AP Biology Practice Quiz: Natural Selection
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Test your understanding with short quizzes. This quiz has 15 questions to check your progress.
Question 1 of 15
All Questions (15)
A) The genetic code of an individual
B) The phenotypic variations present in a population
C) The rate of mutation within a species
D) The collective desires of a population to survive
Correct Answer: B
The provided content explicitly states that 'Natural selection acts on the phenotypic variations present in populations.' The phenotype is the observable trait upon which environmental pressures can act.
A) To increase the rate of new mutations
B) To ensure all organisms have equal fitness
C) To apply selective pressures to populations
D) To eliminate all phenotypic variation
Correct Answer: C
The content specifies that 'Changing environments apply selective pressures to populations.' These pressures determine which traits are advantageous or disadvantageous.
A) The variation is irrelevant because the predator will adapt to eat all color types equally.
B) The variation ensures that some individuals may have a coloration that provides camouflage, increasing their fitness.
C) The variation will cause all insects to spontaneously change to the most advantageous color.
D) The variation will decrease the overall fitness of the population, leading to extinction.
Correct Answer: B
Phenotypic variation is crucial because it provides the raw material for natural selection. In this scenario, the selective pressure (predation) will favor individuals whose existing coloration increases their fitness, as described in points 1 and 5.
A) It eliminates the need for phenotypic variation.
B) It stops the environment from applying selective pressures.
C) It can enhance the population's ability to survive and reproduce in diverse environments.
D) It guarantees that all individuals will be perfectly adapted to any environment.
Correct Answer: C
The content directly states that 'Variation in the number and types of molecules within cells can enhance a population's ability to survive and reproduce in diverse environments.' This molecular diversity can lead to advantageous traits.
A) The plants will alter the environment to make it wetter, eliminating the selective pressure.
B) All plants will spontaneously develop new traits for drought resistance in a single generation.
C) The selective pressure of the dry environment will cause all plants to have decreased fitness, leading to guaranteed extinction.
D) Natural selection will favor individuals with pre-existing phenotypic variations that confer drought resistance, increasing their fitness.
Correct Answer: D
This scenario combines multiple concepts. The changing environment (drier conditions) applies a selective pressure (Point 4). Natural selection acts on existing phenotypic variations (Point 3). Variations that help with water conservation will increase an organism's fitness (Point 5), and those individuals will be more likely to survive and reproduce.
A) Its fitness would increase further.
B) Its fitness would remain unchanged.
C) Its fitness could decrease.
D) Its fitness would become irrelevant to survival.
Correct Answer: C
According to the content, 'Some phenotypic variations can increase or decrease an organism's fitness in specific environments.' A trait that is advantageous in one environment (cold) may become a disadvantage (e.g., causing overheating) and thus decrease fitness in another (warm).
A) Because variation ensures that every individual in the population will survive any environmental change.
B) Because if all individuals are identical, there are no differences in fitness for environmental pressures to select for or against.
C) Because phenotypic variation is the only mechanism that causes environments to change.
D) Because variation guarantees that some individuals will be able to reproduce asexually.
Correct Answer: B
Natural selection works by favoring certain traits over others. If there is no phenotypic variation, all individuals are the same, and there is no basis for differential survival and reproduction. This highlights the 'importance of phenotypic variation in a population' (Point 1).
A) The molecular variation is unrelated to survival, as natural selection only acts on large-scale physical traits.
B) The toxin will cause all bacteria to develop the correct enzyme needed for survival.
C) Natural selection will act on the resulting phenotype (ability to neutralize the toxin), which is connected to the molecular variation (the enzyme).
D) The presence of any molecular variation will automatically decrease the fitness of all bacteria in the new environment.
Correct Answer: C
This question links molecular variation to fitness and natural selection. The variation in the enzyme molecule (Point 2) leads to a phenotypic variation (ability to survive the toxin). Natural selection then acts on this phenotype (Point 3), increasing the fitness of resistant individuals in the new environment (Point 5).
A) A lack of phenotypic variation.
B) A new selective pressure being applied by a changing environment.
C) An increase in fitness for all individuals in the population.
D) A process where molecular variation ceases to be important.
Correct Answer: B
The fire represents a 'changing environment' that 'applies selective pressures to populations' (Point 4). In this new environment, the phenotypic variation of dark fur is advantageous, increasing the fitness of those individuals (Point 5).
A) Organisms can intentionally change their phenotypes to suit the environment.
B) Phenotypic variations can increase or decrease an organism's fitness in specific environments.
C) Natural selection always leads to the creation of new species.
D) All molecular variations are harmful to an organism.
Correct Answer: B
This is a direct quote of Point 5 from the provided content, which explains that the value of a trait is dependent on its environmental context.
A) The environment selects for or against the observable characteristics of an organism.
B) An organism's genetic code is directly altered by the environment.
C) Only variations that are visible to the human eye can be selected for.
D) Organisms can consciously choose which phenotypes to display to increase their fitness.
Correct Answer: A
The phenotype represents the observable traits of an organism. Natural selection acts on these traits because they are what interact with the environment, leading to differential survival and reproduction (fitness), as covered in points 3 and 5.
A) The drought will cause all individual birds to grow larger beaks within their lifetime.
B) The lack of molecular variation will prevent any change in the population's beak size.
C) The drought is a selective pressure where the pre-existing variation of larger beaks confers higher fitness, leading to an increase in its frequency.
D) All birds will have their fitness decreased equally, and the population will remain unchanged.
Correct Answer: C
This answer correctly synthesizes the key concepts. The initial phenotypic variation (beak size, Point 1) is acted upon by natural selection (Point 3). The changing environment (drought, Point 4) applies a selective pressure. The larger beak variation increases fitness in this specific environment (Point 5).
A) It has no connection, as fitness is only determined by an organism's behavior.
B) Different molecular forms can result in different phenotypes, which may then be selected for or against by the environment.
C) All molecular variations are neutral and have no effect on an organism's phenotype or fitness.
D) It ensures that the organism will be immune to all environmental pressures.
Correct Answer: B
This question addresses Point 2, 'Explain how variation in molecules within cells connects to the fitness of an organism.' Molecular variations can cause phenotypic variations, and it is these phenotypes that natural selection acts upon, thereby affecting fitness.
A) Constant across all possible environments.
B) Dependent on the specific environment it inhabits.
C) Determined solely by its number of offspring, regardless of their survival.
D) Always higher than organisms without that variation.
Correct Answer: B
Point 5 states that phenotypic variations can increase or decrease fitness 'in specific environments,' highlighting that fitness is context-dependent and not an absolute quality of a trait.
A) The importance of phenotypic variation, which means there is no single 'perfect' form.
B) The fact that changing environments apply new selective pressures, meaning a previously 'perfect' trait may become a disadvantage.
C) The connection between molecular variation and fitness, which is always a positive correlation.
D) The principle that natural selection acts on phenotypes, which are always perfect representations of genotypes.
Correct Answer: B
The idea of a 'perfect' organism implies a static, optimal state. The content's emphasis on 'Changing environments apply selective pressures' (Point 4) and fitness being specific to the environment (Point 5) directly refutes this. An organism adapted to today's environment may be poorly adapted to tomorrow's, so perfection is a moving target that is never reached.