Viruses have no cell walls, no bacterial ribosomes and no bacterial DNA replication machinery — there is nothing for antibiotics to target.
Viruses live INSIDE host cells — drugs that killed them would also damage the host cell.
Antibiotics were discovered by Alexander Fleming in 1928 — he noticed Penicillium mould was killing bacteria on a petri dish.
Antibiotic Resistance — A Global Crisis
Antibiotic resistance is one of the greatest threats to global health.
How it develops through NATURAL SELECTION:
1. Within a population of bacteria, random MUTATIONS occur naturally during reproduction.
2. Occasionally, a mutation gives a bacterium resistance to an antibiotic.
3. When antibiotics are used, non-resistant bacteria are killed.
4. Resistant bacteria SURVIVE and REPRODUCE — passing on the resistance gene to offspring.
5. Over time, the entire population becomes resistant — the antibiotic no longer works.
Why resistance is spreading:
OVER-PRESCRIBING — doctors prescribing antibiotics for viral infections or 'just in case'.
NOT COMPLETING COURSES — stopping early leaves some bacteria alive; the survivors are more likely to be partially resistant.
AGRICULTURE — antibiotics used to promote growth in livestock, creating resistant bacteria in food chains.
Consequences: Infections once easily treated (e.g. tuberculosis, some pneumonias) are becoming dangerous again. MRSA (methicillin-resistant Staphylococcus aureus) is an example of a serious antibiotic-resistant bacterium.
How to slow resistance:
Only use antibiotics when genuinely necessary.
Always complete the full course.
Never share or save antibiotics for later.
Reduce agricultural antibiotic use.
Painkillers
Painkillers (analgesics) relieve pain and reduce fever — but they do NOT kill pathogens or treat the cause of infection.
Common painkillers: paracetamol, ibuprofen, aspirin.
They treat SYMPTOMS — making the patient feel more comfortable — but the immune system still needs to fight the infection.
A patient with a bacterial infection may take BOTH:
Antibiotics — to kill the bacteria (treating the cause).
Painkillers — to manage fever, pain and discomfort (treating the symptoms).
ANTIVIRAL DRUGS are medicines that do treat viral infections — but they are much harder to develop than antibiotics because viruses use the host cell's own machinery.
Examples: oseltamivir (Tamiflu) for influenza, antiretroviral drugs (ARVs) for HIV.
Antivirals don't kill viruses outright — they usually prevent replication.
⚠️ Common Mistake
Painkillers do NOT treat infections — they only relieve symptoms. A patient taking only paracetamol for a bacterial infection is NOT treating the infection. Also: always complete antibiotic courses — stopping early is a major driver of resistance because the bacteria that survive are likely to be the more resistant ones.
📌 Key Note
Antibiotics: kill bacteria, NO effect on viruses, target bacterial cell walls/ribosomes. Antibiotic resistance: natural selection of resistant mutants — avoid misuse. Painkillers: treat symptoms only, don't kill pathogens.
🎯 Matching Activity — Antibiotic, Painkiller or Antiviral?
Sort each statement to the correct type of drug. — drag the symbols on the right to match the component names on the left.
Antibiotic
Drop here
Painkiller
Drop here
Antiviral
Drop here
Antibiotic
Drop here
Painkiller
Drop here
Examples: paracetamol, ibuprofen, aspirin
Kills bacteria — works by targeting bacterial cell walls or ribosomes
Relieves fever and pain — does not kill any pathogens
Prevents viral replication — used for HIV and influenza
Has no effect on viral infections — useless against flu or measles
⭐ Higher Tier Only
Antibiotic resistance develops through natural selection: random resistance mutations exist in a bacterial population → antibiotics act as selection pressure killing non-resistant bacteria → resistant bacteria survive, reproduce and pass on resistance genes → resistance spreads. MRSA is a clinically important example. Students should be able to explain why reducing unnecessary antibiotic use and completing courses slows resistance development.
🎯 Test Yourself
Question 1 of 2
1. Why can't antibiotics treat viral infections?
2. Why is it important to always complete a full course of antibiotics?
⭐ How Well Do You Understand This Topic?
Be honest with yourself — this helps you know what to revise!
Don't get itGetting thereNailed it!
🤖 Ask Mr Badmus AI
Stuck? Just ask! 💬
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