Overall, students demonstrated disappointingly modest improvements on many BCI questions (see Figure S1 and the BCI answering file in Supplementary Data). Our concern is the students’ weak understanding of molecular interactions, which leads to a naive understanding of concepts like diffusion or energetic properties of molecules.
The students’ BCI scores were analyzed using the pairwise Wilcoxon test. There were no significant differences between the individual pre-test and post-test scores of the two cohorts (Kruskal-Wallis test, χ2(df = 1)pretest = 0.23, ppretest = 0.63; χ2(df = 1)posttest = 2.24, pposttest = 0.13, alpha < 0.05). The scores of students from the two universities were pooled together into single pre- and post-test groups.
As a first example, the question (Q15) asks: “How does a molecule bind to its correct partner and avoid “incorrect” interactions?” (Figure 1). In the pre-test, 62% of students think that molecules bind perfectly, like puzzle pieces (answer 4), while the best answer was that correctly interacting molecules have a lower (negative) interaction energy (answer 3). In the post-test, ~59% of students selected the best answer. The scores of the pre-test and post-test were significantly different (McNemar, χ2(df = 1) = 60.98 , p-value = 5.77e-15, alpha < 0.05), and an intermediate normalized change was calculated (41%)Marx 2007 Hake 1998 . Consequently, for ~40% of participants, the limitations of analogies need to be clearly articulated in terms of energetic propertiesOrgill 2015 . The schematization of abstract phenomena is essential for analogical reasoningNiebert 2012 . However, what a student takes away from an analogy may not correspond to, or might even conflict with, the instructional purpose of itNiebert 2012 .
Only few students, before or after instruction, appreciate the fact that the dissociation of a molecular complex is driven by random molecular collisions with surrounding molecules (Figure 2). For example, on this question (Q16), “Once two molecules bind to one another, how could they come back apart again?,” there was no significant difference between the pre- and the post-test scores (McNemar, χ2(df = 1) = 0.36 , p = 0.55, alpha < 0.05). In the post-test, even more students, namely 73%, have selected the wrong answer (“A chemical reaction must change the structure of one of the molecules”). This misconception may be caused by presenting students with reaction models in which reactants bind and products dissociate from a catalytic (enzymatic) complex without emphasizing the role of molecular movements and collisions for substrate binding and release.
We were wondering how biology textbooks used in the introductory biology courses of two Swiss universities use analogies to explain the characteristics or behavior of molecules. In fact, authors often present analogies like the key and lock model, the hand in a glove, or ball and stick representations or the drunken walk when illustrating molecular structures or interactions. Even though those similes may help students to visualize microscopic properties of molecules, the energetic properties on a molecular level and the stochasticity are not explicitly considered. The fact that molecules do not only interact with its specific partner but rather with a range of partners is not easily reconciled with this perspective (one reason that drugs have “non-specific” side effectsLounkine 2012 ). Thus, the question remains whether instructors use analogies to explain molecular interactions and whether they explicitly discuss their inherent limitations.
We examined lesson plans and slide presentations of introductory biology courses, revealing that the role of randomness in biological mechanisms is only superficially taught, if considered at all. As an example, the drivers of molecular motion (diffusion) and molecular dissociation associated with thermal random motion are not mentioned or stressed as universal features of molecular systems. Our participants were not attracted by answers related to the concept of randomness on the majority of BCI questions. For example, a question (Q20) asks: “Imagine an ADP molecule inside a bacterial cell. Which best describes how it would manage to "find" an ATP synthase so that it could become an ATP molecule?”. In the pre-test, ~70% of students selected one of the three distractors, all of which represent “active” driver processes; ~42% selected “active processes like electronegativity of molecules” (answer 2); while 25% selected “active pumping” (answer 3) rather than the best answer that “random movements bring the molecule to the ATP synthase” (answer 4). The improvement from the pre- to the post-test was significant (McNemar, χ2(df = 1) = 70.69, p = 4.18e-17, alpha < 0.05) and the normalized learning change was equal to ~35%, corresponding to an intermediate change. In the post-test, still approximately 50% of students select active processes to explain the movement of molecules. The ubiquity of stochastic processes at the molecular level appears to be in conflict with our tendency towards a teleological thinking, which means seeing active purposeful processes of molecular motionsColey 2012 Haglund 2015 . The kinetic properties of molecules and the stochasticity of biological processes are, at best, superficially explained to first- and second-year undergraduates, and based on our observations, current teaching does not result in students clearly recognizing or understanding stochastic biological processes.
Understanding molecular interactions requires fundamental knowledge of chemistry and physicsCooper 2013 . The interdisciplinary nature of these concepts is rarely explicitly presented to students studying in a biology curriculum at universityAres 2004 . Despite the fact that the first two years studying biology are commonly devoted to learning fundamental knowledge of chemistry, physics, and biology, our results indicate that most of our participants do not appear to develop an appropriate interdisciplinary approach to processes on a molecular level. We suspect that disciplinary silo teaching (not referring to processes and phenomena in other disciplines) is likely responsible for students’ weak ability to apply cross-disciplinary thinking. While we often expect that students automatically transfer knowledge from one discipline or domain to another and develop scientific literacy abilities, this appears not to be the caseLoertscher 2014 Nagel 2015 .
The questions of the BCI were developed based on the biological thinking of a group of American studentsGarvin Doxas_2007 . Interviews with these students revealed that many are using analogies to explain their understanding and demonstrated some teleological thinking on how biological mechanisms should or must work. Consequently, many distractors of the BCI questions represent common misunderstandings. Our results on the BCI demonstrated that many students of two first-rate Swiss universities select these distractors and so are likely to share the same misconceptions concerning molecular interactions. It would appear that, regardless of different educational systems, some biological misconceptions are universal.