AP BIO MIDTERM 2
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. (Picture) NO ENZYME 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
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
The figures below illustrate the similarities between ATP synthesis in mitochondria and chloroplasts. (picture) 3.26 The figures can best assist in answering which of the following questions? A Do electron transport chains create a gradient so that ATP synthase can generate ATP molecules? B What are the sources of energy that drive mitochondrial and chloroplast electron transport systems? C What is the optimal temperature at which ATP synthase chemically converts ADP and a phosphate group into one molecule of ATP? D What is the evolutionary relationship between the ATP synthase in mitochondria and the ATP synthase in chloroplasts?
A
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? A The SRYSRY gene produces a protein that binds to specific regions of DNADNA in certain tissues, which affects the development of these tissues. B The SRYSRY gene produces a protein that deletes portions of the XX chromosome in males so that male characteristics can develop. C The SRYSRY gene produces an RNARNA segment that is exported from specific cells and targets the developing gonads. D The SRYSRY gene is found only in tissues of the developing gonads.
A
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. (Should be a picture here) According to the results of this experiment, germination of tobacco seeds during the first week is A increased by exposure to light B unaffected by light intensity C prevented by paper towels D accelerated in green-leaved seedlings
A
Antidiuretic hormone (ADH) is important in maintaining homeostasis in mammals. ADH is released from the hypothalamus in response to high tissue osmolarity. In response to ADH, the collecting duct and distal tubule in the kidney become more permeable to water, which increases water reabsorption into the capillaries. The amount of hormone released is controlled by a negative feedback loop. Based on the model presented, which of the following statements expresses the proper relationship between osmolarity, ADH release, and urine production? A As tissue osmolarity rises, more ADH is released, causing less water to be excreted as urine. B As tissue osmolarity rises, less ADH is released, causing less water to be excreted as urine. C As tissue osmolarity rises, more ADH is released, causing more water to be excreted as urine. D As tissue osmolarity rises, less ADH is released, causing more water to be excreted as urine.
A
Butterflies of the genus Colias live in the Rocky Mountains, where they experience a wide range of temperatures. Different variants of a particular glycolytic enzyme in the flight muscles are optimally active at different temperatures. Within the same population, some individual butterflies fly most effectively at 29°C , while others fly most effectively at 40°C. Still others can be equally active at both temperatures. Which of the following claims is most consistent with the observed butterfly behavior? A Butterflies that express two variants of the enzyme are active over a greater range of temperature. B Butterflies that are active over a wide range of temperatures produce greater amounts of the enzyme. C Temperature has little effect on the activity of butterflies. D Butterflies that are active at warmer temperatures produce more offspring.
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 sugar is oxidized to pyruvic acid A B C D E
A
For following group of questions first study the description of the situation and diagrams and then choose the one best answer to each question following it and fill in the corresponding oval on the answer sheet. A student studied the effects of light intensity on oxygen production in green algae. The algae were suspended in water inside a sealed glass jar, and the jar was placed into a constant-temperature, lightproof box containing a light source. A probe was inserted into the jar to record the concentration of oxygen. The probe was connected to a recording device. The setup is shown below. (Picture) The student decreased the intensity of the light hourly and recorded the corresponding changes in oxygen concentration. The graph below shows the results from the recording device. (Picture) An increase in the rate of oxygen production by algae would be accompanied by a comparable increase in the rate of production of which of the following substances? A C6H12O6 B CO2 C CH4 D NH3 E H2O
A
Most cells that have become transformed into cancer cells have which of the following characteristics when compared to normal, healthy cells? A Shorter cell cycle B More carefully regulated rates of cell division C Lower rates of mitosis D Higher rates of protein translation E Identical DNA
A
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. (picture) 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 ATPATP production by the phosphagen system increases and decreases rapidly following the start of the exercise period. B ATPATP production by the phosphagen system increases gradually and continuously throughout the entire exercise period. C The ATPATP produced by the phosphagen system contains more energy per molecule than does the ATPATP produced by the other pathways. D ATPATP hydrolysis in muscle cells occurs immediately after the start of the exercise period but stops before the end of the exercise period.
A
The diagram below shows energy changes in a specific chemical reaction with and without the addition of an enzyme to the reaction. (Picture) 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 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 describes the role of mitosis in the cell cycle? A Distributing replicated chromosomes to daughter nuclei B Dividing the cytoplasm to form four gametes C Producing organelles and replicating chromosomes D Exchanging genetic material between homologous chromosomes
A
(Picture) Researchers investigating the regulation of neurotransmitter release from presynaptic neurons proposed a model (Figure 1) in which CDK5, a protein expressed in axon terminals, inhibits the movement of synaptic vesicles to the presynaptic membrane. To test their model, the researchers used a modified version of green fluorescent protein. In slightly alkaline conditions, exhibits a bright green fluorescence. In acidic conditions, exhibits no fluorescence. Using standard techniques, the gene encoding is easily introduced into living cells. By engineering the expression of in laboratory-cultured nerve cells, the researchers found that a bright green fluorescence was exhibited only when a presynaptic neuron was given a certain stimulus. Based on the model, which of the following best explains how regulation of neurotransmitter release might increase the range of responses to a stimulus in the nervous system? A In the absence of any stimulus, neurons can still release neurotransmitters. B Different neurons in the same neural network can release different amounts of neurotransmitter. C In the depolarization phase of an action potential, postsynaptic neurons can adjust the amount of neurotransmitter bound to receptors on their surface. D In the recovery phase following a stimulus, enzymes can be mobilized to degrade molecules present in the synaptic vesicles.
B
(Picture) MITO The figure above shows an organelle typically found in eukaryotic cells. Which of the following best describes the function of the double membrane system of this organelle? A The outer membrane allows the transport of all molecules into the intermembrane space, while the inner membrane serves as the regulatory boundary. B The inner membrane has specialized proteins that create a hydrogen ion concentration gradient between the intermembrane space and the matrix. C The outer membrane contains transport proteins that establish a sodium ion concentration gradient used for ATP production, while the inner membrane contains transport proteins that establish a hydrogen ion concentration gradient used for glucose production. D The toxins and wastes entering a cell cross the outer membrane and are detoxified by digestive enzymes stored within the intermembrane space.
B
A researcher claims that the synthesis of ATP from ADP and inorganic phosphate (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
A researcher examining a root tip observes a plant cell with condensed sister chromatids, kinetochores with attached microtubules, and individual chromosomes that are aligned at the equatorial plate of the cell. Which of the following best describes what the next process will be in the cell? A Homologous chromosomes (each with two sister chromatids) will move toward opposite poles of the cell. B Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell. C The nuclear envelope will break down, and the spindle will begin to form. D The chromatin will decondense, and the daughter cell will enter interphase.
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
Carbohydrate-synthesizing reactions of photosynthesis directly require A light B products of the light reactions C darkness D O2 and H2O E chlorophyll and CO2
B
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 mitosis, which of the following normally occurs? A Homologous chromosomes pair. B Replicated chromosomes line up on the equatorial plate. C Tetrads form. D Unreplicated chromosomes become oriented in the center of the cell. E Maternal and paternal chromatids pair.
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
Figure 1 is a proposed model of the feedback system controlling erythrocyte (red blood cell) production. (Picture) Figure 1. Model of erythrocyte production control 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? A More erythropoietin will be secreted from the kidneys, decreasing production of erythrocytes. B More erythropoietin will be secreted from the kidneys, increasing production of erythrocytes. C Less erythropoietin will be secreted from the kidneys, decreasing production of erythrocytes. D Less erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.
B
Figure 1 shows a model of a signal transduction cascade, initiated by the binding of a ligand to the transmembrane receptor protein A. (picture) Figure 1. Model of signal transduction cascade incorporating 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? A Production of activated molecule 1 will stop, but production of activated molecules 2 and 3 will continue. B The molecule that normally binds to protein AA will no longer attach, deactivating the cellular response. C The molecule that normally binds to protein AA will not enter the cell, thus no cellular response will occur. D Since protein AA is embedded in the membrane, the mutation will be silent and not affect the cellular response.
B
For following group of questions first study the description of the situation and diagrams and then choose the one best answer to each question following it and fill in the corresponding oval on the answer sheet. A student studied the effects of light intensity on oxygen production in green algae. The algae were suspended in water inside a sealed glass jar, and the jar was placed into a constant-temperature, lightproof box containing a light source. A probe was inserted into the jar to record the concentration of oxygen. The probe was connected to a recording device. The setup is shown below. (Picture) The student decreased the intensity of the light hourly and recorded the corresponding changes in oxygen concentration. The graph below shows the results from the recording device. (Picture) Based on the data shown, changes in the light intensity resulted in changes in the rate of which of the following processes? A Excretion B Photosynthesis C Respiration D Translation E Transcription
B
For the following questions: Graphs I-IV depict the effect of pH on the activity of four different hydrolytic enzymes. (picture) 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
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. (picture) 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 mammals, an increase in the concentration of sodium in the blood triggers the release of antidiuretic hormone (ADH) from the pituitary gland. As the concentration of sodium in the blood returns to previous levels, the release of ADH from the pituitary gland is reduced. Based on the information presented, which of the following describes the most likely role of ADH in maintaining blood osmolarity? A ADH promotes an increase in the movement of sodium into the bloodstream. B ADH promotes an increase in the movement of water into the bloodstream. C ADH promotes an increase in the excretion of water from the body. D ADH promotes an increase in the secretion of additional ADH from the pituitary gland.
B
The chemical reaction for photosynthesis is 6CO2 + 12H2O + light energy → C6H12O6 + 6O2 + 6H2O If the input water is labeled with a radioactive isotope of oxygen, 18O, then the oxygen gas released as the reaction proceeds is also labeled with 18O. Which of the following is the most likely explanation? A During the light reactions of photosynthesis, water is split, the hydrogen atoms combine with the CO2, and oxygen gas is released. B During the light reactions of photosynthesis, water is split, removing electrons and protons, and oxygen gas is released. C During the Calvin cycle, water is split, regenerating NADPH from NADP+, and oxygen gas is released. D During the Calvin cycle, water is split, the hydrogen atoms are added to intermediates of sugar synthesis, and oxygen gas is released.
B
The endocrine system incorporates feedback mechanisms that maintain homeostasis. Which of the following demonstrates negative feedback by the endocrine system? A During labor, the fetus exerts pressure on the uterine wall, inducing the production of oxytocin, which stimulates uterine wall contraction. The contractions cause the fetus to further push on the wall, increasing the production of oxytocin. B After a meal, blood glucose levels become elevated, stimulating beta cells of the pancreas to release insulin into the blood. Excess glucose is then converted to glycogen in the liver, reducing blood glucose levels. C At high elevation, atmospheric oxygen is more scarce. In response to signals that oxygen is low, the brain decreases an individual's rate of respiration to compensate for the difference. D A transcription factor binds to the regulatory region of a gene, blocking the binding of another transcription factor required for expression.
B
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. (Picture) 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
The mechanism of action of many common medications involves interfering with the normal pathways that cells use to respond to hormone signals. Which of the following best describes a drug interaction that directly interferes with a signal transduction pathway? A A medication causes the cell to absorb more of a particular mineral, eventually poisoning the cell. B A medication enters the target cell and inhibits an enzyme that normally synthesizes a second messenger. C A medication enters the target cell's nucleus and acts as a mutagen. D A medication interrupts the transcription of ribosomal RNA genes.
B
Which of the following is true of mitosis? A It is also known as cytokinesis. B It maintains the same chromosome number in the daughter cells as in the parent cell. C It is the last phase of interphase. D It regulates the transfer of genetic information from one daughter cell to another. E It moves homologous chromosomes to opposite poles.
B
A researcher claims that only a portion of the light energy captured by green plants is available for growth and repair. Which of the following observations best helps justify the researcher's claim? A Light-capturing pigment molecules in green plants absorb red, blue, and violet light but reflect green light. B The energy of a photon of light is proportional to its frequency and inversely proportional to its wavelength. C As light energy is converted to chemical energy by metabolic processes, some of the energy is lost as heat. D Captured energy is stored in the molecular bonds of organic molecules, including simple sugars and starch.
C
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. THE BOILED ONE 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 pHpH. B It will provide a measurement of amylase activity at a basic pHpH. 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
Cancer can result from a variety of different mutational events. Which of the following is LEAST likely to result in the initiation of a cancerous tumor? A A receptor mutation results in activation of a cell-division pathway in the absence of the appropriate ligand. B A mutation results in the loss of the ability to produce a tumor-suppressor protein. C A defect in a cell-cycle checkpoint prevents a cell from entering the S phase. D At the anaphase checkpoint, separation of chromatids occurs without all centromeres being attached to kinetochore microtubules from both poles.
C
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: 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
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 carbon from CO2 is incorporated into organic molecules A B C D E
C
Figure 1 shows the number of chromosomes observed in an actively dividing human cell at each stage of cell division. (Picture) Figure 1. Number of chromosomes in a human cell at different stages of cell division Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1 ? A DNADNA replication occurs between metaphase and anaphase, doubling the number of chromosomes. Between telophase and cytokinesis, the cell divides in two, with each cell receiving half of the replicated chromosomes. B New chromosomes formed during prophase are doubled during anaphase and are recombined before cytokinesis. C Chromosomes enter metaphase containing two chromatids attached by a centromere. During anaphase, the chromatids are separated, each becoming a chromosome. Cytokinesis distributes the chromosomes into two separate cells. D At anaphase a cell contains two identical copies of each chromosome, but following telophase, one of the copies is broken down into nucleotides.
C
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. (Picture) 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
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 (CAMs) interact, causing them to change shape so that the growth-factor signaling proteins that normally associate with CAMs are replaced by another protein, called M. Both pathways are depicted in the figures below. (Picture) 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 withCAMs, causing the cell cycle to stop permanently. B The ras protein will remain bound to DNA, blocking 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
Researchers performed an experiment to determine the effect of certain genetic mutations on mitosis in tropical fruit fly embryos. They determined the percentage of cells in each of four phases of mitosis as shown in (Picture) 4.5 Figure 1. Figure 1. Percent of cells in phases of mitosis Which of the following patterns is shown by the data? A Mutant 1 cells are more similar to mutant 3 cells than to wild-type cells. B In wild-type cells, the percent of cells in anaphase is twice the amount of those in telophase C In mutant 3 cells, more time is spent in prophase/prometaphase than in the later stages of mitosis. D The percent of mutant 2 cells in anaphase is higher than that of mutant 1 cells.
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 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
(Picture) Based on the model of eukaryotic cell cycle regulation shown in the figure, which of the following best describes the effect of a drug that blocks the production of the mitotic cyclin? A The cell cycle would proceed uncontrollably, and the cell would become cancerous. B The G1 cyclin would functionally replace mitotic cyclin, and the cell would continue dividing normally. C DNA synthesis would be prevented, and the cell would stop dividing. D The cell would be prevented from entering mitosis, and the cell would stop dividing.
D
(Picture) The figure above shows a model of a ligand precursor being cleaved to produce an active ligand that binds to a specific receptor. Which of the following is most likely to reduce the binding of the active ligand to its receptor? A A change in the cytoskeletal attachment of transmembrane proteins B The presence of a large amount of the precursor form of the ligand C An increase in the ratio of the number of unsaturated to the number of saturated fatty acid tails of the membrane lipids D A mutation in the receptor gene that causes a substitution of a charged amino acid for a nonpolar amino acid in the ligand binding site of the receptor
D
(Picture) What most likely causes the trends in oxygen concentration shown in the graph above? A The water becomes colder at night and thus holds more oxygen. B Respiration in most organisms increases at night. C More organisms are respiring at night than during the day. D Photosynthesis produces more oxygen than is consumed by respiration during the day. Related Content & Skills Topic3.5 SkillSkill 2.C Related Videos 3.5: Daily Video 1
D
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
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
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? 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
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
Damaged tissue releases chemicals that activate platelets and stimulate the formation of blood clots. Which of the following predictions about the activity of platelets best describes a positive feedback mechanism? A Activated platelets release chemicals that inhibit blood clot formation. B Activated platelets release signaling molecules that inhibit cell division in damaged tissue. C Activated platelets constrict the blood vessels, stopping blood flow. D Activated platelets release chemicals that activate more platelets.
D
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? A Membrane-bound organelles B Condensed, duplicated chromosomes C Branched polysaccharides D Small, water-soluble molecules
D
In response to elevated blood glucose levels, beta (β) cells in the pancreas release insulin, a regulatory hormone. Insulin signals body cells to take up glucose from the blood, which returns blood glucose levels back to normal. Type 1 diabetes is an autoimmune disorder that destroys β-cells, resulting in elevated blood glucose levels. Researchers have proposed that diabetes could be treated by implanting human embryonic stem cells (hESCs) that have been induced to develop into β-cells (hESC-β). To test the proposed treatment, the researchers set up two groups of genetically identical mice and implanted the mice from one group with hESC-β cells. Several weeks after the hESC-β implant, both groups of mice were given a drug (STZ) that selectively destroys the naturally occurring mouse β-cells but does not affect the implanted hESC-β cells. Figure 1 shows a comparison of average blood glucose levels in both groups of mice. (Picture) Figure 1. Average blood glucose levels in mice after STZ treatment. Error bars indicate standard deviation. In a continuation of the experiment, the researchers removed the hESC-β implant from one of the mice 16 weeks after STZ treatment. Figure 2 shows the blood glucose levels in the mouse over the duration of the experiment. (Picture) Figure 2. Blood glucose levels for an individual mouse over the duration of the experiment. Based on the data in Figure 2, which of the following best justifies the researchers' claim that hESC-β implants can functionally replace the mouse's naturally occurring β-cells? A The mouse with an hESC-β implant demonstrated a decrease in blood glucose levels for the duration of the experiment. B The mouse with an hESC-β implant demonstrated an increase in blood glucose levels before STZ treatment. C The mouse with an hESC-β implant successfully regulated blood glucose levels by regenerating its naturally occurring β-cells. D The mouse with an hESC-β implant successfully regulated blood glucose levels after STZ treatment but not after the implant was removed.
D
Researchers determined the average amount of time that a particular type of eukaryotic cell spends in each phase of the cell cycle. The data collected by the researchers are represented in Figure 1. (picture) Figure 1. The average amount of time spent by a particular type of eukaryotic cell in each phase of the cell cycle Based on Figure 1, what percent of the time required to complete a full cycle do the cells typically spend in interphase? A 5%5% B 35%35% C 50%50% D 95%95%
D
Steroid hormones, such as testosterone, pass through the plasma membrane and bind to an intracellular protein, as shown in the diagram below. The hormone-receptor complex then enters the nucleus, where it interacts with DNA to promote transcription of a specific gene. Based on the information presented, which of the following will also occur in response to steroid signaling? A Histone protein synthesis will increase because histones maintain the DNA in an optimal conformation for chromosome assembly. B Ribosome production will increase because ribosomes are specific for the mRNA with which they bind during translation. C DNA replication will increase as a result of the binding of the hormone-receptor complex to the DNA. D Production of a specific mRNA will increase as a result of the binding of the hormone-receptor complex to the DNA.
D
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
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. (Picture) 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? A Epinephrine is a signaling molecule that binds to a transmembrane protein. B The G protein in the epinephrine signaling pathway consists of three different subunits. C Phosphorylase kinase catalyzes the hydrolysis of ATPATP. D Glycogen phosphorylase catalyzes the conversion of glycogen to glucose-1-phosphate.
D
The relative amount of DNA in a cell at various stages of the cell cycle is shown in Figure 1 . (Picture) Figure 1. Amount of DNA per cell during different stages of the cell cycle, relative to the beginning of the G1 stage Which of the following best describes how the amount of DNA in the cell changes during M phase? A The amount of DNADNA doubles as the DNADNA is replicated. B The amount of DNADNA slightly increases as a result of new organelle synthesis. C The amount of DNADNA does not change while the cell grows. D The amount of DNADNA is halved as the cell divides into two daughter cells.
D
A human cell in prophase of mitosis can be distinguished from a human cell in prophase I of meiosis by the presence of A kinetochores in the mitotic cell B a spindle in the mitotic cell C twice as many chromosomes in the meiotic cell D half as many chromosomes in the meiotic cell E paired homologous chromosomes in the meiotic cell
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
