A population of bacteria is treated with an antibiotic. After several weeks almost every bacterium in the population is resistant to that antibiotic. Which statement explains this change?
The antibiotic caused all of the bacteria to become resistant to it
The bacteria became resistant because they were exposed to it often
The antibiotic caused a mutation that made every bacterium resistant
A few bacteria were already resistant, survived and then reproduced
41 exam-style questions on AQA GCSE Biology 6.2 Variation and evolution, covering 6.2.1 Variation, 6.2.2 Evolution, 6.2.3 Selective breeding, 6.2.4 Genetic engineering, and 6.2.5 Cloning. Each one has a worked solution and a mark scheme showing where the marks go.