Antibiotics and resistanceEdexcel A-Level Biology B: Subtopic test

1. 1
   A microbiologist adds penicillin to a growing culture of bacteria and tetracycline to a second, identical culture. In the penicillin culture the number of living cells falls to almost zero within several hours. In the tetracycline culture the number of living cells stays roughly constant but does not increase. When the tetracycline is washed out, the cells begin to divide again.

   (a)

   Which term describes the action of penicillin on the bacteria?

   [1 mark]

   • ABacteriostatic
   • BBactericidal
   • CAntiviral
   • DAntigenic

   (b)

   Which statement best describes the effect of tetracycline in the second culture?

   [1 mark]

   • AIt digests the cell walls so the cells burst
   • BIt kills the cells so that none can ever divide again
   • CIt has no effect on the culture
   • DIt stops the bacteria multiplying without killing them, so growth resumes when it is removed

   (c)

   Explain how penicillin kills growing bacteria but does not harm human cells.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Researchers are testing a new compound, X, that binds to a site on bacterial ribosomes and prevents them from reading mRNA. Bacteria exposed to X do not die at once but cannot grow. Human liver cells exposed to the same dose of X are unaffected.

   (a)

   Which process in the bacteria is most directly inhibited by compound X?

   [1 mark]

   • ATranslation (protein synthesis)
   • BDNA replication
   • CPhotosynthesis
   • DCell wall synthesis

   (b)

   Which statement best explains why the human liver cells are unaffected by X?

   [1 mark]

   • AHuman cells have a cell wall that blocks X
   • BHuman liver cells do not make proteins
   • CHuman ribosomes differ in structure from bacterial ribosomes, so X does not bind to them
   • DX is broken down by enzymes in the nucleus of human cells

   (c)

   Compound X is bacteriostatic. Explain why a patient's own immune system is still needed to clear the infection.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A patient with an infected wound is treated with an antibiotic. At first the infection responds, but after several days the bacteria in the wound are no longer killed. Tests show that the bacterial population now contains a gene for an enzyme that destroys the antibiotic. The gene is carried on a plasmid. Before treatment only about one bacterium in ten million carried it.

   (a)

   Explain how treatment with the antibiotic led to a bacterial population that was mostly resistant.

   [3 marks]

   (b)

   The resistance gene is on a plasmid. Explain how this allows resistance to spread to other bacteria, and suggest why this makes the spread harder to control.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A health ministry is planning a national strategy to control antibiotic resistance. At present antibiotics can be bought without a prescription in some regions, they are added to animal feed on many farms to promote growth, and many patients stop taking their course as soon as they feel better. One proposal is to stop doctors prescribing antibiotics for viral infections.

   (a)

   Explain how the practices described contribute to the development and spread of antibiotic resistance.

   [6 marks]

   (b)

   Evaluate the difficulties of controlling the spread of antibiotic resistance and justify which measure you think would be most effective.

   [6 marks]

   Total for question 4: 12 marks

End of questions