AP Biology College Board Q&A

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.

DNA and RNA are nucleic acids that can store biological information based on the sequence of their nucleotide monomers. Figure 1 shows a short segment of each of the two types of nucleic acids. Which of the following best describes a structural difference between DNA and RNA?

The backbone of DNA contains deoxyribose, whereas the backbone of RNA contains ribose.

Which of the following best describes the structures of carbohydrates?

They occur as monomers, chains of monomers, and branched structures.

Which of the following is responsible for the cohesive property of water?

Hydrogen bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule

Figure 1 represents a nucleic acid fragment that is made up of four nucleotides linked together in a chain. Figure 1. Nucleic acid fragment. Which of the following characteristics of Figure 1 best shows that the fragment is RNA and not DNA?

The identity of each nitrogenous base

Figure 1. Testosterone movement across the cellular membrane. 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 researcher claims that increased atmospheric carbon dioxide levels cause increased growth rates in plants.Which of the following statements best supports the researcher's claim?

Atmospheric carbon dioxide is the raw material for photosynthesis, which plants rely on for producing sugars and other organic compounds.

Figure 1 is a diagram of water molecules at the air-water interface at the surface of a pond. Based on Figure 1, which of the following best describes how the properties of water at an air-water interface enable an insect to walk on the water's surface?

Hydrogen bonds between molecules at the surface of the water provide surface tension, which allows the water surface to deform but not break under the insect.

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. Which of the following actions will provide a negative control for the investigation?

Repeating the experiment using heat-denatured peroxidase

A researcher claims that different enzymes exhibit maximal function over different pH ranges. To test the claim, the researcher carries out an experiment that includes three different enzymes: pepsin, salivary amylase, and arginase. The results of the experiment are represented in Figure 1. Which of the following actions will provide the most appropriate negative control for the experiment?

Repeating the experiment with denatured enzymes

In flowering plants, plasmodesmata are narrow channels through cell walls that connect the cytoplasms of adjacent cells. An explanation of how plant cells communicate across cell walls will most likely refer to the diffusion through plasmodesmata of which of the following?

Small, water-soluble molecules

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.

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.

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.

A researcher claims that spinach leaves capture the most energy from light waves in the range of 500 nm to 600 nm. To test the claim, the researcher will place spinach leaves in separate chambers and expose the leaves to different wavelengths of light. For each chamber, the researcher will measure the amount of oxygen gas (O2) that is produced in one hour. Which of the following graphs best represents data from the experiment that will support the researcher's claim?

at 400 to 500, increase at 500 to 600, constant at 600 to 700, decrease

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

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?

8 light greys and 10 blacks. they are scatted and mixed, NOT in one place

Gelatin is a protein that is derived from collagen which is found in the bones, skin, and connective tissue of animals. To investigate the ability of various enzymes to digest gelatin, a group of students set up an assay involving camera film. Camera film contains gelatin and appears black when exposed to light but turns clear as the gelatin gets broken down. The students incubated pieces of exposed camera film in test tubes, each containing one of three different enzyme solutions (trypsin, lipase, or amylase) as indicated in Figure 1. The students recorded the time it took for the enzymes to digest the gelatin in each test tube, turning the film from black to clear. Figure 1. Diagram of experimental setup. Which of the following would be the most appropriate control for this experiment?

A test tube containing a piece of exposed camera film submerged in water

Which of the following statements best predicts the effect of increasing the permeability of the mitochondrial membranes to large molecules?

ATP production will decrease because of an increase in the occurrence of uncontrolled chemical reactions.

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.

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.

Aquaporins are channel proteins that facilitate the transport of water across the cell membrane. One group of researchers hypothesizes that without functional aquaporins, no water will be able to enter the cell. A different group proposes an alternative hypothesis, stating that even with nonfunctional aquaporins, a small amount of water will still cross the cell membrane. An experiment is set up in which plant cells with mutated (nonfunctional) aquaporins and plant cells with normally functioning aquaporins are both placed in distilled water. Which of the following data would support the alternative hypothesis?

Cells with mutated aquaporins exhibit moderate turgor pressure and are hypertonic.

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.

Alcohol dehydrogenase (ADH) is an enzyme that aids in the decomposition of ethyl alcohol (C2H5OH) into nontoxic substances. Methyl alcohol acts as a competitive inhibitor of ethyl alcohol by competing for the same active site on ADH. When attached to ADH, methyl alcohol is converted to formaldehyde, which is toxic in the body. Which of the following statements best predicts the effect of increasing the concentration of substrate (ethyl alcohol), while keeping the concentration of the inhibitor (methyl alcohol) constant?

Competitive inhibition will decrease because the proportion of the active sites occupied by substrate will increase.

Notch is a receptor protein displayed on the surface of certain cells in developing fruit fly embryos. Notch's ligand is a membrane-bound protein called Delta that is displayed on the surface of adjacent cells. When Notch is activated by its ligand, the intracellular tail of the Notch protein becomes separated from the rest of the protein. This allows the intracellular tail to move to the cell's nucleus and alter the expression of specific genes. Which of the following statements best explains Delta's role in regulating cell communication through the Notch signaling pathway?

Delta restricts cell communication to short distances within a developing embryo.

A scientist claims that Elysia chlorotica, a species of sea slug, is capable of photosynthesis.Which of the following observations provides the best evidence to support the claim?

Elysia chlorotica grows when exposed to light in the absence of other food sources.

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. Figure 1. Selected events in geologic time based on geochemical and fossil evidence. 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

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.

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells. A researcher claims that the epinephrine signaling pathway controls a catabolic process in muscle cells. Which of the following statements best helps justify the researcher's claim?

Glycogen phosphorylase catalyzes the conversion of glycogen to glucose-1-phosphate.

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.

Plant cell walls are composed of cellulose, while fungal cell walls are composed of chitin. A group of scientists hypothesize that this difference means the cell wall has largely different functions in plant cells and fungal cells. Alternatively, another group of scientists hypothesize that despite their biochemical differences, plant and fungal cell walls serve similar functions. Which of the following observations would best support the alternative hypothesis described above?

In both plant cells and fungal cells, the cell wall surrounds the outside of the cell membrane.

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells. Based on Figure 1, which of the following statements best describes the epinephrine signaling pathway?

In involves enzymes activating other enzymes.

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 presence of several different concentrations of the protein.

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells. Which of the following statements best describes the role of adenylyl cyclase in the epinephrine signaling pathway?

It accelerates the production of a second messenger.

In a certain signal transduction pathway, the binding of an extracellular molecule to a cell-surface protein results in a rapid increase in the concentration of cyclic AMP inside the cell. The cyclic AMP binds to and activates cytosolic enzymes that then activate other enzymes in the cell. Which of the following statements best describes the role of cyclic AMP in the signal transduction pathway?

It acts as a second messenger that helps relay and amplify the signal within the cell.

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 ATPATP production, which results in faster cell growth.

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.Figure 1. Simplified diagram of a euglenid, showing the structure of the chloroplast envelope.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.

The CFTR protein is made up of 1,480 amino acids linked together in a chain. Some humans produce a version of the CFTR protein in which phenylalanine (an amino acid) has been deleted from position 508 of the amino acid chain. Which of the following best predicts how the amino acid deletion will affect the structure of the CFTR protein?

It will affect the primary, secondary, and tertiary structures of the CFTR protein

A researcher claims that increasing the environmental temperature by 10°C will double the rate of an enzyme-catalyzed reaction. To test the claim, the researcher designs an experiment that uses a particular enzyme isolated from plants. The design of the experiment is presented in Table 1. For each test tube in the experiment, the researcher will measure the rate of product formation. Which of the following statements best helps justify the inclusion of test tube 5 as a control in the experiment?

It will provide a measurement of product formation in the presence of a denatured enzyme.

Amylase is a protein that catalyzes the conversion of starch to simple sugars. Amylase activity in an aqueous solution can be measured by using iodine as a starch indicator. A solution containing iodine and starch will have a dark-blue color, whereas a solution containing iodine but no starch will have a light-brown color. The color change of an iodine solution from dark blue to light brown can be used to measure the rate at which starch is converted to simple sugars.A student designs an experiment to investigate the effect of environmental pH on amylase function. The design of the experiment is presented in Table 1.Which of the following statements best justifies the inclusion of test tube V as a control in the experiment?

It will show the color change that occurs in the absence of enzyme activity.

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.

Ethylene causes fruits to ripen. In a signaling pathway, receptors activate transcription factors, which ultimately leads to ripening. Which of the following best supports the claim that ethylene initiates the signal transduction pathway that leads to ripening of fruit?

Loss-of-function mutations in ethylene receptors result in changes to the ripening process.

The endosymbiont theory proposes a model for the evolution of mitochondria. According to the model, an ancestral eukaryote engulfed a small, free-living prokaryotic organism. The engulfed prokaryote then formed an endosymbiotic relationship with the eukaryotic host. Which of the following observations best supports the model?

Mitochondria and some prokaryotes share similar metabolic reactions that produce ATP

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.

Changing the shape or morphology of the mitochondrial inner membrane can change the efficiency of mitochondrial function. Which of the following outcomes will most likely result from a change in the shape of the mitochondrial inner membrane from a highly folded surface to a smooth, flat surface?

Mitochondria will become less efficient because the surface area of the inner mitochondrial membranes will decrease.

Figure 1 is a proposed model of the feedback system controlling erythrocyte (red blood cell) production. Air is less dense at very high elevations, so less oxygen is available than in the denser air at sea level. Based on the model in Figure 1, if a person travels from sea level to a high elevation location, which of the following correctly predicts the response to the decreased blood oxygen level?

More erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.

In chloroplasts, ATP is synthesized from ADP plus inorganic phosphate (Pi) in a reaction catalyzed by ATP synthase molecules that are embedded in the thylakoid membrane.Which of the following statements provides evidence to support the claim that no ATP will be synthesized in the absence of a proton gradient across the thylakoid membrane?

No ATP is synthesized when channel proteins that allow the free passage of protons are inserted into the thylakoid membrane.

Which of the following conclusions is most clearly supported by the representations of nucleic acid #1 and nucleic acid #2 ?

Nucleic acid #1 contains adenine-thymine base pairs, whereas nucleic acid #2 does not.

The molecular structures of linoleic acid and palmitic acid, two naturally occurring substances, are shown in the figure. Based on the molecular structures shown in the figure, which molecule is likely to be solid at room temperature?

Palmitic acid, because the absence of carbon-carbon double bonds allows the molecules to pack closely together.

Protein digestion in humans is primarily carried out by three enzymes. Pepsin is found in the stomach (pH2), where it aids in the breakdown of large proteins into smaller peptides, while trypsin and chymotrypsin are found in the small intestine (pH8), where they aid in the further breakdown of the proteins into amino acids and dipeptides that can be absorbed into the bloodstream. Graph 1 shows the effect of pH on the activity levels of the three enzymes. Graph 1. Relative activity of pepsin, trypsin, and chymotrypsin at pH 0 through 11. Which of the following best predicts how the structure and function of pepsin will change as it enters the small intestine?

Pepsin will change in shape because of the basic environment of the small intestine; therefore, its enzymatic activity will decrease.

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 epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells. Cyclic AMP phosphodiesterase is an enzyme that catalyzes the conversion of cyclic AMP to a different molecule. Which of the following best predicts the effect of inhibiting cyclic AMP phosphodiesterase in a muscle cell stimulated by epinephrine?

Phosphorylase kinase will remain active because protein kinase A will no longer be deactivated.

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. *0.3% Saline (Cells swell)/ 0.9% Saline (Cells unchanged)/ 1.5% Saline (Cells shrink)*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.

Which of the following statements best supports the claim that certain organelles within eukaryotic cells evolved from free-living prokaryotic cells?

Some organelles contain their own DNA that is more similar to prokaryotic DNA in structure and function than to the eukaryotic DNA found in the cell's nucleus.

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

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.Figure 1. Section of a cell's plasma membrane, showing ion concentrations and membrane proteins. 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.

A student claims that the Y chromosome contains the sex-determining region gene, known as the SRY gene, which causes male fetuses to develop testes. Which of the following provides correct information about cell signaling that supports the claim?

The SRY gene produces a protein that binds to specific regions of DNA in certain tissues, which affects the development of these tissue

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. Figure 1. The amount of product formed by an enzyme-catalyzed reaction over time. 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.

The carbohydrates glucose, galactose, and fructose have the same chemical formula (C6H12O6) but different structural formulas, as represented in the figure. Which of the following statements about glucose, galactose, and fructose is most likely true?

The carbohydrates have different properties because they have different arrangements of carbon, hydrogen, and oxygen atoms.

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 ATPATP production

Researchers compared similar proteins from related organisms in different habitats. They found that the proteins from organisms living in harsh environments had a greater number of cysteine amino acids than did proteins from organisms not living in harsh environments. The structure of cysteine is shown. Bonds can form between the sulfur atom of different cysteine amino acids (S-S bonds). Which of the following best describes the effect of a greater number of cysteine amino acids on the stability of the proteins?

The change leads to increased protein stability because of an increased number of S-SS-S bonds in the tertiary structure of the proteins.

A team of biologists develop a new drug, and one team member hypothesizes that the drug is incapable of freely passing across the plasma membrane and requires the help of membrane proteins to enter cells. Alternatively, another biologist on the team hypothesizes that the drug can diffuse passively across the plasma membrane like O2 and CO2 can. Which of the following, if true about the drug, best supports the alternative hypothesis that the new drug will exhibit simple diffusion across plasma membranes?

The drug is a small nonpolar molecule.

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. 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.

Glucocorticoids are steroid hormones that control cellular responses through several different signaling pathways. One of the signaling pathways involves the glucocorticoid receptor, an intracellular protein that is activated by binding to a glucocorticoid molecule. A simplified model of the glucocorticoid receptor signaling pathway is represented in Figure 1. Figure 1. A simplified model of the glucocorticoid receptor signaling pathway. Which of the following statements best predicts the effect of a mutation that results in a loss of the glucocorticoid receptor's ligand binding function?

The glucocorticoid receptor will remain associated with the accessory proteins.

Figure 1 represents a nucleic acid fragment that is made up of four nucleotides linked together in a chain. Which of the following characteristics of Figure 1 best shows that the fragment is RNA and not DNA?

The identity of each nitrogenous base

A researcher designs an experiment to investigate the effect of environmental temperature on the function of an enzyme. For each trial included in the experiment, the researcher will add the enzyme and its substrate to an aqueous buffer solution and then measure the amount of product formed over 20 minutes.Which of the following must remain the same for all trials of this experiment?

The initial concentration of the substrate

Which of the following best describes how amino acids affect the tertiary structure of a protein?

The interactions of the different RR-groups with other RR-groups and with their environment determine the tertiary structure of the protein.

The figure shows a process by which a cell might absorb food from its surrounding environment and break it down for use as a source of energy and matter. The process involves lysosomes, which are membrane-bound organelles that contain hydrolytic enzymes. Activation of the hydrolytic enzymes requires an acidic pH, and lysosomes maintain an internal acidic pH by using ion pumps. Which of the following outcomes will most likely result from a loss of ion pump function in the cell's lysosomes?

The internal pH of the lysosomes will increase, which will prevent the activation of hydrolytic enzymes and interfere with the intracellular digestion of food.

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells. Which of the following outcomes will most likely result from the irreversible binding of GDP to the G protein?

The intracellular concentration of glycogen will increase.

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

Figure 1 shows a model of a signal transduction cascade, initiated by the binding of a ligand to the transmembrane receptor protein A. A DNA mutation changes the shape of the extracellular domain of transmembrane receptor protein A produced by the cell. Which of the following predictions is the most likely consequence of the mutation?

The molecule that normally binds to protein AA will no longer attach, deactivating the cellular response.

Water and ammonia interact to form hydrogen bonds, as represented in the figure. Which statement best helps explain the formation of the hydrogen bond represented in the figure?

The nitrogen has a partial negative charge, and the hydrogen attached to the oxygen has a partial positive charge.

Researchers claimed that a particular organelle originated from a free-living prokaryotic cell that was engulfed by a larger cell, as shown in Figure 1. Figure 1. A model showing a cell engulfing a smaller cell. Which of the following provides evidence to best support the researchers' claim?

The organelle has a double membrane.

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

Vertebrate immune responses involve communication over short and long distances. Which of the following statements best helps explain how cell surface proteins, such as MHC proteins and T cell receptors, mediate cell communication over short distances?

The proteins interact directly with proteins on the surfaces of other cells.

The coagulation cascade controls blood clot formation in response to blood vessel injury. Thrombin is an enzyme that plays a key role in regulating the coagulation cascade. A simplified model of thrombin's role in regulating the coagulation cascade is represented in Figure 1. Figure 1. A simplified model of thrombin's role in regulating the coagulation cascade. Argatroban is a competitive inhibitor of thrombin. Which of the following effects on the coagulation cascade is most likely to result from inhibiting thrombin activity with argatroban?

The rate of fibrin formation will decrease.

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 decreases from 0.86 to 0.63, because fewer 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 0.890.89, and the cells are less efficient at transferring oxygen.

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.

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 ATP production.

A researcher claims that some bacteria contain factors that influence the function of a particular enzyme but other bacteria do not. To test the claim experimentally, the researcher will grow two different bacterial strains in separate liquid cultures and isolate the contents of the cells in each culture. The researcher will add different combinations of cellular contents, substrate, and enzyme to test tubes containing a buffer solution adjusted to the optimal pH of the enzyme and then measure the rate of product formation. The design of the researcher's experiment is presented in Table 1.Which of the following statements best justifies the inclusion of test tubes 3 and 7 in the experiment?

They will show whether the isolated cellular contents have enzymatic activity.

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.

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). Graph 1. Comparison of European flycatcher hatching and fledging dates and caterpillar biomass. 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.

The enzyme peroxidase is found in many organisms. It catalyzes the breakdown of hydrogen peroxide into water and oxygen gas. The rate of peroxidase activity at different pH values was assessed by students in the lab. The students' results are shown in graph 1. Graph 1. Effect of pH on peroxidase activity. If the experiment is repeated at pH 11, the observed activity level of the enzyme will most likely be

lower than the level at pH 9

A small protein is composed of 110 amino acids linked together in a chain. As shown in Figure 1, the first and last five amino acids in the chain are hydrophobic (have nonpolar and uncharged R-groups), whereas the remaining 100 amino acids are hydrophilic (have charged or polar R-groups). The nature of the R-group determines if the amino acid is hydrophobic or hydrophilic. A mutation results in the production of a version of the small protein that is only 105 amino acids long, as shown in Figure 2. Five of the hydrophobic amino acids are missing from one end of the chain. Which of the following best depicts the tertiary structures of the two proteins in water? The diagrams in the options are not drawn to the same scale as those in Figure 1 and Figure 2.

original protein- balled up mutated protein- balled up but 1 bead is poked out

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

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?

the graph is constant first, then the albumin added is at 30, then it starts to decrease

The synthesis of protein or carbohydrate polymers always produces which of the following as a byproduct?

water