Students subjected three samples of five different molecules to gel electrophoresis as shown in Figure 1. The three lanes of the gel are numbered 1, 2, and 3 for each of the three samples. Along the left side of the gel, from top to bottom, are the letters A, B, C, D, and E, representing the positions of the five molecules in the samples. A plus symbol is above the top of the gel, and a minus symbol is below the bottom of the gel. Open rectangles representing the sample loading wells are located in each lane, in a horizontal position between the letters B and C. Black rectangles in each represent the molecules in the samples. The data are as follows. In lane 1, there is a black rectangle at position A and a second black rectangle at position B. In lane 2, there is a black rectangle at position C and a second black rectangle at position D. In lane 3, there is a black rectangle at position E. Figure 1. Gel electrophoresis of three prepared samples Which of the following statements best explains the pattern seen on the gel with regard to the size and charge of molecules A and B?

_______ is the enzyme used to position nucleotides during DNA replication.

To investigate the influence of predation risk on ray behavior, a student observed and counted the large marine animals swimming in a shallow, nearshore section of a coral reef ecosystem. The time of each observation was recorded relative to the time of high tide. The student noted that at low tide, when the water level is low, many of the large animals are forced out of the study area and into the deeper waters of the outer reef. During high tides, when the water level is high, the large animals are able to reenter the study area. Over a three-day period, the student observed a total of 604 individual rays belonging to three species: cowtail rays, giant shovelnose rays, and black stingrays. For each ray that was sighted, its body length was estimated and its status as either alone (ungrouped) or found with other rays (grouped) was noted. Occasionally, rays were observed sifting through the sandy substrate of the study area to capture food items such as molluscs and crustaceans. In one instance, an injured ray with bite marks that were likely sustained in a shark attack was sighted. In addition to the rays, the student observed lemon sharks (n = 46) and blacktip reef sharks (n = 39). The results of the study are presented in the figures below. The horizontal axis is labeled “Mean Body Length, in meters,” and the numbers 0 through 1.5, in increments of 0.5, are indicated. The vertical axis gives the three categories of the graph, each of which contains two subcategories. The three categories are Cowtail Rays, Giant Shovelnose Rays, and Black Stingrays. The subcategories are Ungrouped and Grouped. The data are presented as follows. Note that all values are approximate. Cowtail Rays: Ungrouped have a mean body length of 1.5 meters, and the error bar spans plus or minus 0.03. Grouped have a mean body length of 1.35 meters, and the error spans plus or minus 0.05. Giant Shovelnose Rays: Ungrouped have a mean body length of 1.6 meters, and the error bar spans plus or minus 0.04. Grouped have a mean body length of 1.35 meters, and the error spans plus or minus 0.08. Black Stingrays: Ungrouped have a mean body length of 1.4 meters, and the error bar spans plus or minus 0.02. Grouped have a mean body length of 1.3 meters, and the error spans plus or minus 0.05. Figure 1. Comparison of mean body lengths of the grouped and ungrouped rays that were observed in a nearshore section of a coral reef ecosystem. Error bars represent 2SEx̄ The graph shows the mean number of rays per group in the study area relative to stages of the tide cycle. The horizontal axis is labeled “Time Relative to High Tide, in hours,” and the numbers negative 3 through positive 1, in increments of 1, are indicated. The vertical axis is labeled “Mean Group Size,” and the numbers 0 through 6, in increments of 1, are indicated. The line is composed of five points connected by line segments, and error bars are shown for each point. The five points are listed as follows. Note that all values are approximate. Point 1. Time relative to High Tide, negative 3 hours. Mean Group Size, 0.9 plus or minus 0 point 4. Point 2. Time relative to High Tide, negative 2 hours. Mean Group Size, 2 point 5 plus or minus 0 point 2. Point 3. Time relative to High Tide, negative 1 hours. Mean Group Size, 4 point 4 plus or minus 0 point 9. Point 4. Time relative to High Tide, 0 hours. Mean Group Size, 4 point 6 plus or minus 0 point 1. Point 5. Time relative to High Tide, positive 1 hours. Mean Group Size, 3 point 6 plus or minus 0 point 3. Figure 2. Mean numbers of rays per group in the study area at different stages of the tide cycle. High tide occurs at T = 0 hours. The graph shows the relative proportions of rays in groups at different stages of the tide cycle. A key indicates that three different lines represent giant shovelnose rays or black stingrays or cowtail rays. The horizontal axis is labeled “Time relative to High Tide, in hours,” and the numbers negative 3 through positive 1, in increments of 1, are indicated. The vertical axis is labeled “Relative Proportion of Rays Found in Groups” and has an arrowhead at the top end. The line for each type of ray is composed of five points connected by line segments, and error bars are shown for most points. The data for each time point are as follows. Point 1. Time relative to High Tide, negative 3 hours. The proportion of each type of ray is similar, and there are very few of each type. Point 2. Time relative to High Tide, negative 2 hours. The number of cowtail rays increased slightly, and there are about twice as many giant shovelnose rays and six times as many black stingrays as cowtail rays. Error bars are shown for only the cowtail rays and giant shovelnose rays. The upper end of the cowtail rays error bar touches the lower end of the giant shovelnose rays error bar. Point 3. Time relative to High Tide, negative 1 hours. The number of cowtail rays is double the number at negative two hours, and there are about three times as many giant shovelnose rays and five times as many black stingrays as cowtail rays. Error bars are shown for each point. The error bar range for the cowtail rays is very narrow; the error bars for the black stingrays and giant shovelnose rays are broad, but do not overlap. Point 4. Time relative to High Tide, 0 hours. The number of cowtail rays is about three quarters the number at negative one hours, and there are about twelve times as many giant shovelnose rays and nine times as many black stingrays as cowtail rays. The error bar range for the cowtail rays is very narrow; the error bars for the black stingrays and giant shovelnose rays are broad, and the upper end of the black stingrays error bar touches the lower end of the giant shovelnose rays error bar. Point 5. Time relative to High Tide, positive 1 hours. The number of cowtail rays is just slightly greater than the number at 0 hours, and there are about seven times as many giant shovelnose rays and five times as many black stingrays as cowtail rays. The error bar range for the cowtail rays is very narrow; the error bars for the black stingrays and giant shovelnose rays are broad, and the upper end of the black stingrays error bar touches the lower end of the giant shovelnose rays error bar. Figure 3. Relative proportions of rays in groups at different stages of the tide cycle for each of the three different populations. High tide occurs at T = 0 hours. The graph shows the mean numbers of lemon sharks and blacktip reef sharks at different stages of the tide cycle. A key indicates that one line represents lemon sharks, and the other line represents blacktip reef sharks. The horizontal axis is labeled “Time Relative to High Tide, in hours,” and the numbers negative 3 through positive 1, in increments of 1, are indicated. The vertical axis is labeled “Mean Number of Sharks,” and the numbers 0 through 10, in increments of 1, are indicated. The two curves are composed of five points connected by line segments. No error bars are shown. The five points of each line are listed as follows. Note that all values are approximate. The following five points are indicated on the line representing lemon sharks. Point 1. Time relative to High Tide, negative 3 hours. Mean Number of Sharks, 4.2. Point 2. Time relative to High Tide, negative 2 hours. Mean Number of Sharks, 9. Point 3. Time relative to High Tide, negative 1 hours. Mean Number of Sharks, 1.5. Point 4. Time relative to High Tide, 0 hours. Mean Number of Sharks, 0. Point 5. Time relative to High Tide, positive 1 hours. Mean Number of Sharks, 1. The following five points are indicated on the line representing blacktip reef sharks. Point 1. Time relative to High Tide, negative 3 hours, Mean Number of Sharks, 0.3. Point 2. Time relative to High Tide, negative 2 hours, Mean Number of Sharks, 0.3. Point 3. Time relative to High Tide, negative 1 hour, Mean Number of Sharks, 4. Point 4. Time relative to High Tide, 0 hours, Mean Number of Sharks, 7. Point 5. Time relative to High Tide, positive 1 hour, Mean Number of Sharks, 9. Figure 4. Mean numbers of lemon sharks and blacktip reef sharks in the study area at different stages of the tide cycle. High tide occurs at T = 0 hours. Which of the following best justifies the use of the study area to investigate how one species influences the behavior of another?

The lionfish is a venomous fish found primarily in the Red Sea and the Indian Ocean. In the 1990s, lionfish were accidentally released into the Atlantic Ocean, where they found abundant resources and favorable environmental conditions. Which of the following scenarios is most likely to result in the lionfish having a major impact on the communities into which they were introduced?

The fossils in a layer of rock are significantly different from those in the rock layer directly above it. One hypothesis to explain the difference is that a major extinction event occurred at the point in time represented by the transition between the two rock layers. Which of the following is the best plan for collecting data to use in a test of the hypothesis?

The horizontal axis is labeled Species Present, and the vertical axis is labeled Nitrogen Influx in kilograms per year. On the horizontal axis, from left to right, there are evenly spaced tick marks labeled N, B, S, and S B. The vertical axis has evenly spaced tick marks labeled 300 through 600,in increments of 100. The pointover N is at about 375. Its error bar extends from about 350 to about 425. The pointover B is centered at about 375. Its error bar extendsfrom about 360 to about 405. The pointover S is centered at about 430. Its error bar extends from about 410 to about 470. The pointover S B is centered at about 510. Its error bar extendsfrom about 500 to about 530. The caption on the figure reads: Figure 1. Mean nitrogen influx plus or minus 2 times the standard error of the mean as a function of species present. N equals neither salmon nor bears present, B equals only bears present, S equals only salmon present, and S B equals both salmon and bears present. Figure 1. Mean nitrogen influx ±2SEẍ as a function of species present. N = neither salmon nor bears present, B = only bears present, S = only salmon present, and SB = both salmon and bears present. Pacific salmon and black bears have often been cited as examples of keystone species. Pacific salmon spawn in freshwater streams but spend most of their lives at sea. When mature salmon return to the freshwater streams to spawn, they are preyed upon by bears and other predators. When salmon migrate from their marine habitat to the freshwater streams, they bring nitrogen and other marine-derived nutrients that subsequently remain in the areas surrounding the streams—a process called nitrogen influx. In an investigation, the relationship between black bears, salmon, and influx of marine nitrogen into the area around a southwestern Alaskan stream was studied. The investigators established several test plots of the same size along the stream with the following species composition: no salmon or black bears (N), bears but not salmon (B), salmon but not bears (S), and a plot where salmon and bears interact (SB). Nitrogen influx in the different sampling areas was measured as a means of assessing the impact of the different species on the health of the ecosystem. The data are plotted in Figure 1. If a dam is built downstream and prevents salmon migration to the test sites, which of the following most accurately predicts the impact on nitrogen influx?

Phenotype is determined, in part, by which genes are expressed. The diagram below illustrates how the product of gene X regulates the expression of other genes. At the top of the figure is a rectangle in which the middle 60 percent is unshaded, and each end is shaded. The rectangle is labeled “Gene X.” An arrow points from Gene X to a squiggly line with an arrowhead labeled “3 prime” at one end. The other end of the line is labeled “5 prime.” Another arrow leads from the squiggly line to a coiled line labeled “Protein X.” Shown below Protein X are four rectangles, each of which is unshaded in the middle and shaded at each end. From left to right, the rectangles are labeled “Gene 1,” “Gene 2,” “Gene 3,” and “Gene 4”. Arrows point from Protein X to Gene 1, Gene 2, and Gene 4, and the Protein X symbol is superimposed on the left shaded area of Gene 1, Gene 2, and Gene 4. Arrows point from Gene 1, Gene 2, and Gene 4 to squiggly lines below each of the genes. Each of the squiggly lines has an arrowhead labeled “3 prime” at one end. The other end of each line is labeled “5 prime.” Nothing is present below the rectangle labeled Gene 3. Which of the following statements best explains how protein X regulates gene expression?

The graph below shows changes in a population of wild sheep that were introduced to the island of Tasmania in the early 1800’s. The horizontal axis is labeled year from 1820 to 1940 with tick marks in increments of ten. The vertical axis is labeled number of sheep in thousands from zero to two thousand five hundred, with tick marks in increments of 500. The population curve starts at zero in 1820, increases slowly then increases rapidly to two point two five million by 1850. This increase is enclosed in a bracket. After 1850 the population curve fluctuates between two point two five million and one point two five million, with a horizontal dashed line through the middle of these population fluctuations. The type of population growth represented by that portion of the graph line enclosed in the bracket is most accurately termed

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?

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. The single colony found within the clear ring in plate I is most likely made up of the descendants of a bacterial cell that