Biology: CRISPR, Immunity, and Genetics
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1
Scientists model CRISPR-Cas9 editing efficiency at different sgRNA concentrations, assuming all cells respond identically. Experimental results differ from predictions. State TWO limitations of the simulation that could explain these differences. (2 marks)
1. Assumes all cells respond identically, ignoring biological variation. 2. Oversimplifies experimentaliological conditions, omitting factors affecting editing efficiency.\
2
A CRISPR-Cas9 simulation predicts editing efficiencies of 20%, 40%, 60% and 80% at sgRNA concentrations of 10, 20, 30 and 40 units respectively. Observed efficiencies are 18%, 35%, 49% and 52%. Identify where the discrepancy is greatest, using data. (1 mark)
At 40 units, predicted editing is 80% versus observed 52%, a difference of 28 percentage points.\
3
Scientists investigate the effect of sgRNA concentration on CRISPR-Cas9 editing efficiency. Propose a control group and JUSTIFY how it improves validity. (2 marks)
1. Include cells treated with Cas9 and target DNA but WITHOUT sgRNA. 2. Isolates the effect of sgRNA on editing efficiency, improving validity.\
4
Scientists investigate the effect of sgRNA concentration on CRISPR-Cas9 editing efficiency but test only ONE cell culture per concentration. Suggest a modification to improve reliability and EXPLAIN why. (2 marks)
1. Test multiple independent cell cultures at each concentration. 2. Allows assessment of consistency and reduces the influence of random variation, improving reliability.\
5
A vaccine administered to pregnant women stimulates antibody production. Some antibodies cross the placenta and protect newborn infants. IDENTIFY the type of immunity acquired by the infants and EXPLAIN why it is temporary. (2 marks)
1. Naturally acquired passive immunity. 2. Maternal antibodies decline over time and do NOT establish antigen-specific memory cells in the infant.\
6
A maternal vaccination program reduces severe respiratory virus infections in newborn infants. EXPLAIN one economic benefit for the public healthcare system. (2 marks)
1. Reduced severe infections decrease hospital admissions/medical treatments. 2. This reduces healthcare expenditure and demand for public healthcare resources.\
7
A respiratory virus causes severe illness in newborn infants. Other than vaccination or monoclonal antibodies, PROPOSE a measure to reduce transmission and JUSTIFY it in context. (3 marks)
1. Encourage effective handwashing by people handling infants. 2. Reduces transfer of infectious respiratory secretions. 3. Reduces newborn exposure to the virus and therefore infection risk.\
8
An isolated insect population develops new DNA-sequence variants after several generations. IDENTIFY the process responsible for producing these variants. (1 mark)
Mutation.\
9
An isolated insect population develops a toxin-tolerance allele that increases in frequency from 0.10 to 0.65 over subsequent generations. EXPLAIN how this increase could occur. (3 marks)
1. Tolerance allele provides a selective advantage under toxin exposure. 2. Carriers are more likely to survive and reproduce. 3. Allele is inherited by more offspring, increasing its frequency across generations.\
10
A small, non-representative group of insects colonises an isolated island. EXPLAIN why the founding population has lower genetic diversity than the mainland population. (2 marks)
1. Founder effect occurs when a small, non-representative population separates from a larger population. 2. Founders carry only a subset of original alleles, resulting in a reduced gene poolenetic diversity.\
11
Researchers introduce a disease-resistance gene from one strawberry plant into another plant of the SAME species. EXPLAIN why the recipient is genetically modified but NOT transgenic. (2 marks)
1. Genetic material has been deliberately modified through gene insertion. 2. Introduced gene comes from the SAME species, rather than a different species, so it is not transgenic.\
12
Researchers use a recombinant plasmid to deliver a resistance gene to a strawberry plant. The gene integrates into the recipient chromosome, but the complete plasmid does not. DESCRIBE the fate of the gene and plasmid vector. (1 mark)
Resistance gene integrates into the recipient chromosome, but the entire plasmid vector does NOT integrate.\
13
Researchers use CRISPR-Cas9 to disable a susceptibility gene in strawberry plants. OUTLINE the roles of sgRNA and Cas9 in targeting and cutting the gene. (2 marks)
1. sgRNA has a complementary sequence that guides the Cas9 complex to the target DNA. 2. Cas9 endonuclease cuts the target DNA.\
14
Human muscle cells are exposed to 2% versus 10% oxygen. At 2% oxygen, ATP production is lower and lactate accumulation is greater. EXPLAIN these observations. (3 marks)
1. Oxygen is the final electron acceptor in the ETC. 2. Reduced oxygen limits ETC activity/oxidative phosphorylation, decreasing aerobic ATP production. 3. Cells rely more on lactate fermentation to regenerate NAD+ and maintain glycolysis, increasing lactate accumulation.\
15
An experiment finds relative ATP production of 4, 12, 21 and 21 units at oxygen concentrations of 2%, 5%, 10% and 20% respectively. ANALYSE whether increasing oxygen above 10% increases ATP production. (2 marks)
1. ATP production remains 21 units at BOTH 10% and 20% oxygen. 2. Increasing oxygen above 10% does NOT increase ATP production within the tested range, suggesting oxygen is no longer limiting.\
16
A medical treatment activates complement proteins against antibody-labelled B cells. DESCRIBE THREE distinct mechanisms by which complement proteins contribute to their destructionemoval. (3 marks)
1. MAC forms pores in B-cell membranes → lysis. 2. Opsonisation → increased recognition and engulfment by phagocytes. 3. Chemotaxis/inflammation → recruitment of immune cells that contribute to destructionemoval.
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