The food web consists of the following 9 organisms or groups of organisms, from bottom to top and left to right: Plants, Squirrels, Mice, Insects, Spiders , Insectivorous Birds, Foxes, and Hawks and Owls, Snakes. From bottom to top, the food web is organized as follows. From Plants, arrows extend to Squirrels, Mice, and Insects. From Squirrels, arrows extend to Foxes, and Hawks and Owls. From Mice, arrows extend to Hawks and Owls, and Snakes. From Insects, arrows extend to Spiders, and Insectivorous Birds. From Spiders, an arrow extends to Insectivorous Birds. From Insectivorous Birds, arrows extend to Hawks and Owls, and Snakes. Which of the following changes to the environment will most likely lead to more energy entering the meadow community represented above?

A model that represents a process occurring in a cell of a particular organism is shown in Figure 1. where the two strands in the middle portion of the helix have separated from each other. Twelve bases are indicated on each of the two strands. Seven complementary bases, with the sequence A U G A U C U, are shown bound to the bottom of the two DNA strands, starting from the left end of the strand. An arrow above the seven bases points from left to right. Figure 1. Process occurring in a cell Which of the following correctly explains the process shown in Figure 1?

A fish population of 250 in a pond has a maximum annual rate of increase of 0.8. If the carrying capacity of the pond is 1,500 for this species, what is the expected population size after one year?

Iron is an essential nutrient that is acquired by organisms from the environment. When intracellular levels of iron are relatively high, living cells synthesize an iron-storage protein called ferritin. The induction of ferritin synthesis by iron was investigated in rats. Figure 1 shows the results of an experiment in which cellular levels of ferritin protein were measured in the presence or absence of iron and actinomycin D, a drug that inhibits transcription. Figure 2 shows the results of an experiment in which cellular levels of ferritin protein were measured in the presence or absence of iron and cycloheximide, a drug that inhibits translation. The horizontal axes are labeled Treatment, and the vertical axes are labeled Relative Protein Level. Five tick marks appear on the vertical axis, from bottom to top, the first tick mark is labeled zero, the third tick mark is labeled one point zero, and the fifth tick mark is labeled two point zero. The graph on the left is labeled Figure one. Ferritin Protein Levels. Four vertical bars appear along the horizontal axis, and the presence or absence of Iron and Actinomycin D is indicated above each bar. The data in the graph, from left to right, are as follows: Bar 1: Absence of Iron; Absence of Actinomycin D; Relative Protein Level one point zero. Bar 2: Presence of Iron; Absence of Actinomycin D; Relative Protein Level two point two. Bar 3: Absence of Iron; Presence of Actinomycin D; Relative Protein Level zero point nine. Bar 4: Presence of Iron; Presence of Actinomycin D; Relative Protein Level two point zero. The graph on the right is labeled Figure 2. Ferritin Protein Levels. Four vertical bars appear along the horizontal axis, and the presence or absence of Iron and Cycloheximide is indicated above each bar. The data in the graph, from left to right, are as follows: Bar 1: Absence of Iron; Absence of Cycloheximide; Relative Protein Level one point zero. Bar 2: Presence of Iron; Absence of Cycloheximide; Relative Protein Level two point five. Bar 3: Absence of Iron; Presence of Cycloheximide; Relative Protein Level zero point nine. Bar 4: Presence of Iron; Presence of Cycloheximide; Relative Protein Level zero point nine. In individuals with iron-rich diets, intracellular levels of iron are higher than in individuals with iron-poor diets. Which of the following best explains how organisms regulate ferritin protein levels in response to available iron?

The cladogram shown below depicts an accepted model of the evolutionary relationships among selected species. The figure shows a cladogram with the root at the bottom left and three branches. From left to right, the branches are as follows: Horse, with a point labeled W; Gorilla, with a point labeled X, and Human, with a point labeled Y. Past the branches, the main line is labeled Chimpanzee, with a point labeled Z. The amino acid at position 104 in the beta-hemoglobin protein for each of these four organisms is listed below. Amino acid at position 104 in the beta-hemoglobin protein Species Amino Acid 104 Horse Arginine Gorilla Leucine Human Arginine Chimpanzee Arginine The validity of the cladogram is best supported by molecular evidence for which of the following changes in the amino acid composition of the beta-hemoglobin protein during the evolution of these species?

Rhagoletis pomonella is a parasitic fly native to North America that infests fruit trees. The female fly lays her eggs in the fruit. The larvae hatch and burrow through the developing fruit. The next year, the adult flies emerge. Prior to the European colonization of North America, the major host of Rhagoletis was a native species of hawthorn, Crataegus marshallii. The domestic apple tree, Malus domestica, is not native to North America, but was imported by European settlers in the late 1700s and early 1800s. When apple trees were first imported into North America, there was no evidence that Rhagoletis could use them as hosts. Apples set fruit earlier in the season and develop faster, where hawthorns set later and develop more slowly. Recent analysis of Rhagoletis populations has shown that two distinct populations of flies have evolved from the original ancestral population of flies that were parasitic on hawthorns. One population infests only apple trees, and the other infests only hawthorns. The life cycles of both fly populations are coordinated with those of their host trees. The flies of each population apparently can distinguish and select mates with similar host preferences and reject mates from the population specific to the other host tree. There is very little hybridization (only about 5 percent) between the two groups. The divergence between the two populations of Rhagoletis must have occurred very rapidly because

The bottom row consists of grasses, bush, and tree. The second row from the bottom consists of squirrel, grasshopper, and rabbit. The third row from the bottom consists of a shrew. The fourth row from the bottom consists of a hawk, snake, insect eating bird, and deer. The top row consists of a lion. From the tree, arrows extend to the deer and squirrel. From the bush, arrows extend to the squirrel, grasshopper, rabbit, and deer. From the grasses, arrows extend to the grasshopper and rabbit. From the squirrel, an arrow extends to the hawk. From the grasshopper, arrows extend to the shrew and insect eating bird. From the rabbit, arrows extend to the snake and lion. From the insect eating bird, an arrow extends to the hawk. From the deer, an arrow extends to the lion. From the snake, arrows extend to the lion and hawk. From the shrew, arrows extend to the snake, hawk, and lion. The food web represented above does not include bacteria and fungi. Which of the following best describes a consequence of having no bacteria and fungi in the food web?

Methicillin-resistant Staphylococcus aureus (MRSA) can be a serious threat to human health. There is evidence that S. aureus infections are common in hospitals and that MRSA have become resistant to other antibiotics besides methicillin. This suggests that the rapid evolution of resistance in the bacteria poses a serious public-health challenge. Which of the following best explains the ability of MRSA to evade existing drug therapies?

The enzyme lactase aids in the digestion of lactose, a sugar found in the milk of most mammals. In most mammal species, adults do not produce lactase. Continuing to produce lactase into adulthood in people is called lactase persistence. A number of different alleles have been identified that result in lactase persistence. Figure 1 shows the percentage of people in different geographic areas parts of the Old World that exhibit lactase persistence. of Europe, most of Africa, and parts of Asia with distributions of 5 ranges of percent of lactase persistence across the regions. The ranges of percent are 81 to 100 percent, 61 to 80 percent, 41 to 60 percent, 21 to 40 percent, and 0 to 20 percent. The smallest portion of the map is in the 81 to 100 percent range and represents all of the United Kingdom, Denmark, small regions of southern Sweden, and small parts of western Norway. A small portion of the map is in the 61 to 80 percent range and represents most of northern Europe, including the rest of Sweden, Norway, regions of Finland, Estonia, Latvia, Lithuania, Northern Germany, Northern France, and also Senegal in Africa. A large portion of the map is in the 41 to 60 percent range and represents the rest of Western Europe, central Africa, Saudi Arabia, Yemen, Oman, the United Arab Emirates, Qatar, and Pakistan. The largest portion of the map is in the 21 to 40 percent range and represents northern and southern Africa, Turkey, Syria, Iraq, Jordan, Israel, Palestine, parts of Iran, Turkmenistan, Uzbekistan, and almost all of Russia. A small portion of the map is in the 0 to 20 percent range and represents a small region in western Russia, a large portion of Kazakhstan, and southern Spain. Figure 1. Distribution of lactase persistence in Europe, North Africa, and parts of Asia Which of the following best explains the distribution of lactase persistence in the areas shown in Figure 1 ?

The table below describes the action of two genes involved in the regulation of nervous system development in the nematode C. elegans. C. elegans nervous system regulation genes Gene A Gene B Observation Pattern 1 Inactive Inactive No neurons develop Pattern 2 Inactive Active No neurons develop Pattern 3 Active Inactive Greater-than-normal number of neurons develop Pattern 4 Active Active Normal number of neurons develop Which of the following claims is best supported by the data?