bio exam

The energy required to run the Calvin cycle reactions of photosynthesis comes from which two substances produced during the light-dependent reactions? A ATP and NADPH B ADP and PO4 C H+ and PO2 D O2 and CO2 E H2O and CO2

A

Which of the following best supports the statement that mitochondria are descendants of endosymbiotic bacteria-like cells? A Mitochondria and bacteria possess similar ribosomes and DNA. B Mitochondria and bacteria possess similar nuclei. C Glycolysis occurs in both mitochondria and bacteria. D Both mitochondria and bacteria have microtubules. E Neither mitochondria nor bacteria possess chloroplasts.

A

Directions: This group of questions consists of five lettered headings followed by a list of phrases or sentences. For each phrase or sentence, select the one heading to which it is most closely related. Each heading may be used once, more than once, or not at all. (A) Glysolysis(B) Krebs cycle (citric acid cycle)(C) Calvin cycle (light-independent reactions of photosynthesis)(D) Light-dependent reactions of photosynthesis(E) Chemiosmosis Process in which CO2, is released as a by-product of oxidation-reduction reactions A B C D E

B

During respiration, most ATP is formed as a direct result of the net movement of A potassium against a concentration gradient B protons down a concentration gradient C electrons against a concentration gradient D electrons through a channel E sodium ions into the cell

B

Which metabolic process is common to both aerobic cellular respiration and alcoholic fermentation? A Krebs cycle B Glycolysis C Electron transport chain D Conversion of pyruvic acid to acetyl CoA E Production of a proton gradient

B

Which of the following components of the cell membrane is responsible for active transport? A Phospholipid B Protein C Lipid D Phosphate E Cholesterol

B

Which of the following is evidence that eukaryotes and prokaryotes share a common ancestor? A All eukaryotes and prokaryotes contain linear DNADNA. B All eukaryotes and prokaryotes contain ribosomes. C All eukaryotes and prokaryotes use organic molecules as an energy source. D All eukaryotes and prokaryotes are capable of mitosis.

B Although the ribosomes of eukaryotes and prokaryotes have a slightly different structure, both contain ribosomes that perform the same function, suggesting that the trait came from a common ancestor.

A pathogenic bacterium has been engulfed by a phagocytic cell as part of the nonspecific (innate) immune response. Which of the following illustrations best represents the response?

C

Adenine, a nitrogenous base, is an important biological molecule. Which of the following contain adenine? A proteins, carbohydrates, and ATP B Proteins, DNA, and ATP C DNA, RNA, and ATP D DNA, RNA, and cholesterol

C

If ATP breakdown (hydrolysis) is inhibited, which of the following types of movement across cell membranes is also inhibited? A Movement of oxygen into a cell B Movement of water through aquaporins C Passage of a solute against its concentration gradient D Facilitated diffusion of a permeable substance

C

Plants use which process so that they can open their stomata at night and close their stomata during the day to avoid water loss during the hot days, without depleting the plants gas reserves. A Transpiration B Calvin C CAM photosynthesis D Cyclic photophosphorylation

C

Which of the following best describes the hydrolysis of carbohydrates? A The removal of a water molecule breaks a covalent bond between sugar monomers. B The removal of a water molecule forms a covalent bond between sugar monomers. C The addition of a water molecule breaks a covalent bond between sugar monomers. D The addition of a water molecule forms a covalent bond between sugar monomers.

C The hydrolysis of carbohydrates involves the addition of a water molecule, which breaks the covalent bond between monomers.

Which statement is NOT true of triglycerides? A Triglycerides are created through dehydration synthesis of three fatty acid hydrocarbon chains and a glycerol. B Triglycerides are a type of lipid and are hydrophobic. C Triglycerides have an uneven distribution of electrons in the majority of their structure and therefore are hydrophobic. D Triglycerides can be converted to phospholipids by replacing one of the fatty acid hydrocarbons with a phosphate functional group.

C While triglycerides are hydrophobic, this property is due to the even distribution of electrons and are nonpolar molecules.

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? A Pepsin will not change in shape and will continue to break down proteins in the small intestine. B Pepsin will not change in shape but may not work due to the basic environment of the small intestine. C Pepsin will change in shape because of the basic environment of the small intestine; therefore, its enzymatic activity will decrease. D Pepsin will change in shape because of the presence of trypsin and chymotrypsin in the small intestine, both of which act as competitive inhibitors.

C The significant change in pH will disturb the hydrogen bonding and cause denaturation of pepsin. As a result, pepsin will stop working in the small intestine.

Site of transport of materials into and out of the cell A B C D E

D

Bacteriophages are viruses that infect bacteria. In an experiment, bacteriophages were labeled with either radioactive phosphorus or radioactive sulfur. The labeled bacteriophages were incubated with bacteria for a brief amount of time and then removed. The infected bacteria cells were found to contain significant amounts of radioactive phosphorus but not radioactive sulfur. Based on the results of the experiment, which of the following types of molecules did the bacteriophages most likely inject into the bacteria cells? Simple carbohydrate A Amino acid B DNA C Polypeptide D

DNA C

Simple cuboidal epithelial cells line the ducts of certain human exocrine glands. Various materials are transported into or out of the cells by diffusion. (The formula for the surface area of a cube is 6 X S2, and the formula for the volume of a cube is S3, where S = the length of a side of the cube.) Which of the following cube-shaped cells would be most efficient in removing waste by diffusion?

the 10 one

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? A The initial concentration of the substrate B The final concentration of the product C The three-dimensional structure of the enzyme D The temperature of the aqueous buffer solution

A

An analysis of living tissue from an unknown species would likely yield the highest percentage of what element combination? A oxygen and carbon B oxygen and phosphorus C nitrogen and hydrogen D nitrogen and carbon

A

Carbon dioxide enters the plant through the A Stomata B Stroma C Thylakoid D Vein E Bundle Sheath Cell

A

Ultraviolet (UV) radiation can damage DNA by breaking weak bonds. Which of the following best explains how this occurs? A UV radiation disrupts the double helix structure by breaking the covalent bonds between the nitrogenous base pairs. B UV radiation disrupts the double helix structure by breaking the hydrogen bonds between the nitrogenous base pairs. C UV radiation is able to break DNA strands in two by breaking covalent bonds between the sugar-phosphate backbone molecules. D UV radiation is able to break DNA strands in two by breaking hydrogen bonds between the sugar-phosphate backbone molecules.

B Hydrogen bonds, like those found between nitrogenous base pairs, are weaker than covalent bonds and are easily broken by UV radiation.

For the following questions: Graphs I-IV depict the effect of pH on the activity of four different hydrolytic enzymes. Enzymes with their highest activity at an alkaline (basic) pH are represented by which of the following graphs? A I only B II only C III only D I and III only E I and IV only

B

Liver cells manufacture glycoproteins, while adipose cells store fat. Which of the following subcellular structures is likely to be more prominent in liver cells than in adipose cells? A Nucleus B Golgi apparatus C Cytoskeleton D Plasma membrane

B

The vertebrate forelimb initially develops in the embryo as a solid mass of tissue. As development progresses, the solid mass near the end of the forelimb is remodeled into individual digits. Which of the following best explains the role of apoptosis in remodeling of the forelimb? A Apoptosis replaces old cells with new ones that are less likely to contain mutations. B Apoptosis involves the regulated activation of proteins in specific cells of the developing forelimb that leads to the death of those cells. C Apoptosis involves the destruction of extra cells in the developing forelimb, which provides nutrients for phagocytic cells. D Apoptosis in the developing forelimb triggers the differentiation of cells whose fate was not already determined.

B

Which of the following can be used to determine the rate of enzyme-catalyzed reactions? A Rate of disappearance of the enzyme B Rate of disappearance of the substrate C Rate of disappearance of the product D Change in volume of the solution E Increase in activation energy

B

Which of the following questions will best direct an investigation of the mechanism of ATP synthase? A What is the source of the inorganic phosphate that is used to generate ATP from ADP? B Is the phosphorylation of ADP by ATP synthase dependent on the formation of a proton gradient? C Can ATP synthase use the energy released by phosphorylation of ADP to pump protons against a concentration gradient? D Can oxidative phosphorylation be uncoupled from the electron transport chain?

B

A researcher proposes a model of an enzyme-catalyzed reaction in which a reactant is converted to a product. The model is based on the idea that the reactant passes through a transition state within the enzyme-substrate complex before the reactant is converted to the product. Which of the following statements best helps explain how the enzyme speeds up the reaction? A The enzyme's active site binds to and stabilizes the reactant, which decreases the free-energy change of the reaction. B The enzyme's active site binds to and stabilizes the transition state, which decreases the activation energy of the reaction. C The enzyme's active site binds to and stabilizes the product, which increases the amount of energy released by the reaction. D The enzyme's active site binds to and stabilizes both the reactant and the product at the same time, which increases the reaction's equilibrium constant.

B An enzyme typically speeds up a reaction by stabilizing a transition state in the reaction, which decreases the reaction's activation energy. The enzyme's active site binds more tightly to the transition state than to either the substrate or the product, which speeds up the reaction and allows the enzyme to catalyze the same reaction repeatedly.

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-SS-S bonds). Figure 1. Chemical structure of cysteine Which of the following best describes the effect of a greater number of cysteine amino acids on the stability of the proteins? A The change has no effect on the stability of the protein because only one type of amino acid is involved. B The change leads to increased protein stability because of an increased number of S-SS-S bonds in the tertiary structure of the proteins. C The change leads to decreased protein stability because of an increased number of S-SS-S bonds in the tertiary structure of the proteins. D The change leads to increased protein stability only when the added cysteine amino acids are next to other cysteine amino acids in the primary structure.

B An increased number of S-S bonds are possible with the addition of more cysteine in the proteins. The S-S covalent bonds should add more structural stability to the proteins.

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? A It involves the opening and closing of ion channels. B In involves enzymes activating other enzymes. C It involves changes in the expression of target genes. D It involves protons moving down a concentration gradient.

B Based on Figure 1, the epinephrine signaling pathway involves enzymes activating other enzymes. For example, the pathway includes several protein kinases, enzymes that catalyze the transfer of a phosphate group from ATP to a protein substrate. As represented in Figure 1, protein kinase A catalyzes the transfer of a phosphate group from ATP to phosphorylase kinase, which results in the activation of phosphorylase kinase. The activated phosphorylase kinase activates glycogen phosphorylase in a similar manner.

Epinephrine is a protein hormone found in many animals. Epinephrine stimulates a signaling pathway that results in the breakdown of glycogen to glucose in the liver cells. Which of the following describes the initial steps in the process whereby epinephrine stimulates glycogen breakdown? A Epinephrine binds to a cell-surface receptor; the activated receptor stimulates production of the second messenger, cAMP B Epinephrine binds to a cell-surface receptor; the activated receptor catalyzes the conversion of glycogen to glucose. C Epinephrine diffuses through the plasma membrane; the hormone dimerizes in the cytosol. D Epinephrine is taken into the cell by endocytosis; glycogen is converted to glucose in the endocytotic vesicle.

A

For following group of questions first study the description of the data and then choose the one best answer to each question following it and fill in the corresponding oval on the answer sheet. To study the actions of the enzyme catalase on hydrogen peroxide, students performed the following experiment. Catalase was extracted from potatoes by blending raw potatoes in a blender with cold distilled water. The filtrate was stored on ice. The following hydrogen peroxide solutions were made: 1 percent, 5 percent, 10 percent, and 15 percent. Filter paper disks were soaked in the catalase filtrate and dropped into beakers containing the various solutions. The activity of the enzyme was measured by the amount of time it took for the disks to float to the surface of the solution on the bubbles produced by the reaction. The following data were obtained. Which of the following experimental designs should the students use as a control for the experiment? A Place a catalase-soaked disk in a beaker of water. B Drop the disks from different heights into the solution. C Poke the floating disks back down to the bottom of the beaker and retime the rise of the disks. D Shake the beakers during the time the disks are rising. E Dip the disks in the 5% solution before putting them in any other solution.

A

For following group of questions first study the description of the situation or data and then choose the one best answer to each question following it and fill in the corresponding oval on the answer sheet. In the first step of an experiment, rat liver cells were exposed for 5 minutes to amino acids labeled with a radioactive isotope. The cells were then washed to stop any further incorporation of radioactive amino acids. The cells were sampled periodically thereafter, and the radioactivity of a certain protein (protein X) was measured in various cell components, as shown below. Which of the following correctly shows the order in which protein X moves through the cell? A Endoplasmic reticulum→Golgi apparatus→lysosomes B Endoplasmic reticulum→Golgi apparatus→nucleus→cytoplasm→lysosomes C Extracellular space→mitochondria→cytoplasm D Golgi apparatus→cytoplasm→lysosomes E Cytoplasm→mitochondria→extracellular space

A

For the following questions: Graphs I-IV depict the effect of pH on the activity of four different hydrolytic enzymes. The most likely explanation for the results shown in Graph I is that A pH affects the shape of the active site of the enzyme B pH affects the temperature of the reaction C the enzyme has a quaternary structure D the enzyme has disulfide bonds E pH affects the primary structure of the enzyme

A

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

A

Oxygen consumption can be used as a measure of metabolic rate because oxygen is A necessary for ATP synthesis by oxidative phosphorylation B necessary to replenish glycogen levels C necessary for fermentation to take place D required by all living organisms E required to break down the ethanol that is produced in muscles

A

The diagram below shows energy changes in a specific chemical reaction with and without the addition of an enzyme to the reaction. Which of the following questions can best be answered by the diagram? A Does the addition of an enzyme reduce the activation energy required for a reaction? B Does the addition of an enzyme result in the formation of covalent bonds? C Does the addition of an enzyme produce a greater amount of products? D Does the addition of an enzyme change the pathway for the reaction?

A

The following questions refer to an experiment in which a dialysis-tubing bag is filled with a mixture of 3% starch and 3% glucose and placed in a beaker of distilled water, as shown below. After 3 hours, glucose can be detected in the water outside the dialysis-tubing bag, but starch cannot. If, instead of the bag, a potato slice were placed in the beaker of distilled water, which of the following would be true of the potato slice? A It would gain mass. B It would neither gain nor lose mass. C It would absorb solutes from the surrounding liquid. D It would lose water until water potential inside the cells is equal to zero. E The cells of the potato would increase their metabolic activity.

A

Two nutrient solutions are maintained at the same pH. Actively respiring mitochondria are isolated and placed into each of the two solutions. Oxygen gas is bubbled into one solution. The other solution is depleted of available oxygen. Which of the following best explains why ATP production is greater in the tube with oxygen than in the tube without oxygen? A The rate of proton pumping across the inner mitochondrial membrane is lower in the sample without oxygen. B Electron transport is reduced in the absence of a plasma membrane. C In the absence of oxygen, oxidative phosphorylation produces more ATP than does fermentation. D In the presence of oxygen, glycolysis produces more ATP than in the absence of oxygen.

A

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? A They will show whether the isolated cellular contents have enzymatic activity. B They will show whether environmental pHpH affects the function of the enzyme. C They will show the rate of product formation in the absence of bacterial factors. D They will show the rate of product formation in the absence of the substrate.

A The researcher will add cellular contents and the substrate but not the enzyme to test tubes 3 and 7. As such, test tubes 3 and 7 will show whether the cellular contents have enzymatic activity.

A student peeled the skins from grapes, exposing cells with membranes that are only permeable to water and small diffusible solutes. The student measured the mass of the peeled grapes. The student then placed each peeled grape into one of five solutions. After 24 hours, the student removed the peeled grapes from the solutions, measured their final mass, and calculated the percent change in mass (Table 1). In a second experiment (Table 2), the student placed a peeled grape into a solution containing both small diffusible solutes and solutes to which the membrane is impermeable (nondiffusible solutes). Which of the following best explains why larger grapes have a different rate of water absorption per gram of mass than smaller grapes do? A The rate is slower because smaller grapes have a larger surface-area-to-volume ratio than the larger grapes do. B The rate is slower because larger grapes have a larger surface-area-to-volume ratio than the smaller grapes do. C The rate is slower because smaller grapes can expand more than larger grapes to hold excess water. D The rate is slower because larger grapes have more volume to hold excess water than smaller grapes do.

A A grape with a smaller surface-area-to-volume ratio will have a slower rate of water absorption per gram.

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 GDPGDP to the G protein? A The intracellular concentration of glycogen will increase. B The intracellular concentration of activated protein kinase A will increase. C The intracellular concentration of cyclic AMPAMP will increase. D The intracellular concentration of glucose-1-phosphate will increase.

A Activation of the G protein requires the exchange of GDP for GTP. The irreversible binding of GDP to the G protein will block activation of the G protein, which will prevent epinephrine stimulation of glycogen breakdown. Consequently, the intracellular concentration of glycogen will increase.

A typical bag of fertilizer contains high levels of nitrogen, phosphorus, and potassium but trace amounts of magnesium and calcium. Which of the following best matches the fertilizer component with the molecule in which it will be incorporated by organisms in the area? A Nitrogen will be incorporated into nucleic acids. B Phosphorus will be incorporated into amino acids. C Potassium will be incorporated into lipids. D Magnesium will be incorporated into carbohydrates.

A All the bases in the nucleotides that compose nucleic acids contain nitrogen.

Muscle contraction depends on ATP hydrolysis. During periods of intense exercise, muscle cells rely on the ATP supplied by three metabolic pathways: glycolysis, mitochondrial respiration, and the phosphagen system. Figure 1 shows the rates at which the three metabolic pathways produce ATP following the start of an intense period of exercise. Figure 1. ATP production by three metabolic pathways following the start of an intense period of exercise Which of the following correctly uses the data to justify the claim that the phosphagen system is an immediate, short-term source of ATP for muscle cells? A ATP production by the phosphagen system increases and decreases rapidly following the start of the exercise period. B ATP production by the phosphagen system increases gradually and continuously throughout the entire exercise period. C The ATP produced by the phosphagen system contains more energy per molecule than does the ATP produced by the other pathways. D ATP hydrolysis in muscle cells occurs immediately after the start of the exercise period but stops before the end of the exercise period.

A Based on Figure 1, the phosphagen system reaches its maximum rate of ATP production approximately 5 seconds after the start of the exercise period. Because ATP production by the phosphagen system increases and decreases rapidly following the start of the exercise period, the phosphagen system is an immediate, short-term source of ATP.

Which of the following describes the most likely location of cholesterol in an animal cell? A Embedded in the plasma membrane B Dissolved in the cytosol C Suspended in the stroma of the chloroplast D Bound to free ribosomes

A Cholesterol is a nonpolar steroid that can be found embedded in the membrane between phospholipids.

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? A The initial concentration of the substrate B The final concentration of the product C The three-dimensional structure of the enzyme D The temperature of the aqueous buffer solution

A Keeping the initial substrate concentration constant allows the researcher to compare the reaction rates under different environmental conditions. The reaction rates will provide the researcher with information about the enzyme's function in different environments.

An experiment to measure the rate of respiration in crickets and mice at 10oC and 25oC was performed using a respirometer, an apparatus that measures changes in gas volume. Respiration was measured in mL of O2 consumed per gram of organism over several five-minute trials and the following data were obtained. According to the data, the mice at 10oC demonstrated greater oxygen consumption per gram of tissue than did the mice at 25oC. This is most likely explained by which of the following statements? A The mice at 10oC had a higher rate of ATP production than the mice at 25oC. B The mice at 10oC had a lower metabolic rate than the mice at 25oC. C The mice at 25oC weighed less than the mice at 10oC. D The mice at 25oC were more active than the mice at 10oC.

A Mice are endotherms and at cold temperatures will increase their rate of ATP production in order to shiver. This increase in metabolism will produce heat according to the second law of thermodynamics. This heat production will help the mouse maintain a constant internal environment.

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? A The drug is a small nonpolar molecule. B The drug is a small charged molecule. C The drug is a large polar molecule. D The drug is a large charged molecule.

A Small nonpolar molecules freely pass across the plasma membrane. If the drug is a small nonpolar molecule, this supports the alternative hypothesis.

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? A The transduction of the glucocorticoid signal across the plasma membrane will be blocked. B The glucocorticoid receptor will remain associated with the accessory proteins. C The rate of diffusion of glucocorticoid molecules into the cell will increase. D The concentration of glucocorticoid receptors inside the nucleus will increase.

B In the absence of glucocorticoid signaling, the glucocorticoid receptor is maintained in its inactive state in the cytosol by its association with accessory proteins. The binding of a glucocorticoid molecule to the glucocorticoid receptor induces a conformational change in the glucocorticoid receptor that results in its dissociation from the accessory proteins and translocation to the nucleus. A mutation that results in a loss of the glucocorticoid receptor's ligand binding function will result in the glucocorticoid receptor remaining associated with the accessory proteins in a multiprotein complex in the cytosol.

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 A the same as the level at pH 7 B lower than the level at pH 9 C greater than the level at pH 9 D between the levels observed at pH 5 and pH 7.

B Peroxidase activity drops off as the pH increases beyond 5, indicating that the optimal level was closer to pH 5. The enzyme is likely to be further denatured by a pH greater than 9. Since this enzyme occurs in many organisms, it is reasonable that the optimal pH is closer to neutral than to a strongly basic or strongly acidic pH.

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 A The 5′5′ to 3′3′ orientation of the nucleotide chain B The identity of each nitrogenous base C The charges on the phosphate groups D The type of bond linking the nucleotides together

B RNA contains uracil, whereas DNA contains thymine.

A scientist designed an experiment to test an artificial membrane that mimics the phospholipid bilayer of a cell. The scientist built a tube that was divided by an artificial membrane and filled with distilled water. The scientist put a known amount of a protein into the water on one side of the membrane. After some time, the scientist measured the concentration of the protein on either side of the membrane but found that there had been no change. Which of the following experimental changes would allow the scientist to observe transport of a solute across the artificial membrane? A Increase the solute concentration in the solution B Use a small, nonpolar solute instead of a protein C Increase the temperature of the solution D Add artificial aquaporins to the membrane

B Small, nonpolar molecules are able to diffuse through cell membranes, while large proteins are not.

A researcher claims that increasing the environmental temperature by 10°C10°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? A It will provide a measurement of product formation in the absence of the substrate. B It will provide a measurement of product formation in the presence of a denatured enzyme. C It will show the effect of doubling the amount of substrate on the rate of product formation. D It will show the effect of increased enzyme activity on the rate of product formation.

B The contents of test tube 5 will be pretreated by boiling. The pretreatment will denature the plant enzyme used in the experiment. As such, test tube 5 will provide a measurement of product formation in the presence of a denatured enzyme.

High levels of certain plant nutrients in runoff can lead to rapid growth of algae (an algal bloom) in aquatic ecosystems. These algal blooms are generally followed by algal death and decomposition, which consumes large amounts of dissolved oxygen in the water and results in oxygen levels insufficient to support aerobic respiration. This process is known as eutrophication. The amount of algae present in a body of water can be estimated from the amount of chlorophyll a in a sample of the water. A researcher studying eutrophication collected samples at different times of the year in a freshwater ecosystem. The samples were analyzed for total nitrogen and chlorophyll a concentration (Figure 1) as well as total phosphorus and chlorophyll a concentration (Figure 2). Figure 1. Amount of chlorophyll a in relation to the amount of total nitrogen Figure 2. Amount of chlorophyll a in relation to the amount of total phosphorous Which of the following describes the relationship between the amount of chlorophyll a in a water sample and the concentration of nitrogen in that sample? A As the concentration of chlorophyll a increases, the concentration of nitrogen decreases. B The concentrations of nitrogen and chlorophyll a are directly correlated. C The concentrations of chlorophyll a and nitrogen increase throughout the year. D There is no relationship between the concentrations of chlorophyll a and nitrogen.

B The data indicate that as the amount of nitrogen increases, the amount of chlorophyll in the water sample increases.

Which of the following best explains how the extensive folding of the inner mitochondrial membrane benefits a eukaryotic cell? A It enlarges the volume of the matrix, which allows for more enzymatic reactions. B It increases the area available for proteins involved in energy transfer. C It allows for greater area for the diffusion of water into and out of the mitochondria. D It provides better insulation for reactions in the matrix from conditions outside the mitochondria.

B The extensive folding provides more surface area for proteins involved in energy transfer.

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 oxygen has a partial positive charge, and the nitrogen has a partial negative charge. A The nitrogen has a partial negative charge, and the hydrogen attached to the oxygen has a partial positive charge. B The hydrogen attached to the oxygen has a partial negative charge, and the nitrogen also has a partial negative charge. C The nitrogen has a partial positive charge, and the hydrogen attached to the oxygen also has a partial positive charge. D

B The greater electronegativity of oxygen and nitrogen compared with hydrogen makes for unequal sharing of electrons, which results in partial negative charges associated with the oxygen and nitrogen atoms and partial positive charges associated with the hydrogen atoms in both molecules. The attraction between opposite charges results in the formation of the hydrogen bond represented in the figure.

A researcher claims that the synthesis of ATPATP from ADPADP and inorganic phosphate (Pi)(Pi) is essential to cellular function. Which of the following statements best helps justify the researcher's claim? A ADPADP is a small molecule that some cells release into their environment as a way of communicating with other cells. B ATPATP hydrolysis is an energy-releasing reaction that is often coupled with reactions that require an input of energy. C Inorganic phosphate (Pi)(Pi) is a substance that cells typically acquire from their environment. D ATPATP synthase is a mitochondrial enzyme that catalyzes the conversion of ADPADP and PiPi to ATPATP.

B Many cellular processes necessary for maintaining the internal organization of the cell are coupled with the hydrolysis of ATP. Without a supply of ATP, these activities will stop and the cells will die.

Cell communication is critical for the function of both unicellular and multicellular eukaryotes. Which of the following is likely true of cell signaling? A Cell signaling uses the highest molecular weight molecules found in living cells. B Cell signaling has largely been replaced by other cell functions in higher mammals. C Similar cell signaling pathways in diverse eukaryotes are evidence of conserved evolutionary processes. D Cell signaling functions mainly during early developmental stages.

C

Directions: Each group of questions below concerns an experimental or laboratory situation or data. In each case, first study the description of the situation or data. Then choose the one best answer to each question following it and fill in the corresponding circle on the answer sheet. Dialysis tubing is permeable to water molecules but not to sucrose. Four dialysis tubes are half filled with 5 percent, 10 percent, 20 percent, and 40 percent sucrose solutions, respectively, and two dialysis tubes are half filled with distilled water. The dialysis tubes are all sealed at both ends, and the initial masses are determined. Five dialysis tubes are placed into beakers containing distilled water, and the sixth dialysis tube, containing distilled water, is placed into a 40 percent sucrose solution. The masses of the dialysis tubes are recorded at 30-minute intervals for 90 minutes, as shown in the table below. To model a plant cell, a permeable, nonflexible case is placed around each piece of dialysis tubing. The greatest pressure potential will develop within dialysis tube number A 2 B 3 C 4 D 5 E 6

C

Directions: Each group of questions below concerns an experimental or laboratory situation or data. In each case, first study the description of the situation or data. Then choose the one best answer to each question following it. The following questions refer to the data in Figures 1 through 4 below, which were collected during a study of the growth of plant seedlings. The concentration of all gibberellins 65 days after planting is approximately A 5 ng/gram B 10 ng/gram C 20 ng/gram D 120 ng/gram E 150 ng/gram

C

Directions: This group of questions consists of five lettered headings followed by a list of phrases or sentences. For each phrase or sentence, select the one heading to which it is most closely related. Each heading may be used once, more than once, or not at all. This group of questions refers to molecules of the following substances. (A) Cytochrome(B) FADH2(C) NAD+(D) NADP+(E) Oxygen (O2) An intermediate electron acceptor for oxidations that occur in both glycolysis and in Krebs cycle reactions A Cytochrome B FADH2 C NAD+ D NADP+ E Oxygen (O2)

C

Many human cells can be stimulated to divide by hormonelike growth factors that bind to receptor proteins (R) on the plasma membrane and trigger an internal signal-transduction cascade. In many cases, however, the process of contact inhibition prevents mitosis when cells are in direct contact with one another. Contact inhibition occurs when proteins called cell adhesion molecules interact, causing them to change shape so that the growth-factor signaling proteins that normally associate with are replaced by another protein, called M. Both pathways are depicted in the figures below Which of the following statements accurately uses the information presented to support the hypothesis that interruption of M function in a single body cell can result in cancer? A Protein 3 will be prevented from interacting with causing the cell cycle to stop permanently. B The ras protein will remain bound to DNA, blocking the expression of genes required for mitosis. C Growth-factor signaling can trigger mitosis in cells that are in direct contact with other cells. D The receptor proteins of body cells will no longer bind to growth-factor proteins.

C

The diagram above represents a typical rod-shaped bacterium. Which of the following best describes a feature shown in the diagram that is unique to archaea and bacteria? A The organism is surrounded by a cell wall. B The organism contains ribosomes. C The organism does not have a nuclear membrane surrounding its genetic material. D The organism is not capable of making or providing itself with ATP.

C

The figure above represents a rough endoplasmic reticulum. Which of the following best describes the role of the structure labeled Y? A Structure Y contributes the raw materials required for the synthesis of proteins. B Structure Y packages proteins for export from the cell. C Structure Y is the location where proteins are synthesized. D Structure Y contains enzymes that cut and activate proteins.

C

The following questions refer to the following diagram. For each phrase or sentence, select the labeled part to which it is most closely related. Each option may be used once, more than once, or not at all for each group. Site of modification and packaging of proteins and lipids prior to export from the cell A B C D E

C

Which of the following describes a metabolic consequence of a shortage of oxygen in muscle cells? A An increase in blood pH due to the accumulation of lactic acid B No ATP production due to the absence of substrate-level phosphorylation C A buildup of lactic acid in the muscle tissue due to fermentation D A decrease in the oxidation of fatty acids due to a shortage of ATP

C

Which of the following is responsible for the cohesive property of water? A Hydrogen bonds between the oxygen atoms of two adjacent water molecules B Covalent bonds between the hydrogen atoms of two adjacent water molecules C Hydrogen bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule D Covalent bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule E Hydrogen bonds between water molecules and other types of molecules

C

he figure above shows a series of microscope images taken over time of ovalbumin production in chick oviduct cells in response to stimulation with estrogen. The ovalbumin protein was detected using a fluorescent dye as shown by the white areas in the time-lapse sequence. The microscope images indicate that ovalbumin A is synthesized on soluble ribosomes and packaged into lysosomes, from which it is secreted into the oviduct B is synthesized on ribosomes bound to the rough endoplasmic reticulum, and then secreted directly into the oviduct C crosses the endoplasmic reticulum membrane as it is translated, then moves to the Golgi apparatus, then to vesicles from which it is secreted D crosses the Golgi apparatus membrane post-translationally, is taken up by the Golgi apparatus and endoplasmic reticulum, then is packaged into secretory vesicles

C

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 the same properties because they have the same number of carbon, hydrogen, and oxygen atoms. A The carbohydrates have the same properties because they each have a single carbon-oxygen double bond. B The carbohydrates have different properties because they have different arrangements of carbon, hydrogen, and oxygen atoms. C The carbohydrates have different properties because they have different numbers of carbon-carbon bonds. D

C Compounds that have the same chemical formula but different structural formulas usually have different properties.

Figure 1. Formation of a peptide bond Which of the following best describes the formation of the bond shown in Figure 1 ? An ionic bond is formed between a carbon atom of one amino acid and the nitrogen atom of the other amino acid. A An ionic bond is formed when the negative charge of an OH group is balanced by the positive charge of a hydrogen ion. B A covalent bond is formed between a carbon atom and a nitrogen atom along with the formation of H2O. C A covalent bond is formed that replaces the hydrogen bond between the OH group and the H atom. D

C Even though the water molecule that is produced is not shown in Figure 1, it shows the formation of the peptide bond and the missing H and OH

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 A test tube containing no camera film B A test tube containing only a piece of exposed camera film C A test tube containing a piece of exposed camera film submerged in water D A test tube containing a piece of exposed camera film and all three enzyme solutions

C Having one test tube with only water and camera film will show that water is not the substance that causes the film to change color.

Membrane-bound organelles have been an important component in the evolution of complex, multicellular organisms. Which of the following best summarizes an advantage of eukaryotic cells having internal membranes? A Eukaryotic cells are able to reproduce faster because of the presence of organelles. B Some organelles, such as mitochondria and chloroplasts, are similar to prokaryotic cells in structure. C Organelles isolate specific reactions, increasing metabolic efficiency. D Compartmentalization leads to a higher mutation rate in DNA, which leads to more new species.

C It demonstrates understanding and provides an explanation of how internal membrane-bound organelles contribute to cell function by providing a favorable local environment for metabolic reactions, and by protecting the cell from potentially damaging metabolic reactions.

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. Figure 1. The effect of pH on three different enzymes Which of the following actions will provide the most appropriate negative control for the experiment? A Repeating the experiment with a fourth enzyme B Repeating the experiment at several different temperatures C Repeating the experiment with denatured enzymes D Repeating the experiment using several different methods for measuring pH

C Repeating the experiment with denatured enzymes will provide an appropriate negative control for the experiment. The negative control will show that the changes observed in the experiment result from changes in enzyme function.

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? A It will provide a measurement of amylase activity at an acidic pH. B It will provide a measurement of amylase activity at a basic pH. C It will show the color change that occurs in the absence of enzyme activity. D It will show the color change that occurs in the absence of the amylase protein.

C Test tube V will contain all the components of the reaction mixture, but the amylase protein will be inactive because it will have been denatured during the pretreatment. Test tube V is an appropriate control in the experiment because it will show the color change that occurs in the absence of amylase activity.

Which of the following statements best helps explain the reaction specificity of an enzyme? A The free energy of the reactants is greater than the free energy of the products. B The equilibrium constant of the reaction is much greater than 1. C The shape and charge of the substrates are compatible with the active site of the enzyme. D The concentration of the enzyme inside living cells is greater than the concentration of substrate.

C The reaction specificity of an enzyme is determined by the compatibility of the substrate with the enzyme's active site. A substrate's shape and charge affect how it fits into an enzyme's active site and whether it forms favorable interactions with the enzyme.

A student placed 20 tobacco seeds of the same species on moist paper towels in each of two petri dishes. Dish A was wrapped completely in an opaque cover to exclude all light. Dish B was not wrapped. The dishes were placed equidistant from a light source set to a cycle of 14 hours of light and 10 hours of dark. All other conditions were the same for both dishes. The dishes were examined after 7 days and the opaque cover was permanently removed from dish A. Both dishes were returned to the light and examined again at 14 days. The following data were obtained. Additional observations were made on day 21, and no yellow-leaved seedlings were found alive in either dish. This is most likely because A yellow-leaved seedlings were unable to absorb water from the paper towels B taller green-leaved seedlings blocked the light and prevented photosynthesis C yellow-leaved seedlings were unable to convert light energy to chemical energy D a higher rate of respiration in yellow-leaved seedlings depleted their stored nutrients

C This option is correct. The only difference between the two plants after day 14 was the leaf color. Without chlorophyll, the yellow seedlings could not absorb enough light energy to convert to chemical energy to sustain growth. Therefore, no yellow seedlings were found alive in either dish after day 21.

Both myoglobin and hemoglobin are proteins that bind reversibly with molecular oxygen. The graph below shows the oxygen-binding saturation of each protein at different concentrations of oxygen. Which of the following statements is correct? A At 10 mm Hg partial pressure, hemoglobin binds oxygen but myoglobin does not. B At 20 mm Hg partial pressure, myoglobin and hemoglobin bind oxygen in equal amounts. C At 40 mm Hg partial pressure, myoglobin has a greater affinity for oxygen than hemoglobin has. D At 80 mm Hg partial pressure, myoglobin binds twice as much oxygen as hemoglobin binds.

C This option is correct. The question tests whether the student can read the graph to analyze the data. The graph indicates that at 40 mm Hg pressure, myoglobin binds a greater amount of oxygen than hemoglobin.

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? A It converts a polymer to its monomer subunits. B It moves substances across the plasma membrane. C It accelerates the production of a second messenger. D It transfers phosphate groups from ATPATP to protein substrates.

C When activated, adenylyl cyclase accelerates a reaction in which ATP is converted to cyclic AMP, which acts as a second messenger in the epinephrine signaling pathway.

According to the chemiosmotic theory (chemiosmotic coupling), the energy required to move protons from the mitochondrial matrix to the intermembrane space against a concentration gradient comes most directly from A photons of red or blue light B the hydrolysis of ATP C the breakdown of high-energy fatty acids inthe mitochondrial matrix D electrons flowing along the electron transportchain E substrate-level phosphorylation

D

Cortisol is a hormone produced in response to stress, including starvation, in humans. Which of the following is most likely an immediate effect of a starvation-induced increase in cortisol secretion? A Increased activation of the immune system B Increased urine production by the kidneys C Increased bone and collagen formation D Increased mobilization of fatty acids from fat cells

D

For following group of questions first study the description of the data and then choose the one best answer to each question following it and fill in the corresponding oval on the answer sheet. To study the actions of the enzyme catalase on hydrogen peroxide, students performed the following experiment. Catalase was extracted from potatoes by blending raw potatoes in a blender with cold distilled water. The filtrate was stored on ice. The following hydrogen peroxide solutions were made: 1 percent, 5 percent, 10 percent, and 15 percent. Filter paper disks were soaked in the catalase filtrate and dropped into beakers containing the various solutions. The activity of the enzyme was measured by the amount of time it took for the disks to float to the surface of the solution on the bubbles produced by the reaction. The following data were obtained. Which of the following best describes why the disks rose to the surface faster in the more concentrated hydrogen peroxide solutions? A There was more enzyme present in the more concentrated solutions. B A greater amount of heat was generated in the more concentrated solutions. C The more concentrated solutions lowered the activation energy of the reaction. D The higher substrate concentrations in the more concentrated solutions speeded the reaction. E The density of the water was lower in the more concentrated solutions.

D

Individuals with an inherited autosomal recessive disorder called primary ciliary dyskinesia (PCD) often have severe respiratory problems due to defective cilia. Males with PCD are often sterile because they produce sperm with defective flagella. Which of the following most likely explains the effect of the recessive allele? A The mitochondria are defective and do not produce sufficient protein to synthesize microtubules in the cilia and flagella. B The plasma membrane of the alveoli is not permeable to carbon dioxide during respiration because it is too hydrophobic. C The Golgi bodies secrete an enzyme that destroys the proteins in the flagella and cilia. D The cells do not produce functional motor proteins in flagella and cilia.

D

The manner in which several different ions and molecules move through a cell membrane is shown in the diagram above. For each ion or molecule, the relative concentration on each side of the membrane is indicated. Which of the following accurately describes one of the movements taking place? A Glucose is transported into the cell by active transport. B Na+ is transported into the cell by active transport. C The movement of glucose through the membrane requires ATP hydrolysis. D Na+ transport out of the cell requires ATP hydrolysis.

D

Two groups of students attempted to re-create the primitive atmospheric conditions of early Earth using the apparatus represented below. Each group ran the experiment with different gas mixtures in the apparatus. Which of the following statements best justifies the claim that the conditions in at least one of the experiments could generate the molecular building blocks essential for life? A The carbon dioxide gas and water vapor in experiment 1 could react spontaneously to produce the phospholipids required by the first life forms. B The nitrogen gas and ammonia gas in experiment 1 could provide the elemental nitrogen required for the formation of amino acids. C The sulfur dioxide gas in experiment 2 could donate the excited electrons required to drive the process of photosynthesis. D The methane gas in experiment 2 could act as the electron acceptor required to complete the process of cellular respiration

D

When hydrogen ions are pumped out of the mitochondrial matrix, across the inner mitochondrial membrane, and into the space between the inner and outer membranes, the result is A damage to the mitochondrion B the reduction of NAD C the restoration of the Na-K balance across the membrane D the creation of a proton gradient E the lowering of pH in the mitochondrial matrix

D

Which of the following is a photosynthetic process that has ATP as its sole product. There is no oxygen and no NADPH produced from these reactions. A Transpiration B Calvin cycle C CAM photosynthesis D Cyclic photophosphorylation

D

Which of the following is most directly responsible for water's unique properties? A It contains oxygen atoms. B It contains hydrogen atoms. C It is an ionic compound. D It forms hydrogen bonds. E It is nonpolar.

D

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 have no observable effect on the structure of the CFTR protein. A It will affect the primary structure of the CFTR protein, but the other levels of protein structure will not be affected. B It will affect the secondary and tertiary structures of the CFTR protein, but the primary structure will not be affected. C It will affect the primary, secondary, and tertiary structures of the CFTR protein. D

D A change in the primary structure of the CFTR protein will lead to changes in the secondary and tertiary structures. As a result, the protein will not fold properly and will not function normally.

The figure shows a model of the exchange of matter between the organisms that live together in an aquarium. The model includes matter exchange between plants, fish, and bacteria. The bacteria are represented as rod-shaped organisms living in the gravel at the bottom of the aquarium. Which of the following statements best describes how molecules released by the fish become nutrients for the plants? he carbon dioxide molecules released by the fish are converted by the bacteria to oxygen atoms, which are used by the plants to make water molecules. A The oxygen molecules released by the fish are converted by the bacteria to ammonia molecules, which are used by the plants to make lipids and fatty acids. B The nitrites released by the fish are converted by the bacteria to carbon dioxide molecules, which are used by the plants to make carbohydrates. C The ammonia molecules released by the fish are converted by the bacteria to nitrates, which are used by the plants to make proteins and nucleic acids. D

D As shown in the figure, the ammonia molecules released by the fish are converted by the bacteria to nitrites and nitrates. The plants absorb the nitrates, which are nitrogen-containing nutrients that the plants use to make the amino acids and nucleotides needed for building proteins and nucleic acids.

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? A Atmospheric carbon dioxide is produced by the burning of fossil fuels, which are formed from the remains of living organisms such as plants. B Atmospheric carbon dioxide is a byproduct of cellular respiration, which is a metabolic process that occurs in plants and other living organisms. C Atmospheric carbon dioxide typically enters plant leaves through stomata, which plants rely on for regulating gas exchange with the atmosphere. D Atmospheric carbon dioxide is the raw material for photosynthesis, which plants rely on for producing sugars and other organic compounds.

D Atmospheric carbon dioxide is the raw material for photosynthesis, which is the metabolic process by which green plants use energy in sunlight to produce sugars and other organic compounds. The plants use the sugars and organic compounds to support growth, repair, and reproduction

The enzyme hexokinase catalyzes the conversion of glucose to glucose-6-phosphate, which is an important step in glycolysis. The reaction involves the transfer of a phosphate group from ATP to glucose. Either a glucose molecule or a water molecule can fit in the active site of hexokinase. The presence of a water molecule in hexokinase's active site would result in the hydrolysis of ATP to ADP instead of the conversion of glucose to glucose-6-phosphate. Which of the following statements best helps explain the reaction specificity of hexokinase? A Both glucose and water are polar molecules that form favorable interactions with charged and polar amino acid side chains in hexokinase's active site. B Both glucose and water have oxygen atoms that can form covalent bonds with the phosphorus atoms of phosphate groups. C Glucose is an energy-rich organic molecule that can be broken down by glycolysis to produce ATPATP, whereas water is an inorganic molecule. D Glucose has the right shape and charge to cause hexokinase to undergo a structural change needed for catalysis, whereas water does not.

D Hexokinase catalyzes the conversion of glucose to glucose-6-phosphate but not the hydrolysis of ATP. Hexokinase's reaction specificity is explained by the compatibility of glucose and hexokinase's active site, which results in part from glucose's shape and charge. Because of this compatibility, hexokinase undergoes a structural change when it binds to glucose but not to water, and the structural change is necessary for hexokinase to become catalytically active.

Figure 1 is a diagram of water molecules at the air-water interface at the surface of a pond. Figure 1. Alignment of water molecules at air-water interface 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? A Covalent bonds between water molecules and the air above provide cohesion, which causes tiny bubbles to form under the feet of the insect. B Ionic bonds between molecules at the surface of the water provide an electric charge, which attracts the feet of the insect, keeping it on the surface. C Polar covalent bonds between molecules at the surface of the water provide adhesion, which supports the weight of the insect. D 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.

D Hydrogen bonds form between water molecules due to the partial charges produced as a result of the polarity of the water molecule. The strength of the attraction between the water molecules allows organisms to walk across the surface without breaking the hydrogen bonds.

Alcohol dehydrogenase (ADH) is an enzyme that aids in the decomposition of ethyl alcohol (C2H5OH)(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? A There will be an increase in formaldehyde because ADHADH activity increases. B Competitive inhibition will be terminated because ethyl alcohol will bind to methyl alcohol and decrease ADHADH activity. C The peptide bonds in the active site of the enzyme will be denatured, inhibiting the enzyme. D Competitive inhibition will decrease because the proportion of the active sites occupied by substrate will increase.

D The increase in amount of substrate will increase the number of enzyme-ethanol complexes formed, increasing the amount of nontoxic product formed from ethyl alcohol.

Polypeptides are continuously being formed and degraded. One of these processes is shown. Figure 1. Polypeptide reaction Which statement is the most accurate description of the reaction shown in Figure 1? A It represents monomers linked by dehydration synthesis. B It represents a polypeptide chain that folds to form the tertiary structure. C It represents a polypeptide chain that is denatured into the primary structure. D It represents a polypeptide chain that is broken down through a hydrolysis reaction.

D The reaction shows the polypeptide being split into two smaller units with the addition of a hydroxide ion and a hydrogen ion from water. This facilitates the breaking of the bond holding the polypeptide together.

A scientist determined the rate of an enzyme-catalyzed reaction by measuring the amount of product formed over time. The following curve was generated from the data collected. During which time interval is the reaction rate lowest? A 0-1 minute B 1-2 minutes C 2-3 minutes D 3-4 minutes E 4-5 minutes

E

Directions: Each group of questions below concerns an experimental or laboratory situation or data. In each case, first study the description of the situation or data. Then choose the one best answer to each question following it and fill in the corresponding circle on the answer sheet. Dialysis tubing is permeable to water molecules but not to sucrose. Four dialysis tubes are half filled with 5 percent, 10 percent, 20 percent, and 40 percent sucrose solutions, respectively, and two dialysis tubes are half filled with distilled water. The dialysis tubes are all sealed at both ends, and the initial masses are determined. Five dialysis tubes are placed into beakers containing distilled water, and the sixth dialysis tube, containing distilled water, is placed into a 40 percent sucrose solution. The masses of the dialysis tubes are recorded at 30-minute intervals for 90 minutes, as shown in the table below. A net movement of water into the beaker occurs in which of the following dialysis tubes? A 2 B 3 C 4 D 5 E 6

E

Directions: Each group of questions below concerns an experimental or laboratory situation or data. In each case, first study the description of the situation or data. Then choose the one best answer to each question following it and fill in the corresponding circle on the answer sheet. Dialysis tubing is permeable to water molecules but not to sucrose. Four dialysis tubes are half filled with 5 percent, 10 percent, 20 percent, and 40 percent sucrose solutions, respectively, and two dialysis tubes are half filled with distilled water. The dialysis tubes are all sealed at both ends, and the initial masses are determined. Five dialysis tubes are placed into beakers containing distilled water, and the sixth dialysis tube, containing distilled water, is placed into a 40 percent sucrose solution. The masses of the dialysis tubes are recorded at 30-minute intervals for 90 minutes, as shown in the table below. The contents of which dialysis tube are initially isotonic to the distilled water in the beaker? A 1 B 2 C 3 D 4 E 5

E

Which of the following best describes the functionof the coenzymes NAD+ and FAD in eukaryoticcellular respiration? A They participate in hydrolysis reactions byaccepting protons from water molecules. B They participate directly in thephosphorylation of ADP to ATP. C They serve as final electron acceptors in theelectron transport chain. D They aid vitamins such as niacin in the breakdownof glucose. E They accept electrons during oxidation-reductionreactions.

E

Which of the following is an important difference between light-dependent and light-independent reactions of photosynthesis? A The light-dependent reactions occur only during the day; the light-independent reactions occur only during the night. B The light-dependent reactions occur in the cytoplasm; the light-independent reactions occur in chloroplasts. C The light-dependent reactions utilize CO2 and H2O; the light-independent reactions produce CO2 and H2O. D The light-dependent reactions depend on the presence of both photosystems I and II; the light-independent reactions require only photosystem I. E The light-dependent reactions produce ATP and NADPH; the light-independent reactions use energy stored in ATP and NADPH.

E

Which of the following statements about mitochondrial chemiosmosis is NOT true? A A proton gradient is established across the inner membrane of the mitochondrion. B The potential energy released from the mitochondrial proton gradient is used to produce ATP. C The mitochondrial proton gradient provides energy for muscle contraction. D Proteins embedded in the inner mitochondrial membrane play an important role in ATP synthesis. E Heat energy is required to establish the electron transport chain.

E

or following group of questions first study the description of the data and then choose the one best answer to each question following it and fill in the corresponding oval on the answer sheet. To study the actions of the enzyme catalase on hydrogen peroxide, students performed the following experiment. Catalase was extracted from potatoes by blending raw potatoes in a blender with cold distilled water. The filtrate was stored on ice. The following hydrogen peroxide solutions were made: 1 percent, 5 percent, 10 percent, and 15 percent. Filter paper disks were soaked in the catalase filtrate and dropped into beakers containing the various solutions. The activity of the enzyme was measured by the amount of time it took for the disks to float to the surface of the solution on the bubbles produced by the reaction. The following data were obtained. If the potato solution was boiled for 10 minutes and cooled for 10 minutes before being tested, the average time for the disks to float to the surface of the hydrogen peroxide solution would be A less than 1 second B 5 seconds C 10 seconds D 30 seconds E more than 30 seconds

E