AP Biology : Natural Selection

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #2 : Understanding Biological Fitness

A harmless species of butterfly mimics the coloration of a poisonous species. This is an example of which of the following?

Possible Answers:

Aposematic coloration 

Mullerian mimicry

Cryptic coloration 

Batesian mimicry

Communal camouflage 

Correct answer:

Batesian mimicry

Explanation:

Batesian mimicry involves a harmless species mimicking an unpalatable or harmful species, such as the butterfly in the example. Mullerian mimicry involves two unpalatable or harmful species resembling each other. This also helps predators learn which types of species to avoid. Cryptic coloration is more simply known as camouflage. Aposematic coloration is warning coloration, such as bright colors on poisonous tree frogs or venomous snakes. 

Example Question #3 : Understanding Biological Fitness

Darwin's Theory of evolution by natural selection is based on all of the following postulates except __________.

Possible Answers:

individuals within a population are variable

at least in part, variations among individuals are passed on from parents to offspring

the survival and reproduction of individuals is random

some individuals are more successful in surviving and reproduction than others

the survival and reproduction of individuals is not random

Correct answer:

the survival and reproduction of individuals is random

Explanation:

According to Darwin's theory, the survival and reproduction of individuals is not random. Survival and reproduction is tied to the variations among individuals. Those with the most favorable variations are more fit; therefore, they are naturally selected.

Example Question #4 : Understanding Biological Fitness

Which of the following must be true for natural selection to take place in a population?

Possible Answers:

The population must be in competition with another population

Phenotypic variation is based on differences in genotypes

Adaptation to different environmental niches

There must be sexual dimorphism in the population

Correct answer:

Phenotypic variation is based on differences in genotypes

Explanation:

In order for natural selection to take place, members of a population must have different biological fitnesses (a measure of how likely it is that an individual will pass on its genes through reproduction). Different biological fitnesses are a result of different phenotypes. Organisms with phenotypes better suited to their environments will have a higher fitness. 

Natural selection does not require sexual dimorphism or competition between populations. Adaptation to environmental niches can result from natural selection over time.

Example Question #21 : Natural Selection

Recently a nursing home had an increase in the number of Staph infections. Doctors began treating the infections with methicillin, but within a few months over 75% of infections were resisting this treatment. What is the most likely cause of this phenomenon?

Possible Answers:

A small number of bacteria were resistant to methicillin from the start. These bacteria survived treatment with methicillin and reproduced, eventually comprising most of the bacteria.

The bacteria built up an immunity to methicillin over time.

A new patient brought a methicillin-resistant strain of the bacteria to the nursing home. 

Some bacteria were able to survive treatment by changing the structure of their membrane to keep methicillin from penetrating it.

Correct answer:

A small number of bacteria were resistant to methicillin from the start. These bacteria survived treatment with methicillin and reproduced, eventually comprising most of the bacteria.

Explanation:

Initially, the population of bacteria was composed of mostly bacteria vulnerable to methicillin and a small number of resistant bacteria. Treatment with methicillin destroyed all of the vulnerable bacteria. leaving only the resistant alive to reproduce. Over time, the resistant bacteria became the majority.

Although it's possible a new patient could have introduced the first resistant bacteria, it's unlikely to have occurred in such a short time frame. 

It's also unlikely the bacteria possessed the ability to resist the bacteria from the start, as methicillin treatment wouldn't have worked on any of them.

Bacteria do not possess a mechanism by which they can build up immunity to antibiotics over time.

Example Question #21 : Natural Selection

A population of birds encounters a dramatic event that results in a severe decrease in population size. As a result of the newly-decreased population, what type of genetic drift does this population now exhibit?

Possible Answers:

Effect size

None of these

Founder effect

Artificial selection

Bottleneck effect

Correct answer:

Bottleneck effect

Explanation:

A sharp decrease in population size caused by environmental or human impact is known as the bottleneck effect, where the bottlenecking occurs in the relative population diversity. This is mainly due to the fact that the individuals who survived rarely represent the genetic makeup of the initial population as a whole. The effect size is a statistical measurement of the strength of a phenomenon, which can be applied in the study of population dynamics, but is not a type of genetic drift. Artificial selection is the deliberate selection of mating preferences by humans in order to alter the proportion of traits in the offspring. However, this type of selection is not caused by a dramatic event, nor does it result in a severe decrease in population size. The founder effect does pertain to small populations but specifically on how genetic variation is lost in a small population that comes from a larger population due to misrepresentation. 

Example Question #22 : Natural Selection

Which of the following would best determine the fitness of an organism?

Possible Answers:

The number of mates with which the organism has successfully produced offspring. 

How much food the organism consumes in its lifetime.

The number of offspring produced by the organism’s own offspring.

The number of offspring produced by the organism.

How large the organism grows.

Correct answer:

The number of offspring produced by the organism’s own offspring.

Explanation:

This would be equivalent to the number of “grandchildren” produced by the organism. Biological fitness is defined by how capable the organism is of increasing the frequency of its own alleles. While individuals that consume more food grow larger, or have more mates than other members of their species are clearly thriving in their environment, which does not always mean that they produce more offspring. Also, it is possible that an organism could produce a large number of offspring that are infertile, which would ultimately not increase the frequency of its alleles. Therefore, the best determination of an organism’s fitness is the production of offspring that are themselves able to successfully produce offspring.

Example Question #23 : Natural Selection

In an ecosystem, factors such as food supply, climate, and predator population are known as which of the following?

Possible Answers:

Charles Darwin's rules of survival

Evolutionary catalysts

Social Darwinism

Survival of the fittest

Selection pressures

Correct answer:

Selection pressures

Explanation:

Selection pressures is the correct answer here. A selection pressure is any factor that affects fertility or mortality, or anything that can cause a population to change genetically.

Example Question #24 : Natural Selection

How does inbreeding negatively impact a population?

Possible Answers:

It reduces the number heterozygous individuals, preventing beneficial alleles from being efficiently selected for.

It impedes evolution, because the frequency of alleles does not change within the population.

All of these

It increases the number of homozygous individuals, allowing potentially harmful recessive alleles to express themselves more frequently.

None of these

Correct answer:

All of these

Explanation:

Breeding with genetically different individuals tends to "scramble" the alleles of a population. When genetically similar individuals breed, they tend to produce homozygous genotypes in their offspring, so potentially dangerous recessive alleles appear more frequently and beneficial alleles are not as efficiently selected for. Thus, inbred populations have a lower survival rate over time. This is called inbreeding depression.

Example Question #25 : Natural Selection

Which of these is a predictive power of evolutionary theory?

Possible Answers:

Evolution provides a framework for observations to form a unifying explanation for a wide range of phenomena.

Evolution provides explanations about the origins of the diversity of life.

Evolution can be used to form hypotheses about how bacterial strains are likely to mutate over time.

None of these

Evolution can be supported by observational evidence.

Correct answer:

Evolution can be used to form hypotheses about how bacterial strains are likely to mutate over time.

Explanation:

Each of the above is true, but the predictive power of evolution lies in its ability to form testable hypotheses. Natural selection and descent with modification can be most visibly observed in bacterial populations, where new generations can arise in as little as forty minutes. Biologists in every field form hypotheses based on how a mechanism, organism, or process is adaptive to its environment.

Example Question #27 : Natural Selection

A bacteriologist places an antibiotic drug in a petri dish containing a strain of E. coli bacteria. How is this likely to affect the bacterial population?

Possible Answers:

The bacteria will sense the need to develop a resistance to the antibiotic, which they will pass on to the resulting generation.

Those with strong resistance to the antibiotic will survive and multiply, and eventually the resulting population will become resistant.

None of these

The antibiotic will kill the entire population of bacteria.

The initial strain will be able to develop a resistance, but since it will not change the genetic code, the next generation will be vulnerable to it and die out.

Correct answer:

Those with strong resistance to the antibiotic will survive and multiply, and eventually the resulting population will become resistant.

Explanation:

This is an example of a prediction made by the theory of natural selection.

There must have been individuals in the population who were already resistant to the antibiotic. They would survive while the non-resistant bacteria would die out, leaving only the resistant individuals to pass on their genes by multiplication.

The bacteria themselves do not grow resistant to the antibiotic, and they cannot change their genetic makeup in response to the environment.

Since the drug is an antibiotic, not a sterilization method, it will not succeed in killing the entire population of bacteria.

This principle is particularly important in the field of immunology, as biologists work to figure out how antibiotic-resistant strains can be fought or maintained.

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