In the Classroom
Introductory Chemistry and Biology Taught as an Interdisciplinary Mini-Cluster Adele J. Wolfson* and Mona L. Hall Department of Chemistry, Wellesley College, Wellesley, MA 02181 Mary M. Allen Department of Biological Sciences, Wellesley College, Wellesley, MA 02181
Many recent articles and conferences have pointed out the increasingly interdisciplinary nature of scientific research (for examples, see 1, 2). In particular, topics in chemistry that generate the most interest often fall on the boundaries between chemistry and other fields (3). Even the names of divisions and graduate programs, such as biochemistry, molecular biology, biophysics, chemical physics, reflect the open way in which scientists move among departments. Undergraduate students, on the other hand, often see only strict categories such as chemistry, biology, and physics and fail to see how concepts learned in one field could be relevant to another. As biochemists and cell biologists teaching in separate departments of Chemistry and Biology, we have been especially concerned with the lack of coordination between the introductory courses in these subjects. To facilitate interdepartmental and interdisciplinary connections, we designed and offered a “mini-cluster” consisting of one section of introductory cell biology and one section of (second-semester) introductory chemistry. Students were enrolled in both courses simultaneously, classes were taught in back-to-back sections, and the material from each class was related to concepts presented in the other. Our goal in creating and teaching the combined module was to make the connections between chemistry and biology immediately obvious to students early in their undergraduate studies. Except for one, all 28 undergraduates were in their first year of college. (The class also included two post-baccalaureate premed students.) As we taught the course, sitting in on one another’s lectures and meeting frequently with all the laboratory and lecturing faculty involved, we found that teaching was also enriched by the coordinated approach, as we learned subject matter and teaching strategies from colleagues. By having both class periods available to us, we were able to use the time more flexibly than usual, occasionally taking both periods for one class or the other, using one class period for a guest lecture, extra-help session, or group work. Each of the two courses covered essentially the same material as the more traditional individual departmental offerings and served as prerequisite for the upper-level courses in both departments. The differences were in the order of topics and the emphasis on examples that allowed crossdisciplinary connections to be made, both in the classroom and in the laboratories. The general syllabus for the chemistry section of this course is shown below, with the connections to biology topics noted below each heading. Topics taken directly from the Biology syllabus are italicized; potential areas of connection are noted in roman type. *Corresponding author;
[email protected].
Curriculum for Second-Semester Introductory Chemistry with Connections to Introductory Cell Biology I. Introduction to Chemical Equilibria chemical reactions metabolic pathways II. Acid–Base Chemistry special properties of water biological macromolecules biological implications of acid rain buffers in the blood III. Solubility and Complex Ion Equilibria drug design water fluoridation IV. Entropy and Free Energy coupled reactions bioenergetics V. Chemical Kinetics enzymes metabolic pathways VI. Electrochemistry electron transport photosynthesis VII. Solutions and Colligative Properties osmotic pressure sickle cell anemia biological membranes VIII. Nuclear Chemistry radiation in medicine mutations
The core materials that connected the two subjects were supplementary exercises associated with the chemistry laboratories. The laboratory experiments themselves for the two courses were unchanged from those offered for the traditional sections. However, supplementary exercises were designed to focus on the biological aspects of the chemical topics. For example, in the first laboratory period, an experiment in solubility and identification of precipitates was accompanied by an exercise that required the student to identify which components of a common biological buffer might precipitate if the buffer were prepared as a tenfold-concentrated solution. A second example is presented in the box. In this case, the chemistry laboratory dealt with chemical kinetics, specifically the order of reaction and determination of the rate law for fading of bromphenol blue (4 ). The supplementary exercise for the mini-cluster was to compare rates and rate laws for two types of reactions involved in studying photosynthesis. The topics of exercises for the semester’s chemistry laboratories
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In the Classroom
Supplementary Exercise to Accompany Kinetics Lab Photosynthesis and the study of its reaction pathway gives us two examples of reaction rates to examine: 1. The decay of an excited complex to a more stable state 2. The decay of a radioisotope to a more stable product The overall photosynthesis reaction is: 6CO2 + 6H2O → C6H12O6 + 6O2 The initial electron-transfer reaction that occurs in photosynthesis is one of the fastest reactions known. The electron donor and acceptor react together as a unit within a protein. The excited complex decays spontaneously to a more stable state. 1. (a) Use the half-life method to determine if the values in the data table are consistent with first-order or second-order kinetics. Also calculate k, the rate constant. (HINT: Determine if the half-life is independent of the initial concentration.)
are outlined in Table 1. The supplementary exercises were assigned as homework to be completed before the laboratory experiment was carried out. These cluster pre-lab assignments took the place of other pre-lab assignments required in all introductory chemistry courses. A short lecture–discussion by the lab instructor before the students began their lab served to ensure that all students understood the connection between the pre-lab and lab work. By such references to biological topics in chemistry and to chemical topics in biology, material was reinforced and connections were made explicit. Another coordinated effort allowed buffers made in the chemistry lab to be used for a study of enzyme kinetics in the biology lab. In chemistry labs unconnected to the biology course, these buffers are made but never used, and students often fail to see the point of preparing buffers. Furthermore, in the labs for biology unconnected to chemistry, a provided
(b) Explain how a graphical method could also be applied to determine the order of the reaction. (c) How long will it take for 60% of the complex to decay to the more stable state? (HINT: Check to see if your answer is logical by reviewing the data in the table.)
Data Table. Spontaneous Decay of Excited Complex Time/ ps
Conc of Excited Complex/µmol L{1
0
20
0.35
18
0.96
15
2.31
10
4.62
5
2. In another set of experiments, 7.67 2 the radioactive isotope 14C was used to trace the path of carbon during photosynthesis. The order of the reaction for 14C decay is the same as that for the excited complex, but the decay proceeds with a rate constant of 8 14 × 10{12 s{1. How long will it take for 60% of the C to decay?
buffer offers no insight to the acid–base chemistry involved in buffering. Students were surveyed about their reasons for enrolling in the mini-cluster at the beginning of the semester and on their evaluations of its success at the end of the term. Their reactions to the combination were almost entirely positive. They found the supplementary exercises associated with the chemistry laboratories to be of particular value. Interest in majoring in chemistry, biochemistry, or biology was constant or increased by participation in the mini-cluster (for 26 of 27 respondents). The majors chosen by this group one year after completion of the mini-cluster reflect increased numbers in chemistry and biological chemistry compared to their cohort (Table 2). Assessment will be continued by following course selections, retention, and final choice of major for this group, compared to peers in the traditional sections.
Table 1. Coordination of Chemistry Laboratory and Supplementary Exercises Demonstrating the Chemistry of Biological Systems Topic
Laboratory
Exercise
Precipitation reactions
Use of solubility rules and observations to identify a precipitate
Use of solubility rules to predict if a precipitate will form in a 10-fold concentrated biological buffer
Spectrophotometry
Establish the Beer’s law relationship for the thiocyanatoiron(III) ion
Use of absorption at 280 nm and a standard curve to determine protein concentration of an unknown
Equilibrium
Determine the formation constant for the thiocyanatoiron(III) ion
Examine the Keq expression of the amino acid glycine to predict which species will exist at different pH levels
Acids and bases
Standardize a solution of NaOH using a primary standard
Calculate the pKa values of glycine; derive the expression for an isoelectric point by relating pH to pKa1 and pKa2
Acid and bases (continued)
Determine the amount of acid neutralized by an antacid using indirect titration
Sketch a titration curve of an amino acid. Identify the pKa and species present in a distribution plot
Weak acids
Determine the acetic acid content in vinegar and pKa of acetic acid by titration
Calculate the isoelectric point of several amino acids and predict their relative locations in an isoelectric focusing gel
Buffers
Use of Henderson-–Hasselbalch equation to prepare a buffer system at various pH levels; then compare buffering capacities
Use of Henderson–Hasselbalch equation to design a buffer appropriate for the study of an enzyme in the biology laboratory
Hess’s law
Compare the energy released for the one-step and twoDetermine the enthalpy change for the onestep and two-step formation of CuII tetraammine step hydrolyses of ATP to AMP + 2Pi
Kinetics
Determine the rate law for the fading of bromphenol blue in basic solution
Determine the reaction order for the initial electrontransfer reaction in photosynthesis
Electrochemistry
Potentiometric determination of equilibrium constants and electrochemical cells
Calculate how many moles of ATP are produced for every mole of NADH in the electron transport pathway
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In the Classroom Table 2. Mini-Cluster Impact on Declared Majors Class of 1999, One Year after Mini-Cluster Course Selection as First-Year Students/% Mini-Cluster (n = 28)
Chem and Bio Separately (n = 23)
Biological Science
14
13
23
Chemistry
21
0
4
Biological Chemistry
14
4
6
Major
Chem or Bio but not Both (n = 94)
There is currently a great deal of interest in integrated science courses (for example, ref 5). While these may be ideal in some situations, they depend on the few individuals able and willing to teach outside of their primary discipline. We believe that a cluster such as the one described here can serve as an alternative, cost-effective model for interdisciplinary teaching and learning in a variety of institutions. Our minicluster is similar to the cluster model described by Gabelnick et al. in their scheme of learning community models (6 ). Departmental offerings need not be reduced because of a new course; faculty teach the same number of units as for a traditional course; the number of students taught is the same as for a traditional course. Many such groupings can be envisioned, at both the introductory and advanced level. Majors
as well as nonmajors can benefit from the integrated approach, and faculty may find great intellectual stimulation in the cross-disciplinary dialog. Acknowledgments The initial offering of the mini-cluster was made possible by a grant from the Wellesley College Committee on Educational Research and Development. We are grateful to the members of the departments of Chemistry and Biological Sciences for their administrative and intellectual support of the experimental courses and to Larry Baldwin for institutional research. Literature Cited 1. Benowitz, S. Scientist 1995, 9 (June 26), 1, 4. 2. Honan, W. H. Academic Disciplines Increasingly Entwine, Recasting Scholarship; The New York Times, March 23, 1994, p A19. 3. Schwartz, T. Cited in: Tobias, S.; Chubin, D. E.; Aylesworth, K. Rethinking Science as a Career; Research Corporation: Tucson AZ, 1995; p 87. 4. Merritt, M. V.; Schneider, M. J.; Darlington, J. A. J. Chem. Educ. 1993, 70, 660–662. 5. Trefil, J.; Hazen, R. M. The Sciences, Wiley: New York, 1995; Preface. 6. Galbenick, F.; MacGregor, J.; Matthews, R. S.; Smith, B. L. New Directions for Teaching and Learning 1990, 41, 21–37.
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