A student reads about the development of penicillin. Alexander Fleming noticed in 1928 that a mould called Penicillium was killing bacteria growing on a Petri dish. Decades later, penicillin became one of the most widely used medicines in the world. Explain why penicillin can be described as a naturally occurring substance and outline the key stages that would have been needed before penicillin could be approved for use as a medicine.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Alexander Fleming discovered in 1928 that the mould Penicillium produced a substance that killed bacteria. This substance was eventually developed into the antibiotic medicine penicillin, which is used to treat bacterial infections.
Model answer (5 marks)
Penicillin is a naturally occurring substance because it is produced by the mould Penicillium, a living organism.
The active ingredient must first be extracted from the mould and then purified to give a usable drug.
The purified penicillin is then tested for safety – to ensure it does not cause harmful side effects in patients.
It is also tested for efficacy – to demonstrate that it effectively kills or inhibits the growth of bacterial infections.
Finally, clinical trials are carried out in humans to confirm safety and efficacy before the medicine can be approved and sold.
The active ingredient must first be extracted from the mould and then purified to give a usable drug.
The purified penicillin is then tested for safety – to ensure it does not cause harmful side effects in patients.
It is also tested for efficacy – to demonstrate that it effectively kills or inhibits the growth of bacterial infections.
Finally, clinical trials are carried out in humans to confirm safety and efficacy before the medicine can be approved and sold.
Examiner tips
- Use the exact phrases: ‘naturally occurring’, ‘extracted and purified’, ‘tested for safety’, ‘tested for efficacy’, ‘clinical trials’.
- Show the sequence of stages – extraction → purification → safety testing → efficacy testing → clinical trials.
- Keep each point brief and to the point, matching the 5 marks.
Common mistakes
- Confusing ‘natural’ with ‘synthetic’ – students may say it’s made in a lab.
- Omitting the step of purification or safety testing.
- Using vague terms like ‘tested’ without specifying safety or efficacy.
Mark scheme (5 marks)
- Penicillin is naturally occurring because it is extracted/produced from a living organism (the mould Penicillium / a fungus)
- The active ingredient/substance would need to be extracted and purified from the mould
- The medicine must be tested to check it is safe (does not harm the patient / no harmful side effects)
- The medicine must be tested to show it is effective / that it works against bacterial infections
- Clinical trials must be carried out (tested on humans) before the medicine can be approved/sold
Key terms in this question
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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