151-3 disc-22fa HW5

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151

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Biology

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Oct 30, 2023

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151-3 Introductory Biology - Discussion Homework 5 Week of October 10, 2022 Name: Katie Scheer Reminder: Submit your homework on Canvas by the start of your scheduled discussion section! Please use a different font color so that your answers stand out. Intro Bio 151/153 – Discussion assignment for the week of October 10 th Complete as much of this assignment as you can before going to your discussion section. This week, your TA will only be checking questions 1-16 for completion, the rest you’ll do during discussion. It will be the basis of your exam review. There will be no in-class worksheet this week. What you see below is all the material for this week. We strongly suggest you do the optional modeling exercises below the questions (i.e., questions 17 & 18) before you come to class and before you answer the following questions. Model these the same way you modeled respiration and fermentation in discussion last week. Photosynthesis 1. For the table below, fill in where the molecules are used or produced. If neither used nor produced, leave the space blank. Are the compounds listed below used or produced in the processes listed at right? Non-cyclic electron flow Cyclic electron flow The Calvin cycle G3P (i.e., the 3-carbon sugar that comes out of the Calvin cycle) produced O 2 produced CO 2 used ATP produced produced used ADP + P i used used NADPH produced used NADP + used 2. The various reactions in photosynthesis are segregated from each other spatially within the chloroplast. a. Where in the chloroplast do the light reactions occur? In the thylakoid membrane b. Where in the chloroplast is the chemiosmotic gradient developed? Across the thylakoid membrane c. Where in the chloroplast does the Calvin cycle occur? In the stroma

3. Which light reaction system (cyclic or non-cyclic) would a chloroplast use in each situation described below? a. Plenty of light is available, but the cell contains little NADP + . b. There is plenty of light, and the cell contains a high concentration of NADP + . If there’s little NADP+, that would mean there’s a lot of NADPH. This means the NADPH is not being used up in the Calvin cycle, so this must be cyclic . If there’s a high concentration of NADP+, that means the NADPH is constantly being used up. So this would be non-cyclic which produces NADPH. 4. To the best of your ability, fill in the blanks on the diagram below of the Calvin Cycle. Don’t worry too much about the numbers – just try to put in the “major players” in this cycle. a. Based on your understanding of the function of the chloroplasts, why does turning on the light cause the pH in the solution outside the thylakoids to increase? Photosystem I and II (electron transfer) in the thylakoid membrane resulted in H+ pumping from the stroma (outside) to the thylakoid (inside). This led to the H+ concentration becoming lower (pH increasing) outside of the thylakoid.

5. All living organisms require a constant supply of ATP to maintain life. If no light is available, how can a plant make ATP? ATP and NADPH produced by light reactions are used in the Calvin cycle to reduce CO2 to sugar. 6. Chloroplast thylakoids can be isolated and purified for biochemical experiments. Shown below is an experiment in which pH was measured in a suspension of isolated thylakoids before and after light illumination and chemical addition. The pH was measured outside the thylakoids (in the stroma). The light was added at the point in time indicated by the first arrow. At the time indicated by the second arrow, a chemical compound was added to the thylakoids. Examine these data and address the following questions. b. Given the response of pH; the chemical added was probably an inhibitor of: i. oxidative phosphorylation ii. ATP synthase iii. NADPH breakdown iv. Electron transport chain between photosystems II and I v. Rubisco Inhibiting the electron transport chain between photosystems II and I would prevent the transport of H+ ions into the thylakoid, resulting in the reduction of the concentration of H+ (increased pH). 7. What is the role of Rubisco? It catalyzes the first step of carbon fixation in the Calvin cycle during photosynthesis. 8. What are the two reactions that RuBisCo facilitates? Carboxylase and Oxygenase 9. How does photorespiration resemble respiration? Why is photorespiration a “bad” process from the plant's perspective? Both ultimately consume oxygen and release CO2. It can be considered bad because it consumes ATP and results in the loss of C atoms (in the form of CO2) that were previously incorporated in the Calvin cycle. 10. In C 4 plants, where does the Calvin cycle occur? Where does the initial fixation of the carbon from atmospheric CO 2 take place? Be specific. In C4 plants, the Calvin cycle occurs in the bundle-sheath (cells) . The initial fixation of the carbon from atmospheric CO2 takes place in the chloroplast by the enzyme PEP 11. What are the benefits and problems of C 4 photosynthesis?

151-3 disc-22fa HW5

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