God help

Testosterone is a small steroid hormone that is important in cell signaling. Which of the following indicates where testosterone enters a cell and why it is able to cross at that point?

1, because testosterone is nonpolar and can diffuse through the membrane.

A student used microscopy to investigate the relative lengths of the different stages of mitosis. The student prepared slides of cells isolated from a growing onion root tip and viewed the slides under a dissecting microscope. The student then made diagrams of cells that were in different stages of mitosis and counted the number of cells that were in each of those stages. The student's data are presented in Table 1. Table 1. Number of cells in each of four different stages of mitosis Based on the data, the percent of the mitotic cells that were in metaphase is closest to which of the following?

18%

Scientists have estimated that it takes yeast cells approximately 20 hours to complete the entire cycle. Table 1 shows the amount of time in each phase of the life cycle for yeast cells. Based on Table 1, what percent of the life cycle of yeast cells is spent in DNA replication?

25 percent

Which of the following steps in a signaling pathway typically occurs first once a chemical messenger reaches a target cell?

A ligand binds to a receptor.

A researcher proposes a model to explain how enzyme-substrate interactions determine enzyme specificity. The model is based on the idea that substrate molecules form favorable interactions with the amino acid side chains in an enzyme's active site. Based on the model, which of the following statements best explains an enzyme's specificity for a particular substrate molecule?

A molecule with negative charges interacts with positively charged side chains in the enzyme's active site.

(Melanin question) Which of the following best explains a process occurring between point 1 and point 2 in Figure 3 ?

A poly‑A tail is added to RNA

(Polysaccharide question) Which of the following best describes the process that adds a monosaccharide to an existing polysaccharide?

A specific enzyme removes the hydrogen (H) from the monosaccharide and the hydroxide (OH) from the polysaccharide, creating a bond between the two and creating a water (H2O) molecule.

A researcher claims that a certain herbicide suppresses plant growth by inhibiting chloroplast function. To test the claim, the researcher treats isolated chloroplasts with increasing concentrations of the herbicide. The data from the experiment are presented in Table 1. Which of the following statements best clarifies how the data support the researcher's claim?

ATP synthase activity depends on a proton gradient across the thylakoid membrane.

A study was conducted to understand the factors controlling the rate at which molecules or ions travel across cell membranes. An artificial membrane was created that was composed of a phospholipid bilayer only. The speed at which various substances crossed this membrane was measured. Some substances can pass through an actual cell membrane much faster than they passed through the artificial membrane in this study. Which of the following statements best explains this finding?

Actual cell membranes have a variety of proteins embedded in the membrane that are absent in the artificial membrane.

Researchers have discovered details about apoptosis (programmed cell death) by studying embryologic development of a nematode worm, Caenorhabditis elegans. Apoptosis is a normal developmental process in C. elegans. They found several genes involved in apoptosis, including ced−9 and ced−3 . The ced−3 gene was found to promote cell death, and ced−9 to inhibit it. The ced−9 gene serves as a regulator that prevents apoptosis in the absence of a signal promoting apoptosis. Which of the following statements best justifies the claim that changes in the expression of ced−9 in C. elegans can affect regulation of apoptosis in the cell?

An experiment showed that a mutation in the ced−9 gene led to excessive cell death in C. elegans.

In vascular plants, water flows from root to leaf via specialized cells called xylem. Xylem cells are hollow cells stacked together like a straw. A student explains that evaporation of water from the leaf pulls water up from the roots through the xylem, as shown in Figure 1. Which statement describes how water is pulled up through the xylem to the leaves of the plant?

As water exits the leaf, hydrogen bonding between water molecules pulls more water up from below.

Two competing hypotheses exist regarding the cell membrane structure. One hypothesis states that membrane structure is static and membrane components throughout the bilayer are rigidly bound. Alternatively, the other hypothesis states that cell membranes are a fluid mosaic in which membrane components may drift within the bilayer around the surface of the cell. An experiment is set up in which membrane proteins of two different cells are fluorescently labeled with two different colors and then fused as shown in Figure 1. Which of the following results, one hour after membrane fusion, best supports the alternative hypothesis that the cell membrane is a fluid mosaic?

Black and grey are mixed randomly throughout

Figure 1 represents a segment of DNA. Radiation can damage the nucleotides in a DNA molecule. To repair some types of damage, a single nucleotide can be removed from a DNA molecule and replaced with an undamaged nucleotide. Which of the four labeled bonds in Figure 1 could be broken to remove and replace the cytosine nucleotide without affecting the biological information coded in the DNA molecule?

Bonds Y and Z at the same time

Which of the following best describes a structural similarity between the two molecules shown in Figure 1 that is relevant to their function?

Both molecules contain nucleotides that form base pairs with other nucleotides, which allows each molecule to act as a template in the synthesis of other nucleic acid molecules.

A magnesium sulfate solution taken orally can cause a net movement of water into the large intestine, which results from water molecules diffusing through aquaporins embedded in the cells of the intestinal lining. By which of the following mechanisms do the water molecules most likely move into the large intestine?

By passive transport from an area of low osmolarity to an area of high osmolarity

Aldosterone (a steroid hormone) is a small, nonpolar, hydrophobic molecule that enters a target cell by moving across the plasma membrane, down a concentration gradient. Based on the information presented, how does aldosterone most likely enter target cells?

By simple diffusion

The cell membrane is selectively permeable due to its structure. Thus, the internal environment of the cell is distinct from the external environment of the cell. One biologist hypothesizes that small nonpolar molecules readily pass through the membrane. Another biologist alternatively hypothesizes that these types of molecules require channel and transport proteins that are embedded in the membrane in order to move across the membrane. Which of the following data would best refute this alternative hypothesis?

CO2 and N2 movement in and out of cells is unaffected when membrane protein activity is blocked.

(Polysaccharide question) Which of the following would most likely occur if cattle lost the ability to maintain a colony of microorganisms in their digestive tract?

Cattle would no longer be able to use cellulose as a primary source of glucose.

Some cells, such as intestinal cells, exchange a lot of material with their surroundings. The surface-to-volume ratio of these cells affects the efficiency of material exchange. The table provides measurements of four different eukaryotic cells. Based on the data, which cell is likely to be most effective in the exchange of materials?

Cell 2

During a fight-or-flight response, epinephrine is released into the body's circulatory system and transported throughout the body. Some cells exhibit a response to the epinephrine while other cells do not. Which of the following justifies the claim that differences in components of cell signaling pathways explain the different responses to epinephrine?

Cell signaling depends on the ability to detect a signal molecule. Not all cells have receptors for epinephrine. Only cells with such receptors are capable of responding.

A student wants to modify model 1 so that it represents an RNA double helix instead of a DNA double helix. Of the following possible changes, which would be most effective in making model 1 look more like RNA than DNA?

Changing the deoxyriboses to riboses by adding −OH groups

An antigen can induce an immune response in a host organism. Antigens are targeted by antibodies that are produced by the organism's immune system in response to contact with the antigen. Antibodies are specific to antigens. Many different cell types are involved in immune responses. Which of the following best describes the role of cell-to-cell communication during a response to an invasion of antigens?

Chemicals that are secreted from antigen-presenting cells then activate helper T cells.

Researchers have proposed a model of chloroplast evolution. According to the model, chloroplasts evolved from a small prokaryotic organism that was engulfed by an ancestral eukaryote. The engulfed prokaryote then formed an endosymbiotic relationship with the eukaryotic host. Which of the following observations best supports the model?

Chloroplasts and some prokaryotes share similar photosynthetic reactions.

Region 1 is hydrophilic because it interacts with an aqueous environment, whereas region 2 is hydrophobic because it interacts with the interior of the membrane. Which of the following models shows how cholesterol molecules most likely interact with the phospholipid bilayer of a cell's plasma membrane?

Cholesterol is within the phospholipids

A student is using dialysis bags to model the effects of changing solute concentrations on cells. The student places one dialysis bag that contains 25 mL of distilled water into each of two beakers that are filled with 200 mL of distilled water. (Figure 1). The membrane of each dialysis bag membrane contains pores that allow small solutes such as monoatomic ions to pass through but are too small for anything larger to pass. After 30 minutes, 5 mL of a concentrated solution of albumin (a medium-sized, water-soluble protein) is added to one of the two beakers. Nothing is added to the other beaker. After two more hours at room temperature, the mass of each bag is determined. There is no change in the mass of the dialysis bag in the beaker to which no albumin was added. Which of the graphs below best represents the predicted change in mass over time of the dialysis bag in the beaker to which albumin was added?

Consistent until aluminum is added, which results in it steadily going down

Cystic fibrosis (CF) is a progressive genetic disease that causes persistent lung infections and affects the ability to breathe. CF is inherited in an autosomal recessive manner, caused by the presence of mutations in both copies of the gene for the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Partial nucleotide sequences and the corresponding amino acid sequences for an unaffected individual and an affected individual are modeled in Figure 1. Based on the information in Figure 1, which type of mutation explains the nature of the change in DNA that resulted in cystic fibrosis in the affected individual?

Deletion, because a thymine is missing, which changes the reading frame.

Scientists conducted a transformation experiment using E. coli bacteria and the pTru plasmid. Samples of the pTru plasmid (lane A) and the chromosomal DNA from two different E. coli strains that the scientists attempted to transform (lane B and lane C) were compared using gel electrophoresis. Which of the following statements best explains the experimental results observed in Figure 1 ?

E. coli in lane C have been successfully transformed and contain additional genetic information.

Labeled nucleotides were supplied to a cell culture before the cells began DNA replication. A simplified representation of the process for a short segment of DNA is shown in Figure 1. Labeled DNA bases are indicated with an asterisk. Which of the following best helps explain how the process represented in Figure 1 produces DNA molecules that are hybrids of the original and the newly synthesized strands?

Each newly synthesized strand remains associated with its template strand to form two copies of the original DNA molecule.

A simplified model of a DNA replication fork is represented in Figure 1. The protein labeled Enzyme 1 carries out a specific role in the DNA replication process. Which of the following statements best explains the role of Enzyme 1 in the DNA replication process?

Enzyme 1 is a topoisomerase that relieves tension in the overwound DNADNA in front of a replication fork.

A researcher claims that the initial rise of oxygen in Earth's early atmosphere, which occurred approximately 2.3 billion years ago, resulted from the metabolic activity of prokaryotic organisms. The claim is based on an interpretation of the geochemical and fossil evidence represented in Figure 1. Which of the following types of evidence will best support the researcher's claim?

Evidence that the cyanobacteria produced oxygen as a by-product of photosynthesis

Blood clots are formed by a positive feedback loop. Two pathways exist, the extrinsic and intrinsic pathways, which converge during clot formation. There are many clotting factors involved, most of which are proteins. Vitamin K is required for the formation of the active form of several of the clotting factors, including Factor X. A simplified model of the blood clotting process is shown in Figure 1. Warfarin is a drug used to treat certain blood clots. Warfarin blocks the formation of the active form of vitamin K-dependent clotting factors. Based on the model, which of the following best predicts the effects of warfarin on a patient?

Factor X will not be activated, which will prevent thrombin from forming.

Researchers investigated the effect of urea on the three-dimensional structure of a certain enzyme. The researchers dissolved the enzyme in an aqueous buffer solution and added urea to the solution. The enzyme did not appear to have a secondary or tertiary structure. The researchers carefully removed the urea from the solution and determined that the enzyme had the original secondary and tertiary structure again. Based on the results of the experiment, which of the following statements best predicts the effect of urea on the enzyme's function?

Function will be disrupted by adding the urea and regained by removing the urea.

Water molecules are polar covalent molecules. There is a partial negative charge near the oxygen atom and partial positive charges near the hydrogen atoms due to the uneven distribution of electrons between the atoms, which results in the formation of hydrogen bonds between water molecules. The polarity of water molecules contributes to many properties of water that are important for biological processes. Which of the following models best demonstrates the arrangement of hydrogen bonds between adjacent water molecules?

H H \ / O - - O / \ H H

Nucleotide base pairing in DNA is universal across organisms. Each pair (T−A; C−G) consists of a purine and a pyrimidine. Which of the following best explains how the base pairs form?

Hydrogen bonds join a double-ringed structure to a single-ringed structure in each pair.

Some viral infections can lead to the rupture of the lysosome membrane. Which prediction of the effect of this disruption of cellular compartmentalization is most likely correct?

Hydrolytic enzymes will be released, which will cause cell death.

Figure 1 depicts a simplified model of a replication bubble. Which of the following best explains how this model illustrates DNA replication of both strands as a replication fork moves?

I is synthesized continuously in the 5′ to 3′ direction, and III is synthesized in segments in the 5′ to 3′ direction.

Signal transduction may result in changes in gene expression and cell function, which may alter phenotype in an embryo. An example is the expression of the SRY gene, which triggers the male sexual development pathway in mammals. This gene is found on the Y chromosome. Which statement provides the evidence to justify the claim that signal transduction may result in an altered phenotype?

If the SRY gene is absent or nonfunctional, the embryo will exhibit female sexual development.

A person's blood glucose level fluctuates during the day, as represented in Figure 1. Two hormones, insulin and glucagon, are directly involved in regulating the blood glucose level to maintain a healthy level. Insulin acts to lower the blood glucose level, and glucagon acts to increase the blood glucose level. Which of the following best predicts what will happen to the blood glucose level if the person has another meal at 5 p.m.?

Immediately after the meal, the blood glucose level will increase, and then insulin will be secreted to counter the increase.

The epidermal growth factor receptor EGFR is a cell surface receptor. When a growth factor binds to EGFR, the receptor is activated. The activated EGFR triggers a signal transduction pathway, which leads to increased frequency of cell division. Which of the following best predicts the effect of a mutation that causes EGFR to be active in the absence of a growth factor?

Increased cell division will lead to the formation of a tumor.

Researchers investigate the transport of a certain protein into cells by endocytosis. In an experiment, the researchers incubate the cells in the presence of the protein and measure the amount of the protein that is absorbed into the cells over a five-minute period. Based on their observations, what should the researchers do to further clarify how the availability of the protein outside the cells affects the rate of endocytosis of the protein?

Incubate the cells in the absence of the protein.

Aminolevulinate dehydratase (ALAD) is an enzyme that relies on zinc as a coenzyme. A zinc ion binds to the ALAD active site, where it forms favorable interactions with the side chains of three amino acids. Researchers have found that substituting a lead ion for a zinc ion in the ALAD active site causes inhibition of ALAD. Which of the following statements best helps explain how the lead ion causes inhibition of ALAD?

It changes the three-dimensional structure of the active site so that ALAD is no longer compatible with its substrate.

In an experiment, researchers compared the growth of two different plants, plant X and plant Y. The researchers maintained the plants under nearly identical conditions and observed that plant X grew faster than plant Y. The researchers also observed that the inner mitochondrial membranes of plant X had more folds than did those of plant Y. Which of the following conclusions about increasing the number of folds in the inner mitochondrial membrane is best supported by the results of the experiment?

It increases the surface area available for ATP production, which results in faster cell growth.

Figure 1 shows a short segment of a double-stranded nucleic acid molecule. Which of the following statements is correct about the molecule shown in Figure 1 ?

It is DNA because of the nucleotides present.

Metformin is a drug used to treat type 2 diabetes by decreasing glucose production in the liver. AMP-activated protein kinase (AMPK) is a major cellular regulator of glucose metabolism. Metformin activates AMPK in liver cells but cannot cross the plasma membrane. By blocking AMPK with an inhibitor, researchers found that AMPK activation is required for metformin to produce an inhibitory effect on glucose production by liver cells. Which of the following best describes the component that metformin represents in a signal transduction pathway that regulates glucose production in the liver?

It is a ligand that activates the signal transduction pathway of the activation of AMPK

Euglenids are single-cell eukaryotes that live in aquatic environments. The chloroplasts found inside euglenids are enveloped by three membranes, as represented in Figure 1. The inner membrane of euglenid chloroplasts resembles the thylakoid membrane. Which of the following claims about the origin of the euglenid chloroplast is best supported by the three-membrane structure of the envelope?

It originated from the incorporation of a photosynthetic prokaryote into a eukaryotic cell by two endosymbiotic events.

In an experiment, researchers provided a radiolabeled amino acid to living plant cells. After one hour, the researchers determined the amount of the radiolabeled amino acid that was in each of several subcellular compartments. The results of the experiment are represented in the table. Which of the following conclusions about the radiolabeled amino acid is best supported by the results of the experiment?

It was mostly incorporated into proteins that regulate and manage metabolic reactions.

Pectinase is a protein that catalyzes the breakdown of pectic polysaccharides in plant cell walls. A researcher designs an experiment to investigate the effect of salinity on the ability of pectinase to lower the activation energy of the reaction involved. The design of the experiment is presented in Table 1. For each test tube, the researcher will measure the amount of product formed over 20 minutes. Which of the following statements best helps justify the inclusion of test tube 5 in the experiment?

It will act as a control for test tube 6 by showing the effect of the presence or absence of the enzyme.

A researcher designs an experiment to investigate whether soil bacteria trigger the synthesis of defense enzymes in plant roots. The design of the experiment is presented in Table 1. For each group in the experiment, the researcher will determine the average rate of change in the amount of defense enzymes in the roots of the seedlings. Which of the following statements best helps justify the inclusion of group 2 as one of the controls in the experiment?

It will show whether the changes observed in group 1 depend on the metabolic activity of soil bacteria.

(Melanin question) Which of the following claims best explains why keratinocytes do not produce melanin?

Keratinocytes do not express the MITF gene.

Which of the following observations best supports the claim that mitochondria evolved from once-free-living prokaryotic cells by the process of endocytosis?

Mitochondria are surrounded by a double membrane.

Which of the following is common feature of the illustrated reactions showing the linking of monomers to form macromolecules?

Monomers are joined by a covalent bond, and a water molecule is produced.

Researchers grew seedlings of corn, Zea mays, in loose and compact sand. The researchers measured the amount of time required for the cells in the growing root tips of the seedlings to double in number. The mean cell doubling times for the two groups of seedlings are shown in Figure 1. Based on the sample means, which of the following conclusions about the cells in the growing root tips of Zea mays seedlings is best supported by the results of the experiment?

More cells are produced per unit of time in the root tips growing in compact sand than in the root tips growing in loose sand.

Phosphofructokinase (PFK) is a key enzyme in glycolysis. ATP is one of the two substrates for the reaction catalyzed by PFK. ATP is also an allosteric regulator of PFK. Figure 1 shows the enzyme-substrate interactions of PFK. A researcher found a mutation that resulted in the PFK enzyme being unable to bind ATP to the allosteric site. Which of the following best predicts the effect of the mutation?

Negative feedback regulation does not occur, so the enzyme will be active when glycolysis is not needed.

Researchers investigated the influence of environmental pH on the activity of peroxidase, an enzyme that catalyzes the conversion of hydrogen peroxide to water and oxygen gas. In an experiment, the researchers added a hydrogen peroxide solution containing guaiacol to several identical test tubes and adjusted the solution in each test tube to a different pH. The researchers included the guaiacol because it caused the solutions to change color as the reactions proceeded, which the researchers relied on for measuring reaction rates. Finally, the researchers added the same amount of peroxidase to each test tube and measured the rate of each reaction at 23°C. The results of the experiment are represented in Figure 1. Based on Figure 1, which of the following statements best predicts the effect that a change from a moderately acidic environment (pH near 6) to a basic environment will have on peroxidase activity?

Peroxidase activity will decrease.

The figure shows a representation of a protein embedded in a cell membrane. The numbers indicate different structural regions of the protein. Based on the figure, which of the following statements best describes the relationship between regions 1 and 2 of the protein?

Region 1 is hydrophilic because it interacts with an aqueous environment, whereas region 2 is hydrophobic because it interacts with the interior of the membrane.

Intravenous (IV) therapy is used for fluid replacement in instances of dehydration in humans and other animals. One type of IV fluid is essentially a saltwater solution. To determine the best concentration for therapy in people, a team of students is researching the effects of solutions of different salt concentrations on red blood cells. The following observations were made from three different red blood cell samples viewed under a microscope. The team wants to extend the research project. What should the team of students do next to obtain data that are more conclusive?

Repeat the process with other salt concentrations.

(Peroxidase question) Which of the following actions will provide a negative control for the investigation?

Repeating the experiment using heat-denatured peroxidase

All cells must transcribe rRNA in order to construct a functioning ribosome. Scientists have isolated and identified rRNA genes that contribute to ribosomal structure for both prokaryotes and eukaryotes. Figure 1 compares the transcription and processing of prokaryotic and eukaryotic rRNA. Which of the following statements provides the best explanation of the processes illustrated in Figure 1 ?

Sections of the pre-rRNA are removed, and the mature rRNA molecules are available to combine with proteins to form the ribosomal subunits.

A cell culture commonly used in research was selected to study the effect of a specific virus on the timing of cell cycle phases. Two separate cultures were started, one untreated and one inoculated with the virus. Both cultures were incubated under identical conditions. After a period of time, 200 cells from each culture were observed and classified as shown in Table 1. Which of the following most accurately describes an observation and an effect of the viral infection indicated by the data in Table 1?

Seventy-five percent of the virus-infected cells are found in mitosis. The virus stimulates frequent cell division.

Huntington's disease, an autosomal dominant disorder, is caused by a mutation in the HTT gene. The HTT gene contains multiple repeats of the nucleotide sequence CAG. A person with fewer than 35 CAG repeats in the HTT gene is unlikely to show the neurological symptoms of Huntington's disease. A person with 40 or more CAG repeats almost always becomes symptomatic. Due to errors in meiosis, an individual without symptoms of Huntington's disease can produce gametes with a larger number of CAG repeats than there are in their somatic cells. A woman develops Huntington's disease. Her father had the disorder. Her mother did not, and there is no history of the disorder in the mother's family. Which of the following best explains how the woman inherited Huntington's disease?

She inherited an allele with more than 40 CAG repeats in the HTT gene from her father.

(Melanin question) Based on the information provided in Figure 1 and Figure 2, which of the following best predicts the effects of a mutation in the promoter of the TYR gene that prevents it from being transcribed?

Skin pigmentation will not be able to change, resulting in a negative selection pressure.

Which of the following describes a key difference among the 20 amino acids that are used to make proteins?

Some amino acids are hydrophobic.

A researcher claims that genetic variation provides organisms with the ability to survive and reproduce in different environments. To support the claim, the researcher makes the following observation: bacteria that contain plasmids (small DNA molecules) are resistant to a wider range of antibiotics than are bacteria that contain no plasmids. Which of the following statements best establishes a connection between the observation and the researcher's claim?

Some plasmids contain antibiotic resistance genes.

Figure 1 represents a portion of a process that occurs during protein synthesis. Which claim is most consistent with the information provided by the diagram and current scientific understanding of gene regulation and expression?

Some sequences of DNA can interact with regulatory proteins that control transcription.

An evolutionary biologist hypothesizes that two morphologically similar plant species are not closely related. To test the hypothesis, the biologist collects DNA samples from each of the two plant species and then uses restriction enzymes to cut the DNA samples into fragments, which are then subjected to gel electrophoresis. Given the results shown in Figure 1, which of the following correctly describes a relationship between the two species?

Species B has more short fragments of DNA than species A does.

Different polysaccharides are used by plants for energy storage and structural support. The molecular structures for two common polysaccharides are shown in Figure 1. Starch is used by plants for energy storage, and cellulose provides structural support for cell walls. The monomer used to construct both molecules is glucose. A study determined the effect of two different digestive enzymes, A and B, on these two polysaccharides. Table 1 presents the data from the study. Mammals do not produce digestive enzyme B. However, sheep and cattle are two types of mammals that contain microorganisms in their digestive tract that produce enzyme B. Based on Figure 1, which of the following best compares the atomic structures of starch and cellulose?

Starch and cellulose are composed of repeating glucose monomers; however, in cellulose every other glucose monomer is rotated 180 degrees.

The relative amounts of DNA present in the nucleus of a cell at four different stages of the life cycle are shown in Figure 1. Based on Figure 1, which of the following statements correctly links a stage of the cell cycle with the event occurring at that stage?

Synthesis of sufficient DNA for two daughter cells occurs in stage II

A student designs an experiment to investigate the influence of temperature on enzyme function. The student's plan is presented in Table 1.

Test tubes 1, 3, 5, and 7

Some membrane proteins help maintain the concentrations of ions inside a cell by transporting the ions across the cell's plasma membrane. Other membrane proteins form pores in the plasma membrane through which the ions can diffuse. A model showing the influence of membrane proteins on the movement of sodium (Na+) and potassium (K+) ions across a plasma membrane is presented in Figure 1. Based on the model presented in Figure 1, which of the following changes will most likely result from a depletion of available ATP stores inside the cell?

The Na+ concentration inside the cell will increase.

Figure 1 shows three amino acids that are part of a polypeptide chain. Figure 2 shows the same section of the chain after a mutation has occurred. How might this change affect the structure and function of the protein?

The R-group of the new amino acid, valine, has different chemical properties than the R-group of cysteine. This will cause the protein to misfold and not function properly in the cell.

In mammals, the dark color of skin, hair, and eyes is due to a pigment called melanin. Melanin is produced by specialized skin cells called melanocytes. The melanin is then transferred to other skin cells called keratinocytes. Melanocytes synthesize melanin in a multistep metabolic pathway (Figure 1). The amount of melanin produced is dependent on the amount of the enzymes TYR, TRP2, and TRP1 present inside melanocytes. Which of the following claims about the TYR, TRP2, and TRP1 mammalian genes is most likely to be accurate?

The TYR, TRP2, and TRP1 genes may be located on different chromosomes but are activated by the same transcription factor.

The phosphorus-starved plant was unable to synthesize both the required nucleic acids and lipids, limiting growth. As shown in Figure 1, an amino acid must have which of the following properties in order to be incorporated into a polypeptide?

The ability to form a covalent bond with both its NH2 group and its COOH group

Acetylcholinesterase (AChE) is a protein that catalyzes the conversion of acetylcholine to acetate and choline. When the concentration of AChE in an aqueous solution is held constant, the rate of the reaction catalyzed by AChE increases with increasing concentrations of substrate. At low concentrations of acetylcholine, a small increase in the substrate concentration results in a large increase in the reaction rate. At high concentrations of acetylcholine, however, a large increase in the substrate concentration results in only a small increase in the reaction rate. Which of the following statements correctly explains the observed effect of the acetylcholine concentration on the rate of the enzyme-catalyzed reaction?

The active site of AChE is specific for acetylcholine, and only one substrate molecule can occupy the active site at a time.

Phycobiliproteins are a complex of accessory pigments and proteins found in cyanobacteria but not in green algae. A researcher claims that the phycobiliprotein pigments in cyanobacteria allow the cyanobacteria to survive in certain aquatic niches better than green algae can. Which of the following statements best justifies the researcher's claim?

The additional pigments absorb light at wavelengths that green algae cannot absorb; this may allow cyanobacteria to capture more light energy for photosynthesis than green algae can in certain areas.

In an experiment, a researcher prepares a reaction mixture by dissolving a substance in a buffered solution. The substance is the substrate of a certain enzyme. The researcher adds a small amount of the enzyme to the reaction mixture and measures the amount of product that is formed over time. The data are represented in Figure 1. Which of the following best predicts the immediate result of adding more substrate to the reaction mixture at the point indicated by the arrow in Figure 1?

The amount of product will increase until the reaction reaches its equilibrium point or until the substrate is used up by the reaction.

A group of mutations, known as MT-ND1, have been identified in mitochondrial DNA. These mutations are associated with a number of debilitating diseases stemming from the production of nonfunctional proteins in the mitochondria. Which of the following cellular deficiencies would most likely be related to these MT-ND1 mutations?

The cell is unable to complete reactions related to electron transport and ATP production.

Eukaryotes transcribe RNA from DNA that contains introns and exons. Alternative splicing is one post transcriptional modification that can create distinct mature mRNA molecules that lead to the production of different proteins from the same gene. Figure 1 shows a gene and the RNA produced after transcription and after alternative splicing. A cell needs to metabolize the substrate illustrated in Figure 1 for a vital cellular function. Which of the following best explains the long-term effect on the cell of splicing that yields only enzyme C mRNA?

The cell will die because it is unable to metabolize the substrate without enzyme A, which is structurally specific for the substrate shown.

(Polysaccharide question) Based the information provided, which of the following statements best describes why starch and cellulose provide different functions in plants?

The differences in the assembly and organization of the monomers of these two polymers result in different chemical properties.

(Peroxidase question) One of the researchers proposes using oxygen gas production to measure reaction rates. Which of the following statements best justifies the use of the proposed modification as a way of creating an appropriate control for the investigation?

The experiment can be repeated without guaiacol, which will reveal the effect of guaiacol on the reaction rates.

A hydrophilic peptide hormone is produced in the anterior pituitary gland located at the base of the brain. The hormone targets specific cells in many parts of the body. Which of the following best explains a possible mechanism that would enable the hormone to efficiently reach all of the target cells in the body?

The hormone is released into the bloodstream where it can be transported to all cells with the correct receptors.

The figure shows the results of an experiment to investigate the effects of an enriched CO2 environment on plant growth. Identical plants were separated into different groups and grown either in a standard CO2 environment (400 ppm CO2) or in an enriched CO2 environment (700 ppm CO2). Of the plants in each environment, half were grown under ideal conditions and half were grown under stressed conditions.

The increase in atmospheric CO2 resulted in a greater increase in plant growth under stressed conditions than under ideal conditions.

Lynch syndrome is an inherited condition associated with an increased risk for colon cancer, as well as certain other cancers. Mutations in one of several genes involved in DNA repair during DNA replication have been associated with Lynch syndrome. DNA sequencing was performed for an individual. The results indicated that the individual carries one of the dominant alleles that has been associated with Lynch syndrome. Which of the following best explains how the results should be interpreted?

The individual has an increased risk of developing colon cancer.

Fibroblast growth factor receptors (FGFRs) are transmembrane proteins that regulate cellular processes such as cell proliferation and differentiation. The extracellular domains of FGFR proteins bind specifically to signaling molecules called fibroblast growth factors. The intracellular domains of FGFR proteins function as protein kinases, enzymes that transfer phosphate groups from ATP to protein substrates. (...) Which of the following changes in the FGFR signaling pathway is most likely to result in uncontrolled cell proliferation?

The irreversible association of FGFR proteins

Which feature of model 1 best illustrates how biological information is coded in a DNA molecule?

The linear sequence of the base pairs

Lysosomes digest food particles brought into a cell by endocytosis. After a vesicle containing food particles fuses with a lysosome, H+ ions are transported into the lysosome from the cytosol. This significantly lowers the pH of the lysosome relative to the cytosol and activates the enzymes that digest the particles. Which of the following best predicts what will happen to the lysosomal enzymes if the proteins that transport H+ ions from the cytosol into the lysosome are damaged?

The lysosomal enzymes will not become active, since there will be no active transport of H+ ions.

Gaucher disease is an inherited disorder in which cells of the body are unable to break down a particular type of lipid, resulting in a buildup of the lipid in some tissues and organs. Based on the information provided, Gaucher disease results most directly from a defect in the function of which of the following organelles?

The lysosome

(Melanin question) Researchers discovered a mutant form of the TYR gene with a deletion of a single guanine nucleotide in the beginning of the coding sequence. Which of the following best predicts the phenotype of an individual who is homozygous for this TYR mutation?

The mutation will change all subsequent amino acids in the TYR protein, leading to nonfunctional TYR protein. Individuals with this mutation will lack melanin in their hair, skin, and eyes and will not tan in response to UV radiation.

Phosphorous (P) is an important nutrient for plant growth. Figure 1 shows Arabidopsis thaliana plants grown under phosphorus‐sufficient (left) and phosphorus‐starved (right) conditions for six weeks. Which of the following is the most likely reason for the difference in leaf growth?

The phosphorus-starved plant was unable to synthesize both the required nucleic acids and lipids, limiting growth.

A certain type of specialized cell contains an unusually large amount of rough endoplasmic reticulum (ER). Which of the following functions is this cell type most likely specialized to perform?

The production and secretion of proteins

The beta-2 adrenergic receptor is a membrane-bound protein that regulates several cellular processes, including the synthesis and breakdown of glycogen. The receptor binds specifically to the hormone epinephrine. The binding of epinephrine to the beta-2 adrenergic receptor triggers a signal transduction cascade that controls glycogen synthesis and breakdown in the cell. A simplified model of the signal transduction cascade is represented in Figure 1. Which of the following outcomes will most likely result from the inactivation of the beta-2 adrenergic receptor?

The rate of glycogen synthesis in the cell will increase.

Stomata are pores on the surfaces of the leaves and stems of plants that regulate gas exchange between the plants and the atmosphere. Researchers found that the stomata density on the leaves of a species of plant change as the concentration of CO2 in the atmosphere changes. When grown at 350 ppm CO2 the plant has an average density of 300 stomata per mm2, but when grown at 400 ppm CO2 the plant has an average density of 250 stomata per mm2. Which of the following best describes how the ratio of the density of stomata (stomata per mm2) per CO2 concentration (ppm CO2) changes as the CO2 concentration increases?

The ratio increases from 1.2 to 1.6, because more stomata are needed at higher CO2 concentrations.

Hereditary spherocytosis (HS) is a disorder of red blood cells that causes the cells to be smaller and spherical instead of having the usual flattened, biconcave shape. The average diameter of normal red blood cells is 7.2μm, and the average diameter of red blood cells in a person with HS was found to be 6.7μm. The normal red blood cell has an average surface area of 136μm2 and an average volume of 91μm3. Which of the following provides an accurate calculation of the surface area to volume ratio of an HS red blood cell, as well as a prediction of its effect on the efficient transferring of oxygen compared to a normal red blood cell?

The ratio is 0.89, and the cells are less efficient at transferring oxygen.

Retroviruses such as HIV and hepatitis B virus use RNA as their genetic material rather than DNA. In addition, they contain molecules of reverse transcriptase, an enzyme that uses an RNA template to synthesize complementary DNA. Which of the following best predicts what will happen when a normal cell is exposed to a retrovirus?

The reverse transcriptase will produce DNA from the viral RNA, which can be incorporated into the host's genome and then transcribed and translated.

A scientist is studying the various prokaryotic and eukaryotic species found floating in a sample of water taken from a marine ecosystem. Which cellular component will be found in the widest range of organisms in the sample?

The ribosome, since all organisms need to synthesize proteins.

The insulin receptor is a transmembrane protein that plays a role in the regulation of glucose homeostasis. The receptor's extracellular domain binds specifically to the peptide hormone insulin. The receptor's intracellular domain interacts with cellular factors. The binding of insulin to the receptor stimulates a signal transduction pathway that results in the subcellular translocation of GLUT4, a glucose transport protein that is stored in vesicles inside the cell. A simplified model of the insulin receptor-signaling pathway is shown in Figure 1. Which of the following statements best predicts the effect of a loss of function of the insulin receptor's intracellular domain?

The storage of GLUT4 in vesicles inside the cell will increase.

A researcher claims that the incorporation of carbon dioxide into organic molecules during photosynthesis does not violate the second law of thermodynamics. Which of the following statements best helps justify the researcher's claim?

The total system that includes photosynthetic organisms and the Sun becomes less ordered over time.

Which of the following transport mechanisms will be affected most directly by a temporary shortage of ATP molecules inside the cell?

The transport of glucose molecules against a concentration gradient

Brown fat is a type of fat tissue found in hibernating mammals. Inside the mitochondria of these fat tissue cells, these mammals have an uncoupling protein embedded in the inner mitochondrial membrane. This uncoupling protein allows hydrogen ions to leak from the intermembrane space back into the mitochondrial matrix. Figure 1 shows details of the processes in the inner mitochondrial membrane. Which of the following statements provides reasoning that supports the claim that brown fatty tissue keeps an animal warm?

The uncoupling protein in this tissue reduces the proton gradient across the membrane and thus produces heat to warm the animal without ATPATP production.

Researchers conducted an experiment to investigate the effects of a valinomycin treatment on skeletal muscle cells. Valinomycin is a naturally occurring substance that can be used as a drug. The results of the experiment are presented in the table. Which of the following claims about the effects of the valinomycin treatment is best supported by the data presented in the table?

The valinomycin treatment caused a decrease in the activity of the mitochondria.

As shown in the diagram, when environmental temperatures drop below freezing, a layer of ice typically forms on the surface of bodies of freshwater such as lakes and rivers. Which of the following best describes how the structure of ice benefits the organisms that live in the water below?

The water molecules in ice are farther apart than those in liquid water, so the ice floats, maintaining the warmer, denser water at the lake bottom.

Figure 1 represents the relative time and sequence of the phases of the cell cycle. Which statement best predicts why a cell's progression through the cell cycle might be halted at the G1/S checkpoint?

There are not enough nucleotides available to construct new DNA

Researchers tracked the amount of DNA (measured in picograms) over time beginning with a single cell and continuing through several rounds of cell division. The researchers observed threadlike chromosomes prior to cell division. The threadlike chromosomes disappeared from view shortly after each division. The amount of DNA in picograms per cell over several rounds of cell division is shown in Figure 1. Which of the following statements is consistent with the data in Figure 1?

There is a change from 3 to 6 picograms of DNA because DNA is replicated before each round of cell division.

Adjacent plant cells have narrow channels called plasmodesmata that pass through the cell walls of the connected cells and allow a cytoplasmic connection between the cells. Which of the following statements best describes a primary function of plasmodesmata?

They allow the movement of molecules from one cell to another, enabling communication between cells.

Exposure to ultraviolet (UV) radiation is the leading cause of skin cancer in humans. Figure 1 shows a model of how UV exposure damages DNA. Which of the following statements best explains what is shown in Figure 1 ?

UV photons cause dimers to form, leading to misshapen DNA, which results in replication and transcription errors.

The tumor suppressor protein p53 binds to DNA and activates target genes, which results in the synthesis of p21, CD95, and other proteins. The p21 protein promotes cell-cycle arrest, whereas the CD95 protein promotes apoptosis. Which of the following will most likely result from a loss of p53 function?

Uncontrolled cell proliferation

Certain bacteria can use both ethyl alcohol and acetate as sources of nutrients. In an experiment where both nutrients are available to a bacterial population, the following results were obtained and graphed. What additional procedure would best help determine whether these movements are due to active transport or to passive transport?

Use two additional treatments, one containing only ethyl alcohol and one containing only acetate. Include a substance known to block ATP use by the plasma membrane. Compare the graphs of these two treatments to the original graph.

Beetroot cells contain a family of dark red pigments called betalains. The selectively permeable nature of the beetroot cells keeps the internal environment of the cell separate from the external environment of the cell. Researchers are interested in determining whether the selective permeability of beetroot cells is due to the cell membrane or if it is due to the cell wall. Exposure to cellulase is known to damage the structure of the cell wall. An experiment is set up in which beetroot cells are placed in an aqueous solution with cellulase and in one without cellulase. Which of the following results best refutes the alternative hypothesis that selective permeability is a consequence of the cell wall?

When beetroot cells are placed in a solution with cellulase, the solution remains clear.

(Melanin question) Which of the following pieces of evidence would best support the researchers' claim above?

When researchers applied a drug that activates adenylyl cyclase to the mutant mice's ears, the level of melanin increased.

Small single-stranded RNA molecules called microRNAs (miRNAs) are capable of base pairing with specific binding sites in the 3′ untranslated region of many mRNA transcripts. Transcription of gene Q yields an mRNA transcript that contains such an miRNA binding site, which can associate with miRNA‑delta, a specific miRNA molecule. Which of the following best supports the claim that binding of miRNA‑delta to the miRNA binding site inhibits translation of gene Q mRNA?

When the miRNA binding site sequence is altered, translation of Q mRNA occurs in the presence of miRNA-delta.

The trp operon in E. coli is an example of a repressible operon that consists of genes coding for enzymes used to synthesize tryptophan. When tryptophan levels are high, the operon is turned off and these genes are not transcribed. However, it is also known that tryptophan does not bind directly to the operator DNA sequence. A regulatory gene called trpR has also been discovered although it is not part of the trp operon. The proposed model of how tryptophan acts as a corepressor is shown in Figure 1. Which of the following evidence best supports a claim that tryptophan functions as a corepressor?

When trpR is mutated, the trp operon is transcribed regardless of tryptophan levels.

A researcher claims that budding yeast are able to survive in different environments because they produce enzymes that allow them to use different molecules as sources of matter and energy. Which of the following statements best helps justify the researcher's claim by providing a relevant example?

Yeast cells produce invertase, which is an enzyme that catalyzes the conversion of the disaccharide sucrose into glucose and fructose.

European flycatchers feed caterpillars to their hatchlings. Graph 1 shows the average dates of hatching and fledging (leaving the nest), and the biomass of the caterpillars between early May (when flycatcher young hatch) and June (when fledging of young occurs). Based on the data, scientists claim that the reproductive behavior of European flycatchers is influenced by the availability of energy sources. Which of the following statements best justifies this claim?

Young European flycatchers hatch from eggs when caterpillar biomass is available for the young birds to consume and convert into energy for growth.

G proteins are a family of receptor proteins that are involved in transmitting signals from outside a cell to inside a cell. When a signaling molecule binds to a G protein, the G protein is activated. The G protein then activates an enzyme that produces a second messenger called cAMP. Which of the following describes a critical role of cAMP during the transduction stage of a G protein signal transduction pathway?

cAMP results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules.

Catalase is an enzyme found in yeast cells that facilitates the chemical breakdown of hydrogen peroxide to water and oxygen gas. An experiment was conducted to determine the effect of pH on catalase function. Five buffer solutions of varying pH (2, 4, 6, 8, and 10) were prepared and added to separate test tubes. Hydrogen peroxide (H2O2) was added to each test tube. Yeast was added, and the reactions were timed. After 1 minute the amount of oxygen gas released was determined by measuring the foam layer produced in each test tube. Figure 1 illustrates the experimental setup. A set of five additional test tubes were prepared and used as controls. Which of the following best describes the contents expected to be contained in one of the five control test tubes?

pH 4 buffer solution and hydrogen peroxide only