Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.
Figure 1 shows a stage in the elongation of a polypeptide during protein synthesis.
State the next mRNA codon to be translated as elongation continues.
Explain how the ribosome adds the next amino acid and continues elongation from the stage shown in Figure 1.
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.
| Cell sample | Mean percentage of cells undergoing division in 48 hours |
|---|---|
| Non-tumour skin cells | 8% |
| Tumour cells | 35% |
Determine the expected genotype ratio among the parents’ offspring and the probability that an offspring will have PKU.
Explain why the daughter with genotype Pp does not have PKU, and how she could pass allele p to a child who has PKU.
Describe the difference in cell division between the two cell samples in the table.
Using the information about mutation T, explain how it could contribute to cancer and whether it could be inherited by the daughter’s offspring.
Give one limitation of the cell-culture results in deciding whether mutation T caused the higher rate of cell division.
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.
| Growing conditions | Cuttings (asexual), out of 40 | Seedlings (sexual), out of 40 |
|---|---|---|
| Stable | 36 | 28 |
| Hotter and drier | 8 | 25 |
Calculate the difference between the proportions of marketable cuttings and seedlings in the hotter and drier conditions. Give your answer as a proportion or in percentage points.
If conditions remain stable and the cultivar is already suited to them, recommend a propagation method. Explain why it may be advantageous.
Explain how sexual reproduction could produce offspring better suited to hotter and drier conditions.
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.
| Soil colour | Shell pattern | Number at start | Number alive after two weeks |
|---|---|---|---|
| Dark | Plain | 40 | 24 |
| Dark | Speckled | 40 | 32 |
| Pale | Plain | 40 | 32 |
| Pale | Speckled | 40 | 24 |
Assume shell pattern is inherited as described and does not change with soil colour. Surviving beetles are equally likely to reproduce.
Explain how the mutation described could provide heritable variation in the beetle population.
Use a genetic cross to determine the expected genotype and phenotype ratios among the offspring of the two heterozygous beetles. State how sexual reproduction generates variation in this cross.
Calculate the percentage survival of each shell pattern on each soil colour. Use the results to explain how natural selection may act on variation in this population, distinguishing the role of mutation from the role of natural selection.
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
| Restoration approach | Mean number of native plant species per 20 quadrats after 15 years |
|---|---|
| Non-native tree plantation | 7 |
| Native forest regeneration | 19 |
| Restored peat-forming wetland | 15 |
Identify the restoration approach with the greatest increase in carbon stored after 10 years.
Calculate the mean annual increase in carbon stored in the restored peat-forming wetland between years 5 and 15. Give your answer with a unit.
Describe and compare the changes in carbon stored in the three restoration approaches over the 15-year period.
Explain how tree-based restoration and restoration of a peat-forming wetland can each increase carbon storage.
A project manager argues that non-native tree plantations should be chosen as the best option, considering carbon storage and native plant diversity over the first 15 years. Evaluate this claim using Figure 1 and Table 1.
Suggest one limitation of the investigation’s design and explain how it could affect the comparison of restoration approaches.
Unlock every question in this topic, then type, photograph or draw your answer and have it marked against the markscheme. Find out where you are dropping marks.