top of page

6.2 Antibiotics and Painkillers

GCSE Biology · AQA · Chapter 6: Preventing and Treating Disease

A free GCSE Biology lesson for AQA (8461) from OBA School: how antibiotics treat bacterial infections, why they do not work on viruses, painkillers, and antibiotic resistance. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

  • Explain how antibiotics help to cure bacterial disease
  • Explain why antibiotics cannot treat viral diseases
  • Describe what painkillers and other medicines do
  • Explain how antibiotic-resistant strains of bacteria arise and spread
  • Describe how the spread of resistance can be reduced

Key words

  • Antibiotic: A medicine that kills bacteria (or stops them growing) inside the body, e.g. penicillin.
  • Painkiller: A medicine, e.g. paracetamol or ibuprofen, that relieves symptoms but does not kill pathogens.
  • Resistant: Not affected by an antibiotic; resistant bacteria survive treatment.
  • Mutation: A random change in DNA. It can give a bacterium a new feature, such as resistance.
  • Strain: A type of bacterium within a species that has particular features.
  • MRSA: A strain of Staphylococcus aureus bacteria resistant to many antibiotics.

Antibiotics

Antibiotics such as penicillin kill infective bacteria inside the body (or stop them reproducing) without harming the body’s own cells. Different antibiotics work in different ways, for example by damaging the bacterial cell wall or stopping the bacteria making proteins.

Specific bacteria should be treated with specific antibiotics, so doctors need to identify the bacterium. Antibiotics have greatly reduced deaths from infectious bacterial disease since they came into use in the 1940s.

Worked example: comparing clear zones

The clear zone around disc A has a diameter of 16 mm. Area = πr² = π × 8² = 201 mm² (3 s.f.).
The zone around disc B has a diameter of 10 mm. Area = π × 5² = 78.5 mm².
Ratio of areas A : B = 201 ÷ 78.5 = 2.56, so A’s zone is about 2.6 times larger.

Answer: A is the more effective antibiotic against these bacteria

Why antibiotics do not work on viruses

Viruses reproduce inside the body’s own cells. Antibiotics do not affect viruses, and it is difficult to develop drugs that destroy viruses without also damaging body tissues. So antibiotics are not used for colds and flu, which are caused by viruses.

Key fact: Antibiotics kill bacteria only. They do not kill viruses, and they do not kill fungi in the way antifungal medicines do.

Painkillers and other medicines

Painkillers (e.g. paracetamol, ibuprofen, aspirin) and medicines such as cough mixtures treat the symptoms of a disease. They make the patient feel better but do not kill the pathogen. The immune system still has to destroy the pathogen.

Antibiotic resistance

Bacteria reproduce very quickly. A random mutation can make one bacterium resistant to an antibiotic. When the antibiotic is used, non-resistant bacteria are killed but the resistant one survives and reproduces, so the resistant strain spreads. This is natural selection. People have no immunity to the new strain and there is no effective treatment.

  • Doctors do not prescribe antibiotics for viral or non-serious infections; Why it helps Fewer chances for resistant bacteria to be selected
  • Patients complete the full course; Why it helps All bacteria are killed, so none survive to mutate or form resistant strains
  • Restrict antibiotic use in farming; Why it helps Less selection for resistance in farm animals
  • Good hygiene in hospitals (hand washing, isolating patients); Why it helps Stops resistant strains such as MRSA spreading

Exam tip: Resistance develops in the bacteria, not in the person. Say “the bacteria become resistant”, never “the patient becomes resistant”.

Common mistakes

  • Saying antibiotics can treat flu or colds. These are caused by viruses.
  • Saying the antibiotic causes the mutation. Mutations are random; the antibiotic only kills the non-resistant bacteria.
  • Saying the patient’s body becomes resistant. It is the bacteria that are resistant.
  • Thinking painkillers cure disease. They only relieve symptoms.

Revision questions

Try these, then check your answers below each one.

Question 1. What do antibiotics do? (Choose from: Kill bacteria inside the body, Kill viruses inside body cells, Relieve pain only, Make antibodies.)

Answer: Kill bacteria inside the body

Working: Antibiotics such as penicillin kill infective bacteria inside the body.

Question 2. True or false? Antibiotics can be used to cure the common cold.

Answer: False

Working: False. Colds are caused by viruses, and antibiotics do not affect viruses.

Question 3. Why is it difficult to develop drugs that kill viruses? (Choose from: Viruses live inside body cells, so the drug may damage body tissue, Viruses are too large, Viruses have cell walls, Viruses do not have DNA.)

Answer: Viruses live inside body cells, so the drug may damage body tissue

Working: Viruses reproduce inside our cells, so a drug that destroys them may also harm the cells.

Related lessons

Continue in the full course

This lesson is section 6.2 (AGCBH0602) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.

 

 

 

 

 

 

 

Previous
Next
bottom of page