Chemical Education Today
News from Online Respiration Lynn Diener Science Department, Mount Mary College, Milwaukee, Wisconsin 53222
[email protected] Take a nice deep breath... Do not relax, though. Instead, think about all of the extraordinary chemistry going on every time you do that, such as the chemical reactions in your muscles allowing your lungs to expand, the diffusion of gases from high to low pressure, or the low solubility of oxygen in your blood (enhanced by hemoglobin). Everyone can relate to breathing; we do it all the time! Take another deep breath, and let us delve into resources on the chemistry of respiration. We will follow the air into our lungs and throughout the body, learning a little bit about the resources available online at each step. Gas Laws and Breathing Dalton's law of partial pressures is often covered in introductory chemistry, and it is often hard for students to understand. The air we breathe, a mixture of N2, O2, and other gases, is governed by Dalton's law. A Web site at Davidson College has a clear, concise explanation of Dalton's law along with a calculator that looks at a simple mixture of two inert gases (O2 and N2) (1). The calculator starts with the two gases in separate flasks with a stopcock connecting the two. Each flask contains a certain volume, and the pressures of the individual gases in the flasks are given. Students are asked to calculate the final pressure of the gases after the stopcock has been opened and the gases mix. Another Web site is a chapter from an online textbook appropriate for high school or college students that covers the ideal gas law and Henry's law in addition to Dalton's law. (2) It has an interactive tutorial that covers Dalton's law, including a series of questions to check students' understanding. If you are looking for something more fun, why not try using the activity Dalton's Law of Gummy Bears by Chris Farrell (3)? In this activity, gummy bears represent gas molecules, and each color of gummy bear is a specific gas. Gummy bears are placed in a Petri dish, and each gummy bear represents 5% of the air content (16 nitrogen bears and 4 oxygen bears to start with). The activity begins when the original gummy bears are “inhaled” (not literally, of course) and travel to the alveoli (see Figure 1). The activity then shows the diffusion of oxygen into the blood and CO2 out of the blood, looking at how the partial pressures of each gas change in the original inhaled air according to Dalton's law. It is a fun, hands-on way to get your students engaged in learning Dalton's law with a particular focus on breathing;and it is yummy, too. I also recommend an article by Dorothy Feigl published in this Journal in 1974 (4). Her activity focuses on Dalton's gas law and breathing;students actually measure the PCO2 of expired air using a simple and affordable method;so it is a perfect fit.
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Figure 1. Artistic representation of the alveoli of the lungs. Reproduced with permission of the artist, Katelyn McKagan.1
The Chemistry of Hemoglobin After oxygen diffuses into the body according to its partial pressure, it binds to an extraordinary protein called hemoglobin. When students discover how little oxygen is soluble in our bodies' water (plasma) at atmospheric pressure and body temperature, the importance of hemoglobin becomes obvious. You can use this as an opportunity to talk about the solubility of O2 in water. Fred Senese's Web site offers a brief explanation and a simple calculator that allows students to determine the concentration of oxygen and water vapor pressure for any temperature and partial pressure of oxygen (5). A Web site at East Tennessee State University (6) provides a general overview of hemoglobin and gives students a sense of what hemoglobin does in the body. For all learners in your classroom, “Hemoglobin Is a Protein” on the Springfield Technical Community College Web site (7) describes the structure and function of hemoglobin thoroughly in words and graphics. Another Web site students may find useful is available at the University of Massachusetts;Amherst (8). This site provides a tutorial on hemoglobin using three-dimensional Jmol images to guide students through the structure of normal hemoglobin and sickle hemoglobin (found in people with sickle cell anemia). Mitochondria and Cellular Respiration Hemoglobin takes oxygen from your lungs (see Figure 2) and transports it to your body's cells. Inside those cells are mitochondria that use oxygen to release energy for cellular work.
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r 2009 American Chemical Society and Division of Chemical Education, Inc. pubs.acs.org/jchemeduc Vol. 87 No. 1 January 2010 10.1021/ed8000254 Published on Web 12/18/2009
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cellular respiration is found at J. S. Carter's Cellular Respiration and Fermentation site (13), but for advanced students I really like Metabolic Pathways of Biochemistry (14). This site has more than just the overall chemical reactions for all of the pathways in cellular respiration: It also includes each step in the pathways. Perhaps my favorite resources are the molecular animations from the MRC Dunn Human Nutrition Unit (15). This site has a collection of animations of ATP synthase working to create ATP. These beautiful animations show how very like a tiny turbine ATP synthase really is. Your students will not be able to look away; I know I cannot! Anaerobic Respiration Figure 2. Depiction of lungs as organic, tree-like structures. Reproduced with permission of the artist, Ashlyn Harris.1
So, how does oxygen get from the blood into the cell? The Teachers' Domain has an interactive resource that uses Flash media to let students choose any number of physiologically important chemicals (O2, glucose, CO2, etc.) and see how they enter the cell (9). Students learn that, although oxygen can easily diffuse through the cell membrane, glucose is too big and polar to do so and must be brought in by transport proteins in the cell membrane. Mitochondria (see Figure 3) are the powerhouses of the cell: they use oxygen and glucose to produce adenosine triphosphate (ATP), the molecule that quickly releases energy for the cell. It is best to review mitochondria with your students before moving farther into this topic. Fortunately, the Teachers' Domain has a PDF with an overview of mitochondria, their structure, and their function as well as some informative pictures (10). At the Dolan DNA Learning Center, a video clip discusses the endosymbiotic theory of mitochondria. The theory suggests that bacteria either entered or were engulfed by a single-celled eukaryotic host millions of years ago, an event that eventually resulted in eukaryotic cells (11). Students most likely will be fascinated to find that we may have beneficial bacteria in our cells.
Figure 3. Rendering of a single mitochondrion. Reproduced with permission of the artist, Samantha Phillips.1
Once students understand that cellular respiration largely occurs in the mitochondria, I like to offer an overview of that process. Kimball's Biology Pages, an online textbook, has a simple overview of cellular respiration and describes how mitochondria fit into it (12). The Web site excludes glycolysis because it focuses on mitochondria and their role. A more thorough explanation of
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Although most cells in our bodies use aerobic respiration, some cells routinely undergo fermentation. Undoubtedly, you have felt the burn of lactic acid, a byproduct of fermentation, building up in your muscles after a sprint. Many microorganisms use anaerobic respiration to meet their energy requirements. Refer to the Cellular Respiration and Fermentation Web page for an overview of fermentation (13). An interactive tutorial from the American Society of Microbiology's Microbe Library lets your students explore both aerobic and anaerobic respiration (16). The tutorial focuses on microbial anaerobic respiration that uses nitrate as a final electron acceptor. A page from the Exploratorium focuses on the lactic acid bacteria that create pickles (17). Although the scientific explanation is basic, it will grab students' interest, especially if they like pickles and wonder how a sweet, juicy cucumber becomes so sour. It is also fascinating for students to think that the chemical reactions that make pickles are similar to the chemical reactions taking place in their muscles during a difficult sprint. Finally, an activity from Teach Engineering focuses on the anaerobic respiration of yeast (18). Here students get the opportunity to quantify yeast anaerobic respiration. Pulling It All Together How can you bring all these elements together to show students the big picture? I really like The Powerhouse of the Cell, a video clip from the Teachers' Domain (19). It pulls together many of the concepts of respiration and tells students how they actually work in the body, focusing on muscles (some of the most metabolically active tissue in our bodies). I also use a couple of case studies to tie things together. “The Case of the Poisoned Firefighters” (20) nicely connects and reinforces students' understanding of hemoglobin and respiration by focusing on respiration gone wrong when some firefighters are exposed to air during a rescue that has either hydrogen cyanide (HCN) or carbon monoxide (CO) present. This case study combines the chemistry with the physiology, which I find students have an easy time relating to. The second case study, from the National Center for Case Study Teaching in Science (21), has slightly more adult content, so I would recommend it for more advanced students. It focuses on a murder mystery in which one of the victims was poisoned by a substance that interfered with her cells' ability to produce ATP. Respiration is a fascinating subject. Because we do it every minute of the day, it is something that all of us can easily relate to (and breathing is intriguing to visualize; see Figure 4). It is also something that many students probably do not understand very well. With the resources described in this article, you can use respiration as a way to teach a variety of chemistry concepts.
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Figure 4. Illustration of the act of breathing. Reproduced with permission of the artist, Caitlin Greener.1
Note 1. The artwork in this piece is the result of an ongoing collaboration between Lynn Diener and Mount Mary Art Professor Jordan Acker Anderson and her art students. See “A CrossDisciplinary Collaboration” by Diener and Acker Anderson in the February 2008 issue of the Journal (pp 156-157).
Literature Cited 1. Blauch, D. L. Gas laws: Dalton's law of partial pressure. 2001,http:// www.chm.davidson.edu/ChemistryApplets/Gaslaws/Daltons Law.html (accessed Nov 2009). 2. Gilbert, T. R.; Kirss, R. V.; Foster, N.; Davis, G. Properties of Gases and the Air That We Breathe. In Chemistry: The Science in Context, 2nd ed.; W. W. Norton and Co.: New York, 2008; Chapter 8, http://www.wwnorton.com/college/chemistry/gilbert/overview/ ch8.htm (accessed Nov 2009). 3. Farrell, C. Dalton's Law of Gummy Bears. HAPS Educator 2005, 9 (3), 7–8, http://msjensen.cehd.umn.edu/HAPSED/2005/2005_ spr_haps_ed.pdf (accessed Nov 2009) . 4. Feigl, D. L. A Dalton's Law Experiment for Students in the Health Sciences. J. Chem. Educ. 1974, 51, 273–274. 5. Senese, F. General Chemistry Online! How Can I Predict Oxygen Solubility in Water? http://antoine.frostburg.edu/chem/senese/ 101/solutions/faq/predicting-DO.shtml (accessed Nov 2009). 6. Currie, D. The Hemoglobin Page. http://faculty.etsu.edu/currie/ hemoglobin.htm (accessed Nov 2009).
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7. Tamarkin, D. A. Hemoglobin. http://faculty.stcc.edu/AandP/ AP/AP2pages/Units18to20/blood/hemoglob.htm (accessed Nov 2009). 8. Hemoglobin Tutorial. http://www.umass.edu/molvis/tutorials/ hemoglobin/ (accessed Nov 2009). 9. Teachers Domain. Cell Membrane: Just Passing Through. http:// www.teachersdomain.org/resource/tdc02.sci.life.cell.membrane web/ (accessed Nov 2009). 10. Ross, J. Teachers Domain. Mitochondria. 2002, http://www. teachersdomain.org/resource/tdc02.sci.life.cell.mitostruc/. 11. Wallace, D. DNAI. Mitochondria from the Beginning. http:// dnalc02.cshl.edu/mydnalc/?a=dnai:244 (accessed Nov 2009). 12. Kimball, J. W. Kimball's Biology Pages. Cell. Respiration 2008, http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/ CellularRespiration.html (accessed Nov 2009). 13. Carter, J. S. Cellular Respiration and Fermentation. 1996, http:// biology.clc.uc.edu/Courses/bio104/cellresp.htm (accessed Nov 2009). 14. Miller, K. J. Metabolic Pathways of Biochemistry. 1998, http://www. gwu.edu/∼mpb/index.html (accessed Nov 2009). 15. MRC Dunn Human Nutrition Unit ATP Synthase Group Page. http://www.mrc-dunn.cam.ac.uk/research/atp_synthase/ rotarymech.php (accessed Nov 2009). 16. Terry T. M. American Society for Microbiology. Microbe Library. Aerobic and Anaerobic Respiration. http://www.microbelibrary. org/microbelibrary/files/ccImages/Articleimages/Tterry/Images/ respiration.html (accessed Nov 2009). 17. Exploratorium. The Accidental Scientist, The Science of Cooking. The Race of Microorganisms. http://www.exploratorium.edu/cooking/ pickles/salt.html. (accessed Nov 2009) 18. Teach Engineering Web Site. Hebrank, M. R. Yeast Cells Respire, Too ( But Not Like Me and You). 2004, http://www.teachengineering. org/view_activity.php?url=http://www.teachengineering.com/ collection/duk_/activities/duk_cellresp_mary_act/duk_cellresp_ mary_act.xml (accessed Nov 2009). 19. Teachers Domain. The Powerhouse of the Cell. http://www. teachersdomain.org/resource/tdc02.sci.life.cell.mitochondria/ (accessed Nov 2009). 20. Cook, B.; Shuster, M. A. Case of Poisoned Firefighters. http://www. apsarchive.org/resource.cfm?submissionID=1484&BEN=1 (accessed Nov 2009). 21. Bode C.; Jablonski, A. A. Rigorous Investigation: The Relationships between Cellular Respiration, Muscle Contraction and Rigor Mortis. The National Center for Case Study Teaching in Science. 2003, http://www.sciencecases.org/rigor_mortis/ rigor_mortis.asp (accessed Nov 2009).
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