Antibiotics, resistance and zoonoses
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Question
What is an antibiotic?
Answer
A medicine that **kills bacteria** (or stops them growing) by attacking a structure or process **only bacteria have**.
Question
Name a target that antibiotics attack in bacteria.
Answer
The **cell wall** (its building), or bacterial **ribosomes** / **enzymes** — structures unique to bacterial cells.
Question
Why can't antibiotics treat a virus such as influenza?
Answer
A **virus is not a cell** — it has no cell wall, no ribosomes and no metabolism of its own, so there is **no bacterial target** for the antibiotic to attack.
Question
Why do antibiotics harm bacteria but not human cells?
Answer
They attack targets **unique to bacteria** (e.g. cell-wall building, bacterial ribosomes) that human cells do not have.
Question
Define antibiotic resistance.
Answer
The ability of some **bacteria to survive** an antibiotic that would normally kill them.
Question
How does antibiotic resistance evolve?
Answer
By **natural selection**: a few bacteria are already resistant → the antibiotic kills the non-resistant ones → the **resistant survivors reproduce** → the strain becomes common.
Question
Do individual bacteria 'learn' to resist an antibiotic?
Answer
**No** — resistance comes from existing **variation** (often a mutation) and is **selected** by the antibiotic; it is not learned during a bacterium's life.
Question
Why might the same antibiotic fail against a second infection?
Answer
A **resistant strain** has been selected — the resistant bacteria survived the first time and reproduced, so the drug no longer kills them.
Question
In an experiment, why might bacterial colonies grow despite an antibiotic?
Answer
Those colonies are a **resistant strain** that can survive the antibiotic.
Question
Define a zoonosis.
Answer
An infectious disease that can be transmitted **directly from an animal to a human**.
Question
Give three examples of zoonoses.
Answer
**Rabies** (from a bite), some forms of **tuberculosis** (from cattle) and **Japanese encephalitis** (animal reservoir in pigs/birds).
Question
What do rabies, TB and Japanese encephalitis have in common?
Answer
They are all **zoonoses** — they can pass from an **animal to a human**.
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Defence against infectious disease
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