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There are two small black, shaded circles on the plate. The one on the left is labeled A and is surrounded by an unshaded circle on the agar. There is also another small black dot next to the circle. The other circle is labeled P and has no other visible change on the agar. A sterile agar plate, I, is streaked with a pure culture of bacteria by means of aseptic techniques. Paper discs treated with the antibiotics Aureomycin (A) and penicillin (P) are placed at opposite sides of the plate, as shown in the diagram above. The plate is examined after a 24-hour incubation period, and a clear ring is discovered around disc A, but not around disc P. Within the clear ring around disc A, a single bacterial colony with physical characteristics like those of the pure culture is observed. A second sterile agar plate, II, is then streaked with this single colony and also incubated with antibiotics. Which of the following would most likely be observed in plate II after 24 hours?

Researchers investigated the habitat preferences of two species of garter snakes, Thamnophis sirtalis and Thamnophis atratus. To create a choice chamber, the researchers built a meshed enclosure and positioned one end of the enclosure at the edge of a small pond. Zone I of the enclosure was located in the water, whereas zone IV of the enclosure was located 2–3 meters away from the water, as represented in the figure below. Snakes inside the enclosure were able to move freely between zones. From left to right, the zones are labeled 4 through 1. The side length of each square is 1 meter. A large semicircular shaded region, labeled “Pond,” completely covers square 1 and a very small part of square 2. The “Pond” region also extends beyond square 1 to the outside of the enclosure. In a series of experiments, the researchers introduced a single snake into zone IV of the enclosure at 7:00 A.M. The researchers recorded the location of the snake at six time points throughout the day. In a related experiment, the researchers introduced two snakes, one of each species, into the enclosure at the same time and observed the location of each of the two snakes at the same six time points as before. The researchers repeated both the one-snake and two-snake experiments using different individual snakes of each species. The results are presented in the table. The title of the table is ZONES MOST FREQUENTLY OCCUPIED BY GARTER SNAKES IN A MESHED ENCLOSURE. The top row contains the column labels, from left to right: column one, Time of Day; column two, Zone Most Frequently Occupied by T. atratus; column three, Zone Most Frequently Occupied by T. sirtalis; column four, Zone Most Frequently Occupied by T. Both species of garter snakes prey on the California newt, Taricha torosa, a small amphibian that produces a potent neurotoxin (TTX) in its skin. However, neither species of garter snake is affected by TTX. The resistance to TTX is associated with mutations in the SCN4A gene. Which of the following best supports a claim that TTX resistance arose independently in T. atratus and T. sirtalis?

Which of the following statements correctly describes a typical trend during the initial stages of succession in a terrestrial ecosystem?

The TAS2R38 gene encodes a receptor protein that influences the ability to taste bitterness. The gene has two alleles: a dominant, wild-type allele that enables an individual (taster) to taste bitterness and a recessive, mutant allele that interferes with the ability of an individual (nontaster) to taste bitterness. Three single nucleotide mutations in the coding region of the TAS2R38 gene are associated with the nontaster allele. The nucleotides present at the three positions are shown in the table below. The table shows the position in the Nucleotide Sequence for different species. The data are as follows. Human nontaster; 145, G; 785, T; 886, A. Human taster; 145, C; 785, C; 886, G. Bonobo; 145, C; 785, C; 886, G. Chimpanzee; 145, C; 785, C; 886, G. Gorilla; 145, C; 785, C; 886, G. A cladogram representing the evolutionary relatedness of selected primates is shown below. From left to right, the branches are as follows: Orangutan, Gorilla, and Chimpanzee. Past the branches, the main line is labeled Human. Another branch, labeled Bonobo, is connected to the Chimpanzee branch. The TAS2R38 receptor protein has been detected on the surface of cells from individuals who are homozygous for the nontaster allele of the TAS2R38 gene. Which of the following is the most likely effect of the mutations associated with the nontaster allele on TAS2R38 gene expression?

Scientists are studying the two primary vocalizations made by Belding’s ground squirrels (Urocitellus beldingi). The trill call consists of a series of medium-pitched notes given rapidly, while the whistle call consists of a single high-pitched note. The objective of the experiment is to determine the function of each vocalization. Recordings of the calls were played to four different groups of squirrels, and the response of each individual squirrel was documented. The responses are summarized in Table 1. Table 1. Response of ground squirrels to recorded vocalizations Column 1 contains row headers for Groups A through D. The data presented in columns 2 through 9 represent the percentage of Squirrels responding. In columns 2 through 5, the data presents responses for the Trill Alarm Call. In columns 6 through 9, the data presents responses for the Whistle Alarm Call. For each type of Alarm Call, the following four response types are given: Crouching; Posting (standing on hind legs); Run to shelter; and Other or no response. There are 4 rows of data which are presented as follows. Row 1, Group A. Trill Alarm Call. Crouching, 12 percent. Posting, 65 percent. Run to shelter, 22 percent. Other, 1 percent. Trill Alarm Call. Crouching, 42 percent. Posting, 2 percent. Run to shelter, 51 percent. Other, 5 percent. Row 2, Group B. Trill Alarm Call. Crouching, 9 percent. Posting, 58 percent. Run to shelter, 31 percent. Other, 2 percent. Trill Alarm Call. Crouching, 38 percent. Posting, 0 percent. Run to shelter, 60 percent. Other, 2 percent. Row 3, Group C. Trill Alarm Call. Crouching, 15 percent. Posting, 64 percent. Run to shelter, 18 percent. Other, 3 percent. Trill Alarm Call. Crouching, 48 percent. Posting, 4 percent. Run to shelter, 44 percent. Other, 4 percent. Row 4, Group D. Trill Alarm Call. Crouching, 11 percent. Posting, 66 percent. Run to shelter, 21 percent. Other, 2 percent. Trill Alarm Call. Crouching, 1 percent. Posting, 1 percent. Run to shelter, 57 percent. Other, 1 percent. Which of the following correctly identifies the dependent variable and the independent variable for the experiment?

The horizontal axis is labeled Years of Study, and the numbers appearing on it, from left to right, are one through 22 in increments of 1. The left side of the vertical axis is labeled Proportion of Population Infected and the right side of the vertical axis is labeled Relative Population Size. The numbers appearing on each vertical axis, from bottom to top, are zero, zero point 2, zero point 4, zero point 6, zero point 8, and one point zero. Below the graph is a key indicating the solid line represents Proportion of Population Infected, and the dashed line represents Relative Population Size. A dashed line representing Relative Population Size begins on the vertical axis at one point zero and moves slightly down and to the right until about 8 years of study where it then moves more gradually down and to the right to approximately zero point six along the vertical axis at 11 years of study. The dashed line continues to the right through 14 years of study and then begins to move gradually up and to the right at 15 years of study. The line begins to move horizontally with a slight vertical increase at zero point nine along the vertical axis and at 19 years of study, until it ends at zero point nine eight along the vertical axis at 22 years of study. A solid line representing Proportion of Population Infected begins on the vertical axis at approximately zero point three eight and moves slightly up and to the right until about 8 years of study where it then moves more gradually up and to the right to approximately zero point seven eight along the vertical axis and 11 years of study. The solid line continues to the right with a slight vertical increase through 14 years of study and then begins to move gradually down and to the right at 15 years of study. The line begins to move horizontally with a slight vertical decrease right at zero point four two along the vertical axis and at 19 years of study, until it ends at zero point four along the vertical axis at 22 years of study. Chytridiomycosis is a potentially lethal fungal infection that adversely affects some frog populations. The incidence and severity of the fungal infection can vary over time. Which of the following statements best describes the changes in the frog population that are depicted in the model above?

In Darwinian terms, the fittest individuals of a species are those that

Table 1 shows a trend of increasing milk yield for cows. Part of the increase in milk production can be attributed to improved nutrition and health protocols for dairy cows. Table 1. Average milk production per cow (in kilograms per cow per year) Year Average Annual Milk Production (kg/cow) 1924 2,300 1937 2,300 1950 2,600 1963 3,400 1976 4,800 1989 6,400 2002 8,400 2015 10,000 Based on the information provided, which of the following best describes the source of the rapid increase in milk production from 1976 to 2015?

The graph below illustrates a logistic growth curve for a population of Euglena. with x-axis labeled time in days from zero to twenty, and y-axis labeled population size in organisms per milliliter. The growth curve starts with a population just above zero at zero days and increases exponentially to three-hundred organisms per milliliter at day ten, then flattening out and remaining at three-hundred. There is a point labeled Q on the curve at day twenty. The population density at point Q indicates that

By discharging electric sparks into a laboratory chamber atmosphere that consisted of water vapor, hydrogen gas, methane, and ammonia, Stanley Miller obtained data that showed that a number of organic molecules, including many amino acids, could be synthesized. Miller was attempting to model early Earth conditions as understood in the 1950s. The results of Miller’s experiments best support which of the following hypotheses?