Natural Selection — Drills · Grade 10 Science

Chapter: Evolution, Ancestry & Biodiversity

What these drills covers

By the end of Natural Selection you should be able to:

I can explain the four factors — heritable variation, overproduction, competition, and differential survival and reproduction — that together drive natural selection.
I can use the concept of fitness to predict how the traits of a population will shift over many generations in a given environment.

6 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: natural selection, variation, overproduction, fitness, adaptation, selective pressure.

Problem 1

Natural selection acts on

variation that arises in response to need
heritable variation already present in a population
individuals that choose to change
acquired skills

Answer and explanation

heritable variation already present in a population

Selection can only favour or disfavour variation that already exists and is heritable; it does not generate variation on demand.

Problem 2

In evolutionary biology, an organism's fitness refers to its

physical strength
lifespan alone
reproductive success in its environment
body size

Answer and explanation

reproductive success in its environment

Fitness is measured by surviving offspring contributed to the next generation, which may have little to do with strength or size.

Problem 3

In a population of 500 beetles, 80 carry a dark-colour allele pair. What percentage is that?

Answer and explanation

16 %

80 / 500 × 100 = 16 percent. Tracking such percentages across generations is how a change in a population is measured.

Problem 4

A resistant bacterial strain makes up 2 percent of a population; after antibiotic exposure it makes up 90 percent. By what factor has its share risen?

Answer and explanation

90 / 2 = 45 times. The resistant cells were present beforehand; the antibiotic changed which cells survived to reproduce.

Problem 5

Explain the error in saying that bacteria "became resistant because of the antibiotic."

Answer and explanation

Resistant variants arise by mutation independently of the antibiotic and are present in the population before exposure. The antibiotic does not create resistance; it removes susceptible cells, so the resistant ones reproduce and come to dominate. The cause of the change in the population is differential survival and reproduction of pre-existing variation, not a response induced by the drug.

Response criteria

State a biologically accurate conclusion.
Show the data, mechanism, or calculation that supports it.
Include units, conditions, or limits where relevant.

Problem 6

State the three conditions a population must meet for natural selection to change it, and explain why all three are required.

Answer and explanation

There must be variation among individuals, that variation must be heritable, and it must affect survival or reproduction. Without variation there is nothing to select between; without heritability the differences are not passed on, so the next generation is unchanged; without an effect on survival or reproduction the variants leave equal numbers of offspring and their proportions do not shift. All three together produce a change in the population's composition over generations.

Response criteria

State a biologically accurate conclusion.
Show the data, mechanism, or calculation that supports it.
Include units, conditions, or limits where relevant.

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