AP Biology : Natural Selection

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #11 : Understanding Types Of Selection

Which of the following is true regarding balancing selection?

Possible Answers:

An example is heterozygote advantage

It maintains variation in a population

All of these

It is the opposite of purifying selection

Correct answer:

All of these

Explanation:

Balancing selection is a type of natural selection that maintains genetic variation in a population, making it the opposite of purifying selection. Examples of balancing selection include heterozygote selection, in which there is adaptive value for heterozygotes of an allele.

Example Question #12 : Understanding Types Of Selection

During which of the following levels of biological organization can natural selection occur?

Possible Answers:

Individual

Group

Gene

All of these

Correct answer:

All of these

Explanation:

Natural selection is defined as survival and reproduction based on a specific phenotype. Phenotypes that increase reproductive fitness are “selected for” on different levels. Natural selection can take place on different levels of biological organization including gene, individual, and group levels.

Example Question #13 : Understanding Types Of Selection

Which of the following types of selection best describes the process in which fitness depends on phenotype frequency?

Possible Answers:

Sexual selection

Disruptive selection

Frequency-dependent selection

Directional selection

Correct answer:

Frequency-dependent selection

Explanation:

Frequency-dependent selection is a type of natural selection in which the fitness of a phenotype depends on frequency. This includes positive frequency-dependent selection—fitness of a phenotype increases when it is common—and negative frequency-dependent selection—fitness of a phenotype decreases when it is common.

Example Question #1 : Understanding Biological Fitness

There are two very different reproductive strategies in nature: r-selection and k-selection. These strategies are so extreme, we typically observe organisms somewhere in between these two strategies.

Which of the following characteristics is not indicative of r-selection?

Possible Answers:

Very little parental care

Small brood size

Very fast maturation of organisms

High brood mortality rate

Correct answer:

Small brood size

Explanation:

The r-selection strategy for reproduction is typically seen in environments that are very volatile and unpredicatable. It has a variety of characteristics including high brood sizes with a high mortality rate, and fast maturation with very little parental assistance. Low brood sizes are typically seen in the k-selection strategy for reproduction.

Example Question #1 : Understanding Biological Fitness

Which characteristic is least likely to affect an organism's biological fitness in the tundra?

Possible Answers:

Exothermic versus endothermic regulation

Color

Fur

Nocturnal versus diurnal activity

Size

Correct answer:

Nocturnal versus diurnal activity

Explanation:

Biological fitness is directly related to the ability of an organism to survive and produce future progeny. There are a lot of factors that will play into an organism's fitness, especially in a harsh place like the tundra. Small size can be beneficial, as smaller animals require less food and can survive better in harsh environments, but large size can be beneficial to help preserve body heat. The color of an animal will help it to hide from predators; many tundra animals are white to help them blend in to the snow. Thermoregulation is extremely important in a cold environment; endotherms are able to regulate their own internal temperature, and will survive better than exotherms, which would be affected by the cold temperature of the air. Finally, fur and feathers help to trap body heat close to the skin and would enhance the fitness of animals in a cold environment.

Size, color, mode of thermoregulation, and fur all impact an animal's ability to survive in the tundra. Nocturnal activity, however, would not necessarily be favored over diurnal activity, as there is no clear advantage of one over the other in this specific environment.

Example Question #2 : Understanding Biological Fitness

In the evolutionary sense, which organism has the highest fitness?

Possible Answers:

A turtle that lays hundreds of eggs each nesting season, although an unusually small number of these eggs hatch successfully

A prairie dog that, though smaller than the average member of her species, has twice as many healthy young in each litter

A dog who cannot give birth due to a hip abnormality, but is healthy in all other respects

A sterile mule that can pull over 800 pounds

A childless human male who lives to be over one hundred years old

Correct answer:

A prairie dog that, though smaller than the average member of her species, has twice as many healthy young in each litter

Explanation:

With regard to evolution and natural selection, fitness refers only to the ability of an organism to contribute to the next generation of its species. In other words, if an organism has a large number of viable offspring, its fitness is high, regardless of other factors like strength, size, and longevity.

Of these answer choices, the only organism with an above-average number of healthy, surviving offspring is the prairie dog. The mule and the dog have below-average fitness because they cannot give birth. The turtle also has below-average fitness because it produces an unusually low number of healthy offspring. The human male has average to below-average fitness; certain traits made him choose not to produce offspring, though he may have been able to produce numerous offspring.

Example Question #2 : Understanding Biological Fitness

Humans regulate their internal body temperature within a very narrow range. This is an example of __________.

Possible Answers:

evolution

constancy

homeostasis

metabolism   

Correct answer:

homeostasis

Explanation:

Homeostasis is the tendency of the body to maintain stable, constant states. Homeostasis is often mediated by negative feedback systems, which prevent the measure from getting too high or too low. Regulation of body temperature within a narrow range would be an example of homeostatic regulation. Other examples include blood glucose concentration and blood calcium concentration.

Metabolism refers to the chemical processes of the body. These processes can help maintain homeostasis, but are not directly responsible for body regulation.

Example Question #1 : Understanding Biological Fitness

Which of the following would be considered innate behavior?

Possible Answers:

Inflexible behavior

Decisions

Classical conditioning

Communicating

Courtship

Correct answer:

Inflexible behavior

Explanation:

Innate behavior is known as inflexible behavior, in which learning plays no role in the behavior. Communicating, courtship, and decision making all rely on learned behavior from the environment. 

Example Question #1 : Understanding Biological Fitness

Which organism would be considered the most biologically fit?

Possible Answers:

Lives 45 years and produces 3 offspring

Lives 70 years and produces no offspring

Lives 27 years and produces 1 offspring

Lives 36 years and produces 6 offspring

Lives 94 years and produces 5 offspring

Correct answer:

Lives 36 years and produces 6 offspring

Explanation:

The most biologically fit organism is one that produces the most fertile offspring. Lifespan can correlate to the number of offspring produced, but is not a direct factor in determining fitness.

Since the organism that lives 36 years produced the most offspring (6), it is the most biologically fit.

Example Question #6 : Understanding Biological Fitness

In regard to the theory of evolution, “fitness” most likely refers to which of the following?

Possible Answers:

Reproductive success

All of these

Physical abilities of an individual

Flexibility of an individual

Correct answer:

Reproductive success

Explanation:

In evolutionary terms, “fitness” refers to the reproductive success or reproductive potential of an organism—its contribution to its species' gene pool.

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