This case study was developed for the first-semester foundations course for our college biology major. The majority of students are freshman or sophomores, with some junior-level community college transfer students and students majoring in sciences other than biology. The class is a large (200+) lecture class that meets twice a week for 75 minutes. There is no separate laboratory or discussion section and so all group work is conducted within the large lecture section. Twenty to 30 minutes were allotted for group work associated with this case.
The case draws upon two recently published and conflicting reports on the status of nanobacteria as living organisms and the potential role of "nanobacteria"-mediated calcification (biomineralization) in the formation of kidney stones. The problem was selected because it addresses basic concepts related to the biological definition of life and the process of scientific investigation. In addition to engaging students with the topics listed above, the case highlights the ambiguities inherent in science, and creates a forum for debate and discussion regarding the ability to arrive at "right answers."
Students were allowed to form "ad hoc" cooperative learning groups of no more than five members. Information relevant to the case was primarily self-contained, with limited need for students to seek other resources beyond their textbook. Some activities associated with the case were assigned as individual homework, with time provided during the lecture section for group members to share and discuss their ideas. The product of the group discussions was collected, either on 3x5 cards at the end of the class period, or through class discussion and "debriefing" on a specific topic.
Upon completion of this case, students should be able to:
Part I of the case study was distributed to the students near the end of the first class meeting. It was explained that the function of the case study was to provide an alternative method for learning about biology. The role of the student in the learning process was also discussed. Students were asked to think about properties of life and to bring three examples with them to the next class period. Students were encouraged to use their textbook (Biology, Campbell, 5th edition) as a resource.
Students formed ad hoc cooperative learning groups to share their examples of properties of life. Following small group work (approximately 10 minutes), the class shared their overall results while the instructor wrote selected examples of these on an overhead transparency. Class discussion dealt with the ability to generalize properties to all living things and possible methods of testing for the various properties of life.
After completing this section of the case, students will be able to:
Data from the work of Kajander and Ciftcioglu (1998) are summarized and presented in Part II of the case. The handout was distributed to students as a homework assignment designed to encourage students to identify the "specialized vocabulary" that might be unfamiliar to them (terms such as disruptable, gamma radiation, 16S rRNA, negative stain, SEM, or pathogen). Students prepared questions regarding terms and techniques in advance and these questions were answered as a class discussion.
Following this discussion, students worked in their groups to evaluate the data presented in this part of the case. Students were asked to make explicit connections between the data and the property of life it would support using the matrix provided. Each group was asked to select the experimental result that they found most convincing for the hypothesis that nanobacteria are living. These contributions were collected on 3x5 cards. Results were tallied by the professor and presented in graphical form at the next class meeting.
After completing this section of the case, students will be able to:
Part III of the case provides students with more experimental data supporting the hypothesis that nanobacteria are living from the work of Kajander and Ciftcioglu (1998). Three "key" experiments are presented. Working in their groups, students were asked to read through the summarized experimental results and determine (1) what might be concluded from the experiment and (2) whether the experiment supported the hypothesis that nanobacteria are living. Group work was "debriefed" as a whole class discussion focusing on relating the conclusions reached by the students back to the ideas of properties of life.
After completing this section of the case, students will be able to:
Part IV of the case presents a new set of data regarding the role of nanobacteria in the formation of kidney stones reported by the lab of Cisar et al. (2000). The work by Cisar's group is notable as an example of the process of "replication of results" that is often cited as part of the scientific process but seldom so clearly demonstrated. This work is also exciting in that the Cisar group, using experimental procedures and data similar to those reported by Kajander and Ciftcioglu, reach completely opposite conclusions as to the status of nanobacteria as a living organism.
Students were given this part of the case and asked to review the material in advance of the next class session and to identify terms and techniques that were new or unclear. Prior to the start of the group work session, a whole class discussion was held to review terms and technologies that might be unfamiliar to students. In particular, the techniques of PCR (polymerase chain reaction), protein gel electrophoresis, and UV spectrophotometery were briefly reviewed. Most textbooks for biology majors cover some or all of these techniques; however, online resources are also available for students (see "For More Information on..."). Working in groups the students then evaluated the summarized results from Cisar et al. in comparison to the results presented by Kajander and Ciftcioglu. At the end of the period, the groups were asked to determine which of the new results was most damaging to the hypothesis that nanobacteria were living. These results were collected on 3x5 cards, tallied, and presented in graphical form during the next class session for discussion.
After completing this section of the case, students will be able to:
The final installment of the case drives home the controversy surrounding the status of nanobacteria as living organisms. Throughout the previous sections of the case, students have been reinforcing the assumption that nanobacteria are living based on the evidence of growth and reproduction. Three key experiments from the Cisar group are presented to explain these observations and to provide an alternate hypothesis for the process of biomineralization and the formation of biofilms.
Students working in their groups discuss the implications of the three experiments summarized in the case from the perspective of the Cisar lab. The discussion requires the students to reflect on their understanding of the properties of life and how these experiments address whether the nanobacteria are living. Students are also encouraged to consider alternate conclusions. One variation on this activity would be to assign groups a perspective: either "pro-life" (perspective of Kajander and Ciftcioglu) or "anti-life" (perspective of Cisar et al.).
Finally, the students are asked to consider which set of data they find most convincing and whether they (1) believe nanobacteria are real, living organisms, (2) believe nanobacteria are a non-living artifact, or (3) are undecided on the issue. This question is debated during the following class session, and the larger issue of science as a human endeavor is discussed. One useful technique for class debates in a large lecture section is to divide the room into sections reflecting a position. Students sit in the section that matches their opinion but are free to get up and move should their opinion change during the course of the debate.
Answers to the questions posed in the case study are provided in a separate answer key to the case. Those answers are password-protected. To access the answers for this case, go to the key. You will be prompted for a username and password. If you have not yet registered with us, you can see whether you are eligible for an account by reviewing our password policy and then apply online or write to answerkey@sciencecases.org.
PCR
http://people.ku.edu/~jbrown/pcr.html
http://allserv.rug.ac.be/~avierstr/principles/pcr.html (animation of PCR process)
Ribosomes
http://ntri.tamuk.edu/cell/ribosomes.html
Acknowledgements: This case study was developed with support from The Pew Charitable Trusts.
Date Posted: 12/05/01 nas
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Originally published at http://www.sciencecases.org/nanobacteria/nanobacteria_notes.asp
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