Natural Selection Effects Practice Test

A population of bacteria has variation in antibiotic resistance: some are resistant (R) and some are not resistant (N). An antibiotic is added to the environment. The table shows the number of bacteria after 24 hours.

Start: R = 10, N = 990

After antibiotic: R = 800, N = 5

Which explanation best describes natural selection in this population using the evidence? (Natural selection affects populations, not individuals.)

In a population of beetles, there is trait variation in shell color: light tan and dark brown. A bird predator hunts by sight on dark soil after a wildfire. The table shows the number of adult beetles that survived to reproduce each year.

Table (Adults that survived to reproduce):

Year 0: Light 50, Dark 50

Year 1: Light 18, Dark 42

Year 2: Light 10, Dark 45

Year 3: Light 6, Dark 47

Which explanation best describes how natural selection changed the trait distribution in this population over generations? (Remember: natural selection affects populations, not individuals.)