Version A. AP* Biology: Biochemistry. Name: Period

Transcription

1 Name: Period Version A AP* Biology: Biochemistry Directions: Each of the questions or incomplete statements below is followed by four suggested answers or completions. Select the one that is best in each case and enter the appropriate letter in the corresponding space on the answer sheet. 1. Biomolecules have intramolecular forces that hold them together as a unit. Biomolecules also exhibit intermolecular forces when interacting with other biomolecules. Which of the following is an example of a hydrogen bond? 3. A) The peptide bond between amino acids in a protein B) The bond between carbon and hydrogen in methane C) The bond between an oxygen atom and a hydrogen atom in the carboxyl group of a fatty acid D) The attraction between a hydrogen of one water molecule and the oxygen of another water molecule 2. An experimental apparatus similar to that used by S. L. Miller is shown above. In this classic experiment it was demonstrated that a discharge of sparks through a mixture of gases could result in the formation of large variety of organic compounds. Which of the following gases was NOT used in this experiment? The chemical structure for the nitrogenous base adenine is shown above. It is an important biomolecule and is found in which three of the following? A) hydrogen B) oxygen C) water vapor D) ammonia mixed with methane A) Proteins, carbohydrates, and ATP B) Proteins, ATP, and DNA C) ATP, DNA, and RNA D) Chlorophyll, ATP, and DNA (1)Test Questions are Copyright by College Entrance Examination Board, Prenceton, NJ. All rights reserved. For face-to-fact teaching purposes, classroom teachers are permitted to reproduce the questions. Web or Mass distribution prohibited. (2) AP is registered traemark of the College Entrance Examination Borard. The College Entrance Examination Board was not involved in the production of and does not endorse this product. Permissionis granted of individual classroom teahcers to reproduce the activity sheets and illustation for their own classroom use. Any other type of reproduction of these material is strictly prohibited. 2

2 Version A Questions 4-6 In a laboratory experiment using spectrophotometry, an enzyme is combined with its substrate at time zero. The absorbance of the resulting solution is measured at time zero and at five-minute intervals. In this procedure an increase in absorbance is related to the amount of product formed during the reaction. The experiment is conducted using the three preparations shown in the table below. Enzyme Preparation Absorbance 0 min 5 min 10 min 15 min 20 min I. 3 ml of enzyme preparation ml of substrate ph 5.0 II. 3 ml of boiled enzyme preparation ml of substrate ph 5.0 III. 3 ml of enzyme preparation ml of substrate ph According to the data, the absorbance fails to increase significantly after 10 minutes in preparation III. This is most likely explained by which of the following? A) The reaction is thermodynamically impossible at ph 6.0. B) A ph of 6.0 prevents color development beyond an absorbance of C) The enzyme is degraded more rapidly at ph 6.0 than it is at ph 5.0. D) Most of the substrate was digested during the first 10 minutes. 5. Which of the following statements is best supported by the data? A) Increasing the ph to 7.0 would yield an absorbance higher than 0.30 after 5 minutes. B) The enzyme demonstrates more activity at ph 6.0 than at ph 5.0. C) A ph of 5.0 is the optimum for the activity of the enzyme. D) The enzymatic activity is independent of ph. 6. According to the data, which of the following can best be concluded from a comparison of the results of preparation II with those of preparation I? A) Heating the enzyme is required to increase the absorbance. B) Boiling does not break down the substrate. C) Most of the increase in the amount of product in preparation I was due to an enzymatic degradation of the substrate. D) Products resulting from the breakdown of the enzyme are responsible for the absorbance increase in preparation II. 7. Both organic and inorganic chemical reactions can be affected by the addition of a catalyst. 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) Increase in activation energy 2

3 Version A 8. Within complex biological systems, many chemical reactions that, by themselves, require energy input (have a positive free-energy change or + G) can occur because the reactions A) may be coupled to the hydrolysis of ATP B) take place very slowly C) take place when the cells are at unusually high temperatures D) are catalyzed by enzymes 9. Proteins are polymers composed of structural monomers called amino acids. Which of the following pairs of functional groups characterizes the structure of an amino acid? 10. Adenosine triphosphate or ATP is composed of adenine, ribose and three phosphate groups. The phosphate groups have a negative charge and as a result the bonds holding them onto the molecule are weak thus easily broken. Which of the following best explains why ATP serves as a common energy source for organisms? A) ATP is the smallest energy molecule. B) ATP energy can be easily transferred to do cellular work. C) ATP is extremely stable and can be stored in the cell for long periods of time. D) Traces of ATP have been found in fossils of ancient organisms dating back to the beginning of life on Earth. 11. Aqueous buffer solutions are common in biochemical systems and are beneficial in that they resist changes in ph. Which of the following methods for the transport of CO 2 provides a buffering system for the blood? A) CO 2 is dissolved in the plasma. B) CO 2 combines with H 2 O to form carbonic acid and then bicarbonate. C) CO 2 combines with hemoglobin to form carboxyhemoglobin. D) CO 2 is converted to CO for plasma transport. A) A B) B C) C D) D 12. Anabolism is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy. The synthesis of protein or carbohydrate polymers always produces which of the following as a byproduct of these synthesis reactions? A) ATP B) Carbon dioxide C) Urea D) Water 3

4 Version A 13. A metabolic pathway is comprised of a series of chemical reactions. Often these reactions are catalyzed by a variety of enzymes. In the series of enzyme reactions shown above, product Z is able to occupy the active site of enzyme E 2. Product Z can therefore first inhibit the production of A) E 1 B) X C) E 2 D) Y 14. A substrate may bind to the active site of an enzyme in a variety of ways. Which of the following is NOT a valid mechanism for substrate-enzyme binding? A) hydrogen bonds B) peptide bonds C) ionic bonds D) van der Waals interactions 15. 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. Sampling Time (minutes) Endoplasmic Reticulum Radioactive Counts (Protein X) Cell Component Golgi Apparatus Cytoplasm Nucleus Mitochondria Lysosomes Extracellular Space In graphing the data from this experiment, the sampling time would be shown on the x-axis because A) radioactivity level shows the most variation B) time values are always located on the horizontal axis C) all quantitative values are represented on the x-axis D) sampling time is the independent variable 4

5 Version A Questions The activity of digestive enzymes was examined in three regions of the digestive system of a crayfish. The stomach, the digestive gland, and the intestine were assayed for enzyme activity at 25 C and ph 7.6. The following results were recorded after repeated measurements. Enzyme Activity ( mole substrate hydrolyzed/min/ml extract) Enzyme Stomach Digestive Gland Intestine Amylase Protease Lipase According to the data, which of the following can correctly be concluded about crayfish? A) Most digestive enzymes are produced in the stomach. B) Most digestive enzymes are found in the digestive gland. C) Amylase is produced in the esophagus. D) The primary function of the intestine is to digest proteins. 17. Which of the following statements regarding crayfish digestion is most consistent with the data? A) Little digestions occurs before food enters the stomach. B) Most digestion occurs in the stomach. C) Little digestion occurs in the stomach. D) Digestion is optimal at 25 C 18. The experiment demonstrates which of the following about the digestive system of crayfish? A) Amylase is the most active digestive enzyme. B) Crayfish have only three kinds of digestive enzymes. C) Most enzyme activity occurs in the intestine. D) Different regions of the digestive system are specialized for different functions. 19. Which of the following would be useful as a substrate to measure the activity of amylase in crayfish? A) Cellulose B) Starch C) Glucose D) An amino acid 5

6 Version A Questions 20 and 21 Researchers applied radioactive phosphorus and radioactive calcium to a freshly cut tree stump. Eight days later, they came back to measure the distribution of the radioisotopes. They found that nineteen different species of shrubs and trees within a seven-meter radius had taken up the radioactive elements. No radioactivity was detected in the air. 20. Radioactive isotopes were never detected in any samples containing just soil taken during the experiment. The finding implies that the A) soil does not provide the ecosystem with minerals B) isotopes were undetectable in very small amounts C) isotopes were transported via vascular tissues D) plants quickly return minerals to the soil in which they grow 21. Radioactively labeled starch was later added to the stump; in subsequent observations, no labeled starch molecules were ever detected in neighboring plants. Which of the following is the most logical explanation for the observation? A) Starch molecules are too large to cross cell membranes. B) The radioactivity caused the starch molecules to break down. C) Water in the soil dissolved the starch molecules. D) The radioactive carbon atoms decayed into other atoms that are undetectable. 6

7 Version A Questions 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. Hydrogen Peroxide Solution Average Time, in Seconds, for Disks to Float 1% 30 sec 5% 25 sec 10% 20 sec 15% 10 sec 22. 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 reactions. D) The higher substrate concentrations in the more concentrated solutions speeded the reaction. 23. 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) Poke the floating disks back down to the bottom of the beaker and retime the rise of the disks. C) Shake the beakers during the time the disks are rising. D) Dip the disks in the 5% solution before putting them in any other solution. 24. Which of the following best describes why ice was used during this experiment? A) To increase the activity of the enzyme B) To retard the breakdown of the catalase. C) To purge the solution of excess air trapped during blending. D) To slow the catalase molecules to increase the probability of contact with the hydrogen peroxide molecules. 25. 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) 5 seconds B) 10 seconds C) 30 seconds D) more than 30 seconds 7

8 Version A Questions The solid curve and the dashed curve in the diagram above represent alternate pathways for the same reaction. One pathway is enzyme catalyzed. 26. Which of the following best describes the portion of the curve labeled B? A) Activation energy of the enzyme-catalyzed reaction B) Total G of the catalyzed reaction C) Total G of the reaction that is not enzyme-catalyzed D) Energy state of the products of the pathway that is not enzyme-catalyzed 28. Which of the following best describes the portion of the curve labeled E? A) Activation energy of the enzyme-catalyzed reaction B) Total G of the enzyme-catalyzed reaction C) Total G of the reaction that is not enzyme-catalyzed D) Energy state of the products of the pathway that is not enzyme-catalyzed 27. Which of the following best describes the portion of the curve that combines B + D? A) Activation energy of the enzyme-catalyzed reaction B) Total G of the catalyzed reaction C) Total G of the reaction that is not enzyme-catalyzed D) Energy state of the products of the pathway that is not enzyme-catalyzed 8

9 Version A Questions 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. 29. According to the data presented solely on the curve, what can be said concerning the calculated reaction rates at 1 minute and at 2 minutes? A) The rate after 2 minutes is greater than the rate after 1 minute. B) The rates are the same at 1 minute and at 2 minutes. C) The rates are affected by high concentrations of inhibitors. D) The greater the rate, the faster the enzyme is denatured. 30. The rate of the reaction could also be determined by A) measuring the change in the amount of enzyme B) measuring the change in the amount of substrate C) adding more substrate D) adding more enzyme 31. During which time interval is the reaction rate lowest? A) 1-2 minutes B) 2-3 minutes C) 3-4 minutes D) 4-5 minutes 32. What is the most likely explanation for the change in the slope of the line between 3 and 5 minutes? A) The enzyme had denatured. B) The enzyme had achieved its maximum velocity. C) A large amount of the substrate had been consumed. D) An allosteric inhibitor appeared. 9

10 AP Biology Biochemistry Unit Exam Part B Directions: These three questions require numeric answers. Calculate the correct answer for each question, and enter your answer on the grid following each question. Examples of correct entry for the grid-in questions are shown below. The actual questions for this exam begin on the next page. Integer Answer Integer Answer Decimal Answer Fraction Answer / / 1 0 In all cases, accept a reasonable range of numerical answers due to students rounding numbers at each stage of the calculation. (Discourage this practice since the other AP exams involving any sort of mathematics require students to leave all calculations in the calculator and round only at the end of the process. We recommend leniency on the AP Biology exam since students are not allowed to use graphing calculators which facilitate retrieving previously calculated answers to a greater precision.) (1) Test Questions are Copyright by College Entrance Examination Board, Princeton, NJ. All rights reserved. For face-to-face teaching purposes, classroom teachers are permitted to reproduce the questions. Web or Mass distribution prohibited. (2) AP is a registered trademark of the College Entrance Examination Board. The College Entrance Examination Board was not involved in the production of and does not endorse this product. Permission is granted for individual classroom teachers to reproduce the activity sheets and illustrations for their own classroom use. Any other type of reproduction of these materials is strictly prohibited.

11 1. The brown color, which usually develops when a potato or apple is cut or bruised, is the result of a chemical catalyzed by several enzymes. One of the most important of these enzymes is catecholase which is brought into contact with its substrate, catechol, when cells are ruptured and exposure to the O 2 in air resulting in the oxidation of catechol to the brownish colored benzoquinone. This so called wound reaction is apparently protective since the quinones are toxic to microorganisms. Five test tubes were labeled with varying hydrogen ion concentrations expressed in molarity, [H + ]. Each tube was filled with 3 ml phosphate buffer at the designated [H + ] and 10 drops of catechol was added to each test tube, followed by 10 drops of potato extract. Each tube was stoppered and inverted many times. After a waiting period of 3 minutes it was observed that a brown substance was accumulating in the tubes. The absorbance of each solution was measured and the following results were obtained. Calculate the ph of the test tube containing the optimum [H + ]. Give your answer to the hundredth of a ph unit. 2. A student is asked to make 500 ml of a buffer solution for an upcoming laboratory investigation that requires 50.0 ml of 3.0 M phosphoric acid. The student searches the acid cabinet in the stockroom but can only find 4.5 M phosphoric acid. Calculate the amount of 4.5 M phosphoric acid the student should dilute to a total volume of 500 ml. Give our answer to the nearest tenth of a ml. [H + ] Absorbance

12 3. After an enzyme is mixed with its substrate, the amount of product formed is determined at 10-second intervals for 1 minute. A graph of the data collected during this experiment is shown below: Determine the rate of change for the amount of product formed during the first 30 seconds of data collection. Give your answer to the nearest hundredth.

13 Name: Period Version B AP* Biology: Biochemistry Directions: Each of the questions or incomplete statements below is followed by four suggested answers or completions. Select the one that is best in each case and enter the appropriate letter in the corresponding space on the answer sheet. Questions 1 and 2 Researchers applied radioactive phosphorus and radioactive calcium to a freshly cut tree stump. Eight days later, they came back to measure the distribution of the radioisotopes. They found that nineteen different species of shrubs and trees within a seven-meter radius had taken up the radioactive elements. No radioactivity was detected in the air. 1. Radioactive isotopes were never detected in any samples containing just soil taken during the experiment. The finding implies that the A) soil does not provide the ecosystem with minerals B) isotopes were undetectable in very small amounts C) isotopes were transported via vascular tissues D) plants quickly return minerals to the soil in which they grow 2. Radioactively labeled starch was later added to the stump; in subsequent observations, no labeled starch molecules were ever detected in neighboring plants. Which of the following is the most logical explanation for the observation? A) Starch molecules are too large to cross cell membranes. B) The radioactivity caused the starch molecules to break down. C) Water in the soil dissolved the starch molecules. D) The radioactive carbon atoms decayed into other atoms that are undetectable. (1)Test Questions are Copyright by College Entrance Examination Board, Prenceton, NJ. All rights reserved. For face-to-fact teaching purposes, classroom teachers are permitted to reproduce the questions. Web or Mass distribution prohibited. (2) AP is registered traemark of the College Entrance Examination Borard. The College Entrance Examination Board was not involved in the production of and does not endorse this product. Permissionis granted of individual classroom teahcers to reproduce the activity sheets and illustation for their own classroom use. Any other type of reproduction of these material is strictly prohibited. 2

14 Version B Questions 3-6 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. 3. According to the data presented solely on the curve, what can be said concerning the calculated reaction rates at 1 minute and at 2 minutes? A) The rate after 2 minutes is greater than the rate after 1 minute. B) The rates are the same at 1 minute and at 2 minutes. C) The rates are affected by high concentrations of inhibitors. D) The greater the rate, the faster the enzyme is denatured. 4. What is the most likely explanation for the change in the slope of the line between 3 and 5 minutes? 5. During which time interval is the reaction rate lowest? A) 1-2 minutes B) 2-3 minutes C) 3-4 minutes D) 4-5 minutes 6. The rate of the reaction could also be determined by A) measuring the change in the amount of enzyme B) measuring the change in the amount of substrate C) adding more substrate D) adding more enzyme A) The enzyme had denatured. B) The enzyme had achieved its maximum velocity. C) A large amount of the substrate had been consumed. D) An allosteric inhibitor appeared. 2

15 Version B Questions 7-10 The activity of digestive enzymes was examined in three regions of the digestive system of a crayfish. The stomach, the digestive gland, and the intestine were assayed for enzyme activity at 25 C and ph 7.6. The following results were recorded after repeated measurements. Enzyme Activity ( mole substrate hydrolyzed/min/ml extract) Enzyme Stomach Digestive Gland Intestine Amylase Protease Lipase Which of the following would be useful as a substrate to measure the activity of amylase in crayfish? A) Cellulose B) Starch C) Glucose D) An amino acid 8. According to the data, which of the following can correctly be concluded about crayfish? A) Most digestive enzymes are produced in the stomach. B) Most digestive enzymes are found in the digestive gland. C) Amylase is produced in the esophagus. D) The primary function of the intestine is to digest proteins. 9. The experiment demonstrates which of the following about the digestive system of crayfish? A) Amylase is the most active digestive enzyme. B) Crayfish have only three kinds of digestive enzymes. C) Most enzyme activity occurs in the intestine. D) Different regions of the digestive system are specialized for different functions. 10. Which of the following statements regarding crayfish digestion is most consistent with the data? A) Little digestions occurs before food enters the stomach. B) Most digestion occurs in the stomach. C) Little digestion occurs in the stomach. D) Digestion is optimal at 25 C 3

16 Version B Questions The solid curve and the dashed curve in the diagram above represent alternate pathways for the same reaction. One pathway is enzyme catalyzed. 11. Which of the following best describes the portion of the curve labeled E? A) Activation energy of the enzyme-catalyzed reaction B) Total G of the enzyme-catalyzed reaction C) Total G of the reaction that is not enzyme-catalyzed D) Energy state of the products of the pathway that is not enzyme-catalyzed 13. Which of the following best describes the portion of the curve that combines B + D? A) Activation energy of the enzyme-catalyzed reaction B) Total G of the catalyzed reaction C) Total G of the reaction that is not enzyme-catalyzed D) Energy state of the products of the pathway that is not enzyme-catalyzed 12. Which of the following best describes the portion of the curve labeled B? A) Activation energy of the enzyme-catalyzed reaction B) Total G of the catalyzed reaction C) Total G of the reaction that is not enzyme-catalyzed D) Energy state of the products of the pathway that is not enzyme-catalyzed 4

17 Version B Questions In a laboratory experiment using spectrophotometry, an enzyme is combined with its substrate at time zero. The absorbance of the resulting solution is measured at time zero and at five-minute intervals. In this procedure an increase in absorbance is related to the amount of product formed during the reaction. The experiment is conducted using the three preparations shown in the table below. Enzyme Preparation Absorbance 0 min 5 min 10 min 15 min 20 min I. 3 ml of enzyme preparation ml of substrate ph 5.0 II. 3 ml of boiled enzyme preparation ml of substrate ph 5.0 III. 3 ml of enzyme preparation ml of substrate ph According to the data, the absorbance fails to increase significantly after 10 minutes in preparation III. This is most likely explained by which of the following? A) The reaction is thermodynamically impossible at ph 6.0. B) A ph of 6.0 prevents color development beyond an absorbance of C) The enzyme is degraded more rapidly at ph 6.0 than it is at ph 5.0. D) Most of the substrate was digested during the first 10 minutes. 15. According to the data, which of the following can best be concluded from a comparison of the results of preparation II with those of preparation I? A) Heating the enzyme is required to increase the absorbance. B) Boiling does not break down the substrate. C) Most of the increase in the amount of product in preparation I was due to an enzymatic degradation of the substrate. D) Products resulting from the breakdown of the enzyme are responsible for the absorbance increase in preparation II. 16. Which of the following statements is best supported by the data? A) Increasing the ph to 7.0 would yield an absorbance higher than 0.30 after 5 minutes. B) The enzyme demonstrates more activity at ph 6.0 than at ph 5.0. C) A ph of 5.0 is the optimum for the activity of the enzyme. D) The enzymatic activity is independent of ph. 5

18 Version B 17. Aqueous buffer solutions are common in biochemical systems and are beneficial in that they resist changes in ph. Which of the following methods for the transport of CO 2 provides a buffering system for the blood? 19. Biomolecules have intramolecular forces that hold them together as a unit. Biomolecules also exhibit intermolecular forces when interacting with other biomolecules. Which of the following is an example of a hydrogen bond? 18. A) CO 2 is dissolved in the plasma. B) CO 2 combines with H 2 O to form carbonic acid and then bicarbonate. C) CO 2 combines with hemoglobin to form carboxyhemoglobin. D) CO 2 is converted to CO for plasma transport. The chemical structure for the nitrogenous base adenine is shown above. It is an important biomolecule and is found in which three of the following? A) Proteins, carbohydrates, and ATP B) Proteins, ATP, and DNA C) ATP, DNA, and RNA D) Chlorophyll, ATP, and DNA A) The peptide bond between amino acids in a protein B) The bond between carbon and hydrogen in methane C) The bond between an oxygen atom and a hydrogen atom in the carboxyl group of a fatty acid D) The attraction between a hydrogen of one water molecule and the oxygen of another water molecule 20. Within complex biological systems, many chemical reactions that, by themselves, require energy input (have a positive free-energy change or + G) can occur because the reactions A) may be coupled to the hydrolysis of ATP B) take place very slowly C) take place when the cells are at unusually high temperatures D) are catalyzed by enzymes 21. A substrate may bind to the active site of an enzyme in a variety of ways. Which of the following is NOT a valid mechanism for substrate-enzyme binding? A) hydrogen bonds B) peptide bonds C) ionic bonds D) van der Waals interactions 6

19 Version B Questions 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. Hydrogen Peroxide Solution Average Time, in Seconds, for Disks to Float 1% 30 sec 5% 25 sec 10% 20 sec 15% 10 sec 22. 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) Poke the floating disks back down to the bottom of the beaker and retime the rise of the disks. C) Shake the beakers during the time the disks are rising. D) Dip the disks in the 5% solution before putting them in any other solution. 23. Which of the following best describes why ice was used during this experiment? A) To increase the activity of the enzyme B) To retard the breakdown of the catalase. C) To purge the solution of excess air trapped during blending. D) To slow the catalase molecules to increase the probability of contact with the hydrogen peroxide molecules. 24. 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 reactions. D) The higher substrate concentrations in the more concentrated solutions speeded the reaction. 25. 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) 5 seconds B) 10 seconds C) 30 seconds D) more than 30 seconds 7

20 Version B 26. 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. Sampling Time (minutes) Endoplasmic Reticulum Radioactive Counts (Protein X) Cell Component Golgi Apparatus Cytoplasm Nucleus Mitochondria Lysosomes Extracellular Space In graphing the data from this experiment, the sampling time would be shown on the x-axis because A) radioactivity level shows the most variation B) time values are always located on the horizontal axis C) all quantitative values are represented on the x-axis D) sampling time is the independent variable A metabolic pathway is comprised of a series of chemical reactions. Often these reactions are catalyzed by a variety of enzymes. In the series of enzyme reactions shown above, product Z is able to occupy the active site of enzyme E 2. Product Z can therefore first inhibit the production of A) E 1 B) X C) E 2 D) Y 28. Anabolism is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy. The synthesis of protein or carbohydrate polymers always produces which of the following as a byproduct of these synthesis reactions? A) ATP B) Carbon dioxide C) Urea D) Water 29. Both organic and inorganic chemical reactions can be affected by the addition of a catalyst. 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) Increase in activation energy 8

21 Version B 30. Adenosine triphosphate or ATP is composed of adenine, ribose and three phosphate groups. The phosphate groups have a negative charge and as a result the bonds holding them onto the molecule are weak thus easily broken. Which of the following best explains why ATP serves as a common energy source for organisms? 32. A) ATP is the smallest energy molecule. B) ATP energy can be easily transferred to do cellular work. C) ATP is extremely stable and can be stored in the cell for long periods of time. D) Traces of ATP have been found in fossils of ancient organisms dating back to the beginning of life on Earth. 31. Proteins are polymers composed of structural monomers called amino acids. Which of the following pairs of functional groups characterizes the structure of an amino acid? An experimental apparatus similar to that used by S. L. Miller is shown above. In this classic experiment it was demonstrated that a discharge of sparks through a mixture of gases could result in the formation of large variety of organic compounds. Which of the following gases was NOT used in this experiment? A) hydrogen B) oxygen C) water vapor D) ammonia mixed with methane A) A B) B C) C D) D 9

22 AP Biology Biochemistry Unit Exam Part B Directions: These three questions require numeric answers. Calculate the correct answer for each question, and enter your answer on the grid following each question. Examples of correct entry for the grid-in questions are shown below. The actual questions for this exam begin on the next page. Integer Answer Integer Answer Decimal Answer Fraction Answer / / 1 0 In all cases, accept a reasonable range of numerical answers due to students rounding numbers at each stage of the calculation. (Discourage this practice since the other AP exams involving any sort of mathematics require students to leave all calculations in the calculator and round only at the end of the process. We recommend leniency on the AP Biology exam since students are not allowed to use graphing calculators which facilitate retrieving previously calculated answers to a greater precision.) (1) Test Questions are Copyright by College Entrance Examination Board, Princeton, NJ. All rights reserved. For face-to-face teaching purposes, classroom teachers are permitted to reproduce the questions. Web or Mass distribution prohibited. (2) AP is a registered trademark of the College Entrance Examination Board. The College Entrance Examination Board was not involved in the production of and does not endorse this product. Permission is granted for individual classroom teachers to reproduce the activity sheets and illustrations for their own classroom use. Any other type of reproduction of these materials is strictly prohibited.

23 1. The brown color, which usually develops when a potato or apple is cut or bruised, is the result of a chemical catalyzed by several enzymes. One of the most important of these enzymes is catecholase which is brought into contact with its substrate, catechol, when cells are ruptured and exposure to the O 2 in air resulting in the oxidation of catechol to the brownish colored benzoquinone. This so called wound reaction is apparently protective since the quinones are toxic to microorganisms. Five test tubes were labeled with varying hydrogen ion concentrations expressed in molarity, [H + ]. Each tube was filled with 3 ml phosphate buffer at the designated [H + ] and 10 drops of catechol was added to each test tube, followed by 10 drops of potato extract. Each tube was stoppered and inverted many times. After a waiting period of 3 minutes it was observed that a brown substance was accumulating in the tubes. The absorbance of each solution was measured and the following results were obtained. Calculate the ph of the test tube containing the optimum [H + ]. Give your answer to the hundredth of a ph unit. 2. A student is asked to make 500 ml of a buffer solution for an upcoming laboratory investigation that requires 50.0 ml of 3.0 M phosphoric acid. The student searches the acid cabinet in the stockroom but can only find 4.5 M phosphoric acid. Calculate the amount of 4.5 M phosphoric acid the student should dilute to a total volume of 500 ml. Give our answer to the nearest tenth of a ml. [H + ] Absorbance

24 3. After an enzyme is mixed with its substrate, the amount of product formed is determined at 10-second intervals for 1 minute. A graph of the data collected during this experiment is shown below: Determine the rate of change for the amount of product formed during the first 30 seconds of data collection. Give your answer to the nearest hundredth.

25 Name: Period Version C AP* Biology: Biochemistry Directions: Each of the questions or incomplete statements below is followed by four suggested answers or completions. Select the one that is best in each case and enter the appropriate letter in the corresponding space on the answer sheet. Questions 1-4 The activity of digestive enzymes was examined in three regions of the digestive system of a crayfish. The stomach, the digestive gland, and the intestine were assayed for enzyme activity at 25 C and ph 7.6. The following results were recorded after repeated measurements. Enzyme Activity ( mole substrate hydrolyzed/min/ml extract) Enzyme Stomach Digestive Gland Intestine Amylase Protease Lipase Which of the following would be useful as a substrate to measure the activity of amylase in crayfish? A) Cellulose B) Starch C) Glucose D) An amino acid 2. According to the data, which of the following can correctly be concluded about crayfish? A) Most digestive enzymes are produced in the stomach. B) Most digestive enzymes are found in the digestive gland. C) Amylase is produced in the esophagus. D) The primary function of the intestine is to digest proteins. 3. The experiment demonstrates which of the following about the digestive system of crayfish? A) Amylase is the most active digestive enzyme. B) Crayfish have only three kinds of digestive enzymes. C) Most enzyme activity occurs in the intestine. D) Different regions of the digestive system are specialized for different functions. 4. Which of the following statements regarding crayfish digestion is most consistent with the data? A) Little digestions occurs before food enters the stomach. B) Most digestion occurs in the stomach. C) Little digestion occurs in the stomach. D) Digestion is optimal at 25 C (1)Test Questions are Copyright by College Entrance Examination Board, Prenceton, NJ. All rights reserved. For face-to-fact teaching purposes, classroom teachers are permitted to reproduce the questions. Web or Mass distribution prohibited. (2) AP is registered traemark of the College Entrance Examination Borard. The College Entrance Examination Board was not involved in the production of and does not endorse this product. Permissionis granted of individual classroom teahcers to reproduce the activity sheets and illustation for their own classroom use. Any other type of reproduction of these material is strictly prohibited. 2

26 Version C Questions 5-8 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. Hydrogen Peroxide Solution Average Time, in Seconds, for Disks to Float 1% 30 sec 5% 25 sec 10% 20 sec 15% 10 sec 5. 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 reactions. D) The higher substrate concentrations in the more concentrated solutions speeded the reaction. 6. Which of the following best describes why ice was used during this experiment? A) To increase the activity of the enzyme B) To retard the breakdown of the catalase. C) To purge the solution of excess air trapped during blending. D) To slow the catalase molecules to increase the probability of contact with the hydrogen peroxide molecules. 7. 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) 5 seconds B) 10 seconds C) 30 seconds D) more than 30 seconds 8. 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) Poke the floating disks back down to the bottom of the beaker and retime the rise of the disks. C) Shake the beakers during the time the disks are rising. D) Dip the disks in the 5% solution before putting them in any other solution. 2

27 Version C Both organic and inorganic chemical reactions can be affected by the addition of a catalyst. 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) Increase in activation energy 12. A substrate may bind to the active site of an enzyme in a variety of ways. Which of the following is NOT a valid mechanism for substrate-enzyme binding? An experimental apparatus similar to that used by S. L. Miller is shown above. In this classic experiment it was demonstrated that a discharge of sparks through a mixture of gases could result in the formation of large variety of organic compounds. Which of the following gases was NOT used in this experiment? A) hydrogen B) oxygen C) water vapor D) ammonia mixed with methane 10. Anabolism is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy. The synthesis of protein or carbohydrate polymers always produces which of the following as a byproduct of these synthesis reactions? A) ATP B) Carbon dioxide C) Urea D) Water A) hydrogen bonds B) peptide bonds C) ionic bonds D) van der Waals interactions 13. Adenosine triphosphate or ATP is composed of adenine, ribose and three phosphate groups. The phosphate groups have a negative charge and as a result the bonds holding them onto the molecule are weak thus easily broken. Which of the following best explains why ATP serves as a common energy source for organisms? A) ATP is the smallest energy molecule. B) ATP energy can be easily transferred to do cellular work. C) ATP is extremely stable and can be stored in the cell for long periods of time. D) Traces of ATP have been found in fossils of ancient organisms dating back to the beginning of life on Earth. 3

28 Version C Questions 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. 14. According to the data presented solely on the curve, what can be said concerning the calculated reaction rates at 1 minute and at 2 minutes? A) The rate after 2 minutes is greater than the rate after 1 minute. B) The rates are the same at 1 minute and at 2 minutes. C) The rates are affected by high concentrations of inhibitors. D) The greater the rate, the faster the enzyme is denatured. 15. The rate of the reaction could also be determined by A) measuring the change in the amount of enzyme B) measuring the change in the amount of substrate C) adding more substrate D) adding more enzyme 16. During which time interval is the reaction rate lowest? A) 1-2 minutes B) 2-3 minutes C) 3-4 minutes D) 4-5 minutes 17. What is the most likely explanation for the change in the slope of the line between 3 and 5 minutes? A) The enzyme had denatured. B) The enzyme had achieved its maximum velocity. C) A large amount of the substrate had been consumed. D) An allosteric inhibitor appeared. 4

29 Version C 18. Biomolecules have intramolecular forces that hold them together as a unit. Biomolecules also exhibit intermolecular forces when interacting with other biomolecules. Which of the following is an example of a hydrogen bond? 21. Proteins are polymers composed of structural monomers called amino acids. Which of the following pairs of functional groups characterizes the structure of an amino acid? A) The peptide bond between amino acids in a protein B) The bond between carbon and hydrogen in methane C) The bond between an oxygen atom and a hydrogen atom in the carboxyl group of a fatty acid D) The attraction between a hydrogen of one water molecule and the oxygen of another water molecule 19. The chemical structure for the nitrogenous base adenine is shown above. It is an important biomolecule and is found in which three of the following? A) Proteins, carbohydrates, and ATP B) Proteins, ATP, and DNA C) ATP, DNA, and RNA D) Chlorophyll, ATP, and DNA 20. Within complex biological systems, many chemical reactions that, by themselves, require energy input (have a positive free-energy change or + G) can occur because the reactions A) A B) B C) C D) D 22. Aqueous buffer solutions are common in biochemical systems and are beneficial in that they resist changes in ph. Which of the following methods for the transport of CO 2 provides a buffering system for the blood? A) CO 2 is dissolved in the plasma. B) CO 2 combines with H 2 O to form carbonic acid and then bicarbonate. C) CO 2 combines with hemoglobin to form carboxyhemoglobin. D) CO 2 is converted to CO for plasma transport. A) may be coupled to the hydrolysis of ATP B) take place very slowly C) take place when the cells are at unusually high temperatures D) are catalyzed by enzymes 5

30 Version C 23. 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. Sampling Time (minutes) Endoplasmic Reticulum Radioactive Counts (Protein X) Cell Component Golgi Apparatus Cytoplasm Nucleus Mitochondria Lysosomes Extracellular Space In graphing the data from this experiment, the sampling time would be shown on the x-axis because A) radioactivity level shows the most variation B) time values are always located on the horizontal axis C) all quantitative values are represented on the x-axis D) sampling time is the independent variable A metabolic pathway is comprised of a series of chemical reactions. Often these reactions are catalyzed by a variety of enzymes. In the series of enzyme reactions shown above, product Z is able to occupy the active site of enzyme E 2. Product Z can therefore first inhibit the production of A) E 1 B) X C) E 2 D) Y 6

31 Version C Questions In a laboratory experiment using spectrophotometry, an enzyme is combined with its substrate at time zero. The absorbance of the resulting solution is measured at time zero and at five-minute intervals. In this procedure an increase in absorbance is related to the amount of product formed during the reaction. The experiment is conducted using the three preparations shown in the table below. Enzyme Preparation Absorbance 0 min 5 min 10 min 15 min 20 min I. 3 ml of enzyme preparation ml of substrate ph 5.0 II. 3 ml of boiled enzyme preparation ml of substrate ph 5.0 III. 3 ml of enzyme preparation ml of substrate ph According to the data, which of the following can best be concluded from a comparison of the results of preparation II with those of preparation I? A) Heating the enzyme is required to increase the absorbance. B) Boiling does not break down the substrate. C) Most of the increase in the amount of product in preparation I was due to an enzymatic degradation of the substrate. D) Products resulting from the breakdown of the enzyme are responsible for the absorbance increase in preparation II. 26. According to the data, the absorbance fails to increase significantly after 10 minutes in preparation III. This is most likely explained by which of the following? A) The reaction is thermodynamically impossible at ph 6.0. B) A ph of 6.0 prevents color development beyond an absorbance of C) The enzyme is degraded more rapidly at ph 6.0 than it is at ph 5.0. D) Most of the substrate was digested during the first 10 minutes. 27. Which of the following statements is best supported by the data? A) Increasing the ph to 7.0 would yield an absorbance higher than 0.30 after 5 minutes. B) The enzyme demonstrates more activity at ph 6.0 than at ph 5.0. C) A ph of 5.0 is the optimum for the activity of the enzyme. D) The enzymatic activity is independent of ph. 7