Ch 10 and Review Questions 1. What is reduction? What is the trick for knowing something has been reduced in ? What is oxidation? What is the trick for knowing something has been oxidized in biology? Reduction is the gain of electrons, if a molecule gains (and the electrons needed to attach it to the molecule) it has been reduced. Oxidation is the loss of electrons, is a molecule loses hydrogen it has usually been reduced. (Please don’t confuse this with the gain or loss of a hydrogen ion in acid/base reactions) 2. What are the three types of phosphorylation we have learned about? Substrate level phosphorylation: an enzyme directly transfers a phosphate from a high reactant to ADP to form ATP. The energy needed to phosphorylate ADP comes from the rearrangement of the reactant into a more stable product. This is an example of a coupled reaction. Oxidative Phosphorylation: Uses a series of reaction in an where the final electron acceptor is . The redox reactions do not directly phosphorylate ADP but instead are used to pump hydrogen ions into a small space generating a proton motive force. The proton motive force drives the phosphorylation of ADP to make ATP by through chemiosmosis through ATP synthase. Photophosphoryaltion: Light energized electrons are passed down an electron transport chain. These electrons are used to generate a proton motive force which produces ATP through chemiosmosis through ATP Synthase 3. What are the two phases of and where does each part occur? Light reactions occur in the thylakoid on the membrane of the thylakoid. The occurs in the of the . 4. Write out the net reaction of photosynthesis, and then break it down into half reactions. What process carries out each half reaction, label each half as oxidation or reduction.

Net Reaction: 6CO2 + 6H2O  C6H12O6 + 6O2

Reduction half reaction, Calvin Cycle: 6CO2  C6H12O6

Oxidation half reaction, Light reactions: 6H2O  6O2 5. Use the absorption spectrum from your notes to describe why plants need light from approximately the 330 nm through 525 nm range. These are the range of wavelengths of light that the pigment molecules a, b, and beta carotene can absorb. 6. Use the absorption spectrum from your notes to explain why chlorophyll a is a blue-green pigment and chlorophyll b is a yellow-green pigment. Chlorophyll a is a blue green color because it absorbs violet and red light and reflects colors in the blue- yellow range. All of these colors of light are reflected into your eye. The eye integrates or averages the input and interprets it as a blue green color. Chlorophyll absorbs violet and blue light and reflects green and yellow light. The yellow and green wavelengths are integrated and interpreted as a light green color. 7. What does II do? What is the reaction center of Photosystem II called? PSII is uses the energy from light to excite an electron and passes it to an electron transport chain. After it loses an electron, the p680 reaction center takes electrons from water, splitting it and forming O2 8. What does the electron transport chain that includes Pq, Cytochrome complex and Pc generate and how does it make it? This electron transport chain uses the electrons to generate a proton motive force inside the thylakoid, the proton motive force is allowed to diffuse down its concentration gradient through ATP synthase in a process called chemiosmosis. ATP synthatse uses the flow of protons to phosphorylate ADP forming ATP. 9. Where does Pc transport the electrons? PC transports electrons to PSI reaction center 10. What does Photosystem I do? What is the reaction center of Photosystem I called? The p700 reaction center of PSI excites electrons using light. The electrons are passed to another electron transport chain that attaches the electrons to NADP+ forming the high energy electron carrier NADPH. 11. Where did the electrons that were used to reduce NADP+ to NADPH originate? These electrons were harvested from water by the P680 reaction center in photosystem II 12. What does the second electron transport chain generate (the one that includes Fd and NADP+ Reductase) It generates NADPH, a high energy electron carrier. 13. Why do plants need to use cyclic electron flow? Because the Calvin cycle requires more ATP than linear electron flow can produce. Cyclic electron transport flow generates an abundance of ATP to drive the Calvin cycle. 14. What photosystem and electron transport chain get used by cyclic electron flow? Cyclic electron transport uses photosystem I, Fd (ferredoxin), the cytochrome complex and Pc to transport the electrons in a cycle that generates ATP. 15. What are the two useful products of the light reaction and where are they generated in the chloroplast? The light reactions generate ATP and NADPH; they are generated on the outside of the thylakoid in the stroma where they can be used by the calvin cycle. 16. What is the purpose of the Calvin cycle? Where does the Calvin cycle occur? The Calvin cycle fixes and makes a 3 carbon sugar G3P which can be used to make sugar or other needed organic molecules. 17. What are the three phases of the Calvin cycle? Carbon Fixation, Reduction, Regeneration. 18. What enzyme is responsible for fixing CO2 in the Calvin cycle? Rubisco fixes carbon in the Calvin cycle. 19. What are NADPH and ATP used for in the Calvin cycle? NADPH and ATP are used in the reduction phase of the Calvin cycle. Conceptually this step is transferring the energy from light and the electrons from water to the sugar G3P. 20. What is the three carbon sugar that is generated by the Calvin cycle? G3P, glyceraldehydes 3 phosphate 21. When it is hot or arid, plants respond by closing their stomata. What counterproductive process occurs when the stomata remain closed for too long in C3 plants? This causes a build-up of Oxygen in the plant which will be taken up by the Calvin cycle (the enzyme Rubisco is not very selective and will bind to Oxygen and attached to ribulose bisphosphate- the 5C sugar that normally accepts CO2 in the carbon fixation step of the Calvin cycle). The Calvin cycle then starts releasing CO2. This process is called and drains the plant of energy and carbon. 22. What is the C4 adaptation to preventing photorespiration? C4 plants have adapted by using the enxyme PEP carboxylase to fix carbon in the mesophyll cells. The 4 carbon organic

acid is then transported to the bundle sheath cell where the CO2 is released directly to Rubisco where it enters the Calvin cycle. This is considered the special separation of the initial carbon fixation step and prevents photorespiration by delivering CO2 directly to Rubisco. 23. What is the CAM adaptation to preventing photorespiration?

CAM plants open their stomata only at night and use PEP carboxylase to fix CO2 into organic acids. The organic acids are stored in a large vacuole for use during the day. The Calvin cycle occurs during the day: the stomata remain closed and the organic acids (carboxylic acids) are used as a CO2 source and are fed into the Calvin cycle. This is considered a temporal (time) separation of carbon fixation from the Calvin cycle and prevents photorespiration by delivering CO2 directly to Rubisco.