Natural Selection and Evidence for Evolution

Question 1

Explain Darwin’s theory of evolution by natural selection.

Answer 1

• Natural selection describes how beneficial alleles become more common in a population
• Selection pressures such as competition and predation mean that not all organisms will survive and reproduce
• Individuals with alleles that make them better adapted to their environment are more likely to survive and pass on their alleles to their offspring

Question 2

Bacteria can quickly evolve resistance to a particular antibiotic.

Suggest one reason why bacteria can evolve quickly.

Answer 2

They reproduce rapidly

Question 3

Explain how a bacterium could become less affected by a particular antibiotic.

Answer 3

A mutation in the bacterium’s DNA may give it resistance to the antibiotic

Question 4

State the selection pressure involved when bacteria develop resistance to an antibiotic.

Answer 4

Exposure to the antibiotic

Question 5

(Exam-style question)

Explain how antibiotic resistance becomes more common in a population over time.

Answer 5

• Bacteria with the antibiotic resistance allele are more likely to survive than bacteria without the allele
• Therefore, they reproduce many more times
• This leads to the allele for antibiotic resistance being passed on to lots of offspring, so it becomes more common in the population

Question 6

(Exam-style question)

Answer 6