Microbiology MCQ

Arctic foxes typically have a white coat in the winter. In summer, when there is no snow on the ground, the foxes typically have a darker coat. Which of the following is most likely responsible for the seasonal change in coat color?

A) The decrease in the amount of daylight in winter causes a change in gene expression, which results in the foxes growing a lighter-appearing coat.
• B) The diet of the foxes in summer lacks a particular nutrient, which causes the foxes to lose their white coat and grow a darker colored coat.
• C) Competition for mates in the spring causes each fox to increase its camouflage with the environment by producing a darker-appearing coat.
• D) The lower temperatures in winter denature the pigment molecules in the arctic fox coat, causing the coat to become lighter in color.

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Which of the following procedures was most likely followed to determine the change in beak size?

A) A few finches were trapped in 1981 and again in 1987, and their beak sizes were compared.
• B) The beak size in fifteen finches was measured in 1987, and the beak size in the original finches was determined by estimation.
• C) The beak size in a large number of finches was measured every year from 1981 to 1987.
• D) Finches were captured and bred in 1981, and the beak size of the offspring was measured.

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Which of the following statements might best explain the increase in average beak size in the finch population during the drought?

A) Finches with bigger beaks are better able to crack thick-walled seeds and produce more surviving offspring.
• B) Finches with bigger beaks can attack and kill finches with smaller beaks.
• C) Finches with bigger beaks possess more powerful flight muscles and are able to find more food.
• D) Finches that crack large seeds develop larger beaks over time.

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Which of the following best describes the mechanism behind the change in beak size in the finch population?

A) The formation of two new finch species from a single parent species.
• B) A change in gene frequencies in the finch population due to selective pressure from the environmental change.
• C) A new allele appearing in the finch population as a result of mutation.
• D) The achievement of dynamic equilibrium in the finch population as a result of homeostasis.

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The biologist discovered that from 1988 to 1993, the average beak size declined to pre-1981 levels. The reversal in beak size from 1988 to 1993 was most likely related to which of the following events?

A) A loss of food supply for the finches
• B) The end of the drought
• C) An increase in drought conditions
• D) An increase in predators consuming finches

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Five new species of bacteria were discovered in Antarctic ice core samples. The nucleotide (base) sequences of rRNA subunits were determined for the new species. The table below shows the number of nucleotide differences between the species. Which of the following phylogenetic trees is most consistent with the data?

A) C)
• B) A
• C) B
• D) D

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Which of the following includes the most likely change in the coloration of the beetle population after pollution and a correct rationale for the change?

A) The coloration range shifted toward more light-colored beetles, as in diagram I. The pollution helped the predators find the darkened tree trunks.
• B) The coloration in the population split into two extremes, as in diagram II. Both the lighter-colored and the darker-colored beetles were able to hide on the darker tree trunks.
• C) The coloration range became narrower, as in diagram III. The predators selected beetles at the color extremes.
• D) The coloration in the population shifted toward more darker-colored beetles, as in diagram IV. The lighter-colored beetles were found more easily by the predators than were the darker-colored beetles.

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The area covered by tropical rain forest is reduced by millions of hectares per year due to agriculture and logging. Which of the following best describes a likely result of tropical rain forest deforestation?

A) Populations of plants and animals will decrease as more rain forest disappears, leading to a decrease in biodiversity.
• B) An increase of soil moisture will lead to a rapid increase in new vegetation coverage.
• C) An increase in atmospheric carbon dioxide will lead to higher levels of ultraviolet radiation reaching the surface of Earth.
• D) More oxygen will be available to other organisms as plant numbers decrease.

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The diagram above shows the progression of ecological events after a fire in a particular ecosystem. Based on the diagram, which of the following best explains why the oak trees are later replaced by other trees?

A) Eventually the other trees grow taller than the oak trees and form a dense canopy that shades the understory.
• B) Oak trees alter the pH of the soil, making the forest better suited for shrubs and other trees.
• C) Roots of shrubs proliferate in the soil of the forest and prevent the oak trees from obtaining water.
• D) Oak trees succumb to environmental pollutants more readily than do either the shrubs or the other trees.

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In most freshwater fish, nitrogenous waste is primarily excreted as ammonia, which is highly soluble in water and is toxic at low concentrations. In terrestrial mammals, ammonia is converted to urea before it is excreted. Urea is also highly soluble in water but is less toxic than ammonia at low concentrations. Which of the following best explains why freshwater fish do not convert ammonia to urea for excretion?

A) The metabolic pathways of fish do not normally involve nitrogen consumption.
• B) The dilution of ammonia by direct excretion into freshwater conserves energy.
• C) Ammonia is concentrated in tissues, where it is stored prior to excretion.
• D) The nitrogen in ammonia is recycled for use in protein and nucleotide synthesis.

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