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. Which of the following statements is best supported by the data?

Gibberellic acid stimulates the cells of germinating grass seeds to produce mRNA molecules that code for hydrolytic enzymes. In this case the role of gibberellic acid can best be described as that of

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?

Two groups of students attempted to re-create the primitive atmospheric conditions of early Earth using the apparatus represented below. Each group ran the experiment with different gas mixtures in the apparatus. The two apparatuses are the same except for the gases being used. The apparatuses are as follows, from top left clockwise: there is a horizontal pipe with an arrow pointing to the right. The pipe bends down into a round area labeled Gases. There are two wires carrying electric current into the gases, and a label indicating Spark Discharge where the wires enter the round area. From there, a pipe continues down through a condenser, with an arrow pointing straight down next to the pipe. Water Out to the right is indicated at the top of the condenser, and Water In to the left is indicated at the bottom of the condenser. Below the condenser, the pipe continues and there is another arrow pointing straight down. The pipe then curves to the left and bends around a trap, which is labeled Water Containing Organic Compounds. The pipe continues to the left to a round area labeled Boiling Water. The pipe continues up from there, and there is an arrow next to it pointing straight up. There is a branch in the pipe about halfway up the left side of the apparatus, labeled To Vacuum Line, with an arrow pointing to the left. The pipe continues past the branch to where it started. The Gases area in Experiment 1 is labeled: N 2, C H 4, N H 3, H 2 O, and C O 2. The Gases area in Experiment 2 is labeled: S O 2, H 2 S, H 2 O, C H 4, and C O 2. Which of the following statements best justifies the claim that the conditions in at least one of the experiments could generate the molecular building blocks essential for life?

with regulatory sequences P and O preceding the structural genes B, A and D in order. The regulatory sequences of the operon controlling arabinose metabolism (ara operon) were studied to determine whether bacteria can respond to changes in nutrient availability. It is predicted that if those regulatory sequences are functioning properly, the bacteria will produce the enzymes involved in arabinose metabolism (structural genes B, A, and D) in the presence of arabinose. If a gene that encodes a green fluorescent protein (GFP) is substituted for the structural genes of the operon, activation of the regulatory sequences can be assayed by GFP expression. A culture of E. coli cells underwent a transformation procedure with a plasmid containing the regulatory sequences of the ara operon directly upstream of the gene encoding the GFP. The plasmid also confers ampicillin resistance to bacteria. Samples were then plated on different types of culture media. (Note: The GFP fluoresces only under UV light, not under white light.) The table below shows the results. The title of the table is Transformation Results. The table has a legend: the sign plus indicates the presence of the indicated substance in the culture media; the sign minus indicates the absence of the indicated substance in the culture media. The top row contains the column labels: column one, Type of Culture Media; column two, Color of Colonies Under White Light; column three, Color of Colonies Under U V Light. The 3 sub-columns under the first column Type of Culture Media are: sub-column one, Agar; sub-column two, Ampicillin; sub-column three, Arabinose. From left to right the data is as follows: Row two: Type of Culture Media: Agar, present; Ampicillin, absent; Arabinose, absent; Color of Colonies Under White Light, All white; Color of Colonies Under U V Light, All white. Row three: Type of Culture Media: Agar, present; Ampicillin, present; Arabinose, absent; Color of Colonies Under White Light, All white; Color of Colonies Under U V Light, All white. Row four: Type of Culture Media: Agar, present; Ampicillin, absent ; Arabinose, present; Color of Colonies Under White Light, All white; Color of Colonies Under U V Light, Mostly white, some green. Row five: Type of Culture Media: Agar, present; Ampicillin, present; Arabinose, present; Color of Colonies Under White Light, All white; Color of Colonies Under U V Light, All green. Which of the following can best be used to justify why the GFP is expressed by E. coli cells after transformation with the plasmid?

The three-spined stickleback (Gasterosteus aculeatus) is a small fish found in both marine and freshwater environments. Marine stickleback populations consist mostly of individuals with pronounced pelvic spines, as shown in Figure 1. Individuals in freshwater stickleback populations, on the other hand, typically have reduced pelvic spines, as shown in Figure 2. Each figure shows an image of a stickleback fish with a genetic structure below it. The left figure is labeled Figure 1. Marine stickleback. A long Pelvic Spine on the fish is labeled. The genetic structure below the fish contains three enhancers, a promoter, and a gene. From left to right, the Enhancer Sequences are labeled Hindlimb, Pituitary, and Jaw. To the right of the Enhancer Sequences is a Promoter with an arrow moving up and to the right, over the top of the Pitx1 gene. The right figure is labeled Figure 2. Freshwater stickleback. A short Pelvic Spine on the fish is labeled. The genetic structure below the fish contains three enhancers, a promoter, and a gene. From left to right, the Enhancer Sequences are labeled Hindlimb, Pituitary, and Jaw. The Hindlimb enhancer is crossed out with an X, and it is labeled Disabled Due to Mutation. To the right of the Enhancer Sequences is a Promoter with an arrow moving up and to the right, over the top of the Pitx1 gene. As represented in Figure 1 and Figure 2, the phenotypic difference between marine and freshwater sticklebacks involves Pitx1, a gene that influences the formation of the jaw, pituitary gland, and pelvic spine. Enhancer sequences upstream of the Pitx1 genetic locus regulate expression of the Pitx1 gene at the appropriate times and in the appropriate tissues during development. Previous studies have found that a mutation in the hindlimb enhancer interferes with the formation of a pronounced pelvic spine. In sticklebacks, which of the following is most likely to occur if the jaw enhancer is disabled instead of the hindlimb enhancer?

Which of the following is an example of a density-independent limitation on a population?

The diagram below illustrates the results of electrophoresis of DNA sequences obtained from a family of two adults and three children, and amplified using PCR. The bands represent short repeating sequences of variable length. Results for another female (X) are included for comparison. Beginning with the origin there are six lengths of DNA fragments that have separated on the gel. For each fragment the individual that has a band at that basepair length on their gel will be listed. The largest fragment, fragment one: father, child one. Fragment two: child three. Fragment three: mother, child one, child two, X. Fragment four: X. Fragment five: father, child two, child three. Fragment six: mother. Which of the following is the best explanation for the fragment pattern for individual X ?

A new mutation that arose in one copy of gene X in a somatic cell resulted in the formation of a tumor. Which of the following pieces of evidence best describes how the new mutation directly caused the tumor?

Both liver cells and lens cells have the genes for making the proteins albumin and crystalline. However, only liver cells express the blood protein albumin and only lens cells express crystalline, the main protein in the lens of the eye. Both of these genes have enhancer sequences associated with them. The claim that gene regulation results in differential gene expression and influences cellular products (albumin or crystalline) is best supported by evidence in which of the following statements?