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Practice Questions Set 8 Photosynthesis Theodor W. Engelmann illuminated a filament of algae with light that passed through a prism, thus exposing different segments of algae to different wavelengths of light. He added aerobic bacteria and then noted in which areas the bacteria congregated. He noted that the largest groups were found in the areas illuminated by the red and blue light. 1. An outcome of this experiment was to help determine a. the relationship between heterotrophic and autotrophic organisms. b. the relationship between wavelengths of light and the rate of aerobic respiration. c. the relationship between wavelengths of light and the amount of heat released. d. the relationship between wavelengths of light and the oxygen released during photosynthesis. e. the relationship between the concentration of carbon dioxide and the rate of photosynthesis. What did he manipulate? What did he observe? Manipulate: exposing different segments of algae to different wavelengths of light Observed: noted in which areas the bacteria congregated (whether it was red or blue) 2. What was the big question being asked in Engelmann’s experiment? What wavelength of light does bacteria prefer? What would be a reasonable alternative hypothesis? The bacteria would prefer the red and blue light to undergo photosynthesis. What would be the null hypothesis for the alternative hypothesis? The bacteria would NOT prefer the red and blue light to undergo photosynthesis. What would be the experimental prediction? If the bacteria were to be put in a glass prism where the only source of light was a refracted ray of light that produces a spectrum of lights, then the bacteria would move towards the red and blue wavelengths because the chlorophyll a and chlorophyll b prefer a certain wavelength of light. Think about the relationship between wavelengths of light and rate of photosynthesis.

3. The splitting of carbon dioxide to form oxygen gas and carbon compounds occurs during

a. photosynthesis. b. respiration. c. both photosynthesis and respiration. d. neither photosynthesis nor respiration. e. photorespiration. 4. Vertically oriented leaves like those of grass seen in the slide from lecture notes a. have only palisade mesophyll b. intercept light coming only from above c. have well-differentiated palisade and spongy mesophyll d. have uniform mesophyll cells

5. Explain why your answer to the previous question makes sense for the plant. The vertically oriented leaves are shaped in a way that will constantly open and close the stomata within the epidermis depending on whether or not the sun is hitting it. That is why they have uniform mesophyll so the chloroplasts will constantly be going through photosynthesis.

6. Review the slides of the horizontal and vertical leaves from lecture notes. Explain why there are differences in the types of mesophyll cells and the location of stomata between these two leaf types. In your answer consider the direction from which light is received, as well as the effect of that on temperature and water loss. Consider the demand for CO2 versus supply and how that relates to location of the stomata and which stomata would be open at what times for the leaves. The horizontal leaves will have stomata on the bottom so that the sun’s rays will not expose the open stomata to the light. If the open stomata is exposed to light, the water within will actually evaporate. The vertical leaves however, will constantly open and close whether the sun’s rays are hitting it or not. If it is closed when the sun’s rays are hitting it, the water within will not evaporate. If it is open and the sun’s rays are hitting it, the water within will evaporate.

7. How is the volume inside the chloroplast compartmentalized? The inner part of the chloroplast that is within the granum that is in between the Stroma and Lumen. It acts as a membrane to allow things into the lumen and out into the

stroma. Consider the thylakoids, the lumen, and the stroma.

8. Review the figure in your lecture notes showing the gradual increase in the concentration of carbon dioxide in the atmosphere as measured in Mauna Loa. Explain why the concentration has been increasing. Explain why every year the concentration rises and dips on a seasonal basis with a maximum concentration during the northern hemisphere’s winter and a minimum concentration during the southern hemisphere’s winter. Consider human activity including deforestation and the burning of fossil fuels, as well as the rate of photosynthesis by the plants and algae. Consider the land masses in the Northern versus Southern hemisphere and why one might dominate over the other. Consider global air circulation patterns and why we see this effect in Hawaii. The human population has increased during the past years. The demand for burning fossil fuels has increased as well. Deforestation has increased, causing the increase of CO2. More suburbs and more agriculture has also increased the CO2 rate. The northern hemisphere uses more fossil fuels, during its winter people use more fossil fuels and there are less plants. 9. Parts of the tropical rainforest have been cut to promote intensive agriculture through what is called slash and burn: trees are cut and burned, and the mineral-rich ash is used as fertilizer to supplement the nutrient-poor soil of the tropical rainforest that has been cleared of its trees. Describe two reasons why this type of intensive agriculture is leading to the increase in CO2 concentration in the atmosphere. Consider the carbon that was stored in the trees that is now being burned. Consider the rate of photosynthesis of that land area and the potential intake of CO2 by the plants: the trees that were there and are no longer there, and the crops that have replaced them, and what happens after a couple of years when the soil cannot support the crops any longer.

10. What is the significance of the “ash” used in slash and burn agriculture? Ash is rich metal ion that works as a strong fertilizer. Think of the poor quality soils in the tropics. What is concentrated in the ash when the trees are burned? How does that help the crops?

11. In slash and burn agriculture what happens to the soil after a few years of harvesting crops? The nutrients are not recycle back to land. As the crops are harvested and removed from the land, the mineral nutrients are not recycled back to the soil because they were removed with the crop! How does that compare to the tropical rain forest that existed there before the trees were cut down? 12. The figure above shows the absorption spectrum for chlorophyll a and the action spectrum for photosynthesis. Why are they different (meaning the peaks and valleys are not a perfect match)? Consider the role of the accessory pigments present in the light harvesting antenna complexes.

13. Sea lettuce (Ulva) and Nori (Porphyra) have different combinations of pigments and absorb light maximally at different wavelengths. See the figure from lecture notes. Sea lettuce is typically found in shallow coastal waters while Nori is found in deeper waters. Some have suggested that the reason they are restricted to their respective depths has to do with the available light and their respective action spectra due to their pigments. However you also have to consider that this depth restriction might have to do with nutrient requirements, the intensity of light (not the wavelengths), and maybe even presence of grazers (animals that eat them). Design an experiment to test whether the available light wavelengths at different water depths and not something else can explain why these algae are found at their respective depths. Make sure to include all of the elements of experimental design we have reviewed in class and lab in your answer. Focus on light wavelengths and survival.

14. You take a plant that has leaves that are normally horizontally oriented. You force the leaves to stand vertically by binding them to wooden stakes. What will happen to the rates of water loss and photosynthesis in this plant? Explain. The water would continuously lose water as the stomata will continue to open and close

in order to get CO2 within the plant considering the stomata’s job is to allow gas exchange. When the stomata is hit directly by light when it is open, it causes the water to evaporate out. This would affect photosynthesis as it not only need CO2 but also water in order to conduct photosynthesis.

15. In the thylakoid membranes, what is the main role of the antenna (LHC) pigment molecules? a. split water and release oxygen to the reaction-center chlorophyll b. harvest photons and transfer energy to the reaction-center chlorophyll c. harvest photons and transfer electrons to the reaction-center chlorophyll d. transfer electrons to ferredoxin and then NADPH e. concentrate photons within the stroma 16. Select all that apply: Look at the figure of electron transport in the thylakoids from lecture notes. The following steps in the photochemical reactions help establish a proton gradient across the thylakoid membrane: a. PC (plastocyanin) passes an electron to P700 in PSI reaction center b. Cyt b6-Cyt f complex passes an electron to P700 in PSI reaction center c. Ferredoxin (Fd) passes electrons to NADP+to reduce it to NADPH d. PQ accepts electrons from QB ? and passes them to the Cytochrome complex

17. Which of the events listed below occur in the photochemical (light) reactions of photosynthesis? a. NADP is produced. b. NADPH is reduced to NADP+. c. carbon dioxide is incorporated into PGA. d. ATP is phosphorylated to yield ADP. e. light is absorbed and funneled to reaction-center chlorophyll a.

18. Look at the figure of electron transport in the thylakoids from lecture notes. Which of the following are directly associated with photosystem I? a. harvesting of light energy by ATP b. receiving electrons from plastocyanin c. extraction of hydrogen electrons from the splitting of water d. passing electrons to plastoquinone

19. Some photosynthetic organisms contain chloroplasts that lack photosystem II, yet are able to survive. The best way to detect the lack of photosystem II in these organisms would be a. to determine if they have thylakoids in the chloroplasts. b. to test for liberation of O2 in the light. c. to test for CO2 fixation in the dark. d. to do experiments to generate an action spectrum. e. to test for production of either sucrose or starch. Review the figure for electron transport in the thylakoids from lecture notes. Where is the OEC?

20. Select all that apply: In a plant cell, where are the ATP synthase complexes located? a. thylakoid membrane b. plasma membrane c. inner mitochondrial membrane d. endoplasmic reticulum Remember that plants are eukaryotes and have mitochondria as well as chloroplasts.

21. Reduction of NADP+ occurs during

a. photosynthesis. b. respiration. c. both photosynthesis and respiration. d. neither photosynthesis nor respiration. e. photorespiration. 22. Review the experiment carried out by Jagendorf from class notes. What is the question being asked? What are the alternative and null hypotheses? What is the experimental prediction? What should be a control treatment (not shown in the figure)?

23. Why is it better to have several small thylakoids stacked into one granum than to have one large thylakoid that occupies the same volume? The thylakoid membrane stacks on each other to form a grana (singular form of granum). This causes an increase in surface area allowing for more thylakoid membrane’s. The more membranes mean more allowance for absorption of light for photosynthesis. Consider the membrane surface area. Why is the surface area of the thylakoid membranes important?

24. What is a reaction center (in any photosystem) made of? Remember those 2 Chl a molecules and associated proteins. 25. How can electron transport from photosystem II to NADP+ lead to the synthesis of ATP? See the figure in your lecture slides. Consider how the proton motive force is established. Where are protons added to the lumen? Where are protons removed from the stroma? How is the proton gradient used?

26. What are the possible fates of an electron of a pigment once it has been raised to an excited state? Consider heat, fluorescence, resonance energy transfer, and redox.

27. When does the first chemical reaction in a given photosystem occur? See the figure in your lecture slides. Consider the difference between transferring energy and transferring electrons (chemistry).

28. Review the figure on the photochemical reactions in your lecture notes. Describe what must happen before the OEC splits water. How many times must the Chl a in the reaction center in PSII get excited and donate an electron to the first electron acceptor (pheophytin)? What is the role of OEC?

29. Some mutations lower the rate of photosynthesis. One such mutation is thought to be due to a mutation in the ATP synthase in the thylakoids that lowers the efficiency with which this protein uses the proton gradient, established through electron transport, to make ATP that is needed for the PCR (Calvin) cycle. Design an experiment to determine whether the mutant ATP synthase is less efficient than the normal one. You can use an artificial lipid vesicle system in your experiment to which you can add your proteins of interest.

For the next two questions, consider the following: In linear electron flow, the enzyme FNR takes electrons from 2 reduced ferredoxins and transfers them to NADP+ to reduce it to NADPH. Zn-Ferrocyanide inhibits FNR and prevents this reaction from happening.

30. In the presence of Zn-Ferrocyanide, what would happen to the pH gradient, and the rates of electron transport, oxygen evolution, and ATP synthesis in the thylakoids? Explain. If ferredoxin cannot donate its electrons to the FNR to reduce NADP+ to NADPH, where else can it donate its electrons? Consider linear and cyclic electron transport. 31. How would you determine whether Zn-Ferrocyanide acts as a competitive or a non-

competitive inhibitor?

Design the experiment. Draw a graph showing the expected results for the experiment. For the expected results, review the graphs you had to draw on the last exam!

32. Review the figure of electron transport in the thylakoids from lecture notes. If nothing else is limiting, and an uncoupler is added to the thylakoids, what will happen to the pH gradient, and the rates of electron transport, oxygen production, and ATP synthesis? Explain. Recall that an uncoupler allows the protons to cross the membrane, down their gradient.

Forests on the March Don’t forget about the article we reviewed in class....