AQA GCSE Biology (8461), Higher tier · Inheritance, variation and evolution › Understanding of genetics and evolution
Practise Resistant bacteria. 14 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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The statements describe how a strain of bacteria that is resistant to an antibiotic can develop and spread. They are in the wrong order. A The resistant bacteria survive and reproduce. B A mutation produces a bacterium that is resistant to the antibiotic. C The antibiotic kills the bacteria that are not resistant. D The population of the resistant strain rises. E The resistant strain spreads, because people are not immune to it and there is no effective treatment. Write the letters in the correct order.
B, C, A, D, E
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Some strains of bacteria are resistant to antibiotics.
(a) Which of these is a strain of bacteria that is resistant to many antibiotics? Tick (✓) one box.[1]
HIV
MRSA
Plasmodium
TMV
(b) Which two actions reduce the rate at which antibiotic-resistant strains develop? Tick (✓) two boxes.[2]
Doctors prescribing antibiotics for viral infections
Patients completing their course of antibiotics
Farmers routinely adding antibiotics to animal feed
Restricting the use of antibiotics in agriculture
Patients sharing leftover antibiotics with family members
(c) The development of new antibiotics is unlikely to keep up with the emergence of new resistant strains. Give one reason why.[1]
Show the answer and mark scheme
(a)Answer: MRSA
(b)Answer: Patients completing their course of antibiotics; Restricting the use of antibiotics in agriculture
(c)
developing new antibiotics is costly / expensive
developing new antibiotics is slow / takes many years
bacteria reproduce / evolve quickly
Question 2Medium8 marks
A patient in hospital had an infection caused by a strain of bacteria. The patient was treated with an antibiotic. Most of the bacteria were killed, but a few survived. The bacteria that survived were resistant to the antibiotic.
(a) Explain how a population of bacteria can become resistant to an antibiotic.[4]
(b) The resistant strain spread to other patients in the hospital. Explain why a resistant strain spreads easily.[2]
(c) Explain why patients should complete their course of antibiotics.[2]
Show the answer and mark scheme
(a)
(random) mutation (of bacterial DNA / genes)
produces a new strain / some bacteria that are resistant
when the antibiotic is used, non-resistant bacteria are killed but resistant bacteria survive
resistant bacteria reproduce (rapidly)
(so) the population of the resistant strain rises / the resistance gene is passed on
(b)
people are not immune to the (new) strain
there is no effective treatment (so infected people stay ill / infectious for longer)
(c)
so that all the bacteria are killed
(so) none survive to mutate and form resistant strains / fewer partly resistant bacteria survive to reproduce
Question 3Hard8 marks
A single bacterium in a wound has a mutation that makes it resistant to an antibiotic. The patient is being treated with this antibiotic, which kills all the non-resistant bacteria. The resistant bacterium divides once every 25 minutes.
(a) Calculate the number of resistant bacteria after 5 hours if none of them die.[3]
(b) In the patient, the number of bacteria after 5 hours would probably be lower than your answer. Suggest one reason why.[1]
(c) Explain why bacteria can evolve resistance much more rapidly than animals can evolve new characteristics.[2]
(d) The patient was then treated with a different antibiotic that killed the resistant bacteria. Doctors use this antibiotic only when other antibiotics have failed. Explain why.[2]
Show the answer and mark scheme
(a)Answer: 4096
(5 × 60) ÷ 25 = 12 (divisions)
212
4096
(b)
some bacteria are destroyed by white blood cells / the immune system
nutrients / oxygen / space may become limited
toxic waste products build up
not all bacteria divide every 25 minutes
(c)
bacteria reproduce at a fast rate / have a short generation time
(so) a resistant mutation can spread through the population / many generations of natural selection occur in a short time
(d)
to reduce the chance of bacteria becoming resistant to this antibiotic
so that it stays effective for treating infections by resistant strains (e.g. MRSA)