Which statement best captures the passage's central claim?

Antibiotics select bacteria that were already resistant, and heavy use speeds that selection. (The first paragraph says resistance exists before the drug arrives and that the drug edits the population; the last says every use adds pressure.)

How can a resistance gene reach bacteria of a different species?

A small loop of DNA can move from one cell into another. (The second paragraph describes bacteria trading genes sideways: a small loop of DNA can move between cells and even between species.)

Why does the passage treat an antibiotic prescribed for a cold as harmful?

Because the drug cannot act on a virus, yet it still selects resistant bacteria in the body. (The text says antibiotics cannot touch viral infections but such prescriptions still 'add selection without adding benefit'.)

In the phrase 'applies this pressure', 'pressure' refers to:

the killing of vulnerable cells, which favours resistant ones (Pressure here is selection pressure: the drug removes cells that cannot survive, so survivors are favoured.)

Why Antibiotics Lose Power: Level 4 Reading Comprehension Questions

An antibiotic does not teach bacteria to resist it. The resistance is already present in a handful of cells, produced by ordinary copying errors long before the drug arrives. What the drug does is edit the population: it kills the cells that cannot survive it and leaves the rare ones that can. Those survivors then divide in an emptied field, with their competition gone, and within days the resistant type is no longer rare.

Two features of bacteria make this loop unusually fast. The first is speed of reproduction; a population can double in twenty minutes, so a number of generations that a mammal would need centuries to produce can pass in a single weekend. The second is that bacteria trade genes sideways. A small loop of DNA carrying a resistance gene can move from one cell to another, and even between species, so a trait that arose in one lineage need not stay there.

Every use of an antibiotic applies this pressure, which is why quantity matters more than intent. Prescriptions written for viral infections, which antibiotics cannot touch, and routine doses given to healthy farm animals both add selection without adding benefit. The drug is not wearing out; the target is changing.

Comprehension questions