AP Biology : Understanding Biological Fitness

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #51 : 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 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.

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.

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 #132 : Evolution And Genetics

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

Artificial selection

Bottleneck effect

Founder effect

None of these

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 #133 : Evolution And Genetics

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. 

The number of offspring produced by the organism.

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

How much food the organism consumes in its lifetime.

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 #131 : Evolution And Genetics

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

Possible Answers:

Social Darwinism

Charles Darwin's rules of survival

Evolutionary catalysts

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 #135 : Evolution And Genetics

How does inbreeding negatively impact a population?

Possible Answers:

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

None of these

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

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

All 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 #51 : 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 #141 : Evolution And Genetics

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 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.

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

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

None of these

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.

Example Question #61 : Natural Selection

The best definition of natural selection is _________.

Possible Answers:

the most fit individuals adapt to their environment better than less fit individuals

survival of the fittest

those who eat better, are healthier, and live longer are the most fit within a population

preservation of traits that lead to increased survival and reproduction

Correct answer:

preservation of traits that lead to increased survival and reproduction

Explanation:

While natural selection is often described as "survival of the fittest," this explanation is not completely accurate. It paints the picture that the most fit individual lives the longest, when the real premise is that the individual with the most benefical combination of genes suited to the current environment reproduces more, thus passing on more genetic information to the next generation.

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