Question

question 12 of 25
scientists sampled a habitats peppered moth population by collecting a
random sample of 100 moths once per year for five years. they recorded the
proportion of the moths that were each color.
colors of collected moths

which event could explain the changes in the population shown in the graph?
a. the proportion of light - colored moths increased because
mutations caused new phenotypes that were not collected.
b. the proportion of dark - colored moths increased because soot
pollution darkened the bark of trees in the habitat.
c. the proportion of dark - colored moths increased because of
random variations in the population from year to year.
d. the proportion of light - colored moths increased because pollution
decreased, and tree bark in the habitat became lighter in color.

Explanation:

In the graph, the number of dark - colored moths increases over the years. This is an example of industrial melanism. When soot pollution darkens tree bark (a change in the environment), dark - colored moths have a camouflage advantage over light - colored moths. Light - colored moths are more easily seen by predators, so their population decreases, and dark - colored moths (which are better camouflaged) have a higher survival rate and their proportion in the population increases.

• Option A: If new phenotypes were not collected, it would not explain the increase in dark - colored moths proportionally as shown in the graph.
• Option C: Random variations alone (without a selective pressure like a change in the environment) do not clearly explain the directional change (increase of dark - colored moths) shown in the graph.
• Option D: If pollution decreased and tree bark became lighter, we would expect the proportion of light - colored moths to increase, which is the opposite of what is shown in the graph.

Answer:

B. The proportion of dark - colored moths increased because soot pollution darkened the bark of trees in the habitat.