Ultraviolet (UVUV) radiation can damage DNADNA by breaking weak bonds. Which of the following best explains how this occurs?

UVUV radiation disrupts the double helix structure by breaking the hydrogen bonds between the nitrogenous base pairs.

If 30%30% of the nucleotides in a single-stranded RNARNA molecule are adenine, then what percent are expected to be thymine?

0%

Prokaryotic and eukaryotic cells generally have which of the following features in common?

Ribosomes

Which of the following processes is most likely to occur as a result of an animal cell receiving a signal to initiate apoptosis?

Lysosomes will release digestive enzymes into the cytosol.

The primary function of the kidney is to exchange molecules across a membrane between the blood and the urine. One type of kidney cell has a basic rectangular shape, except for a single surface, which is lined with tiny, finger-like projections that extend into the surrounding extracellular space.

Which of the following best explains the advantage these projections provide the cell?

The projections increase the surface area–to-volume ratio of the cell, which allows for more efficient nutrient exchange with the environment.

Which of the following describes the most likely location of cholesterol in an animal cell?

Embedded in the plasma membrane

Which of the following best explains how the phospholipid bilayer of a transport vesicle contributes to cellular functions?

The phospholipid bilayer allows the vesicle to fuse with the Golgi apparatus and the plasma membrane, allowing the exocytosis of proteins.

Which of the following accurately describes a model of active transport?

A membrane protein binds a specific molecule outside of the cell and moves the molecule into the cell where there is already a high concentration of the molecule compared with the outside.

If ATP breakdown (hydrolysis) is inhibited, which of the following types of movement across cell membranes is also inhibited?

Passage of a solute against its concentration gradient

The following question refer to the graph below, which illustrates the percent change in the mass of pieces of plant tissue placed in solutions of different sucrose molarities.

Water enters and leaves the plant cells primarily by

osmosis

What evolutionary advantage does compartmentalization of core metabolic processes offer eukaryotes?

Evolution of a nucleus in eukaryotes separates the processes of transcription and translation and they can be regulated separately.

Which of the following groups of cellular components are found in eukaryotic cells but not prokaryotic cells?

An endoplasmic reticulum, mitochondria, and a nucleus

Which of the following can be used to determine the rate of enzyme-catalyzed reactions?

Rate of disappearance of the substrate

A student is investigating photosynthesis in plants. The student planted grass seeds in a tray with three sections and grew the grass under artificial lights for 1414 days (Figure 1). After 1414 days, the student collected all of the grass from section II and recorded its mass (Table 1). The student then placed a clear cover over section IIII and placed an aluminum foil cover over section IIIIII (Figure 2). The student then placed the tray back under the artificial lights for seven additional days. On day 2121, the student collected and measured the mass of the grass from sections IIII and IIIIII (Table 1).

TABLE 1. MASS OF GRASS GROWN IN EACH SECTION

SectionDay Mass was MeasuredMass (gg)II145.1IIII219.6IIIIII214.2

Which of the following best explains the connection between energy, growth, and the maintenance of an ordered system in the experiment?

Energy input from light is required for the grass to grow and maintain an ordered structure.

Which of the following is an important difference between light-dependent and light-independent reactions of photosynthesis?

The light-dependent reactions produce ATP and NADPH; the light-independent reactions use energy stored in ATP and NADPH.

ATP serves as a common energy source for organisms because

its energy can be easily transferred to do cellular work

Insulin is a protein hormone that is secreted in response to elevated blood glucose levels. When insulin binds to its receptors on liver cells, the activated receptors stimulate phosphorylation cascades that cause the translocation of glucose transporters to the plasma membrane.

Based on the information provided, which of the following best describes the role of insulin in this liver cell signal transduction pathway?

It acts as a ligand.

Which of the following statements best describes how a growth factor stimulates cell division from outside a cell?

The growth factor binds to receptors on the cell surface, initiating a signal transduction pathway that activates specific target genes.

The binding of erythropoietin to the erythropoietin receptor (EPoREPoR) stimulates intracellular signaling in certain cells, which causes them to differentiate to red blood cells. The EPoREPoR is a transmembrane protein with two cytoplasmic domains, each of which is bound by a kinase protein, JAK2JAK2. The binding of erythropoietin to the EPoREPoR causes the cytoplasmic domains of the EPoREPoR to undergo conformational changes that activate the bound JAK2JAK2 kinases. The JAK2JAK2 kinases then phosphorylate several intracellular proteins, including STAT5STAT5, whose resulting activity causes the cells to differentiate to red blood cells.

Which of the following explains how a mutation that removes a portion of each cytoplasmic domain of EPoREPoR most likely affects differentiation of the cells?

STAT5STAT5 will not be activated because it will not be phosphorylated by the JAK2JAK2 kinases.

Ethylene gas is an organic molecule that serves many cell signaling roles in flowering plants. Which of the following best explains how a positive feedback mechanism involving ethylene works?

Cells of ripening fruit produce ethylene, which activates the ripening response in other fruit cells.

During mitosis, which of the following normally occurs?

Replicated chromosomes line up on the equatorial plate.

Which of the following occurs during mitosis but not during meiosis I ?

The chromatids of each chromosome are separated.

Which of the following best explains why triploid bananas do not produce seeds?

The production of gametes is disrupted because of unequal pairing of homologous chromosomes during meiosis.

A blue-flowered African violet of unknown ancestry self-pollinated and produced 50 seeds. These seeds germinate and grow into flowering plants. Of these plants, 36 produce blue flowers and 14 produce pink flowers. What is the best explanation for the pink-flowered offspring?

Pink flower color is a trait recessive to blue flower color.

Gregor Mendel’s pioneering genetic experiments with pea plants occurred before the discovery of the structure and function of chromosomes. Which of the following observations about inheritance in pea plants could be explained only after the discovery that genes may be linked on a chromosome?

Most offspring of a given cross have a combination of traits that is identical to that of either one parent or the other.

In the spring and summer, the fur of an arctic fox contains a pigment called melanin that gives the fox’s fur a dark color. In the fall and winter, the fur of the arctic fox is white.

Which of the following most likely explains how the changing seasons result in changing fur color in an arctic fox?

Environmental factors cause changes in gene expression, resulting in seasonal variations in pigment production.

Which of the following occurs in all species of living organisms and may lead to an increase in genetic variation?

Mutations in the genome

Which of the following best describes a characteristic of DNADNA that makes it useful as hereditary material?

Nucleotide bases in one strand can only be paired with specific bases in the other strand.

Which of the following best explains why ligase is required for DNADNA replication?

The lagging strand cannot be replicated continuously, and ligase is needed to join the fragments.

Which of the following best explains how the expression of a eukaryotic gene encoding a protein will differ if the gene is expressed in a prokaryotic cell instead of in a eukaryotic cell?

The protein will be made but will not function, because prokaryotes cannot remove introns.

Beta thalassemia is a disorder caused by mutations in the HBB gene. Examination of the HBBHBB protein in an individual with beta thalassemia shows that the protein is missing many amino acids at its carboxyl terminus.

Which of the following is the most likely explanation for how a mutation in the DNADNA could result in the loss of the carboxyl terminus of the HBBHBB protein?

The mutation changes a codon in the coding region of the HBB transcript to a stop codon such that translation terminates earlier than it should.

Which of the following best explains how the prokaryotic expression of a metabolic protein can be regulated when the protein is already present at a high concentration?

Repressor proteins can be activated and bind to regulatory sequences to block transcription.

Dystrophin is a protein that is expressed in certain muscle cells. In combination with other cellular proteins, dystrophin strengthens protein fibers in muscle cells to allow muscles to contract without injury.

Nucleotide deletions in the gene that encodes dystrophin are associated with the genetic disorder Duchenne Muscular Dystrophy (DMDDMD). Individuals with DMDDMD do not produce functional dystrophin and, as a result, the protein fibers, and then entire muscle cells, become damaged.

The history of DMDDMD for three generations of a family is shown in Figure 1.

Figure 1. Pedigree showing instances of DMDDMD in a family

Individuals III–1III–1 and III–2III–2 plan to have children and wish to first determine whether individual III–2III–2 is a carrier of DMDDMD. Individual III–2III–2 undergoes genetic testing to determine whether individual III-2III-2 carries a particular allele for the mutated dystrophin that is associated with the disorder in this family. The results of gel electrophoresis analysis of the individual’s dystrophin alleles and the alleles of several family members are shown in Figure 2.

Figure 2. Gel electrophoresis showing the dystrophin alleles present in five members of the family

Which of the following best explains how the dystrophin protein is synthesized by certain muscle cells of an individual but not by other cell types?

The presence of different transcription factors in different cell types results in differential gene expression.

Living cells typically have biosynthetic pathways to synthesize at least some of the amino acids used in making proteins. Some strains of E. coli, a prokaryote, can synthesize the amino acid tryptophan, while other E. coli strains cannot. Similarly, some strains of the yeast S. cerevisiae, a eukaryote, can synthesize tryptophan, while other S. cerevisiae strains cannot.

Which of the following describes the most likely source of genetic variation found in the tryptophan synthesis pathways of both species?

Errors in DNA replication lead to genetic variation.

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

leave the greatest number of reproducing descendants

Many species of corals are threatened by the increasing temperatures and decreasing pHpH of ocean waters. One species, Stylophora pistillata, has been found to thrive in water that is warmer and has a lower pHpH than the water that corals typically thrive in. Additionally, researchers have found that the tolerance for the new water conditions is heritable.

Which of the following statements best explains the changes seen in S. pistillata in response to the changing water conditions?

The corals’ adaptation is an example of natural selection because the tolerance is in response to a changing environment and has a genetic basis.

In plants, members of the euphorbia family and the cactus family have separate origins, with the euphorbia evolving in the desert regions of Asia and Africa and the cacti in the desert regions of the Americas. Both have fleshy stems adapted for water storage, protective spines, and leaves that are greatly reduced or absent. The similarities between these two families of plants represent an example of

convergent evolution

The different species of finches on the Galapagos Islands are believed to have arisen as a result of natural selection acting on populations of finches that had experienced

geographic isolation

For following group of questions first study the description of the situation and then choose the one best answer to each question following it and fill in the corresponding oval on the answer sheet.

A survey reveals that 25 percent of a population of 1,000 individuals have attached earlobes (are homozygous recessivefor the trait). For the following questions, assume that the population fits the parameters of the Hardy-Weinberg law.

If p equals the frequency of the dominant allele and q equals the frequency of the recessive allele, which of the following terms represents the frequency of the individuals who show the dominant phenotype?

p ² + 2pq

The placement and development of two bones of the reptilian jaw are very similar to that of two bones of the mammalian middle ear, which probably evolved from the reptile bones. The similarity of these bones is an example of

structural homology

A number of different phylogenies (evolutionary trees) have been proposed by scientists. These phylogenies are useful because they can be used to

evaluate which groups of organisms may be most closely related

All of the following are density-dependent factors that limit animal populations EXCEPT

weather

Different species of bumblebee compete for flower nectar in their ecosystem. While the flowers vary in the length of their petals, bumblebees vary in the length of a mouth part called a proboscis. Bumblebees demonstrate a preference for flowers that correspond to the length of their proboscis. Species with proboscises of similar length tend to occupy different areas. Species that live in the same area tend to have proboscises of different lengths.

Which of the following best explains the relationship between the different bumblebee species living in the same area?

the bumblebees have undergone niche partitioning due to competition.

Wolves, once native to Yellowstone National Park, were hunted to the point of complete extinction in the park. As a result, the elk population in the park flourished, putting extra demands on the carrying capacity of the park. Many other species, such as certain trees and beavers, were negatively affected by the increase in elk.

Years later, wolves were reintroduced into the park. While the elk population decreased after the wolves returned, the beaver and songbird populations began to increase as did the populations of various plant species.

Which of the following best explains how wolves are a keystone species in this ecosystem?

Wolves help balance the population sizes of other species, allowing more species to thrive in the wolves’ presence than in their absence.

The diagram shows how water can adhere to the xylem in the stems of plants, which contributes to water movement in the plant. Which of the following best explains how water is able to move upward from the roots of a plant, through its xylem in the stem, and out to the leaves?

Water and the xylem are both polar. Water molecules have the ability to form hydrogen bonds with each other and with the walls of the xylem.

Figure 1. An amino acid

The amino acid in Figure 1 is found in a region of a polypeptide that folds away from water. Which part of the amino acid most likely contributes to the hydrophobic behavior of this region of the polypeptide?

Methyl (CH3CH3) group

The sequences for two short fragments of DNA are shown above. Which of the following is one way in which these two segments would differ?

Segment 1 would become denatured at a lower temperature than would segment 2 because A-T base pairs have two hydrogen bonds whereas G-C base pairs have three.

The figure below illustrates a eukaryotic cell. Which of the following best describes how the three structures indicated by the arrows work together?

To synthesize and isolate proteins for secretion or for use in the cell

The figure above represents a rough endoplasmic reticulum. Which of the following best describes the role of the structure labeled Y?

Structure Y is the location where proteins are synthesized.

The following questions refer to the following diagram. For each phrase or sentence, select the labeled part to which it is most closely related. Each option may be used once, more than once, or not at all for each group.

Site of transport of materials into and out of the cell

D

The manner in which several different ions and molecules move through a cell membrane is shown in the diagram above. For each ion or molecule, the relative concentration on each side of the membrane is indicated. Which of the following accurately describes one of the movements taking place?

Na⁺ transport out of the cell requires ATP hydrolysis.

The following questions refer to an experiment in which a dialysis-tubing bag is filled with a mixture of 3% starch and 3% glucose and placed in a beaker of distilled water, as shown below. After 3 hours, glucose can be detected in the water outside the dialysis-tubing bag, but starch cannot.

Which of the following best describes the condition expected after 24 hours?

The bag will contain more water than it did in the original condition.

Which of the following best illustrates the flow of information required for the synthesis of proteins encoded in the genome of a retrovirus?

RNA DNA RNA Protein

The diagram above represents a typical rod-shaped bacterium. Which of the following best describes a feature shown in the diagram that is unique to archaea and bacteria?

The organism does not have a nuclear membrane surrounding its genetic material.

Figure 1. Change in the relative concentration of product over time

Figure 1 shows the amount of product produced in an enzyme-catalyzed reaction over five minutes. Which of the following best explains how the rate of the reaction changes over time?

The rate decreases because the ratio of product to substrate increases.

Figure 1. Change in energy over the course of four chemical reactions

Based on the data in Figure 1, which of the following most likely represents the change in energy that occurs when ATPATP hydrolysis is coupled with the phosphorylation of a substrate?

Line 11 represents ATPATP hydrolysis, and line 44 represents phosphorylation of a substrate.

Figure 1. Diagram of the electron transport chain and ATPATP synthase in the membrane of mitochondria

On average, more ATPATP can be produced from an NADHNADH molecule than can be produced from a molecule of FADH2FADH2. Based on Figure 1, which of the following best explains the difference in ATPATP production between these two molecules?

The electrons of FADH2FADH2 are transferred through three complexes of the electron transport chain whereas those of NADHNADH are transferred through all four complexes.

Which of the following best represents two different signaling pathways that share a second messenger?

Figure 1. A model of epinephrine signaling

Two types of cells, alpha and beta cells, produce signaling molecules that affect blood sugar levels in opposite ways (Figure 1). Epinephrine is a chemical, often released during periods of exercise, that ultimately causes an increase in blood sugar levels in the body.

Based on Figure 1, which of the following best explains how exercise causes blood glucose levels to rise?

Epinephrine activates alpha cells, causing the release of glucagon, and inhibits beta cells, blocking the release of insulin.

Insulin, a hormone secreted by pancreatic cells, stimulates glucose uptake in skeletal muscle cells by mobilizing glucose transporter proteins (GLUT4) to the plasma membrane. As depicted in Figure 1, binding of insulin to the insulin receptor triggers an intracellular signaling cascade in which certain molecules activate other molecules in a relay of the hormone signal to cell targets. One outcome of the signaling cascade is mobilization of GLUT4 from vesicle storage sites in the cytoplasm to sites at the cell surface, where GLUT4 allows glucose to enter the cell.

In type 2 diabetes, the cellular response to insulin is disrupted, and individuals with type 2 diabetes cannot properly regulate their blood glucose levels. In an investigation of the insulin signaling pathway, samples of skeletal muscle were isolated from individuals who have type 2 diabetes and from individuals who do not. The results of several experiments that were performed on the muscle samples are shown in Figure 2, Figure 3, and Figure 4.

Based on the experimental results, which of the following describes the most likely defect in muscle cells of patients with type 2 diabetes?

IRS-1 activation is reduced at high insulin concentrations.

Figure 1. A model of an endocrine signaling pathway showing involved body parts and hormones. GnRHGnRH = gonadotropin-releasing hormone, LHLH = luteinizing hormone, and FSHFSH = follicle-stimulating hormone.

Figure 1 shows a model of the endocrine signaling pathway that regulates ovulation. Which of the following observations would provide evidence of a positive feedback mechanism in this system?

Estrogen from the ovaries stimulates the hypothalamus and anterior pituitary to secrete more GnRHGnRH, LHLH, and FSHFSH.

Figure 1. Diagram of the cell cycle with key checkpoints

Which of the following describes a mutation that would lead to an increase in the frequency of nondisjunction?

A mutation affecting checkpoint 33 proteins that prevents attachment of spindle fibers

The diagram above illustrates which of the following processes?

Crossing-over

In the pedigree above, squares represent males and circles represent females. Individuals who express a particular trait are represented by shaded figures. Which of the following patterns of inheritance best explains the transmission of the trait?

Autosomal dominant

The pedigree below shows the inheritance of a dominant allele of a gene in a family over several generations. Circles represent females and squares represent males. Shaded symbols indicate individuals carrying the allele.

The pedigree suggests that the gene is on a nuclear chromosome, and not on mitochondrial DNADNA, because

maternal mitochondrial mutations are inherited by all of a mother’s offspring

The diagram above depicts a karyotype of an individual human. Which of the following statements concerning the karyotype in the diagram is true?

The diagram illustrates the results of nondisjunction during gamete formation.

The following questions refer to the following DNA strand and table of codons.

The mRNA transcribed from the DNA would read

5’ AUC AAG UUU GGC GCA UUG UAA 3’

When DNA replicates, each strand of the original DNA molecule is used as a template for the synthesis of a second, complementary strand. Which of the following figures most accurately illustrates enzyme-mediated synthesis of new DNA at a replication fork?

D

Which of the following best describes an event during step 2 in the simplified model above?

Noncoding sequences are removed from a newly synthesized RNA molecule.

Based on the universal genetic code, which of the following represents the correct polypeptide that will result from translation of the mRNAmRNAmolecule shown, beginning with the first available start codon?

Met−Val−Thr−Lys−Phe−Gly−His

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.

Which of the following statements best explains how protein X regulates gene expression?

Protein X is responsible for activating transcription of some genes but not others.

The p53p53 protein regulates a cellular response to DNADNA damage. Based on the diagram above, which of the following best describes the role of p53p53 in the response to DNADNA damage?

Phosphorylated p53p53 stimulates transcription of p21p21, and the resulting p21p21 protein suppresses cell division until the DNADNA damage is repaired.

Figure 1. A karyotype obtained from a sample of human cells

A karyotype is a representation of all the metaphase chromosomes in a sample of cells from a particular individual (Figure 1).

Which of the following most likely explains how the chromosomes circled in Figure 1 could cause a genetic disorder in the person from whom the cells were obtained?

The extra chromosome will affect the levels of RNARNA transcribed from certain genes and the amount of protein produced from those genes in each cell.

In a transformation experiment, a sample of E. coli bacteria was mixed with a plasmid containing the gene for resistance to the antibiotic ampicillin (amp ^r). Plasmid was not added to a second sample. Samples were plated on nutrient agar plates, some of which were supplemented with the antibiotic ampicillin. The results of E. coli growth are summarized below. The shaded area represents extensive growth of bacteria; dots represent individual colonies of bacteria.

Which of the following statements best explains why there are fewer colonies on plate IV than on plate III?

Not all E. coli cells are successfully transformed.

• Directions: Each of the questions or incomplete statements below is followed by four suggested answers or completions. Select the one that is best in each case and then fill in the corresponding circle on the answer sheet.

The three-spined stickleback (Gasterosteus aculeatus) is a small fish found in both marine and freshwater environments. Marine stickleback populations consist mainly of individuals with armor-like plates covering most of their body surface (completely plated). Approximately 10,000 years ago, some marine sticklebacks colonized freshwater environments. After many generations in the freshwater environments, the freshwater stickleback populations lacked the armor plating (low plated) typical of marine stickleback populations.

Over the period between 1957 and 2005, one freshwater population, in Lake Washington, a lake in a coastal region of the northwestern United States, changed from having a majority of individuals of the low-plated phenotype to having more individuals of the completely-plated phenotype than of the low-plated phenotype. Figure 1 shows the distribution of plated phenotypes in Lake Washington sticklebacks at four time points between 1957 and 2005.

A single gene, ectodysplasin (EDA), is thought to be responsible for the variation in the number of armor plates in sticklebacks. Figure 2 shows a phylogenetic tree constructed by comparing DNA sequences of the EDA gene from a number of stickleback populations with low-plated or completely plated phenotypes. Figure 3 shows a phylogenetic tree constructed by comparing the sequences of 25 genes that were randomly selected from the same populations as shown in Figure 2. In both figures, shaded populations display the completely plated phenotype.

Which of the following best explains the differences in the armor of the Lake Washington stickleback population summarized in Figure 1 ?

Fish exhibiting the low-plated phenotype were selected against in the Lake Washington stickleback population over the last 50 years.

Which of the following describes a scenario that would result in the phenotypic change shown in the graph?

House sparrows that lay smaller-than-average clutches of eggs produce fewer viable offspring, while larger-than-average clutches of eggs result in malnourished chicks that have a higher mortality rate.

Scientists are studying several populations of finches on neighboring islands in the South Pacific. Previous genetic analysis has shown that a single gene controls tail-feather length in the finch populations and that the allele for long tail feathers (L)(�) is dominant to the allele for short tail feathers (l)(�). On two separate islands, the scientists recorded the number of finches with long tail feathers and the number of finches with short tail feathers. The results are shown in the table below.

If the two finch populations are each in Hardy-Weinberg equilibrium and are isolated from each other, then which of the following graphs correctly displays the relative genotype frequencies?

C

Figure 1. Amino acid sequences of certain dehydrogenase enzymes in different species

Portions of the amino acid sequences of some dehydrogenase enzymes found in bacteria, yeast, corn, horses, and sheep are shown in Figure 1. Each letter represents a different amino acid in the sequence.

Based on Figure 1, which of the following conclusions about the enzymes is most likely correct?

These enzymes all evolved from a common prokaryotic dehydrogenase enzyme, so they exhibit regions of sequence similarity.

The gene encoding the catalytic subunit of cytochrome c oxidase (MT-CO1��-��1) is found in the mitochondria of all animals. The gene evolves rapidly and is often used to determine evolutionary relationships among species. Table 1 shows DNA sequence differences among four animal species (II, IIII, IIIIII, and IVIV).

Which of the following cladograms best represents the evolutionary relationships among the four species?

A

Over many generations, two populations of the same species can diverge into separate species through reproductive isolation. The figures below represent a model of speciation and show the results of matings between individuals from two diverging populations at four different stages of speciation. The males represented in the model are heterogametic, which means they have two different sex-determining chromosomes, (e.g., XYXY). The females are homogametic, which means they have two similar sex-determining chromosomes, (e.g., XXXX). The offspring from each mating are labeled interpopulation hybrids.

Figure 1 shows the results of a mating between a male and a female from the two populations. In each subsequent figure, the males are from one of the diverging populations and the females are from the other population. The fertility and viability of the offspring from each mating are indicated in the figures.

Based on the model of speciation presented, which of the following describes the most likely consequence to the populations over time?

Hybrid individuals are less likely to pass their genetic information on to subsequent generations.

As depicted in the diagram, honeybees communicate the location of flower patches to members of their hives with waggle dances that give information about the direction and distance to the flowers. Which of the following statements about how honeybees communicate the position of flower patches is most consistent with the model?

The farther the target flowers from the hive, the longer the waggle phase.

Figure 1. A food chain in the North Pacific Ocean

Based on Figure 1, which of the following is the most likely short-term effect of a decrease in the killer whale population?

The sea otter and kelp populations will increase, while the sea urchin population will decrease.

Which of the following changes to the environment will most likely lead to more energy entering the meadow community represented above?

Increasing the light available to the plants

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?

The presence of black bears and salmon correlates with a significant increase in nitrogen influx.

High levels of certain plant nutrients in runoff can lead to rapid growth of algae (an algal bloom) in aquatic ecosystems. These algal blooms are generally followed by algal death and decomposition, which consumes large amounts of dissolved oxygen in the water and results in oxygen levels insufficient to support aerobic respiration. This process is known as eutrophication. The amount of algae present in a body of water can be estimated from the amount of chlorophyll a in a sample of the water. A researcher studying eutrophication collected samples at different times of the year in a freshwater ecosystem. The samples were analyzed for total nitrogen and chlorophyll a concentration (Figure 1) as well as total phosphorus and chlorophyll a concentration (Figure 2).

Which of the following was the dependent variable in the researcher’s study?

The concentration of chlorophyll a

Figure 1. Domain structure of two proteins

Investigators studied the interactions between two different proteins, protein II and protein IIII. Each protein has two structural domains (Figure 1) that represent different functional parts of the protein. Different combinations of the protein domains were tested for their ability to bind to a known DNA sequence, interact with each other, and activate transcription. The results are shown in Table 1.

TestDomain(s) of Protein IIUsedDomain(s) of Protein IIIIUsedDNA BindingProtein-Protein InteractionTranscription Activation11FGFGLMLM++++++22FGFGNone++−−−−33NoneLMLM−−−−−−44FFLMLM++−−−−55GGLMLM−−++−−66FGFGLL++−−−−77FGFGMM++++++

Which of the following is the most likely result of testing a combination of domains G� and MM?

Protein-protein interaction only

A student formulated a hypothesis that water-soluble pollutants damage living organisms by increasing the permeability of cellular membranes. To test the hypothesis, the student investigated the effect of isopropanol and acetone on beet root cells. The vacuoles of beet root cells contain large amounts of betacyanin, a water-soluble pigment that is released into the extracellular environment as a result of increased membrane permeability.

The student prepared identical samples of beet root tissue and incubated each sample for 15 minutes in the specific solution for that group. At the end of the incubation period, the student measured the absorbance of 460 nm light for each sample. A greater concentration of betacyanin in the solution surrounding the beet root cells results in a greater absorbance of 460 nm light. The results of the experiment are shown in the table above.

Based on the data from the investigation, which of the following is the best scientific question about organisms living in water that is polluted with organic solvents?

Will organisms living in polluted environments exhibit detrimental effects from an increased permeability of their cellular membranes?

A student peeled the skins from grapes, exposing cells with membranes that are only permeable to water and small diffusible solutes. The student measured the mass of the peeled grapes. The student then placed each peeled grape into one of five solutions. After 24 hours, the student removed the peeled grapes from the solutions, measured their final mass, and calculated the percent change in mass (Table 1).

TABLE 1. PERCENT CHANGE IN MASS OF PEELED GRAPES IN SOLUTIONS

In a second experiment (Table 2), the student placed a peeled grape into a solution containing both small diffusible solutes and solutes to which the membrane is impermeable (nondiffusible solutes).

TABLE 2. CONCENTRATION OF SOLUTES IN SECOND EXPERIMENT

Assuming a negligible pressure potential, which of the following best predicts the net movement of the small diffusible solutes and water in the second experiment (Table 2) ?

Small diffusible solutes will diffuse into the grape cells, followed by water.

A scientist designed an experiment to test an artificial membrane that mimics the phospholipid bilayer of a cell.

The scientist built a tube that was divided by an artificial membrane and filled with distilled water. The scientist put a known amount of a protein into the water on one side of the membrane. After some time, the scientist measured the concentration of the protein on either side of the membrane but found that there had been no change.

Which of the following experimental changes would allow the scientist to observe transport of a solute across the artificial membrane?

Use a small, nonpolar solute instead of a protein

The diagram below shows energy changes in a specific chemical reaction with and without the addition of an enzyme to the reaction

Which of the following questions can best be answered by the diagram?

Does the addition of an enzyme reduce the activation energy required for a reaction?

Figure 1. Rate of an enzyme-catalyzed reaction

Researchers investigated the dynamics of a reaction catalyzed by an enzyme. The researchers prepared a series of reactions, each with the same concentration of enzyme but with different concentrations of substrate. The researchers measured the amount of product in each reaction mixture after 55 minutes. The results are shown in Figure 1.

Which of the following questions best addresses whether a particular inhibitor is competitive or noncompetitive?

Does the inhibitor bind to an allosteric site or the active site of the enzyme?

A researcher is investigating the effects of a chemical that makes thylakoid membranes permeable to hydrogen ions (H+H+). Which of the following is the most likely direct effect of adding the chemical to plant cells?

The chloroplasts will generate less ATPATP.

To investigate bacterial metabolism, a researcher divided a population (culture) of Staphylococcus capitis bacteria into two sets of culture tubes containing glucose. The researcher added a chemical to one set of tubes and measured the pHpH of the cultures at 55-minute intervals as the bacteria metabolized the glucose into lactic acid. The data are shown in Table 1.

TABLE 1. AVERAGE CHANGE IN pHpH IN CONTROL AND TREATMENT GROUPS OVER A 4040-MINUTE PERIODTime (min)Average pHpH of Control(±2 SEx¯±2 SE�¯)Average pHpH of Treatment(±2 SEx¯±2 SE�¯)008.04±0.058.04±0.058.04±0.068.04⁢±⁢0.06557.96±0.037.96±⁢0.037.91±0.047.91⁢±0.0410107.88±0.027.88⁢±⁢0.027.85±0.047.85±⁢0.0415157.82±0.027.82±⁢0.027.79±0.067.79⁢±⁢0.0620207.76±0.037.76⁢±⁢0.037.70±0.047.70±⁢0.0425257.71±0.047.71⁢±⁢0.047.67±0.027.67⁢±⁢0.0230307.63±0.037.63⁢±⁢0.037.63±0.027.63⁢±⁢0.0235357.65±0.027.65±⁢0.027.60±0.027.60±⁢0.0240407.65±0.017.65⁢±⁢0.017.59±0.027.59⁢±⁢0.02

Which of the following was the dependent variable in the researcher’s experiment?

pH

Over 100100 different types of GG-protein-linked receptors have been observed in eukaryotes, including scent receptors in animals, mating-signal receptors in yeasts, and light-sensing proteins in vertebrates. The proton pumps of bacteria have protein structures similar to GG-protein-linked receptors. Based on this information, which of the following scientific questions will best guide research on the evolution of GG-protein-linked signal transduction?

Did the GG-protein-linked signal transduction pathway in eukaryotes arise from a precursor in prokaryotes?

Scientists compared the chemical structure of several molecules that various bacterial species use for quorum sensing. Quorum sensing is an ability some bacteria have to detect the number of related cells nearby. The chemical structure of some of these molecules found in certain species of bacteria are shown in Figure 1.

Figure 1. The chemical structure of several molecules used for quorum sensing in three species of bacteria

Which of the following research questions would best guide an investigation of the link between the structure of the signaling molecules and the evolution of quorum sensing?

Did these species evolve from a common ancestor that used a similar signaling molecule?

A researcher is conducting an experiment in which cells in different phases of the cell cycle are fused together. The researcher then records what happens to the nuclei of the resulting cell (Table 1).

TABLE 1. COMBINATIONS OF CELLS THAT WERE FUSED AND THE PHASE OF NUCLEI IN THE RESULTING CELL

Which of the following research questions is best addressed by the experiment?

How do chemical messengers affect a cell’s transition between the phases of the cell cycle?

Hydrangea flowers differ in color based on interactions between a pigment in the flower cells and aluminum ions dissolved in water absorbed from the soil. When aluminum ions are present, the pigment is blue; when aluminum ions are absent, the pigment is pink. The amount of aluminum ions the plant can absorb is dependent on the pHpH of the soil.

Which of the following questions will best help a researcher design an experiment to learn about the relationship between hydrangea flower color, aluminum, and pHpH?

What will be the flower color of hydrangeas grown in soils of varying pHpH with or without aluminum?

Mutations in the MYO6 and POU4F3 genes have been associated with a form of hereditary hearing loss in humans. Researchers studying the genes have proposed that POU4F3 encodes a transcription factor that influences the regulation of MYO6.

Which of the following questions will best help guide the researchers toward a direct test of their proposal?

Do mutations in the POU4F3 gene affect MYO6 mRNAmRNA levels in cells?

Cystic fibrosis is a recessively inherited disorder that results from a mutation in the gene encoding CFTR chloride ion channels located on the surface of many epithelial cells. As shown in the figure, the mutation prevents the normal movement of chloride ions from the cytosol of the cell to the extracellular fluid. As a consequence of the mutation, the mucus layer that is normally present on the surface of the cells becomes exceptionally dehydrated and viscous.

An answer to which of the following questions would provide the most information about the association between the CFTR mutation and the viscous mucus?

How does the disrupted chloride movement affect the movement of sodium ions and water by the cell?

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.

Which of the following biotechnology approaches could be used to identify ferritin mRNA in a sample of total cellular RNA?

RNA samples could be separated by size using agarose gel electrophoresis and incubated with labeled single-stranded DNA molecules that are complementary to the ferritin mRNA.

Figure 1. Experimental steps taken to determine whether the nutrient source in a growth chamber affects mating preference

A population of fruit flies (Drosophila pseudoobscura) grown on a typical nutrient source was separated into several growth chambers. Each of the new chambers was assigned a different source of carbohydrates for nutrition, either starch or maltose, and maintained for many generations (Figure 1).

After a year, male and female flies were paired up in different combinations. The instances of mating between the males and females grown on the same nutrient source and males and females grown on different nutrient sources were recorded (Table 1).

TABLE 1. MATING INSTANCES BETWEEN MALES AND FEMALES GROWN ON

THE SAME OR DIFFERENT NUTRIENT SOURCES

To test whether the mating preferences were simply the result of being isolated in separate growth chambers, the researchers tested the mating preferences of flies that were both grown on starch, but in either the same or different chambers (Table 2).

TABLE 2. MATING INSTANCES BETWEEN MALES AND FEMALES GROWN ON THE SAME NUTRIENT SOURCE IN THE SAME OR DIFFERENT CHAMBERS

Which of the following best represents the null hypothesis for the experiment detailed in Figure 1 ?

The mating preferences of flies are not dependent on the nutrient source on which they are grown.

Some cells release active signaling proteins when membrane-bound precursor proteins are cleaved by proteolytic enzymes. The signaling proteins can then bind to receptors on the surface of a target cell, thereby activating an intracellular signaling pathway and eliciting a response from the target cell.

This mechanism of activating receptor-binding signaling proteins has been observed in a variety of organisms from bacteria to humans. Many of the enzymes responsible for proteolysis of membrane-bound precursor proteins have been isolated and characterized.

Which of the following questions would be most appropriate to investigate whether the proteolytic enzymes are evolutionarily conserved among species?

If a proteolytic enzyme from one species is incubated with a precursor protein from another species, does correct cleavage occur?

• Directions: Each of the questions or incomplete statements below is followed by four suggested answers or completions. Select the one that is best in each case and then fill in the corresponding circle on the answer sheet.

The three-spined stickleback (Gasterosteus aculeatus) is a small fish found in both marine and freshwater environments. Marine stickleback populations consist mainly of individuals with armor-like plates covering most of their body surface (completely plated). Approximately 10,000 years ago, some marine sticklebacks colonized freshwater environments. After many generations in the freshwater environments, the freshwater stickleback populations lacked the armor plating (low plated) typical of marine stickleback populations.

Over the period between 1957 and 2005, one freshwater population, in Lake Washington, a lake in a coastal region of the northwestern United States, changed from having a majority of individuals of the low-plated phenotype to having more individuals of the completely-plated phenotype than of the low-plated phenotype. Figure 1 shows the distribution of plated phenotypes in Lake Washington sticklebacks at four time points between 1957 and 2005.

A single gene, ectodysplasin (EDA), is thought to be responsible for the variation in the number of armor plates in sticklebacks. Figure 2 shows a phylogenetic tree constructed by comparing DNA sequences of the EDA gene from a number of stickleback populations with low-plated or completely plated phenotypes. Figure 3 shows a phylogenetic tree constructed by comparing the sequences of 25 genes that were randomly selected from the same populations as shown in Figure 2. In both figures, shaded populations display the completely plated phenotype.

The phylogenetic trees in Figures 2 and 3 depict two different phylogenies of the same populations of sticklebacks. Which of the following questions will best help determine which tree represents the most accurate phylogeny?

Is the EDA gene as representative of the differences between the populations as the 25 random genes that were examined for Figure 3?

A biologist spent many years researching the rate of evolutionary change in the finch populations of a group of islands. It was determined that the average beak size (both length and mass) of finches in a certain population increased dramatically during an intense drought between 1981 and 1987. During the drought, there was a reduction in the number of plants producing thin-walled seeds.

Which of the following procedures was most likely followed to determine the change in beak size?

The beak size in a large number of finches was measured every year from 1981 to 1987.

Which of the following questions about the origin of life on Earth is most scientifically testable?

Can simple organic molecules form spontaneously in an oxygen-free atmosphere?

Hydrangea macrophylla is a species of plant with blue or pink flowers. Flower color in Hydrangea macrophylla plants is thought to be determined primarily by soil conditions rather than by inherited differences. Which of the following will provide the most direct evidence that flower color in Hydrangea macrophylla is due primarily to soil conditions?

Growing cuttings from the same Hydrangea macrophylla plant under controlled conditions that vary only with regard to soil pH

A student is investigating photosynthesis in plants. The student planted grass seeds in a tray with three sections and grew the grass under artificial lights for 1414 days (Figure 1). After 1414 days, the student collected all of the grass from section II and recorded its mass (Table 1). The student then placed a clear cover over section IIII and placed an aluminum foil cover over section IIIIII (Figure 2). The student then placed the tray back under the artificial lights for seven additional days. On day 2121, the student collected and measured the mass of the grass from sections IIII and IIIIII (Table 1).

TABLE 1. MASS OF GRASS GROWN IN EACH SECTION

Which of the following is an appropriate null hypothesis for the student’s experiment?

The presence of light has no effect on the mass of the grass.

Figure 1. Phytoplankton biomass in two sides of a small lake that is divided by an impermeable curtain

In the early 1970s, researchers hypothesized that carbon was the limiting nutrient in many aquatic ecosystems. To test this hypothesis, the researchers divided a small lake in two roughly equal halves with an impermeable curtain that was fastened and sealed to the bedrock of the lake. Beginning in 1971 the researchers treated one side of the lake with sucrose and the other side with both sucrose and phosphate. From 1971 to 1983 the researchers monitored the phytoplankton biomass in both parts of the lake. The results are shown in Figure 1.

Which of the following treatments would have been the best control treatment for the experiment?

An untreated section of the lake

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.

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.

Which of the following additions to the experimental design will best help test whether the observed habitat preferences were the result of competition between species?

Placing two individuals from the same population together inside the enclosure

A scientist is evaluating a proposal for raising large numbers of fish in ocean pens for human consumption. As part of the evaluation, the scientist is designing a plan for investigating how the fish in the ocean pens might affect nearby ecosystems.

Which of the following is the most appropriate factor to use as the dependent variable in the experimental investigation?

The amount of metabolic wastes in the water where the fish are being raised

Water in a pond contaminated with the weed killer atrazine is suspected of inhibiting metamorphosis in northern leopard frogs. A team of scientists collected fertilized northern leopard frog eggs from a different pond that is not contaminated. Which of the following is the best experimental design to determine whether atrazine is responsible for inhibiting metamorphosis in northern leopard frogs?

Place half of the fertilized eggs in a pool of water with the same concentration of atrazine as the contaminated pond and place the other half of the fertilized eggs in a pool of water that has no atrazine. Monitor the development of the embryos through metamorphosis into adulthood.

High levels of certain plant nutrients in runoff can lead to rapid growth of algae (an algal bloom) in aquatic ecosystems. These algal blooms are generally followed by algal death and decomposition, which consumes large amounts of dissolved oxygen in the water and results in oxygen levels insufficient to support aerobic respiration. This process is known as eutrophication. The amount of algae present in a body of water can be estimated from the amount of chlorophyll a in a sample of the water. A researcher studying eutrophication collected samples at different times of the year in a freshwater ecosystem. The samples were analyzed for total nitrogen and chlorophyll a concentration (Figure 1) as well as total phosphorus and chlorophyll a concentration (Figure 2).

Figure 1. Amount of chlorophyll a in relation to the amount of total nitrogenFigure 2. Amount of chlorophyll a in relation to the amount of total phosphorous

Which of the following describes the relationship between the amount of chlorophyll a in a water sample and the concentration of nitrogen in that sample?

The concentrations of nitrogen and chlorophyll a are directly correlated.

Figure 1. Domain structure of two proteins

Investigators studied the interactions between two different proteins, protein II and protein IIII. Each protein has two structural domains (Figure 1) that represent different functional parts of the protein. Different combinations of the protein domains were tested for their ability to bind to a known DNA sequence, interact with each other, and activate transcription. The results are shown in Table 1.

Based on the data, which structural domain is most likely required for DNA binding?

Domain F

For following group of questions first study the description of the situation or data and then choose the one best answer to each question following it and fill in the corresponding oval on the answer sheet.

In the first step of an experiment, rat liver cells were exposed for 5 minutes to amino acids labeled with a radioactive isotope. The cells were then washed to stop any further incorporation of radioactive amino acids. The cells were sampled periodically thereafter, and the radioactivity of a certain protein (protein X) was measured in various cell components, as shown below.

Which of the following correctly shows the order in which protein X moves through the cell?

Endoplasmic reticulum→→Golgi apparatus→→lysosomes

In an experiment, the efficiency of oxygen exchange across the plasma membrane is being assessed in four artificial red blood cells. The table above lists some properties of those artificial cells. Other conditions being equal, which artificial cell is predicted to be the most efficient in exchanging oxygen with the environment by diffusion?

The cuboidal cell

A student formulated a hypothesis that water-soluble pollutants damage living organisms by increasing the permeability of cellular membranes. To test the hypothesis, the student investigated the effect of isopropanol and acetone on beet root cells. The vacuoles of beet root cells contain large amounts of betacyanin, a water-soluble pigment that is released into the extracellular environment as a result of increased membrane permeability.

The student prepared identical samples of beet root tissue and incubated each sample for 15 minutes in the specific solution for that group. At the end of the incubation period, the student measured the absorbance of 460 nm light for each sample. A greater concentration of betacyanin in the solution surrounding the beet root cells results in a greater absorbance of 460 nm light. The results of the experiment are shown in the table above.

Which of the following graphs is the most appropriate representation of the experimental data?

A

Figure 1. Relative rates of transpiration and water intake for a plant over 1818 hours

Figure 1 shows the relative rates of transpiration (water loss) and water intake for a plant over an 1818-hour period. Which of the following describes the most likely relationship between transpiration and water intake in the plant?

Transpiration from the leaves of the plant stimulates subsequent water intake by the roots of the plant.

Figure 1. Activity levels of two digestive enzymes over a range of pHpH

Trypsin and pepsin are enzymes that function in different areas of the digestive tract. One functions in the stomach, where the pHpH is between 1.51.5 and 3.53.5, while the other functions in the small intestines, where the pHpH is between 66 and 88.

Based on Figure 1, which of the following best describes where each enzyme functions?

Pepsin works in the stomach because the optimal pHpH for pepsin is acidic.

A student placed 20 tobacco seeds of the same species on moist paper towels in each of two petri dishes. Dish A was wrapped completely in an opaque cover to exclude all light. Dish B was not wrapped. The dishes were placed equidistant from a light source set to a cycle of 14 hours of light and 10 hours of dark. All other conditions were the same for both dishes. The dishes were examined after 7 days, and the opaque cover was permanently removed from dish A. Both dishes were returned to the light and examined again at 14 days. The following data were obtained.

According to the results of this experiment, germination of tobacco seeds during the first week is

increased by exposure to light

To investigate bacterial metabolism, a researcher divided a population (culture) of Staphylococcus capitis bacteria into two sets of culture tubes containing glucose. The researcher added a chemical to one set of tubes and measured the pHpH of the cultures at 55-minute intervals as the bacteria metabolized the glucose into lactic acid. The data are shown in Table 1.

TABLE 1. AVERAGE CHANGE IN pHpH IN CONTROL AND TREATMENT GROUPS OVER A 4040-MINUTE PERIOD

Which of the following graphs best represents the data in Table 1 ?

B

Figure 1. Percent saturation of human hemoglobins as a function of the partial pressure of oxygen

The graph in Figure 1 shows the percent saturation of fetal hemoglobin and maternal hemoglobin in humans as a function of the partial pressure of oxygen. Based on the data, which of the following values is closest to the predicted difference in the percent saturation of fetal hemoglobin and maternal hemoglobin at 40mmHg40mmHg?

20

Melanocytes are skin cells that can become cancerous and develop into a cancer known as melanoma. Some cancerous melanocytes have developed resistance to the drugs currently used to treat melanoma. As a result, researchers are investigating the effects of a new compound (drug XX) on four different melanoma cell lines. Researchers analyzed cell survival in two cell lines (Figure 1) and oxygen consumption in the presence of drug XX in all four cell lines (Figure 2). Figure 3 shows the proposed mechanism by which drug XX affects cells.

Figure 1. Percent survival of normal melanocytes and cancerous melanocyte (melanoma) lines 11 and 22 after treatment with different concentrations of drug X

Figure 2. Oxygen consumption per cell in four melanoma lines after treatment with either solvent alone or solvent containing drug XX. Error bars represent ±2SEx¯±2SE�¯.

Figure 3. Pathway leading to cell survival, growth, and proliferation and the likely effect of drug XX

Which of the following best describes the data in Figure 1 ?

At a concentration above 10 μM10 �M, drug XX reduces melanoma cell survival.

Friedreich’s ataxia is an inherited disorder. Friedreich’s ataxia is caused by an insertion mutation in a noncoding portion of the FXN��� gene where a GAAGAA triplet is repeated hundreds of times. The FXN��� gene encodes the protein frataxin. A pedigree of a family with members affected by this disorder is shown in Figure 1.

Figure 1. A pedigree of a family affected by Friedreich’s ataxia

A researcher collected DNADNA from several members of the family and used PCRPCR to amplify the FXNFXN genes from each individual’s DNADNA. The researcher then used DNADNA gel electrophoresis to separate the DNADNA. The results are shown in Figure 2.

Figure 2. FXN��� gene fragment sizes for several family members. A sample of DNADNA with fragments of known lengths was used for comparison.

The researcher also used a computer to model the structure of the mutant FXN��� allele. The model suggests that the repeated GAAGAA triplets in the mutant FXN��� gene may lead to the formation of an unusual triple-stranded configuration of DNADNA (Figure 3).

Figure 3. The modeled DNADNA triple-helix structure that can form in areas with multiple GAAGAA triplets

Based on the data in Figure 1, which of the following best describes the inheritance pattern of Friedreich’s ataxia?

Autosomal recessiveIndividuals III-2III-2 and III-3III-3 carry two different alleles of the FXN��� gene, a mutant allele and a wild-type allele. Individual IV-1IV-1 inherited two copies of the mutant allele.

Friedreich’s ataxia is an inherited disorder. Friedreich’s ataxia is caused by an insertion mutation in a noncoding portion of the FXN��� gene where a GAAGAA triplet is repeated hundreds of times. The FXN��� gene encodes the protein frataxin. A pedigree of a family with members affected by this disorder is shown in Figure 1.

Figure 1. A pedigree of a family affected by Friedreich’s ataxia

A researcher collected DNADNA from several members of the family and used PCRPCR to amplify the FXNFXN genes from each individual’s DNADNA. The researcher then used DNADNA gel electrophoresis to separate the DNADNA. The results are shown in Figure 2.

Figure 2. FXN��� gene fragment sizes for several family members. A sample of DNADNA with fragments of known lengths was used for comparison.

The researcher also used a computer to model the structure of the mutant FXN��� allele. The model suggests that the repeated GAAGAA triplets in the mutant FXN��� gene may lead to the formation of an unusual triple-stranded configuration of DNADNA (Figure 3).

Figure 3. The modeled DNADNA triple-helix structure that can form in areas with multiple GAAGAA triplets

Which of the following statements best describes the results seen in Figure 2 ?

Individuals III-2III-2 and III-3III-3 carry two different alleles of the FXN��� gene, a mutant allele and a wild-type allele. Individual IV-1IV-1 inherited two copies of the mutant allele.

A culture of white-eyed fruit flies (Drosophila melanogaster) was maintained for many generations. Females from the stock white-eyed culture were crossed with red-eyed (wild-type) males. The F₁ females were crossed with the white-eyed males from the original culture. The resulting phenotypes of the progeny are summarized below.

There are white-eyed females in the F₂ generation because

these F₂ females have two white alleles

Researchers investigated whether time of day affects the rate at which certain mRNAsmRNAs produced by plants are broken down. At either 11 hour after the start of the light period (morning) or 88 hours after the start of the light period (afternoon), the researchers treated identical plant seedlings with a compound that blocks transcription (time=0mintime=⁢0⁢⁢min). The researchers measured the percent remaining of two mRNAsmRNAs, mRNA GmRNA G and mRNA HmRNA H, over the course of 120120 minutes. The data are shown in Figure 1.

Figure 1. Degradation of mRNA GmRNA G and mRNA HmRNA H over time after exposure to light for 11 hour (morning) or 88 hours (afternoon)

Based on the data, which of the following best describes the relationship between light and the degradation of mRNA GmRNA G and mRNA HmRNA H?

A longer exposure to light increases the rate of mRNA GmRNA G degradation but not of mRNA HmRNA H degradation.

Researchers studying new viruses analyzed the genetic material found in four different virus samples to determine the percent nitrogen base composition of each virus. The data are shown in the table.

BASE DISTRIBUTION IN FOUR NUCLEIC ACID SAMPLES

Which of the following samples most likely contains a double-stranded RNARNA virus?

Sample 1

The table below describes the action of two genes involved in the regulation of nervous system development in the nematode C. elegans.

Which of the following claims is best supported by the data?

Gene A promotes neuron development; gene B promotes programmed cell death in neuronal precursors.

Individuals of a particular species of ground beetle are either light tan or dark brown. Light-tan beetles are predominant in habitats with light-colored sandy soils, and dark-brown beetles are predominant in habitats with dark-colored loam soils. In an experiment designed to determine the survival rates of light-tan beetles and dark-brown beetles in different habitats, 500 light-tan beetles and 500 dark-brown beetles were released in each of four habitats. Each beetle had been marked with a small spot of red paint on the underside of its abdomen before it was released. One week after the beetles had been released, any marked beetles that could be found were recaptured. The results are presented in the table below. It is assumed that differences in the numbers of beetles recaptured are directly related to differences in survival rates.

Which of the following can be inferred from the data in the table?

Insectivorous birds are predators of this species of ground beetle.

Figure 1. Experimental steps taken to determine whether the nutrient source in a growth chamber affects mating preference

A population of fruit flies (Drosophila pseudoobscura) grown on a typical nutrient source was separated into several growth chambers. Each of the new chambers was assigned a different source of carbohydrates for nutrition, either starch or maltose, and maintained for many generations (Figure 1).

After a year, male and female flies were paired up in different combinations. The instances of mating between the males and females grown on the same nutrient source and males and females grown on different nutrient sources were recorded (Table 1).

TABLE 1. MATING INSTANCES BETWEEN MALES AND FEMALES GROWN ON

THE SAME OR DIFFERENT NUTRIENT SOURCES

To test whether the mating preferences were simply the result of being isolated in separate growth chambers, the researchers tested the mating preferences of flies that were both grown on starch, but in either the same or different chambers (Table 2).

TABLE 2. MATING INSTANCES BETWEEN MALES AND FEMALES GROWN ON THE SAME NUTRIENT SOURCE IN THE SAME OR DIFFERENT CHAMBERS

Which of the following combinations of flies showed the highest number of mating instances?

Males grown on starch paired with females grown on starch

Figure 1. For paired groups of organisms, a comparison of the number of amino acid substitutions in cytochrome c� with the time since the groups diverged from a common ancestor

Researchers analyzed the amino sequence of the protein cytochrome c� in various groups of organisms and determined the number of amino substitutions that have occurred in the different groups of organisms. They plotted the data with respect to the time since divergence of the members of paired groups from a common ancestor (Figure 1). Based on the data, which of the following organisms are most distantly related?

Insects and vertebrates

Scientists are interested in determining the evolution of seven lizard species found on different islands of the Canary Island group. They isolated DNADNA from individuals of each species and sequenced the mitochondrial gene that encodes cytochrome b�. The numbers of genetic differences between species are shown in the table below.

Based on the data in the table, which of the following lizard species are most closely related?

Species EE and species D

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?

Infected individuals gradually died out, and genetically resistant individuals became more common. The frog population recovered because of the increased frequency of resistant individuals.

Diapause is the interruption of an organism’s life cycle in response to environmental cues. The soil nematode Caenorhabditis elegans is capable of entering adult reproductive diapause (ARDARD) when food is scarce. In C. elegans, individuals normally become reproductively mature 2 days after hatching and remain fertile for 18 days. They reproduce either by self-fertilization or by mating with another individual.

In an investigation, researchers examined the survival and reproductive success of C. elegans following different times in ARD. In the first experiment, groups of C. elegans were held in ARDARD without food for 0-30 days. Upon reintroduction of food, average brood sizes (average numbers of offspring per adult) were determined following either self-fertilization or mating with a well-fed male. The results are shown in Figure 1.

Figure 1. Mean brood sizes ±2SEX¯¯¯±2���¯ after different times in ARDARD.

Individual C. elegans were held in ARDARD and subsequently

allowed to reproduce either via self-fertilization (unshaded bars)

or by mating with well-fed males (shaded bars).

In a second experiment, individuals were held in ARDARD without food for 0–300–30 days and monitored for average survival times following reintroduction of food (Figure 2).

Figure 2. Mean survival ±2SEX¯¯¯±2���¯ following different times in ARDARD. Individual C. elegans were held in ARDARD and subsequently given access to food, whereupon their survival times were determined.

Which of the following best describes the reproductive ability of C. elegans following the ARDARD induced in the first experiment?

Mating with a well-fed male consistently produced more offspring than did reproduction via self-fertilization.

In the Arctic Ocean, the predominant primary producers are phytoplankton. Phytoplankton are consumed by zooplankton, which in turn are eaten by codfish. In years when there is more open water (less ice coverage), there are more zooplankton and fish than in years with less open water (more ice coverage). Based on the graph above, the difference is most likely because

the ice blocks the light, so in years with more ice coverage, there is less photosynthesis by the phytoplankton

One model of a sustainable fisheries practice is for individual fish to be removed from a natural population at a rate equal to the highest possible growth rate of an ideal population. The graph above represents a population of bluefin tuna living along the Atlantic coast. At which labeled point in the graph is the population growth rate the highest?

III

Figure 1. Change in the population size of sea lions over time. Error bars represent ±2SEx¯±2SE�¯.

Which of the following best estimates the population size of the sea lions in 2000 based on the data shown in Figure 1?

175,000

To investigate the effects of ground-level ozone pollution on different species of plants, researchers recorded the number of plants in a certain area that had ozone-induced leaf damage. Based on the results of the survey shown in Table 1, which of the following plant species was most affected by ozone pollution?

Wild grape

A scientist is developing a mathematical model of cells of different shapes. To construct the model, the scientist has specified that the width of each cell at its widest point must be 30μm30μm and the height of each cell must be 90 μm90 μm. Table 1 shows the three-dimensional shapes that the scientist is considering for the model cells. Which of the proposed shapes for the model cells will allow the most efficient exchange of materials with the surrounding environment?

Triangular prism

A student formulated a hypothesis that water-soluble pollutants damage living organisms by increasing the permeability of cellular membranes. To test the hypothesis, the student investigated the effect of isopropanol and acetone on beet root cells. The vacuoles of beet root cells contain large amounts of betacyanin, a water-soluble pigment that is released into the extracellular environment as a result of increased membrane permeability.

The student prepared identical samples of beet root tissue and incubated each sample for 15 minutes in the specific solution for that group. At the end of the incubation period, the student measured the absorbance of 460 nm light for each sample. A greater concentration of betacyanin in the solution surrounding the beet root cells results in a greater absorbance of 460 nm light. The results of the experiment are shown in the table above.

The student analyzed the data from the investigation and concluded that the estimate of the mean of one treatment group was unreliable. Which of the following identifies the treatment group most likely to have provided an unreliable estimate of the mean, and correctly explains why the estimate appears unreliable?

Treatment group II; it has a lower than expected mean absorbance and the largest standard error of the mean.

A student peeled the skins from grapes, exposing cells with membranes that are only permeable to water and small diffusible solutes. The student measured the mass of the peeled grapes. The student then placed each peeled grape into one of five solutions. After 24 hours, the student removed the peeled grapes from the solutions, measured their final mass, and calculated the percent change in mass (Table 1).

TABLE 1. PERCENT CHANGE IN MASS OF PEELED GRAPES IN SOLUTIONS

In a second experiment (Table 2), the student placed a peeled grape into a solution containing both small diffusible solutes and solutes to which the membrane is impermeable (nondiffusible solutes).

TABLE 2. CONCENTRATION OF SOLUTES IN SECOND EXPERIMENT

A student hypothesizes that the solute concentration of grape juice is higher than the solute concentration of the actual grape because the grape juice has added sugar.

Based on the data in Table 1, which of the following best evaluates the student’s hypothesis?

The hypothesis is not supported because the mass of the grape increased in the grape juice.

The following questions refer to an experiment that is set up to determine the relative volume of O₂ consumed by germinating and nongerminating (dry) pea seeds at two different temperatures. The change in volume is detected by using a respirometer over a given period of time. The data are given below.

The rate of oxygen consumption in germinating pea seeds at 26ºC is

0.05 mL / min

Scientists investigated the effect of oxygen levels on the net rate of carbon fixation in two types of plants. The plants were grown in either well-watered soil (control) or dry soil and then exposed to either 21%21% or 1%1% O2O2. The net rate of CO2CO2 fixation for both types of plants was measured. Data are shown in Figure 11 and Figure 22.

O2

Which of the following statements about the rate of CO2CO2 fixation in the two types of plants is supported by the data shown in the figures?

At 21%21% O2�2, plant type 22 has a lower rate of CO2CO2 fixation than plant type 11 does in both types of soil.

Certain reef-building corals contain photosynthetic, symbiotic algae that have the ability to make dimethylsulphoniopropionate (DMSPDMSP), a chemical involved in the marine sulfur cycle. DMSPDMSP is released into the surrounding water, where it is converted to the gas dimethyl sulfide (DMSDMS) by microorganisms and enters the atmosphere. Once in the atmosphere, it triggers the formation of sulfate aerosols, which induce cloud formation and block sunlight from heating up the water.

The symbiotic algae produce DMSPDMSP when they are stressed by a high water temperature. If water temperature is too high, corals will expel the symbiotic algae that produce DMSPDMSP. Researchers measured the amount of DMSPDMSP produced by juvenile and adult coral and their symbionts under normal and thermally stressed conditions. The data are shown in the graphs in Figure 1.

Figure 1: DMSPDMSP concentration in juvenile and adult corals and their symbionts in normal and thermally-stressed conditions. Error bars represent ±2SEx¯±2SE�¯.

The researchers also measured the density of the symbiont as well as the photosynthetic yield in adult corals at the two temperatures. Photosynthetic yield is an index measure of energy output compared to sunlight energy input in which larger photosynthetic yield values represent photosynthetic organisms producing more energy.

Figure 2: Variation in symbiont density and photosynthetic yield in adult corals grown in normal and thermally-stressed conditions. Error bars represent ±2SEx¯±2SE�¯.

Which of the following best describes the scientists’ findings concerning the density of symbionts presented in Figure 2 ?

The symbiont density at 32°C32°C was different from the density at 27°C27°C on days 55 and 1010 of the experiment.

Melanocytes are skin cells that can become cancerous and develop into a cancer known as melanoma. Some cancerous melanocytes have developed resistance to the drugs currently used to treat melanoma. As a result, researchers are investigating the effects of a new compound (drug XX) on four different melanoma cell lines. Researchers analyzed cell survival in two cell lines (Figure 1) and oxygen consumption in the presence of drug XX in all four cell lines (Figure 2). Figure 3 shows the proposed mechanism by which drug XX affects cells.

Figure 1. Percent survival of normal melanocytes and cancerous melanocyte (melanoma) lines 11 and 22 after treatment with different concentrations of drug X

Figure 2. Oxygen consumption per cell in four melanoma lines after treatment with either solvent alone or solvent containing drug XX. Error bars represent ±2SEx¯±2SE�¯.

Figure 3. Pathway leading to cell survival, growth, and proliferation and the likely effect of drug XX

Based on Figure 2, which of the following best supports the claim that drug XX inhibits oxygen consumption?

Melanoma line 33 consumes statistically less oxygen per cell in the presence of drug XX than it does in the presence of the solvent alone.

If 2n = 48 for a particular cell, then the chromosome number in each cell after meiosis would be

24

A researcher hypothesizes that, in mice, two autosomal dominant traits, trait Q and trait R, are determined by separate genes found on the same chromosome. The researcher crosses mice that are heterozygous for both traits and counts the number of offspring with each combination of phenotypes. The total number of offspring produced was 6464. The researcher plans to do a chi-square analysis of the data and calculates the expected number of mice with each combination of phenotypes. Which of the following is the expected number of offspring that will display both trait Q and trait R?

36

The data above represent the results of three different crosses involving the inheritance of a gene that determines whether a certain organism is blue or white. Which of the following best explains the mechanism of inheritance of the gene?

The allele for blue is an X-linked dominant allele because there are no blue male offspring in cross 2.

In a species of cactus, the number of spines on a plant is genetically determined. The graph above shows frequency distributions for populations of the cactus species growing in the presence or absence of two herbivores: peccaries (a New World pig) and wasp larvae. Which of the following best accounts for the different frequency distributions in the graph?

Peccaries eat cacti with a smaller number of spines, and wasp larvae eat cacti with a greater number of spines.

The table shows the changes in allele frequencies of a specific gene in two populations of randomly mating small mammals after 30 years. The populations inhabit adjacent equatorial islands that have similar topography and climate. Which of the following is the most reliable conclusion that can be drawn from analysis of the data above?

Genetic drift has occurred in population 1.

A researcher analyzed four different samples of macromolecules, where all macromolecules in each sample are of the same type. The researcher measured the percent of carbon, oxygen, hydrogen, nitrogen, phosphorus, and sulfur atoms in each sample. The results are shown in Table 1.

Which of the following claims is best supported by the data in Table 1 ?

Sample B contains protein.

Figure 1. Domain structure of two proteins

Investigators studied the interactions between two different proteins, protein I and protein II. Each protein has two structural domains (Figure 1) that represent different functional parts of the protein. Different combinations of the protein domains were tested for their ability to bind to a known DNA sequence, interact with each other, and activate transcription. The results are shown in Table 1.

Which of the following claims is best supported by the data from test 55 in Table 1 ?

Domain F� is not required for protein-protein interaction.

A researcher measured the temperature at which two different samples of double-stranded DNADNA denature (separate into single strands). Sample 11 denatured at a significantly lower temperature than sample 22 did. Based on the data, the researcher claims that the DNADNA in sample 22 is composed of a higher percentage of guanine and cytosine than the DNADNA in sample 11 is.

Which of the following best supports the researcher’s claim?

Guanine-cytosine pairs denature at a higher temperature because they have more hydrogen bonds between them than adenine-thymine pairs do

A mutation in the upland cotton plant causes the development of chloroplasts with a single outer membrane and no internal membranes. Which of the following would most likely be observed in chloroplasts of cotton plants with this mutation?

They would be unable to generate the ATPATP and NADPHNADPH needed to make sugars, because these processes occur on membranes within the chloroplast.

A student peeled the skins from grapes, exposing cells with membranes that are only permeable to water and small diffusible solutes. The student measured the mass of the peeled grapes. The student then placed each peeled grape into one of five solutions. After 24 hours, the student removed the peeled grapes from the solutions, measured their final mass, and calculated the percent change in mass (Table 1).

TABLE 1. PERCENT CHANGE IN MASS OF PEELED GRAPES IN SOLUTIONS

In a second experiment (Table 2), the student placed a peeled grape into a solution containing both small diffusible solutes and solutes to which the membrane is impermeable (nondiffusible solutes).

TABLE 2. CONCENTRATION OF SOLUTES IN SECOND EXPERIMENT

Mercurial sulfhydryl is an inhibitor of aquaporins. Which of the following is the most likely effect of adding mercurial sulfhydryl to the distilled water solution?

The grape cells will gain water more slowly because of a lack of facilitated diffusion.

Stickleback fish are found in both marine and freshwater habitats. The marine fish have no scales but have hardened, armorlike plates along their sides. The plates are thought to protect sticklebacks from certain predators.

In the late 1980s, sticklebacks from a marine population colonized Loberg Lake, a freshwater lake in Alaska. Starting in 1990, researchers sampled fish from the lake every four years and recorded the armor-plate phenotypes of the male sticklebacks in each sample. The armor-plate phenotypes were categorized as either complete (plates extending from head to tail), partial (plates extending from head to abdomen), or low (a few plates near the head only). The results are shown in the table below.

ARMOR-PLATE VARIATION IN THE STICKLEBACK POPULATION OF LOBERG LAKE

Intact cells of two unknown cell types were placed into solutions with different concentrations of NaCl. Type I cells swelled and burst in the solution with the lowest concentration of NaCl. Type II cells swelled but did not burst in the solution with the lowest concentration of NaCl.

Which of the following descriptions of cell type I and cell type II are most consistent with the data?

A

Membrane-bound organelles have been an important component in the evolution of complex, multicellular organisms. Which of the following best summarizes an advantage of eukaryotic cells having internal membranes?

Organelles isolate specific reactions, increasing metabolic efficiency.

Which of the following is the strongest evidence supporting the endosymbiont hypothesis?

Mitochondria have their own DNADNA and divide independently of the cell.

Certain chemicals, including sodium fluoride (NaFNaF), are capable of inhibiting specific steps of glycolysis. Figure 1 shows the steps of the glycolysis pathway, indicating where various macromolecules enter the pathway as well as the specific reaction inhibited by NaFNaF.

Figure 1. Key steps in the metabolic pathway of glucose

An increase in the concentration of protons in the cytosol will most likely have which of the following effects on glycolysis?

Glycolytic enzymes will denature as a result of the increased H+H+concentration.

Dichlorophenolindophenol (DCPIPDCPIP) is a chemical dye. When DCPIPDCPIP is chemically reduced, it changes color from blue to clear. DCPIPDCPIP can be used as an electron acceptor in experiments that measure the rate of electron transport through the electron transport chain. A student performed an experiment to study the effects of a chemical, DCMUDCMU, on photosynthesis.

The student prepared four tubes with a liquid buffer and chloroplasts that had been extracted from spinach leaves. The student then added DCPIPDCPIP to three of the tubes and added DCMUDCMU to one of them. Additionally, tube 33 was wrapped in tin foil. The contents of each tube are shown in the table. The student then incubated each tube for 6060 minutes and measured the absorbance (A600A600) of each solution at five-minute intervals. The absorbance readings of each solution are shown in Fi

Figure 1. Absorbance readings of four prepared tubes with various solutions over a 6060-minute period.

Which of the following claims is best supported by the experimental results?

Light is required for the electron transport chain to transfer electrons.

Newborn babies and hibernating animals contain a large amount of brown adipose (fat) tissue (BATBAT). Certain proteins in the BATBAT cells increase the permeability of the inner mitochondrial membrane to protons, disrupting the proton gradient.

Which of the following best predicts the effect of disrupting the proton gradient in BATBAT?

Electron transport and oxidative phosphorylation will be decoupled, generating more heat but less ATPATP.

Excess intracellular iron is toxic to cells (iron-induced toxicity). Ferritin is an intracellular iron storage protein that binds excess iron. The presence of ferritin can protect cells from iron-induced toxicity.

In an experiment to investigate the effects of dietary iron intake on ferritin synthesis, rats were given food containing different amounts of iron. Subsequently, the levels of ferritin protein in the liver were measured. The results are shown in Figure 1.

Based on these and other data, researchers have developed the following model demonstrating how ferritin synthesis is regulated by iron. When iron levels are low, a repressor of translation, iron response protein (IRP), binds to an iron response element (IRE), which is a stem-loop structure near the 5¢ end of ferritin mRNA. When iron levels are high, intracellular iron binds to the IRP, and the iron-IRP complex dissociates from the IRE, permitting ribosomes to proceed with the translation of ferritin mRNA. Figure 2 represents the model of the regulation of ferritin mRNA translation by iron.

After a search of nucleotide sequence databases, researchers identified an IRE in the 5¢ untranslated region of a gene encoding aconitase, an enzyme involved in the Krebs cycle. Which of the following pieces of experimental evidence best supports the claim that the synthesis of aconitase is controlled by a mechanism similar to ferritin regulation?

The relative amount of aconitase protein increases in the presence of high levels of iron.

Figure 2: Blood insulin levels in normal mice and Esp��� mutant mice after exposure to glucose

Hormones are chemical signals that are released by cells in one part of the body that travel through the bloodstream to signal cells in another part of the body. Insulin is a hormone that is released by the pancreas that induces the uptake of glucose molecules from the bloodstream into cells. In this way, insulin lowers the overall blood glucose levels of the body. Osteoblasts and osteoclasts are two types of bone cells that play a role in regulating blood glucose levels (Figure 1).

Binding of insulin to the insulin receptor on osteoblasts activates a signaling pathway that results in osteoblasts releasing a molecule, OPGOPG, that binds to neighboring osteoclasts. In response, the osteoclasts release protons (H+H+) and create an area of lower pHpH outside the cell. This low pHpH activates osteocalcin, a protein secreted in an inactive form by osteoblasts.

The Esp��� gene encodes a protein that alters the structure of the insulin receptor on osteoblasts and interferes with the binding of insulin to the receptor. A researcher created a group of osteoblasts with an Esp��� mutation that prevented the production of a functional Esp��� product (mutant). The researcher then exposed the mutant strain and a normal strain that expresses Esp��� to glucose and compared the levels of insulin in the blood near the osteoblasts (Figure 2).

Based on the information provided, which of the following best justifies the claim that osteocalcin is a hormone?

The osteoblasts in the bone secrete osteocalcin, which causes cells in the pancreas to change their activity.

Figure 2: Blood insulin levels in normal mice and Esp��� mutant mice after exposure to glucose

Hormones are chemical signals that are released by cells in one part of the body that travel through the bloodstream to signal cells in another part of the body. Insulin is a hormone that is released by the pancreas that induces the uptake of glucose molecules from the bloodstream into cells. In this way, insulin lowers the overall blood glucose levels of the body. Osteoblasts and osteoclasts are two types of bone cells that play a role in regulating blood glucose levels (Figure 1).

Binding of insulin to the insulin receptor on osteoblasts activates a signaling pathway that results in osteoblasts releasing a molecule, OPGOPG, that binds to neighboring osteoclasts. In response, the osteoclasts release protons (H+H+) and create an area of lower pHpH outside the cell. This low pHpH activates osteocalcin, a protein secreted in an inactive form by osteoblasts.

The Esp��� gene encodes a protein that alters the structure of the insulin receptor on osteoblasts and interferes with the binding of insulin to the receptor. A researcher created a group of osteoblasts with an Esp��� mutation that prevented the production of a functional Esp��� product (mutant). The researcher then exposed the mutant strain and a normal strain that expresses Esp��� to glucose and compared the levels of insulin in the blood near the osteoblasts (Figure 2).

Which of the following claims is most consistent with the data shown in Figure 2 ?

Esp��� expression is necessary to prevent the overproduction of insulin.

Insulin, a hormone secreted by pancreatic cells, stimulates glucose uptake in skeletal muscle cells by mobilizing glucose transporter proteins (GLUT4) to the plasma membrane. As depicted in Figure 1, binding of insulin to the insulin receptor triggers an intracellular signaling cascade in which certain molecules activate other molecules in a relay of the hormone signal to cell targets. One outcome of the signaling cascade is mobilization of GLUT4 from vesicle storage sites in the cytoplasm to sites at the cell surface, where GLUT4 allows glucose to enter the cell.

In type 2 diabetes, the cellular response to insulin is disrupted, and individuals with type 2 diabetes cannot properly regulate their blood glucose levels. In an investigation of the insulin signaling pathway, samples of skeletal muscle were isolated from individuals who have type 2 diabetes and from individuals who do not. The results of several experiments that were performed on the muscle samples are shown in Figure 2, Figure 3, and Figure 4.

Based on the information presented, which of the following genetic changes in an individual without diabetes is most likely to result in a disrupted cellular response to insulin signaling similar to that of an individual with type 2 diabetes?

A deletion in the gene encoding the insulin receptor that removes only the cytoplasmic domain of the protein

Insulin, a hormone secreted by pancreatic cells, stimulates glucose uptake in skeletal muscle cells by mobilizing glucose transporter proteins (GLUT4) to the plasma membrane. As depicted in Figure 1, binding of insulin to the insulin receptor triggers an intracellular signaling cascade in which certain molecules activate other molecules in a relay of the hormone signal to cell targets. One outcome of the signaling cascade is mobilization of GLUT4 from vesicle storage sites in the cytoplasm to sites at the cell surface, where GLUT4 allows glucose to enter the cell.

In type 2 diabetes, the cellular response to insulin is disrupted, and individuals with type 2 diabetes cannot properly regulate their blood glucose levels. In an investigation of the insulin signaling pathway, samples of skeletal muscle were isolated from individuals who have type 2 diabetes and from individuals who do not. The results of several experiments that were performed on the muscle samples are shown in Figure 2, Figure 3, and Figure 4.

Which of the following is a valid interpretation of the experimental results that explains how individuals with type 2 diabetes differ from individuals without diabetes?

The relatively low levels of glucose uptake in individuals with type 2 diabetes indicate that mobilization of GLUT4 to the cell surface is reduced in muscle cells of those individuals.

Pyruvate dehydrogenase is an enzyme that converts pyruvate to acetyl-CoACoA. Acetyl-CoACoA is further metabolized in the Krebs cycle. A researcher measured the accumulation of acetyl-CoACoA in a reaction containing pyruvate and pyruvate dehydrogenase under several different conditions (Figure 1).

Figure 1. Accumulation of acetyl-CoACoA under different conditions

Which of the following observations provides the best evidence that acetyl-CoACoA negatively regulates pyruvate dehydrogenase activity?

The rate of the pyruvate dehydrogenase–catalyzed reaction is slower in the presence of a higher concentration of acetyl-CoACoA.

The drug 55-fluorouracil inhibits thymine production in eukaryotic cells. Which of the following cell cycle stages will be most directly affected by 55-fluorouracil?

Synthesis of DNA phase (SS)

Researchers have identified a molecule produced by Ecteinascidia turbinata, a marine invertebrate, from which the drug trabectedin is produced. Soft-tissue tumors treated with trabectedin rapidly decrease in size. In a preliminary study, healthy cells and tumor cells sampled from skin cancer patients treated with trabectedin were collected, and several characteristics of the cells were observed. The observed results of the study are shown in the table.

Which of the following best explains the most likely method by which this antitumor drug works?

Trabectedin interferes with the duplication of DNADNA during interphase and thus prevents cancer cells from passing the G2G2 checkpoint.

Humans have a diploid number (2n2n) of 4646. Which of the following statements best predicts the consequence if meiosis did not occur during gametogenesis?

The chromosome number would double with each generation.

Which of the following best supports the claim that organisms of different domains share a common ancestor?

Glycolysis occurs in both prokaryotic cells and eukaryotic cells.

A series of crosses is performed with fruit flies (Drosophila melanogaster) to examine inheritance of the genes vestigial (vg) and cinnabar (cn). The recessive vg allele causes small, malformed wings called vestigial wings. The recessive cn allele causes bright-red eyes called cinnabar eyes.

In the first cross, a female with wild-type wings and eyes is mated with a male with vestigial wings and cinnabar eyes. All the F₁ individuals have wild-type wings and eyes. In the second cross, female F₁ flies are mated with males with vestigial wings and cinnabar eyes. The phenotypes of 500 F₂ individuals are shown in the table

Which of the following is the most likely explanation of the results?

The two genes are linked on an autosome.

Butterflies of the genus Colias live in the Rocky Mountains, where they experience a wide range of temperatures. Different variants of a particular glycolytic enzyme in the flight muscles are optimally active at different temperatures. Within the same population, some individual butterflies fly most effectively at 29°C , while others fly most effectively at 40°C. Still others can be equally active at both temperatures. Which of the following claims is most consistent with the observed butterfly behavior?

Butterflies that express two variants of the enzyme are active over a greater range of temperature.

A spermatocyte produces the following four sperm cells.

These cells are the result of nondisjunction during which of the following phases?

Meiosis I

A scientist adds a chemical to a culture of dividing cells in order to disrupt DNADNA replication. The replicated DNADNA produced by the cells is double-stranded, but sections of it lack covalent bonds between adjacent nucleotides (Figure 1).

Figure 1. Replicated DNADNA produced after a chemical is introduced

Which of the following claims is best supported by the data?

The chemical inhibits DNA ligase.

• Directions: Each group of questions below concerns an experimental or laboratory situation or data. In each case, first study the description of the situation or data. Then choose the one best answer to each question following it.

. . . . glutamine-glutamine-glutamine . . .

. . . serine-serine-serine . . .

Which of the following messenger RNA sequences could code for both of the two amino acid sequences above, simply by a shift in the reading frame?

. . . AGCAGCAGCAGC . . .

The following the DNA sequence is a small part of the coding (nontemplate) strand from the open reading frame of β -hemoglobin gene. Given the codon chart listed below, what would be the effect of a mutation that deletes the G at the beginning of the DNA sequence?

The reading frame of the sequence would shift, causing a change in the amino acid sequence after that point.

Arctic foxes typically have a white coat in the winter. In summer, when there is no snow on the ground, the foxes typically have a darker coat.

Which of the following is most likely responsible for the seasonal change in coat color?

The decrease in the amount of daylight in winter causes a change in gene expression, which results in the foxes growing a lighter-appearing coat.

Lactase is the enzyme needed to digest lactose, the sugar found in milk. Most mammals produce lactase when they are young but stop once nursing ends. In humans however, many people continue to produce lactase into adulthood and are referred to as lactase-persistent.

Which of the following mutations is most likely to cause lactase persistence in humans?

A mutation that increases the binding of transcription factors to the promoter of the lactase gene

Which of the following is the most likely effect of a mutation in the gene coding for a DNADNA repair enzyme?

Mutations will accumulate more quickly because the cell will not be able to fix errors in replication.

Researchers studying the bacterium Escherichia coli split a population of the bacteria into two samples. Sample 11 was transformed with a plasmid containing a gene that makes the bacteria resistant to the antibiotic kanamycin. Sample 22 was transformed with a plasmid lacking the antibiotic resistance gene. A portion of each sample was then added to growth plates containing just nutrients or growth plates containing nutrients and kanamycin.

After being allowed to grow for 2424 hours at 37∘C37∘C, the number of colonies on each growth plate was counted (Table 1).

TABLE 1. BACTERIAL GROWTH FOLLOWING TRANSFORMATION WITH ORWITHOUT THE KANAMYCIN RESISTANCE GENE

Which of the following claims is best supported by the data in Table 1 ?

Only the bacteria that were successfully transformed with the kanamycin resistance gene grew on plate 44.

While there is only one species of Galápagos Island tortoise, there are several subspecies. Larger islands with more wet highlands have lush vegetation near the ground. Tortoises there tend to have high-domed shells and shorter necks, which restrict upward head movement. They also have shorter limbs. They are the heaviest and largest of the subspecies.

Smaller, drier islands are inhabited by tortoises with longer necks and limbs and with shells that are elevated above the neck, which allow them to browse taller vegetation.

Based on the information given, which of the following is a plausible explanation for the ancestry of the tortoise subspecies?

Individuals with different adaptations in shell shape and leg length best exploited the food resources and left more surviving offspring on each island.

Pesticides are chemicals that are often sprayed on crops to kill plant-eating insects, preventing damage to the crops. While pesticides are effective initially, many researchers claim that any single pesticide will see reduced effectiveness in as little as ten to fifteen years.

Which of the following best supports the claim by scientists that the pesticides will eventually lose their effectiveness?

Insects that are naturally resistant to the pesticide will survive and reproduce more than the insects that are sensitive to the pesticide.

Poaching is the illegal hunting or capturing of wild animals. Both male and female African elephants have tusks that are a significant source of ivory used for ornaments and jewelry.

Assuming that the size of the tusks is heritable, which of the following is the most likely long-term effect of poachers targeting African elephants with large tusks?

A decrease in average tusk size because elephants with large tusks are less likely to survive to reproduce

Undersea landslides can disrupt marine habitats by burying organisms that live on the ocean floor. The graph above shows the size of a population of a certain organism that lives on the ocean floor. The population was affected by a recent landslide at the time indicated on the graph. Which of the following best predicts how the population will be affected by the landslide?

The reduced population will likely have allelic frequencies that are different from the initial population.

For following group of questions first study the description of the situation and then choose the one best answer to each question following it and fill in the corresponding oval on the answer sheet.

A survey reveals that 25 percent of a population of 1,000 individuals have attached earlobes (are homozygous recessivefor the trait). For the following questions, assume that the population fits the parameters of the Hardy-Weinberg law.

Unlike most natural populations, this population is best characterized in which of the following ways?

There is genetic equilibrium.

The amino acid sequence of cytochrome c is exactly the same in humans and chimpanzees. There is a difference of 13 amino acids between the cytochrome c of humans and dogs, and a difference of 20 amino acids between the cytochrome c of humans and rattlesnakes.

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

The human is apparently more closely related to the chimpanzee than to the dog or rattlesnake.

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?

Transmission of the methicillin-resistance plasmid would gradually decrease but the plasmid would not entirely disappear from the Staphylococcus aureus population.

The figure shows a phylogenetic tree of various members of the order Proboscidea, which includes modern elephants. Which of the following claims is best supported by the information in the figure ?

The common ancestor of the African elephant and the mastodon is the Palaeomastodon.

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?

Lava has separated the population into two areas: an upland forest and a lowland marsh.

Modern bananas originated from a cross between a tetraploid banana species and a diploid banana species. The product of this cross was the triploid Cavendish banana strain, a sterile hybrid that is only grown asexually. Recently, the Panama fungus has been observed more frequently parasitizing the Cavendish banana, and scientists claim that this type of banana is on the brink of extinction.

Which of the following provides the best explanation of the scientists’ claim regarding the threat to the Cavendish banana?

The lack of genetic diversity of the Cavendish banana decreases the chance that a variation exists in the population that is immune to the fungus.

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?

The molecules essential to life today could have formed under early Earth conditions.

The pesticide DDT was widely used in the 1940s as a method of insect control. In the late 1950s the first DDT-resistant mosquitoes were discovered, and eventually DDT-resistant mosquitoes were found globally. When DDT is used now, the development of DDT resistance in mosquito populations occurs in months rather than years.

Which of the following best explains the observations concerning DDT resistance in mosquitoes?

Natural selection favors DDT-resistant mosquitoes that are already present in a population when DDT exposure occurs.

The following is a food web for a meadow habitat that occupies 25.6km². The primary producers’ biomass is uniformly distributed throughout the habitat and totals 1,500 kg/km²

Developers have approved a project that will permanently reduce the primary producers’ biomass by 50 percent and remove all rabbits and deer.

Which of the following is the most likely result at the completion of the project?

The biomass of coyotes will be dramatically reduced.

In an investigation of interspecies competition, researchers grew the unicellular protozoan Paramecium aurelia in a 5 mL culture and Paramecium caudatum in a separate 5 mL culture. P. aurelia and P. caudatum were grown together in a third 5 mL culture. Each day a small sample of each culture was removed so the total number of individuals could be estimated, and the remainder of the population was transferred to fresh growth medium. The experimental results are represented in the graphs below.

Which of the following conclusions is best supported by the results of the experiment?

Neither population grows as large when cultured together as each does when cultured separately.

Which of the following communities is likely to be most stable?

One with high species diversity

Mosquitoes are frequently a target of insect control strategies because of their ability to spread disease. One strategy is to introduce guppies, a type of freshwater fish, into areas where mosquitoes are a problem. Guppies can consume large numbers of mosquito larvae, which cuts down on the number of mosquitoes living to adulthood.

Researchers assessing the effectiveness of the guppy solution are concerned that the introduction of guppies might cause more problems than it is fixing. Guppies are hardy, tolerant of a wide range of environmental conditions, and fast-reproducing.

Which of the following predicts the most likely ecological problem that would occur if guppies are introduced into new areas to control the mosquito population?

The guppies might have no natural predators, which will result in a dramatic increase in the guppy population and an increase in competition for other native species.