This free quiz has 11 real AQA A-level Biology exam questions on natural selection and adaptation (24 marks, about 30 minutes). It marks itself: the tick-box questions are marked for you, and for written answers you check your work against the real AQA mark scheme.
What the quiz covers (AQA 3.4.4)
reducing the frequency of antibiotic-resistant bacteria in human populations
using evidence to deduce when a mutation arose
identifying the type of selection in experiments and in the evolution of penicillin resistance
why antibiotic resistance can persist after an antibiotic stops being used
aseptic techniques for transferring and spreading bacterial cultures
using a graph of mass at birth to explain stabilising selection
why antibiotic-resistant bacteria are common in hospitals
explaining how selection made malaria resistance and lactase persistence common (4 marks each)
How to use it
Write each written answer in full before you open the mark scheme, then tick only the points you really made. For every natural selection answer, build the same chain: mutation, a new allele, survive and reproduce, pass on the allele, allele frequency increases. Fit each step to the example in the question rather than using a stock answer.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Allele, not gene. Many students wrote “resistance gene” or “LP gene” where the mark scheme needed an allele, and this cost marks in almost every natural selection question.
✔ Gains credit: a mutation produces a new allele of a gene, and it is the frequency of this allele that changes in the population.
Mutations happen by chance. A common misconception was that the environment causes the mutation: “antibiotics cause mutations”, drinking milk caused the mutation, or infection triggered it. These answers were rejected.
✔ Gains credit: the allele arose by a chance mutation; the antibiotic or other factor is only the selection pressure, e.g. it kills non-resistant bacteria.
Resistance, not immunity. Many students said bacteria become “immune” to an antibiotic and then described white blood cells and antibodies. References to immunity were rejected or ignored.
✔ Gains credit: resistant bacteria survive because they have an allele for resistance, e.g. one coding for an enzyme that breaks down the antibiotic.
Survive, reproduce, pass on. Some answers had “alleles surviving and reproducing”, and many left out reproduction and the passing on of alleles altogether.
✔ Gains credit: individuals with the advantageous allele are more likely to survive and reproduce (in bacteria, by binary fission), passing the allele on to their offspring.
Frequency, not number. An increase in allele frequency was often poorly expressed, e.g. “the majority of bacteria will have the allele”. An increase in the number of alleles was ignored.
✔ Gains credit: the frequency of the allele increases in the next generation; “higher proportion” or “more common” also gained credit.
Apply it to the context. Many students used stock phrases about favourable alleles with no mention of mutation or of the example in the question, or referred only to a “beneficial allele”. Fewer than 13% scored more than two marks on lactase persistence, often because no nutrient was named.
✔ Gains credit: name the specific allele and the selection pressure in the question, e.g. milk provides glucose, galactose or protein (not just “sugar” or “lactose”).
Why hospitals favour resistance. Some students blamed over-prescription or not finishing a course of antibiotics, which was ignored because antibiotic use is carefully controlled in hospitals.
✔ Gains credit: antibiotics are used more often in hospitals and patients have weakened immune systems, so resistant bacteria survive, spread and increase in frequency.
Keep practising
The other AQA 3.4 self-marking quizzes: DNA, genes and chromosomes · Protein synthesis · Mutation and meiosis · Species and biodiversity
Topic 3.3 quizzes start with surface area to volume ratio
Genetic diversity: common questions and mark scheme insights
The AQA topic index
weekly AQA group classes: Year 12 on Tuesdays at 5.15pm, Year 13 on Wednesdays or Thursdays at 6.30pm
Questions © AQA, from past A-level and AS Biology papers, with their mark schemes and examiners’ reports.