: beetles with PP or Pp have plain shells, while beetles with pp have speckled shells. A base substitution in a germ cell changed a P allele to p, and the p allele was inherited by descendants.

Two heterozygous beetles mate. In a separate investigation, equal numbers of plain and speckled beetles were placed on dark or pale soil. The number alive after two weeks was recorded.

Assume shell pattern is inherited as described and does not change with soil colour. Surviving beetles are equally likely to reproduce.

A survey measured the mean concentrations of DDT and mercury in the tissues of consumers at trophic levels 2–5 in a lake. Which interpretation is supported by the graph?

A shift in ocean currents leaves surface water in a coastal region warmer during the season when nutrients normally rise from deeper water. Which paired change is most likely?

Three temperate sites were managed using different approaches to restoration: planting non-native trees, allowing native forest to regenerate, or restoring a peat-forming wetland by re-establishing waterlogged conditions. Waterlogging at the wetland limits the decomposition of dead plant material.

Each approach was studied at one site. Three plots were sampled at each site. Figure 1 shows the mean net increase in carbon stored in vegetation and soil relative to the start of restoration. Table 1 shows the mean number of native plant species recorded per 20 quadrats after 15 years, averaged across the three plots.

Table 1