Natural Selection Steps
- Random mutation gives resistance to one bacterium
- Antibiotic = selection pressure
- Non-resistant bacteria killed
- Resistant bacteria survive and reproduce
- Offspring inherit resistance gene
- Resistant strain becomes dominant
How Antibiotics Work
- Penicillin: blocks cell wall synthesis โ cell bursts
- Streptomycin: blocks bacterial ribosomes โ no protein synthesis
- Only affect bacteria โ viruses have no cell wall or bacterial ribosomes
- MRSA: resistant to methicillin + many others
- Disc diffusion: larger zone = more effective
Common Marks Lost
- "Person becomes resistant" โ bacteria become resistant, not people
- "Bacteria learn" โ random mutation, not deliberate adaptation
- Missing "mutation" in natural selection answers
- Not explaining WHY completing course reduces resistance
- Saying antibiotics kill viruses (they do not)
This topic summary covers Knowledge Organiser within Antibiotics and Drug Resistance for GCSE Biology. Antibiotic function, bacterial resistance evolution, responsible use, global health impact It is section 17 of 18 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Antibiotics and Drug Resistance
What do antibiotics kill or stop growing?
Explain how antibiotic resistance develops in bacteria through natural selection. (3 marks)
Quick recall flashcards
Why do antibiotics NOT work against viruses?
Antibiotics target bacterial cell walls and bacterial processes.
Viruses do not have cell walls and use the host cell's own machinery to reproduce.
There is nothing for the antibiotic to target in a virus.
What are antibiotics and what do they target?
Antibiotics are chemicals that kill bacteria or stop them from growing.
They target structures that bacteria have but human cells do not, such as cell walls.
Examples: penicillin, amoxicillin, streptomycin.