BIS2C Study Quiz #3 Microbial Eukaryotes

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Study Quiz 3: Microbial Eukaryotes BIS 2C Fall 2021 Instructions: Below are practice questions that are representative of what you will see on your midterm exam. Please note that these are representative only; your actual exam questions are likely to be different. Your responses here will be graded for completion and effort, not accuracy. Answers that do not show effort will not receive credit. Please work together but be sure your final submission is your own work. This study quiz is due on Friday, October 28 by 5:00p . The assignment must be submitted as a PDF via Gradescope. You can either type your answers into this document and save it as a PDF or you can print this document, handwrite your answers and then scan it into a single PDF file. 1. A eukaryotic cell may contain 2 or 3 distinct genomes. In what structures are these genomes present? (i) (ii) (iii) 2. Contrast the ploidy levels and chromosome shapes of these genomes: 3. Microbiology professor Lynn Margulis was the first proponent of the serial endosymbiont hypothesis for the origin of a eukaryotic cell. What is the central concept of this hypothesis? 4. In which of the three domains of life did photosynthesis arise? 5. Photosynthesis requires an energy source, an electron source and a carbon source: in what way was the photosynthesis carried out by cyanobacteria different from that of other photosynthetic organisms? 1

6. Cyanobacteria were very successful, and their abundance changed the atmosphere of the early earth. What was absent in the oceans and the atmosphere before cyanobacteria became so abundant? What evidence do we have for this change in the early oceans? 7. How could the increased abundance of cyanobacteria have changed the pressures of natural selection so that partnership was beneficial early prokaryotic cells? What feature of at least one cell partner would be important in the changing world? 8. Recall the two-domains discussion given by Professor Ledford and the placement of the eukaryotic clade in the two-domains phylogeny. According to the phylogeny presented in class, what group is the sister taxon to the Eukarya? What does the position of eukaryotes in this phylogeny suggest about one of the partners that merged to form the first eukaryotic cell? 9. Consider your answer to question #8 and think further about the merger that produced the first eukaryotic cell. If one partner was from Loki-Archaeota and the second partner was a bacterium that evolved into a mitochondrion, how can we use the information in the phylogeny below to discern what kind of bacterium became mitochondrial ancestor? You must explain why we made this phylogeny and point out what is important in the phylogeny. 2

10. The first eukaryotic cell was likely a merger between a member of Loki-archaeota and an alpha-proteobacterium. One hypothesis was that alpha-proteobacterium used the toxic oxygen in the environment as the final electron acceptor in the electron transport chain for energy production. Another hypothesis was that the alpha-proteobacterium produced hydrogen that was needed by the Loki-archaeota. In either case, the merger had advantages. However, there was one problem with the idea that the cell from Loki-archaeota was the host cell that engulfed an alpha-proteobacterium to make the first eukaryote. What was that problem? 11. There is phylogenetic and morphological evidence that chloroplasts in the clade Plantae also originated via endosymbiosis. What were the two partners in this primary endosymbiosis? 12. What substance makes up the cell wall of a bacterium? Explain how many antibiotics attack bacteria. 13. Glaucophytes are members of clade Plantae, the group that was produced in the primary endosymbiotic event that led to a chloroplast organelle. Does the presence of a peptidoglycan layer in the chloroplasts of Glaucophytes support or damage the hypothesis that chloroplast originated by primary endosymbiosis? Explain your reasoning. 14. We learned that antibiotics should not be used to treat parasitic infections caused by unicellular eukaryotes. Why is antibiotic treatment not effective on eukaryotes? 3

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15. Secondary and tertiary endosymbiotic events occur when a photosynthetic eukaryote is engulfed by a non-photosynthetic eukaryote. This gives the engulfing cell that ability to do photosynthesis. Look at the top of the phylogeny on the right and trace the origin of the chloroplast in the Apicomplexa . You should see that a member of the red algae was engulfed by the common ancestor of the dinoflagellates and the apicomplexans. This means that the ancestor of the dinoflagellates and the apicomplexans was photosynthetic, even if all the descendants are not. The eukaryotic parasite that causes malaria is called Plasmodium and it is an apicomplexan. Plasmodium has a remnant of the ancestral chloroplast—the remnant now functions in starch metabolism and is called an apicoplast. In BIS 2C, one of the students described being given the antibiotic doxycycline to treat a malarial infection. In question #14, we pointed out that antibiotics should not work on unicellular eukaryotes, so it was important to examine this treatment for malaria more deeply by looking at research papers. A research paper contained the following description of how the antibiotic worked: “ doxycycline has been observed to block the expression of apicoplast genes, leading to nonfunctional apicoplasts in subsequent progeny, and impeding the development of viable parasites.” Explain how this result fits with your answer to question #14. Does this result mean that antibiotics will be effective as a treatment for most unicellular eukaryotic parasites? How could a phylogeny help you decide in which eukaryotic parasites this might work? 4 Tertiary symbiosis Secondary symbiosis Primary endosymbiosis Chloroplast remnant

16. Entamoeba histolytica causes amoebic dysentery. Naegleria fowleri causes primary amoebic meningoencephalitis (PAM). How are these two unicells similar? How are they different? Compare and contrast the mechanism of infection, and likelihood of being cured. 17. A recent massive Red Tide event in Florida killed many fishes, including the endangered goliath grouper. In Florida, the red tide organisms were Karenia brevis cells that produce brevetoxin, not the saxitoxin that we discussed in class. Brevetoxin is exuded from the cells that make it. It has neurological effects that kill fish in the waters where it is released. In windy situations, it can also become an aerosol that causes allergic reactions in humans who inhale it. Contrast a brevetoxin Red Tide outbreak with an outbreak caused by saxitoxin. How would your advice to beachcombers change? 18. What are the three body forms seen in unicellular eukaryotes? How does an amoeba change its shape? What is the shape of the amoeba if there is a shell with holes in it? How does an amoeba engulf its prey without letting the cell cytoplasm leak out? 5

19. The disease leishmaniasis has two hosts: sandflies and humans. Examine the lifecycle of Leishmania and notice that the cells change their body forms. In lab you studied a non-parasitic eukaryote that was also able to rearrange its cytoskeleton. What were the two body forms you saw in lab and how long did it take for Naegleria to rearrange its cytoskeleton? Based on what you observed, which two body forms are not good phylogenetic characters? 20. What do Sudden Oak Death and Potato Late Blight have in common? 21. What is unusual about the way that cellular slime mold makes a multicellular body (the “slug” stage)? 22. Fun with photos: On the next page are 12 photos. i. Which photos show an amoeboid cell? ii. Which photos show a flagellated cell iii. Which photos show a ciliate? iv. In which photo can we see a cell with microvilli? v. Which photo shows the ciliated lining of a human airway? vi. Which photo shows human sperm cells? vii. Which photo shows a human macrophage cell? 6

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