Students investigated the effect of light on the carbon cycle in aquatic ecosystems by performing the controlled experiment summarized below. The students placed equal amounts of water (pH 7.0)  from a large aquarium in glass beakers. The students transferred aquatic plants from the aquarium to several of the beakers, and then they placed equal numbers of the beakers in the light or the dark (Figure 1: Groups I and II). Similarly, the students transferred goldfish from the same aquarium to other beakers, and then they placed equal numbers of those beakers in the light or dark (Figure 1: groups III and IV). Finally, the students placed an equal number of beakers containing water only in the light or dark (Figure 1: Groups V and VI). After exposing the samples to light or dark for one hour, the students recorded the pH of the water in each beaker. Carbon dioxide dissolved in water will lower the pH of an aqueous solution. In the experiment, the students used changes in pH to monitor changes in the amount of carbon dioxide in the water.  For each treatment group, the students calculated the mean pH and standard error, as documented in the table below. The odd-numbered groups are marked Light, and the even-numbered groups are marked Dark. Each group contains a beaker with the same amount of water. From left to right, the beakers are as follows:1, plant. 2, plant. 3, fish. 4, fish. 5, empty. 6, empty. Figure 1. Treatment groups Mean pH of Treatment Groups After 1 Hour Treatment group (n = 10) I II III IV V VI Mean pH 8.2 6.4 5.9 5.6 7.3 6.8 Standard error of the mean 0.3 0.3 0.2 0.3 0.5 0.4 Which of the following observations provides the best evidence that photosynthesis occurred in treatment group I?

There is strong evidence that two species of cliff-dwelling birds have nested in the same environment and fed in the same water for thousands of years, with each having stable population sizes. Based on this information, which of the following statements is the best conclusion?

A scientist used the amino acid sequence of cytochrome c in different species to consider evolutionary relationships. The data below summarize the number of differences in the amino acid sequences of cytochrome c found in selected species. Differences in the amino acid sequences of cytochrome c found in selected species Species Compared Number of Differences Humans – Chimpanzees 0 Humans – Rhesus monkeys 1 Humans – Horses or donkeys 7 Humans – Cows or pigs or sheep 7 Humans – Rabbits 7 Mammals – Birds and reptiles 10-15 Mammals – Fish 18-20 Animals – Plants 45-48 Interpretation of the data supports which of the following statements?

The lac operon in E. coli consists of genes that code for enzymes necessary for the breakdown of lactose. When lactose is absent, the operon is inactive because a repressor protein binds to a specific site in the lac operon. When lactose is present, lactose molecules bind to the repressor protein, causing the repressor protein to dissociate from the binding site. In the absence of glucose (a preferred energy source for bacteria), the protein CAP binds to a regulatory site near the lac promoter to activate transcription of the lac operon. The following symbols represent the macromolecules involved in regulation of the lac operon. The key indicates that an unshaded circle represents “Repressor,” two shaded hexagons connected by a line represent “Lactose,” an unshaded triangle represents “C A P,” an unshaded oval represents “R N A, polymerase,” and a squiggly line indicates “m R N A.” In the diagrams below, the horizontal line represents the lac operon and the bent arrow represents the transcription start site of the lac operon. Which of the following diagrams best represents the scenario in which lactose is available to the cell and glucose is absent?

If a population remains in Hardy-Weinberg equilibrium, what will happen to the frequency of heterozygotes over time?

True or false? “Endangered” is a more critical level of species extinction risk than “threatened.”

MRSA is the acronym for methicillin-resistant Staphylococcus aureus. Many of the strains of the common bacterium are also resistant to other antibiotics in use today. The resistance is linked to a collection of genes carried on plasmids that are passed from one bacterium to another by conjugation. Suppose a newly discovered, chemically different antibiotic is used in place of methicillin. Which of the following would be the most likely effect on Staphylococcus aureus antibiotic resistance?

Life history traits that are selected for at high population densities are called K-selected traits, or ______ traits. 

On a large volcanic island, researchers are studying a population of annual herbaceous plants. Which of the following observations best supports the prediction that speciation will occur within the existing plant population?

The graph is titled Wolf and Elk Population Sizes in Yellowstone National Park. The horizontal axis is labeled Year, and has values from left to right of 1993 to 2006. Each year is represented with a tick mark, and the years 1995, 2000, and 2006 are labeled appropriately. The left vertical axis is labeled Wolf Population and has values from bottom to top of 0 to 20 in increments of five. The right vertical axis is labeled Elk Population and has values from bottom to top of 0 to 120, in increments of 20. Two separate lines with points are shown on the graph. The first line is dashed and is labeled Elk. The second line is solid and is labeled Wolves. The approximate values of each respective line are as follows. Year, 1993; Elk Population, 90. Year, 1993; Wolf Population, 2. Year, 1994; Elk Population, 95. Year, 1994; Wolf Population, 2. Year, 1995; Elk Population, 80. Year, 1995; Wolf Population, 2. Year, 1996; Elk Population, 75. Year, 1996; Wolf Population, 6. Year, 1997; Elk Population, 60. Year, 1997; Wolf Population, 7. Year, 1998; Elk Population, 55. Year, 1998; Wolf Population, 8. Year, 1999; Elk Population, 57. Year, 1999; Wolf Population, 11. Year, 2000; Elk Population, 70. Year, 2000; Wolf Population, 10. Year, 2001; Elk Population, 60. Year, 2001; Wolf Population, 16. Year, 2002; Elk Population, 55. Year, 2002; Wolf Population, 17. Year, 2003; Elk Population, 40. Year, 2003; Wolf Population, 18. Year, 2004; Elk Population, 38. Year, 2004; Wolf Population, 22. Year, 2005; Elk Population, 44. Year, 2005; Wolf Population, 18. Year, 2006; Elk Population, 28. Year, 2006; Wolf Population, 12. Figure 1. Wolf and Elk Population Sizes in Yellowstone National Park The graph is titled Browsing of Aspen in Yellowstone National Park. The horizontal axis is labeled Year, and has values from left to right of 1993 to 2006. Each year is represented with a tick mark, and the years 1995, 2000, and 2006 are labeled appropriately. The vertical axis is labeled Percent Aspen Browsed and has values from bottom to top of 0 to 100 in increments of twenty. Two separate lines with points are shown on the graph. The first line is dashed and is labeled Riparian. The second line is solid and is labeled Uplands. The approximate values of each respective line are as follows. Year, 1998; Percent Aspen Browsed in Uplands, 98. Year, 1998; Percent Aspen Browsed in Riparian, 98. Year, 1999; Percent Aspen Browsed in Uplands, 98. Year, 1999; Percent Aspen Browsed in Riparian, 96. Year, 2000; Percent Aspen Browsed in Uplands, 96. Year, 2000; Percent Aspen Browsed in Riparian, 93. Year, 2001; Percent Aspen Browsed in Uplands, 95. Year, 2001; Percent Aspen Browsed in Riparian, 85. Year, 2002; Percent Aspen Browsed in Uplands, 93. Year, 2002; Percent Aspen Browsed in Riparian, 83. Year, 2003; Percent Aspen Browsed in Uplands, 91. Year, 2003; Percent Aspen Browsed in Riparian, 81. Year, 2004; Percent Aspen Browsed in Uplands, 87. Year, 2004; Percent Aspen Browsed in Riparian, 48. Year, 2005; Percent Aspen Browsed in Uplands, 73. Year, 2005; Percent Aspen Browsed in Riparian, 25. Year, 2006; Percent Aspen Browsed in Uplands, 65. Year, 2006; Percent Aspen Browsed in Riparian, 16. Figure 2. Browsing of Aspen in Yellowstone National Park The graph is titled Growth of Aspen in Yellowstone National Park. The horizontal axis is labeled Year, and has values from left to right of 1993 to 2006. Each year is represented with a tick mark, and the years 1995, 2000, and 2006 are labeled appropriately. The vertical axis is labeled Aspen Height in centimeters, and has values from bottom to top of 0 to 250 in increments of fifty. Two separate lines with points are shown on the graph. The first line is dashed and is labeled Riparian. The second line is solid and is labeled Uplands. The approximate values of each respective line are as follows. Year, 1998; Aspen Height in Centimeters in Uplands, 35. Year, 1998; Aspen Height in Centimeters in Riparian, 35. Year, 1999; Aspen Height in Centimeters in Uplands, 32. Year, 1999; Aspen Height in Centimeters in Riparian, 38. Year, 2000; Aspen Height in Centimeters in Uplands, 29. Year, 2000; Aspen Height in Centimeters in Riparian, 48. Year, 2001; Aspen Height in Centimeters in Uplands, 35. Year, 2001; Aspen Height in Centimeters in Riparian, 58. Year, 2002; Aspen Height in Centimeters in Uplands, 45. Year, 2002; Aspen Height in Centimeters in Riparian, 75. Year, 2003; Aspen Height in Centimeters in Uplands, 50. Year, 2003; Aspen Height in Centimeters in Riparian, 95. Year,2004; Aspen Height in Centimeters in Uplands, 70. Year, 2004; Aspen Height in Centimeters in Riparian, 135. Year, 2005; Aspen Height in Centimeters in Uplands, 90. Year, 2005; Aspen Height in Centimeters in Riparian, 180. Year, 2006; Aspen Height in Centimeters in Uplands, 120. Year, 2006; Aspen Height in Centimeters in Riparian, 225. Figure 3. Growth of Aspen in Yellowstone National Park Wolves, a top predator, were reintroduced to Yellowstone National Park in 1995 after a 50-year absence. In a multiyear study, the numbers of wolves and elk were monitored. The data are shown in Figure 1. In two different environments scientists monitored the percent of aspen trees browsed by herbivores (Figure 2) as well as the growth of the trees (Figure 3). The upland environments consist mostly of flat forested areas. The riparian environments are areas along streams with steep, wooded banks. Which of the following models best predicts the effect on the ecosystem if a deadly communicable disease is introduced into the wolf population?