Exam 3 Summer 06 Key MCB181R Dr. Jorstad

Exam 3 Summer 06 Key MCB181R Dr. Jorstad - MCB 181R Summer...

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MCB 181R Summer Session 2006 Instructor: Dr. S. JorstAd Exam III Name __________KEY_____________________ ANSWERS ARE IN BOLD; IN SOME CASES I HAVE ADDED TEXT TO EXPLAIN QUESTIONS/ANSWERS THAT MANY PEOPLE MISSED. For multiple choice questions , circle all correct answers (there may be more than one). For short essays : confine your answers to the space provided on the scan sheet; do not write on the backs of pages; you may use bulleted points to express yourself, as long as your meaning is clear. 1. Products of the light reactions of photosynthesis include a. ATP * b. NADPH * c. CO 2 d. O 2 * e. Glucose 2. Which of the following statements about the synthesis of ATP during photosynthesis is/ are correct? a. ATP is synthesized during the light reactions by chemiosmosis. * b. ATP is synthesized during the Calvin-Benson cycle by substrate-level phosphorylation. c. The energy to drive the synthesis of ATP comes from photons of sunlight. d. The electrons whose flow drives the synthesis of ATP comes ultimately from water. * e. ATP synthase is required in cellular respiration, but not in photosynthesis. 3. A proton gradient is a source of energy because of a. entropy increases with the release of protons from the thylakoid interior. * b. the charge differences between the stroma and thylakoids of the chloroplast. * [thylakoids are positive (all the H+), stroma comparatively negative] c. the electrons flowing through ATP synthase. [it is PROTONS that flow] d. protons are negatively charged. e. the stroma of the chloroplast is highly acidic. [it is the thylakoids that are acidic] Short Essay #1: Describe the differences in the 3-D shape and chemical properties of the enzymes rubisco and PEPcarboxylase. What problem does PEPcarboxylase solve for C 4 plants? The active site of rubisco is complementary in 3-D shape and chemical properties (e.g., + charge of the O2) to only the O2 part of the CO2 molecule; thus, it can bind either molecule. If it binds O2, photorespiration will occur—essentially undoing PSN. The active site of PEP-carboxylase sense the 3-D shape and chemical 1
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properties (e.g., lack of charge on the C) of the C as well as the O2, so it does not bind O2. C4 plants use PEP-carboxylase to avoid photorespiration. 4. Using the diagram below, what will happen to the process of photosynthesis if an artificial electron acceptor (DCPIP) is added to the chloroplast? (DCPIP oxidizes chlorophyll) DCPIP will prevent e- from flowing thru the ETC; therefore, no ATP, no NADPH a. ATP, NADPH, and glucose will continue to be produced at the normal rate. b. ATP synthesis and NADPH reduction will continue, but no glucose will be produced. c. Protons will leak away through the membrane without flowing through ATP synthase, so no ATP will be made. d.
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This test prep was uploaded on 04/14/2008 for the course MCB 181 taught by Professor Jorstad during the Fall '07 term at University of Arizona- Tucson.

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Exam 3 Summer 06 Key MCB181R Dr. Jorstad - MCB 181R Summer...

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