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Posted on Dec 22, 2025 in Biology

Which of the following statements best describes Darwin’s theory of evolution by natural selection? – Darwin’s theory emphasized that populations vary and change over time.
Which of the following observations would provide evidence supporting Lamarck’s proposed evolutionary mechanism of “inheritance of acquired characteristics”? – A decrease in tail length in dogs after 20 generations of dogs that had their tails docked (cut off) as puppies.
Darwin originally defined evolution as descent with modification.
Which of the following is an example of artificial selection? – A dog breeder mates a friendly, well-trained male dog with a similar female dog.
Which of these conditions do NOT occur in populations evolving due to natural selection? -Individuals pass on most traits that they acquire during their lifetime.
A farmer uses triazine herbicide to control pigweed in his field. For the first few years, the triazine works well and almost all the pigweed dies; however, after several years, the farmer sees more and more pigweed growing once again in the fields. Which of the following statements best explains the return of pigweed to the farmer’s fields? – Triazine-resistant weeds were more likely to survive and reproduce than were non-resistant individuals.
During periods of rapid environmental change, what may happen to a species that was well suited to the former environment? – The species may go extinct – Traits that were favorable in the original environment may be detrimental in the new environment – Individuals with particular traits that provide an advantage in the new environment will have higher reproductive success. – The population may change so much in adapting to the new environment that it is considered a new species.
Claytonia virginica is a plant with flowers that vary from white, to pale pink, to bright pink. Slugs prefer to eat pink-flowering over white-flowering plants (due to chemical differences between the two), and plants experiencing severe herbivory are more likely to die. The bees that pollinate this plant also prefer pink over white flowers, so that Claytonia with pink flowers produce more seeds than Claytonia with white flowers. A researcher observes that the percentage of different flower colors remains stable in the study population from year to year. Given no other information, if the researcher removes all slugs from the study population, what do you predict will most likely happen to the percentage of flower colors in the population over time? – The percentage of pink flowers will increase over time.
Which of the following statements best describes evolution? – Populations change genetically from one generation to the next.
Currently, two living elephant species (X and Y) are classified in the genus Loxodonta, and a third species (Z) is placed in the genus Elephas. Thus, which of the following statements would be accurate? – Species X and Y share a greater number of homologies with each other than either does with species Z.
Vestigial organs are remnants of structures that were useful to an organism’s ancestors but that are now nonfunctional or show reduced function.
Structures as different as human arms, bat wings, and dolphin flippers contain many of the same bones, which develop from similar embryonic tissues. These structural similarities are an example of homology.
Which of the following is the best definition of evolution on the smallest scale? – Change in allele frequencies in a population over time.
Which of the following statements about genetic variation is accurate? – Genetic variation must be present in a population before natural selection can act upon the population.
In a large population of bonobos, the frequency of the recessive allele is initially 0.1. There is no migration and no selection. What is the frequency of the dominant allele? Assume that there are two alleles of this gene. .9
Suppose 64% of the individuals in a remote mountain village can taste phenylthiocarbamide (PTC) and must, therefore, have at least one copy of the dominant PTC taster allele. If this population conforms to Hardy-Weinberg equilibrium for this gene, what percent of the population must be heterozygous for this trait? – 48%E
Which of the following statements is accurate with regard to a population in Hardy-Weinberg equilibrium? – Allele frequencies should not change from one generation to the next.
The value of the Hardy-Weinberg equation is that it allows scientists to perform which of the following assessments? – To detect whether an evolutionary force is acting on a population.
In a Hardy-Weinberg population with two alleles A1 and A2 that are in equilibrium, the frequency of allele A2 is 0.1. What is the frequency of individuals with A1A1 genotype? – 0.81
In a certain group of African people, 4% are born with sickle-cell disease (homozygous recessive). If this group is in Hardy-Weinberg equilibrium, what percentage of the group has the selective advantage of being more resistant to malaria (heterozygous) than those individuals who are homozygous for normal hemoglobin or for sickle-cell disease? – 32%
In which of the following situations would genetic drift most likely cause evolution? – Chance events cause allele frequencies to fluctuate unpredictably.
A population of 15 birds inhabits a fairly new island.
Ten of the birds are dark brown, and five of them are light brown. By chance, two of the dark brown birds and three of the light brown birds die before producing any offspring. All of the birds in the next generation are dark brown. This change in phenotypic frequency can be attributed to genetic drift.
Which of the following processes best describes the cause of a bottleneck effect? – Drastic decrease in the size of a population
An earthquake hits a small island. All but a small group of closely related lizards are eliminated, and the survivors spread out over the island. This is an instance of bottleneck effect.
The Hawaiian Islands are the tops of undersea volcanoes in the Pacific Ocean. The oldest islands are the northwest-most islands. The islands get progressively younger to the southeast. Hawaii, the “big island”, arose from the ocean less than one million years ago. Which of the following processes likely most strongly influenced the evolution of life on the big island when organisms first arrived? – The founder effect.
Over time, humans have steadily increased their movements across the continents of the Earth. Which of the following results has most likely been derived from these movements? – Increased gene flow
Three-spined stickleback fish (Gasterosteus aculeatus) show substantial genetic variation in gill-raker length related to differences in their diets. Longer gill rakers appear to function better for capturing open-water prey, while shorter gill rakers function better for capturing shallow-water prey. Which of the following types of selection is most likely to be found in a large lake (open water in the middle and shallow water around the sides) with a high density of these fish? – Disruptive selection
Most Swiss starlings (birds) produce four to five eggs in each clutch. Starlings producing more or less eggs have reduced fitness. Which of the following terms best describes this situation? – Stabilizing selection
Which statement below is true about sexual selection? – Sexual selection can result in sexual dimorphism-marked differences between the sexes in secondary sexual characteristics that are not associated directly with reproduction.
Which of the following statements about evolutionary forces is accurate? – Unlike the other evolutionary forces, natural selection is the only force that improves the match between the organism and its environment.
Imagine that part of a population of South American finches is blown by a storm onto an island far offshore and manages to survive and reproduce there for an extended period of 10,000 years. After that period, a climate change results in lower sea levels and the reconnection of the island with the mainland. Members of the formerly isolated island finch population can now interact freely with members of the original mainland population. Which of the following observations would, by itself, lead you to conclude unequivocally that the island finch population had evolved into a distinct species, according to the biological species concept? – Individuals from the different populations sometimes mate with each other, but all of the resulting eggs are sterile.
Three populations of crickets look very similar, but the males have different courtship songs. If the cricket populations were to contact each other in the wild, the different courtship songs would most likely function as which type of reproductive isolating mechanism? – Behavioral
Many songbirds breed in North America in the spring and summer, and then migrate to Central and South America in the fall. They spend the winter in these warmer areas where they feed and prepare for the spring migration north and another breeding season. Two hypothetical species of sparrow, species X and species Y, overwinter together in mixed flocks in Costa Rica. In spring, species X goes to the east coast of North America, and species Y goes to the west coast. Which of the following factors most likely keeps these species separate? – The two species reproduce in different geographical areas.
Which of the following statements best describes unity within a species? – Members of a given species have the potential to interbreed in nature and produce viable, fertile offspring.
Two species of frogs belonging to the same genus occasionally mate, but the embryos stop developing after a day and then die. Which of the following mechanisms keep the species separate? – Reduced hybrid viability
Two juniper trees (Juniperus scopulorum and J. Monosperma) have overlapping geographic ranges. Pollen grains (which contain sperm cells) from one species are unable to germinate and make pollen tubes on female ovules (which contain egg cells) of the other species. Which of the following isolating mechanisms keeps the two species separate? – Gametic isolation
House finches (birds) occurred only in western North America until 1939, when a few individuals were released into New York City. These individuals established a breeding population and gradually expanded their range. The western population also expanded its range somewhat eastward, and the two populations have recently come in contact. Which of the following terms best describes the process that had occurred if the two forms did not interbreed when their expanding ranges met?
Two researchers experimentally formed tetraploid frogs by fertilizing diploid eggs from Rana pororsa brevipoda with diploid sperm from Rana nigromaculata. Whe they allowed the tetraploid frogs to mate with each other, most of the offspring that survived to maturity were tetraploid, with chromosome sets of both diploid parent species. Based on these results, if this type of tetraploid formed in the wild, what would be the most likely result?
Beetle pollinators of a particular plant are attracted to its flowers’ bright orange color. The beetles not only pollinate the flowers, but they mate while inside the flowers. A mutant version of the plant with red flowers becomes more common with the passage of time. A particular variant of the beetle prefers the red flowers to the orange flowers. Over time, these two beetle variants diverge from each other to such an extent that interbreeding is no longer possible. Which of the following possible causes of speciation best describes the beetle example and what factor has driven it? – Sympatric speciation; habitat differentiation
A female fly, full of fertilized eggs, is swept by high winds to an island far from the mainland. She is the first, and only, fly to arrive on this island. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species and their geographic ranges overlap. Each species eats a different kind of food. None of the species can fly and the balancing organs of males differ among species and are now used in courtship displays. Fly species W produces fertile offspring with species Y, but not with species X or Z. Furthermore, X and Z do not hybridize. Which of the following statements about species W and Y is most likely to be accurate? – Species W and Y may fuse into a single species if their hybrids remain fertile over the course of many generations.
In the phylogenetic trees shown, each number represents a unique species of organisms. Which two species are represented as sister species in Tree 2 but are not represented as sister species in Tree 1?
– 3 and 4
Some molecular data place the giant panda in the bear family (Ursidae) but place the lesser panda in the raccoon family (Procyonidae). If the molecular data best reflect the evolutionary history of these two groups, then the morphological similarities of these two species is most likely due to which of the following processes? – Possession of analogous (convergent) traits
In the figure, the letters A-G represent individual species that all descended from a common ancestor. (PICTURE)
Which of the following conclusions regarding the phylogeny of these organisms can be made from this tree?
– D is more closely related to E than it is to G
Which of the following statements best describes the rationale for applying the principle of maximum parsimony in constructing phylogenetic trees? – For trees based on morphology, the most parsimonious tree requires the fewest evolutionary events.
Which of the following features permits a gene to act as a molecular clock?
A reliable average rate of mutation
In the tree below, which circled group is paraphyletic? (PICTURE) –
Group 3
Which of the following statements about evolutionary trees is accurate?
Currently, two of the living elephant species (X and Y) are placed in the genus Loxodonta, and a third surviving species (Z) is placed in the genus Elephas. Assuming this classification reflects evolutionary relatedness, which of the following is the most accurate evolutionary tree? (PICTURE) – 3
Use the diagram to answer the next question.
(PICTURE)
Which of the following conclusions is consistent with the information in the evolutionary tree? – The amnion occurs in mammals, birds, and lizards.
Unit 2 Answers:

A group of eagles living around Lake Tahoe would be considered a population
Fish, their predators and the water, sunlight, and plants that they rely on would be considered an ecosystem
When deforestation occurs in an area, what immediate effect does this have on the water cycle? – Less water is returned to the air by respiration
What is one biotic factor that affects the size of a population in an ecosystem?
– Number of predators present
Which is an accurate description of the growth of most natural animal populations? – It is limited by environmental factors
A population of mice occupies a tree stump. For ten years, the population has been stable. Which of the following would likely cause the number of mice to begin to decrease? – An increase in predators
What pattern of growth will a population with limited resources show? – Logistic
Which of the following is true of density-dependent limiting factors? – They have a larger impact on big populations
Which factor is a density-dependent limiting factor on the population of a species? – Competition
Which factor would increase the carrying capacity for white-tailed deer in Eastern temperate forest ecosystem? – The re-introduction of the American chestnut tree, which produces many seeds and leaves for food
Examine the diagram below, and the trend seen by the two lines. Global temperature has been closely linked with the buildup of CO2 in the atmosphere. Which of the following statements is most likely true based on the graph?
– Since 1880, carbon dioxide has caused the temperature to increase by about 1.2 degrees.
What human activity would have the most significant effect on the temperature of the earth? – Burning fossil fuels
The correct order of stages in primary succession of a volcanic island is volcanic rock–lichen–mosses–grasses–coconut trees
A logger clears a forest and the forest re-grows over many years. Which type of succession represents the regrowth of this forest? – Secondary succession
Which of the following statements is not true of secondary succession? – Moss and lichens must be present
An insect gathers pollen and nectar for food, but at the same time is aiding in the plant’s reproduction by spreading pollen to other flowers it visits. What does this relationship demonstrate? – Mutualism
Grazing cows disturb grass and cause insects to fly around the cows as they eat. In turn, birds swoop in and eat the insects. This type of feeding relationship between the birds and the insects is an example of predation
Graph question about the population of mountain lions and wolves in Montana counties – In clay county, mountain lions probably outcompete wolves for food
Bluebirds and cardinals, two different bird species, live in a small wooded area. The cardinals are very aggressive and eventually take over the nests of the bluebirds, leaving the bluebirds without a place to lay their eggs and raise their young. This is an example of competitive exclusion
Graph question about the effect of fungus in presence of plants –
parasitism
One difference between parasitism and predation is that parasites keep their hosts alive for a period of time
2 Graph question about avg temps and total precipitation – Area 2 has a larger annual temperature variation, and it’s considered a hot desert due to its low annual precipitation
(Continuing w/ 2 graphs) Based on the data in the figures, which of the following statements is most consistent with the data? – Area 1 is near or in the tropics
(Graph question) – Which shaded region in the figure is the most representative of the biome with the highest variation in annual precipitation? – 1
(Continuing w/ graph) Which shaded region in the figure is the most representative of the biome with the highest variation in annual temperature? – 4
(Graph question) Which survivorship curve most closely models a population of mice in which females consistently give birth to a large number of offspring, and he mortality rate of the offspring is fairly regular during each year of their lives, regardless of their age? – Curve B (linear line)
(Graph question) Based on the data provided, what factor of those listed below appears to be the most important in stabilizing the population from its initial size over the subsequent 100 years? – A high migration rate
A population of ground squirrels has an annual per capita birth rate of 0.06 and an annual per capita death rate of 0.02. Using these birth and death rates, calculate the total number of individuals added to (or lost from) a population of 1,000 individuals in one year. – 40 individuals added
(Graph question) According to the population pyramid of this country, its population is most likely growing rapidly
(Graph question) According to the population pyramid, Canada’s population is getting smaller
(Graph question) Which of the following curves describes survivorship that is most typical in marine fish or mollusks, which produce large numbers of young with few surviving to reproductive age? – E
(Continuing w/ graph) Which of the following curves best describes survivorship in a typical elephant population which produces few young, most of which survive to reproductive age? – A
(Continuing w/ graph) Which statement best explains survivorship curve B? – Survivorship can only decrease; therefore, this curve could not happen in nature
(Graph question) Which of the following hypotheses is most consistent with the data with respect to survival and clutch size? – Large clutch size correlates with low survival
(Continuing w/ graph question) Based on the data graphed here, which size clutch would likely result in the highest estimated overall reproductive success (fecundity) after one year? – 2
(Graph question) Which of the following claims can be best supported using the data? – Clutch size is inversely related to density
(Graph question) Which of the following conclusions is best supported from the experimental evidence in the figure? – Without direct contact, mussels can sense the presence of crabs
Bouchard and Brooks studied the effect of insect flight on dispersal and speciation in rainforest insects. They sampled all of the insects in the study area and found that 60 insect species are flightless and 19 are able to fly. These results indicate which of the following? – Flightless insects have a higher species richness in the study area
(Graph question) In the figure, species A through F are found among four communities, with the number of circles representing their abundance. Which community has the highest diversity? – 2
(Continuing w/ graph) In the figure, species A through F are found among four communities, with the number of circles representing their abundance. Which community has the lowest diversity? – 1
If there are 25 African elephants (primary consumer) living together in a given area, with an average weight of 4,000 kg each, approximately how much biomass of plant material would hypothetically be necessary as a harvestable food supply to support all of them on an ongoing basis? (Assume a 10% efficiency in energy transfer.) – 1,000,000 kg
Which of the following are the two key emergent properties of an ecosystem? – Energy flow and chemical cycling
Which of the following components is not recycled within an ecosystem? – heat
(Graph question) Which of the following best explains why no arrows lead directly from “Detritus” to primary consumers? – Few primary consumers directly eat detritus, and so its mostly broken down into inorganic compounds by decomposers such as earthworms, fungi, and prokaryotes
(Continuing w/ graph) In the figure, the jagged arrow leaving microorganisms and other detritivores represents which process? – Energy lost as heat from a worm during cellular respiration
(Continuing w/ graph) In the ecosystem figure, which component of the food web has the potential to lose the most energy as heat? – Primary producers
(Graph question) Based on this food web, which species is most likely a decomposer? – 5
(Continuing w/ graph) In the food web, if species 3 is toxic to predators, then which

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