Antibiotics and painkillers — AQA GCSE Biology
Test yourself on Antibiotics and painkillers with AQA GCSE practice questions.
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Antibiotics and painkillers explained
This statement requires you to explain how different medicines treat disease according to cause.
Read the full explanation
Antibiotics treat bacterial infections by killing bacteria or stopping their growth, so they work only when bacteria are the cause. They do not treat viruses such as those causing colds or influenza because viruses lack the bacterial targets antibiotics act on and reproduce inside host cells. Painkillers, such as paracetamol, relieve symptoms such as pain or fever but do not kill pathogens, so they do not cure the infection. Other medicines treat specific conditions: for example, insulin replaces a hormone that is missing in some people with diabetes, and oral rehydration salts replace water and ions lost through diarrhoea. Antivirals may be used for some viral diseases, but antibiotics are ineffective against viruses.
Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body.
This statement defines antibiotics and their mode of action. Antibiotics are medicines that treat bacterial disease by killing infective bacteria inside the body or by stopping their growth, which allows the immune system to clear the infection. Penicillin is a well-known example; it interferes with bacterial cell wall formation, so growing bacteria burst and die. Because human cells do not have the same cell wall structure, penicillin can target bacteria without directly damaging human cells. Antibiotics are prescribed for bacterial infections such as some throat, chest, skin and urinary tract infections. They are not effective against viruses, so they cannot cure viral diseases such as influenza. The medicine must reach the site of infection at an effective concentration, often taken over several days as prescribed.
It is important that specific bacteria should be treated by specific antibiotics.
Different antibiotics act on different bacterial structures or processes, so they are not interchangeable. A broad-spectrum antibiotic affects many types of bacteria, while a narrow-spectrum antibiotic targets particular bacteria. Identifying the causative bacterium through a laboratory test allows a doctor to prescribe the most effective antibiotic. Using the right antibiotic increases the chance of curing the infection and reduces unnecessary damage to helpful bacteria. It also slows the development of antibiotic-resistant strains. Mutations occur randomly, but using the correct medicine at the right dose for the full course ensures targeted bacteria are killed, preventing the survival and reproduction of resistant mutants.
The use of antibiotics has greatly reduced deaths from infectious bacterial diseases.
Antibiotics are medicines that kill bacteria inside the body or stop them growing, so the immune system can clear the infection. Before antibiotics, a simple wound infection or pneumonia could kill; since their introduction, deaths from infectious bacterial diseases such as tuberculosis and septicaemia have fallen dramatically. Antibiotics work only on bacteria because they target bacterial structures, for example the cell wall or bacterial ribosomes, which human cells do not have. A doctor may prescribe a course for a bacterial infection, and the patient must finish the course to reduce the chance of surviving bacteria becoming resistant. Antibiotics do not work on viruses, fungi or other pathogens, so they are not a universal cure.
However, the emergence of strains resistant to antibiotics is of great concern.
Antibiotic resistance arises when random mutations in bacterial DNA give some bacteria an advantage against an antibiotic. These bacteria survive, reproduce rapidly by binary fission, and pass the resistance allele to their offspring, so the resistant strain becomes more common. Resistance can also spread between bacteria by horizontal gene transfer. This is of great concern because infections caused by resistant strains, such as MRSA, may not respond to commonly used antibiotics, leading to longer illness, higher risk of death and fewer effective treatments. Overuse and inappropriate prescribing of antibiotics increase the chance of resistance evolving. Doctors reduce the problem by prescribing antibiotics only when needed, and patients should complete the course so all bacteria are killed.
Antibiotics cannot kill viral pathogens.
Viruses are not cells; they are tiny particles that reproduce only inside host cells. They have no cell wall, no bacterial ribosomes and no other bacterial structures for an antibiotic to target, so antibiotics cannot kill them. A virus such as influenza or measles enters a host cell and uses the cell's machinery to make new virus particles. Because the virus is inside human cells, a medicine that attacked it could also harm the host cells. Viral infections are therefore treated differently: some are prevented by vaccination, some are treated with antiviral medicines, and many are managed by rest and symptom relief while the immune system clears the virus. Antibiotics may be given only if a secondary bacterial infection develops.
Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens.
Painkillers such as paracetamol and aspirin relieve symptoms including pain, fever and inflammation, but they do not kill the pathogens causing the disease. They act on the body's pain and temperature pathways rather than on bacteria or viruses. Other medicines also treat symptoms or manage conditions without killing pathogens; for example, oral rehydration salts replace water and ions lost through diarrhoea, and antihistamines reduce allergic symptoms. Because these medicines do not remove the pathogen, the immune system must still clear the infection, and antibiotics are needed only when the pathogen is a bacterium. This distinction matters because using painkillers for an infection does not cure it, and using antibiotics for a viral infection does not help.
It is difficult to develop drugs that kill viruses without also damaging the body’s tissues.
Viruses are not cells; they reproduce inside host cells, using the host's own machinery and structures to copy themselves. A drug that blocks viral replication therefore risks blocking processes that human cells also use, so it may harm the body's tissues. This is why antibiotics, which target bacterial structures such as cell walls, do not work on viruses, and why developing antiviral drugs is difficult. Because the virus is hidden inside cells and relies on the host's cellular mechanisms, it is hard to reach and destroy the virus without damaging those host cells. Students should explain this intracellular lifestyle when discussing the challenges of treating viral infections.
Your focus
- Explain why antibiotics treat bacterial but not viral infections.
- Distinguish between medicines that cure infection and those that relieve symptoms.
- Describe examples of other medicines and the conditions they treat.
Show all 24 objectives
- Define antibiotics and give penicillin as an example.
- Describe how antibiotics kill infective bacteria inside the body.
- Explain why antibiotics are effective against bacteria but not viruses.
- Explain why different antibiotics are used against different bacteria.
- Describe how identifying the pathogen guides antibiotic choice.
- Relate correct antibiotic use to reducing the spread of resistance.
- State that antibiotics kill bacteria or stop their growth.
- Explain why antibiotic use has greatly reduced deaths from infectious bacterial diseases.
- Give at least one named bacterial disease whose death rate has fallen because of antibiotics.
- Describe how random mutation and selection can produce antibiotic-resistant bacterial strains.
- Explain why antibiotic-resistant strains are of great concern for treating infectious disease.
- Suggest how the overuse of antibiotics contributes to the emergence of resistance.
- State that antibiotics cannot kill viral pathogens.
- Explain why antibiotics are ineffective against viruses in terms of viral structure and reproduction.
- Describe alternative ways of preventing or treating viral infections.
- State that painkillers treat symptoms but do not kill pathogens.
- Distinguish between medicines that relieve symptoms and antibiotics that kill bacteria.
- Explain why treating symptoms alone does not remove the cause of an infectious disease.
- Describe how viruses reproduce inside host cells and why this makes drug targeting difficult.
- Explain why antibiotics are ineffective against viruses.
- Discuss how antiviral drugs can damage body tissues because they affect host cell processes.
Antibiotics and painkillers exam tips
Marking Points
- Antibiotics are effective against bacteria because they kill bacteria or inhibit their growth.
- Antibiotics are not effective against viruses, so viral infections such as colds and influenza are not treated with antibiotics.
- Painkillers relieve symptoms such as pain or fever but do not destroy pathogens or cure the underlying infection.
- Some medicines replace missing substances or treat specific conditions, for example insulin in diabetes or oral rehydration salts in diarrhoea.
- Choosing a medicine depends on the cause of the disease and whether the aim is to kill the pathogen or relieve symptoms.
- Antibiotics are medicines used to treat bacterial disease.
- They work by killing infective bacteria inside the body or by inhibiting bacterial growth.
- Penicillin is an example of an antibiotic that damages bacterial cell walls.
- Antibiotics are effective against bacteria but not against viruses.
- Completing the prescribed course helps ensure the bacteria are cleared and reduces the chance of resistance developing.
- Different antibiotics are effective against different types of bacteria because they target different bacterial structures or processes.
- Identifying the specific bacterium causing an infection helps a doctor choose the most effective antibiotic.
- Using the correct antibiotic improves the chance of curing the infection and reduces harm to useful bacteria.
- Targeted use of specific antibiotics helps slow the development of antibiotic-resistant bacteria.
- Broad-spectrum antibiotics affect many bacteria, whereas narrow-spectrum antibiotics target particular bacteria.
- Antibiotics are medicines that kill bacteria or prevent their growth inside the body.
- They reduce deaths from infectious bacterial diseases because bacterial infections that were once often fatal can now be treated.
- Antibiotics act on bacterial structures such as the cell wall or bacterial ribosomes, which are absent from human cells.
- The immune system still helps clear the infection after the antibiotic has stopped bacterial growth.
- Examples of bacterial diseases whose death rates fell include tuberculosis and septicaemia.
- Completing a prescribed course helps reduce the survival of resistant bacteria.
- Random mutation in bacterial DNA can produce a gene that gives resistance to an antibiotic.
- In the presence of the antibiotic, resistant bacteria survive and reproduce, so the resistant strain becomes more common.
- Bacteria reproduce rapidly by binary fission, so a resistant population can build up quickly.
- Resistance genes can be passed to other bacteria, spreading resistance between strains or species.
- Resistant infections such as MRSA may not respond to commonly used antibiotics, increasing the risk of serious illness or death.
- Overuse and inappropriate use of antibiotics increase the rate at which resistance emerges.
- Viruses are not cells and do not have the bacterial structures that antibiotics target.
- Antibiotics act on structures such as bacterial cell walls or bacterial ribosomes, which viruses lack.
- Viruses reproduce inside host cells, so medicines that attack them risk damaging host cells.
- Viral infections are prevented by vaccination or treated with antiviral medicines where available.
- Many viral infections are managed by treating symptoms while the immune system clears the pathogen.
- Antibiotics may be prescribed if a viral infection leads to a secondary bacterial infection.
- Painkillers relieve symptoms such as pain, fever or inflammation but do not kill pathogens.
- Painkillers act on the body's own pain and temperature pathways, not on the pathogen.
- Other medicines, such as oral rehydration salts, treat the effects of disease without killing pathogens.
- The immune system still has to clear the pathogen when only symptom-relieving medicines are used.
- Antibiotics are the medicines that kill bacteria, so they are used only for bacterial infections.
- Treating symptoms can make a patient more comfortable but does not remove the cause of the disease.
- Viruses reproduce inside host cells, so a drug must enter those cells to reach the virus.
- Viruses use host cell machinery to replicate, so drugs that block this process often affect normal body cells.
- Antibiotics target bacterial structures such as cell walls, which viruses do not have, making antibiotics ineffective against viruses.
- Antiviral drugs must be highly selective, which is difficult because viruses rely on the host's own cellular processes.
- Damage to body tissues can occur because the drug's action may disrupt normal host cell functions.
- This explains why fewer antiviral drugs are available than antibiotics and why their development is challenging.
Examiner Tips
- 💡State the cause of the disease first, then name the suitable medicine and explain its action.
- 💡Use comparative language such as 'antibiotics kill bacteria, whereas painkillers only relieve symptoms'.
- 💡When asked to explain, avoid simply listing medicines; link each medicine to what it does in the body.
- 💡Name penicillin as a specific example when describing antibiotics.
- 💡Use the phrase 'killing infective bacteria inside the body' to show precise understanding.
- 💡Link the action of antibiotics to bacterial cell structures to explain why they are selective.
- 💡Use the phrase 'specific bacteria should be treated by specific antibiotics' and then explain why.
- 💡Refer to identifying the pathogen before prescribing to show understanding of targeted treatment.
- 💡Link correct antibiotic choice to slowing antibiotic resistance for higher-level answers.
- 💡Link the statement to named bacterial diseases such as tuberculosis to show the scale of the reduction in deaths.
- 💡Use the phrase infectious bacterial diseases rather than infections generally, because antibiotics do not affect viral infections.
- 💡When explaining how antibiotics work, refer to a bacterial target such as the cell wall rather than saying they attack germs.
- 💡Use the words mutation, selection and reproduction to describe the evolution of a resistant strain.
- 💡Refer to a named resistant bacterium such as MRSA to make the concern concrete.
- 💡Explain the concern in terms of treatment failure and risk of death, not just that resistance exists.
- 💡Compare viruses and bacteria directly, for example by stating that viruses are not cells and have no cell wall.
- 💡Use a named viral disease such as influenza or measles to support the explanation.
- 💡Mention that antibiotics may be needed only if a secondary bacterial infection occurs.
- 💡Use the terms symptom and pathogen precisely so the distinction between treating effects and killing causes is clear.
- 💡Give a named example such as paracetamol for pain or oral rehydration salts for diarrhoea.
- 💡Explain that the immune system clears the pathogen when only symptom-relieving medicines are used.
- 💡Link the difficulty of developing drugs to the virus's intracellular life cycle, not just to the virus being small.
- 💡Use the contrast with antibiotics to show why bacterial targets are easier to hit selectively without harming human cells.
- 💡When explaining tissue damage, refer to the drug affecting host cell processes as well as viral replication.
Common Mistakes
- Thinking antibiotics cure all infections; correct this by stating they act only on bacteria and not on viruses.
- Confusing painkillers with antibiotics; correct this by explaining that painkillers relieve symptoms but do not kill pathogens.
- Assuming all medicines work by killing pathogens; correct this by giving examples such as insulin replacement or rehydration therapy.
- Saying antibiotics kill viruses; correct this by stating they act on bacteria and are ineffective against viruses.
- Believing antibiotics damage human cells in the same way as bacterial cells; correct this by explaining that they target bacterial structures such as cell walls.
- Thinking antibiotics work instantly; correct this by explaining that they kill or inhibit bacteria over time, so the course must be completed.
- Assuming any antibiotic will treat any bacterial infection; correct this by explaining that different antibiotics target different bacteria.
- Thinking resistance develops because the human body becomes resistant; correct this by stating that bacteria become resistant through selection.
- Believing a stronger or larger dose always works better; correct this by explaining that the correct antibiotic at the prescribed dose for the full course is what matters.
- Saying antibiotics kill all pathogens: correct this by stating they act on bacteria, not viruses.
- Confusing antibiotics with painkillers: correct this by explaining that painkillers treat symptoms while antibiotics kill bacteria.
- Claiming antibiotics directly boost the immune system: correct this by saying they reduce the bacterial population so the immune system can clear the infection.
- Saying bacteria become resistant because they need to survive: correct this by stating that resistance arises from random mutation, and the antibiotic selects the resistant bacteria.
- Thinking resistance develops in the patient's body cells: correct this by explaining that resistance is a feature of the bacterial population.
- Believing a stronger antibiotic can always be used: correct this by noting that some strains are resistant to many antibiotics, so treatment options can run out.
- Saying antibiotics are too weak to kill viruses: correct this by explaining that viruses lack the structures antibiotics target.
- Thinking antibiotics can prevent viral infections: correct this by stating that vaccination is used for prevention.
- Confusing antivirals with antibiotics: correct this by noting that antivirals act on viruses while antibiotics act on bacteria.
- Saying painkillers cure the infection: correct this by stating they only relieve symptoms while the immune system clears the pathogen.
- Believing all medicines kill pathogens: correct this by distinguishing symptom-relieving medicines from antibiotics.
- Thinking antibiotics should be given alongside painkillers for every infection: correct this by stating antibiotics are used only for bacterial infections.
- Thinking antibiotics can treat viral infections: correct this by stating that antibiotics act on bacteria, not viruses, because viruses lack bacterial cell walls.
- Assuming viruses are cells: correct this by describing viruses as non-cellular particles that reproduce inside host cells.
- Believing antiviral drugs are harmless because they target viruses: correct this by explaining that shared host-cell machinery means side effects and tissue damage are possible.