Disease and response · GCSE Biology
Antibiotics and painkillers
Separate antibiotics from painkillers for GCSE Biology: antibiotics kill bacteria or stop growth, they do nothing to viruses, painkillers ease symptoms, and resistance evolves by natural selection (MRSA).
Antibiotics: bacteria only. Painkillers: symptoms only. Antibodies: your proteins. Antivirals: viruses, limited. Resistance: mutation, then selection by the antibiotic.
The important bits
What you need to know
- 1
Antibiotics (for example penicillin) kill bacteria or inhibit their processes (often cell-wall synthesis). They do not affect viruses, which have no cell wall and reproduce inside host cells.
- 2
Painkillers (for example paracetamol) relieve symptoms such as pain and fever. They do not kill the pathogen. Rest and the immune system still have to deal with a virus.
- 3
Measles, influenza and colds are viral: antibiotics are useless against the virus and overuse drives resistance in your bacteria. Gonorrhoea is bacterial and can be treated with antibiotics, though resistant strains exist.
- 4
Antibiotic resistance: a random mutation (or plasmid gene) lets a bacterium survive. Antibiotics kill non-resistant competitors. Resistant bacteria survive and reproduce. The allele becomes more common — natural selection. MRSA is the named example.
- 5
To reduce resistance: finish the course, do not use antibiotics for viral colds, avoid routine use in farming if the question asks, and use specific antibiotics rather than broad ones when possible.
- 6
Antiseptics and disinfectants kill microorganisms on surfaces or skin; they are not the same as antibiotics taken internally.
- 7
Digitalis, aspirin and penicillin are the discovery stories: foxglove, willow, mould. New antibiotics are hard to find, which is why resistance is a global problem.
- 8
Antibodies are not antibiotics. Vaccines prevent; antibiotics treat bacterial infection that is already there (if the strain is sensitive).
Quotations worth analysing
Short evidence. Real method.
“Antibiotics cannot kill viruses.”
Give the reason: viruses reproduce inside host cells and do not have the bacterial targets (such as a cell wall).
“Painkillers treat symptoms but do not kill pathogens.”
Use this when a cold or flu is treated with paracetamol. The virus is still there.
“Resistant bacteria survive and reproduce, so the population becomes resistant.”
Sequence: mutation, selection pressure, survival, reproduction, allele more common. Do not write that bacteria “try to become immune”.
Go deeper
Why can penicillin destroy a bacterium but not a virus?
Many antibiotics stop bacteria building cell walls, so the cells burst. Viruses are capsules of genetic material, not cells with walls, and they hide inside host cells. A drug that smashed every infected human cell would harm the patient. That is why measles needs vaccination and supportive care, not penicillin. Some antiviral drugs interfere with viral replication (HIV reverse transcriptase is the usual GCSE example) but they do not “kill viruses” the way penicillin kills bacteria, and they rarely cure completely. In the exam, classify first. Bacterial: antibiotic possible. Viral: not. Then, if asked, add resistance as the reason we do not use antibiotics “just in case” for every sore throat.
Go deeper
How do I write antibiotic resistance as natural selection, not a story?
Variation: some bacteria have a mutation or a plasmid gene for resistance. Selection: the antibiotic kills non-resistant bacteria. Survival: resistant bacteria live. Reproduction: binary fission copies the gene; plasmids can even transfer to other bacteria. Result: the proportion of resistant bacteria rises. MRSA is Staphylococcus aureus resistant to methicillin. Do not write that the antibiotic caused the mutation; mutation is random, the antibiotic is the selection pressure. Finishing a course matters because leftover bacteria are more likely to be the harder-to-kill ones. Using antibiotics in viral illness applies the selection pressure with no benefit. This paragraph is the same shape as peppered moths or giraffe-neck myths you must not tell — variation first, then selection.
Go deeper
How should I compare antibiotics, painkillers and vaccines in a table?
Vaccine: before infection, antigens, memory cells, prevents disease, works for viruses and bacteria depending on the vaccine. Antibiotic: during bacterial infection, kills or inhibits bacteria, useless on viruses, resistance risk. Painkiller: during illness, reduces pain or fever, no effect on the pathogen. Antibody: made by you, binds antigen. Putting those four in a revision grid stops the vocabulary pile-up. A six-mark “explain why doctors do not give antibiotics for a cold” wants: cold is viral, antibiotics do not affect viruses, overuse selects resistant bacteria, painkillers may ease symptoms, the immune system clears the virus. That is a full answer without a lecture.
See the idea in action
A patient has a cold (virus) and a separate bacterial throat infection. Paracetamol may lower the fever (painkiller, symptoms only). An antibiotic may treat the bacterial infection if prescribed, but will not shorten the cold. If the same patient takes leftover antibiotics for the next cold, they apply selection pressure to their bacteria for no antiviral benefit, increasing the chance of a resistant strain. MRSA is already a resistant bacterium that is hard to treat. Vaccination would have been the measles strategy, not antibiotics.
Exam technique
Turn knowledge into marks
Classify the pathogen first. Antibiotics: bacteria only. Painkillers: symptoms only. For resistance, write mutation then selection, not “bacteria get used to it”. Never swap antibody with antibiotic.
Common mistakes
Do not give these marks away
- 01
Saying antibiotics kill viruses, or that painkillers kill bacteria.
- 02
Writing that bacteria “become immune” on purpose, instead of random mutation and natural selection.
- 03
Confusing antibodies with antibiotics.
Why do antibiotics not treat measles?
AMeasles is caused by a fungus
BMeasles is caused by a virus, and antibiotics do not affect viruses
CThe measles pathogen lives only in mosquitoes
DAntibiotics only work on plant diseases
Show the answer
Measles is caused by a virus, and antibiotics do not affect viruses. Antibiotics target bacterial processes. Viruses reproduce inside host cells and lack those targets. Measles is prevented by vaccination.
Quick questions
If this is the bit you searched
Do antibiotics work on viruses?
No. They kill bacteria or stop bacterial growth. Viruses reproduce inside host cells and are not affected. Vaccination and the immune system are the viral strategy.
What is the difference between antibiotics and painkillers?
Antibiotics destroy or inhibit bacteria. Painkillers reduce symptoms such as pain and fever but do not kill the pathogen.
How does antibiotic resistance develop?
A random mutation (or plasmid) makes a bacterium resistant. Antibiotics kill non-resistant bacteria. Resistant bacteria survive, reproduce, and become more common.
What is MRSA?
A strain of Staphylococcus aureus that is resistant to the antibiotic methicillin, so it is harder to treat.