AP Biology Short Free-Response Questions

August 1, 2021

Section II of the AP Biology exam consists of two long free-response questions and four short free-response questions. The four short free-response questions take about 8 to 10 minutes each, are usually worth 4 points each, focus on scientific investigations, conceptual analysis, analyzing models or visual representations, and analyzing data, and are broken down into four parts each.

Sample AP Biology Short Free-Response Question 

Note: this question is worth 4 points total.

In a population of royal flycatchers in Costa Rica, the allele for a large crown on the head (C) is dominant over the allele for a small crown on the head (c). It has been determined that, for this population, the percentage of royal flycatchers with small crowns has remained at 11% since 1850 (when the population was first studied). 

  • (a) Describe one process that is responsible for the maintenance of the unchanged frequency of small-crowned alleles in this population of royal flycatchers. (1 point) 
  • (b) Explain the standard by which scientists determine which individual is the fittest in any population. (1 point) 
  • (c) Predict what would occur in this population if the royal flycatchers, that were born to a mating couple over several years, experienced a mutation and were all born with a very different colored crown. (1 point) 
  • (d) Justify your prediction (from your answer to part (c)). (1 point)

Sample AP Biology Short Free-Response Answer

  • (a) This population is in Hardy-Weinberg equilibrium. Thus, this population is isolated with no natural selection. 
  • (b) According to Charles Darwin’s theory of natural selection, only the fittest survive. The fittest individual is the individual that has the most offspring and passes more of its genes onto the next generation. 
  • (c) If the mutation is advantageous, its frequency will increase in the population. If the mutation is disadvantageous, its frequency will decrease in the population. 
  • (d) If the mutation is advantageous, the individual with the mutated trait will be more attractive and fitter than other individuals. That individual will then mate with more certainty and have more offspring. Thus, its offspring will carry the mutated trait and then pass it onto their offspring, increasing the frequency of the mutated trait in the population. Conversely, if the mutation is disadvantageous, the individual with the mutated trait will be less fit and will reproduce less. Thus, the frequency of the mutated trait will decrease in the population.

Analysis of Sample AP Biology Short Free-Response Answer

Out of 4 total points possible, this answer would have earned all 4 points. The breakdown of these point distributions is as follows:

Answer Part (a)

The student received a point for correctly stating the following: This population is in Hardy-Weinberg equilibrium. Thus, this population is isolated ­ with no natural selection. (1 point)

The student earned the full 1 point for this response. Thus, the student received 1 point out of a possible 1 point total for part (a).

Similarly, the student could have also earned the full 1 point for any of the following statements: 

  • This population is isolated with no mutation. (1 point) 
  • This population is isolated with no immigration from other populations of royal flycatchers. (1 point) 
  • This population is isolated with random mating. (1 point) 

Answer Part (b)

The student received a point for correctly stating the following: The fittest individual is the individual that has the most offspring and passes more of its genes onto the next generation. (1 point) 

The student earned the full 1 point for this response because it explained how scientists determine which individual is the fittest in any population (by determining which individual has the most offspring and passes more of its genes onto the next generation). Thus, the ­student received 1 point out of a possible 1 point total for part (b)

Answer Part (c)

The student received a point for correctly stating the following: If the mutation is advantageous, its frequency will increase in the population. If the mutation is disadvantageous, its frequency will decrease in the population. (1 point) 

The student earned the full 1 point for this response because it predicted what would occur in this population if the mutation was advantageous and what would happen in this population if the mutation was disadvantageous. Thus, the student received 1 point out of a possible 1 point total for part (c)

Answer Part (d)

The student received a point for correctly stating the following: If the mutation is advantageous, the individual with the mutated trait will be more attractive and fitter than other individuals. That individual will then mate with more certainty and have more offspring. Thus, its offspring will carry the mutated trait and then pass it onto their offspring, increasing the frequency of the mutated trait in the population. Conversely, if the mutation is disadvantageous, the individual with the mutated trait will be less fit and will reproduce less. Thus, the frequency of the mutated trait will decrease in the population. (1 point) 

The student earned the full 1 point for this response because it fully and clearly justified the prediction made in the answer to part (c) of this question. Thus, the student received 1 point out of a possible 1 point total for part (d).

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