Abstract

Osmosis contributes to a range of biological phenomena, from functioning of nephrons in animals to stomatal opening and closing in plants; yet, scientifically simple ideas about osmosis are common. These ideas limit learners’ comprehension of biological processes involving osmosis. They limit, too, science graduates’ potential to contribute to the ecosystem of innovation, which has turned to osmosis for desalinating water and harvesting “blue energy,” for example. To deepen conceptual understanding of osmosis, this ~50-minute lesson asks students to analyze tabulated data, a graph, and photomicrographs related to osmolality of personal lubricants and then to formulate a scientific recommendation for the bulk procurement of personal lubricants. The lesson takes inspiration from an expert review panel convened by the World Health Organization to generate such a recommendation. The lesson includes at its start a consideration of diffusion. This inclusion allows a contrast between osmosis and diffusion to be drawn. The inclusion also deepens students’ understanding of stochastic processes in biology. We have used the lesson in an introductory undergraduate biology course and an upper-level one. Quantitative assessment data were collected from the latter and documented students’ adoption of scientifically rigorous views of osmosis and diffusion. Qualitative data collected from both courses revealed that students found the lesson personally relevant and its information surprising. Students were struck by the apparent inattention to women’s physiology in the design of lubricant. This surprise suggests ways to extend the lesson, for example, into the nature of science, in particular, into the social and cultural embeddedness of science.

Primary Image: Trajectories of three diffusing mastic particles overlying “Diver and Two Octopi.” “Diver and Two Octopi” comes from Kinoe no komatsu, volume 3 (Katsushika Hokusai [Japan, 1760–1849], 1814. Woodblock print. British Museum, asset number 583055001; © The Trustees of the British Museum, who permit use of image under terms of CC BY-NC-SA 4.0). Trajectories (in white) adapted from Figure 6 of “Mouvement Brownien et Réalité Moléculaire” (J. Perrin, Annales de chimie et de physique: tome XVIII. Paris: Gauthier-Villars, 1909. Source: gallica.bnf.fr / Bibliothèque nationale de France).

Citation

Society Learning Goals

Cell Biology

• Membrane Structure and Function
• How do solutes and other materials move across membranes?

Science Process Skills

• Process of Science
• Construct explanations and make evidence-based arguments about the natural world
• Communication and Collaboration
• Work productively in teams with people who have diverse backgrounds, skill sets, and perspectives
• Reflect on your own learning, performance, and achievements

Lesson Learning Goals

• deepen understanding of osmosis, diffusion, and sexual physiology.
• advance in self-efficacy with regard to collaboratively observing, analyzing, evaluating, and making decisions with biological data.

• Flow occurs because of the existence of an energy gradient between two points in the system.

Lesson Learning Objectives

• evaluate consequences of a cell being placed in a solution differing in concentration of impermeant solutes from the intracellular.
• justify the possibility of osmosis and diffusion across the membranes of both living cells and non-living systems (e.g., metabolically poisoned cells).
• collaboratively evaluate tabulated, graphed, and photomicrographical data.
• collaboratively formulate a decision based on these various forms of data.

Introduction

Osmosis and diffusion play pivotal roles in transfer of material (e.g., 2) and consequently appear broadly in biological processes (e.g., capillary filtration) and scientific innovations (e.g., “blue” energy [3]). Simple conceptions about osmosis and diffusion are common in learners and reflect beliefs that molecules make active decisions, that osmosis and diffusion occur only in living organisms (i.e., the processes depend on ATP), and that thermal motion of particles ends in the absence of a concentration gradient (4–6). Contributing to the prevalence and persistence of such views are some high school and university textbooks that reinforce them (7). To advance learners in their understanding of osmosis and diffusion, we designed a lesson that engages students in dialogue about osmosis in the context of sexual health. The dialogic design lends itself to shifting beliefs and mindsets. This introduction to the lesson elaborates three aspects: (i) the rigorous conceptions of osmosis and diffusion to which we wanted students to shift, (ii) the approach taken by the lesson to prompt the shift, and (iii) the lesson’s relationship to previously published lessons on osmosis.

The view of osmosis as diffusion of water down its concentration gradient has appeal in classrooms and textbooks (7): it is simple and graspable. Yet, this conception falls short in multiple ways. For example, using water-¹⁸O and collodion membranes, Mauro (8) observed different time courses for diffusion and osmosis. Similar observations were made by Solomon and collaborators (9, 10) when studying fluxes of tritiated water across membranes of erythrocytes. Additionally, the conception of osmosis as diffusion of water assumes that solutes displace and dilute water; yet, in violation of this assumption, solutes with a negative partial molar volume concentrate water, rather than dilute it. In such cases, osmosis will drive water up rather than down its concentration gradient (e.g., see Table 5.1 of [11]).

Compatible with theory and experimental evidence is the view of osmosis as a convective process, one driven by a pressure difference. Offering an historical account of this view, Guell (12) traces confusion about osmosis—whether diffusive or convective—to a report by Fick in 1855 (13). Fick analyzed osmosis as though it were diffusion; yet, he described a convective process: “[...] a force of suction comes into play on each side of the membrane, proportional to the difference of [salt] concentration” (page 38; [13]). The molecular mechanism for the convective process still remains incompletely settled, but we briefly explain here the idea emerging from theoretical and empirical work. Theoreticians have taken stock of energies due to the motions of solute and solvent particles (i.e., their kinetic energies) and due to forces of interaction between particles (i.e., the potential energies of solvent-solvent, solvent-solute, and solute-solute interactions). This tallying of energies shows that osmotic pressure is dominated by kinetic energy of solute molecules, with a lesser contribution from potential energy of solute-solute interactions (14, and extended by 15). Echoing the central role of solute kinetic energy, Debye (16; reviewed by 17) envisioned that collision of impermeant solute particles with a semi-permeable membrane results in a repelling force on the solute particles. This repelling force is transmitted locally to the solution (solute and solvent), leading to a pressure drop immediately adjacent to the membrane, on its side facing the greater solute concentration. Akin to Fick’s envisioned suction force, this pressure drop drives solvent across the membrane and into the compartment with greater impermeant solute concentration.

In units, pressure is energy per volume; thus, in this rigorous conception of osmosis as a convective process, solvent flows down an energy (pressure) gradient related to the concentration of impermeant solute. Grasping this conception benefits the student seeking a deep understanding of why the concentration of impermeant solute appears as a variable in the equation for water potential or the equation for capillary filtration, for example. Relatedly, grasping this conception leads to seeing osmosis as an example of one of physiology’s core concepts: “Flow occurs because of the existence of an energy gradient between two points in the system” (1). This concept is inherent in a generalized form of Ohm’s Law, with flow per time determined by an energy difference between two spaces and by the conductance to flow between the spaces.

We believed that to reach this level of understanding our students would need to abandon the view of osmosis as diffusion of water down its concentration gradient, as well as commonly held (4–6) views that osmosis and diffusion are active processes (i.e., dependent on ATP) and that osmosis involves movement of solvent from a compartment with higher impermeant solute concentration to one with lower. The rigorous view of osmosis invokes no role for ATP and involves movement of solvent from a compartment with lower impermeant solute concentration to one with higher, since the latter will have a greater pressure drop due to greater repelling force on solute at the membrane.

Views of osmosis and diffusion are held tightly (e.g., 7), so we sought to shift students’ views through collaborative problem-based learning (PBL). Informed by social constructivism, collaborative PBL strives to bring learners to a cognitive impasse by way of an authentic, “real-world” problem (e.g., 18). Important to fruitful resolution of the impasse is productive dialogue, wherein assumptions and insights of all participants are brought to the fore (e.g., 19). Also important for successful resolution is activation of positive academic emotions (e.g., enjoyment) so that negative ones (e.g., boredom) are avoided (e.g., 20, 21).

With these design criteria in mind, we centered our lesson on a problem tackled by an expert advisory group convened by the World Health Organization in 2011 (22). The problem concerns whether a science-supported recommendation can be made regarding osmolality, pH, or ingredients of personal lubricant for bulk procurement. We reasoned that the social and personal relevance of the problem might activate positive academic emotions. Use of lubricant is common (e.g., 23); yet, myths about lubrication persist (e.g., 24, 25). Marketed personal lubricants vary in osmolality from ~10 to ~10,000 mOsm/kg and in pH from ~3 to ~7 (e.g., 26, 27). Lubricants exceeding physiologic values of osmolality can cause vulvovaginal tissue damage and irritation, and ones exceeding physiologic values of pH can alter the vulvovaginal microbiota, potentially leading to infection (e.g., 26, 27). To ensure that conversation within student teams is productive and inclusive, we draw on dialogic scaffolding that was developed independently by two groups (28, 29) to guide discussion of artworks. Lessening the likelihood of premature cognitive commitments, the scaffolding elicits interpretations and decisions only after observations have been inventoried and reflections made upon them. In one group’s formulation (Visual Thinking Strategies, or VTS [28]), the scaffolding emphasizes sustained observation and evidentiary reasoning. For example, it uses questions such as “What more do you see? What makes you say that?” The other group’s formulation (29) goes by the acronym ORID, usefully serving as a mnemonic for the scaffolding’s progression through four stages: observations, reflections, interpretations, and decisions. Multiple ways of using the scaffolding in the educational setting are elaborated by Nelson (29), and Darling et al. (30) describe its use in a CourseSource lesson. Henceforth, we use “ORID” to refer to the scaffolding as conceived by both groups.

This lesson shares with scores of others the goal of shifting students’ conceptions of osmosis and diffusion; yet, this lesson differs in approach. For example, other published lessons enhance understanding of these processes through computer-based visualizations (e.g., 31, 32), drawing (33), engineering-design projects (e.g., 34), hands-on activities (e.g., 35–38), and reasoning through hypotheses (e.g., 39) and problems (e.g., 40). In literature searches, we found no other lesson that considers osmosis in the context of lubrication or with the dialogic scaffolding of ORID.

Intended Audience

The lesson has been used in two undergraduate courses at a liberal arts college: an introductory course focusing on organismal biology and attracting primarily first-year students from a range of intended majors in the sciences and beyond, and an upper-level course on medical physiology serving primarily life sciences majors who intend to pursue careers in biomedical research or medicine. Class enrollments are 30 to 40 students in the introductory course and 15 to 20 in the upper-level one. Gender identities in the introductory course comprise ~69% female, ~27% male, and ~4% non-binary/gender-fluid. In the upper-level course, they are ~75% female, ~20% male, and ~5% non-binary/gender-fluid. Information about racial/ethnic identities is available for the introductory course only: 33% Asian, 7% Black or African American, 10% Hispanic, 77% White (some students have multiple identities, so the summed percentages exceed 100). About half of the introductory class pursues majors in science or math. About 95% of the upper-level class is studying toward a major in the life sciences. The lesson is scalable if the physical or virtual classroom allows formation of discussion groups, each comprising roughly four persons.

Required Learning Time

Completing the lesson takes 48 minutes in class. Done before class, the preparatory readings and pre-lesson assessment add an additional 20 minutes. Done after class, the post-lesson assessment and reflection add an additional 10 minutes.

Prerequisite Student Knowledge

We expect that prior to doing the preparatory readings learners will have familiarity at the high school level with the notion of pH, chemical concentration, eukaryotic cells, and staining of cells for visualization by microscopy. From the preparatory reading, learners will be able to define the terms solvent, solute, semi-permeable, osmolality (or osmolarity), tonicity, and epithelium. It is helpful if learners have familiarity or experience with a dialogic, sense-making strategy that progresses through observational, reflective, interpretative, and decisional stages. Rather than assign a reading on this dialogic strategy, we weave it into each class session over the semester. Also helpful is an understanding among class members of the value of psychological safety and diversity of perspectives in teams. To cultivate this understanding, at the start of semester, we ask our students to read paragraphs 1, 2, and 4 of Simons and Peterson’s study (41) of task and relationship conflict, as well as to view a TEDx talk by Professor Amy Edmondson on psychological safety in groups.

Prerequisite Teacher Knowledge

For instructors, we recommend as core readings the ones from which the problem and data come: World Health Organization (22) on the sexual health problem and the recommendation formulated by an expert panel; Wilkinson et al. (27) on morphology of vaginal epithelial cells exposed to lubricants; and Adriaens and Remon (42) on the slug-based assay of mucosal irritation.

For instructors wishing to gain familiarity with conceptions commonly held by students about osmosis and diffusion, we suggest the articles by Odom (4), Fisher et al. (5), and Tobler et al. (6). Also, these articles provide assessment questions targeting simple conceptions. For instructors desiring additional information about ORID, we recommend Chapter 2 of Nelson (29). Finally, for those seeking scientific elaboration on osmosis and diffusion, we recommend Marbach and Bocquet (3) and Manning and Kay (17).

Scientific Teaching Themes

Active Learning

Van Amburgh et al. (43) describe three key ingredients of an effective active-learning lesson: an explained context, engagement, and reflection. For our lesson, context is provided and elaborated by the problem, namely whether a science-supported recommendation can be made regarding osmolality, pH, or ingredients of personal lubricant for bulk procurement. This context offers an authentic, real-world motivation for thinking about osmolality and fluxes of solvent (water) across the cell membrane. Use of an authentic problem to motivate learning aligns with the overall structure of the two courses in which we implement the lesson: hybrid project-/problem-based learning (e.g., see Prince and Felder [44]; the structure of the introductory course is described by Webster et al. [45]).

Engagement is the second ingredient of active learning and is fostered in this lesson in an inclusive manner through ORID-scaffolded dialogue. In teams of roughly four, learners engage in conversational rounds (orbits) in which each team member has the opportunity to share thoughts while other team members listen mindfully. The orbits progress through observations, reflections, and interpretations/decisions. Thus, the structured dialogue engenders cooperative learning (46) involving collaborative high-end thinking (analyzing, evaluating, synthesizing). In line with cooperative learning, the teams have a goal (formulation of a recommendation on lubricants), as well as tools (ORID-structured orbits) to promote group cohesiveness and productivity. Additionally, by inviting all team members’ perspectives and assumptions into the conversation, the dialogue creates the condition for changing beliefs (19).

The third ingredient of active learning is reflection on the learning activity. Rogers (47) distilled from John Dewey’s writings a four-phase reflective cycle that is proposed to be essential in an active-learning endeavor. The cycle parallels ORID: interpretations (cycle phase 3) and decisions (phase 4) are withheld until the focus of attention has been fully observed (phase 1) and described (phase 2). Note that the descriptive phase operates like ORID’s reflective stage in that assumptions, prior knowledge, and emotions are acknowledged, since they might be limiting or coloring observations. Thus, to complete the active-learning lesson, students compose as “homework” after the lesson an anonymous, ORID-scaffolded reflection on their learning from the lesson. We suggest a reflection of several sentences length. While providing a key ingredient for an active-learning lesson, the reflections contribute data for assessing the lesson and student learning.

Assessment

Assessment had qualitative and quantitative strands. The qualitative strand asked students in both courses—the introductory one and the upper-level one—to reflect anonymously on their learning within a day of completing the activity. Drawing on ORID, the prompt asked students to compose several sentences addressing one or more of the following about the learning activity: “What surprised you? Where did you struggle? What was the insight that you gained? In which ways are the lesson and insight relevant for society and/or you?” We inductively coded and categorized the anonymous reflections via thematic analysis (48). A preliminary coding scheme was formulated with a subset of reflections from the introductory course. The scheme was then tested and found successful with additional reflections from the introductory course, as well as with a subset of reflections from the upper-level one. The scheme was then applied to all of the reflections from the two courses.

The quantitative assessment strand involved students’ completing seven multiple-choice questions from published concept inventories on random motion, diffusion, and osmosis: questions 11a and 11b of the Diffusion and Osmosis Diagnostic Test (DODT; [4]); questions 3, 4, 13, and 14 of the Osmosis and Diffusion Conceptual Assessment (ODCA; [5]); and question R5 of the Molecular Randomness Concept Inventory (MRCI; [6]). The questions and answers are provided in the cited publications, but we note here a correction to a published answer. For question 14 of the ODCA, the published answer, “water molecules move from higher concentration of water to lower concentration of water,” was brought into alignment with data and theory by the following re-phrasing on our assessment: “water molecules move from lower concentration of dissolved particles to higher concentration of dissolved particles.” The context involved impermeant particles. Answered by individual students both prior to the pre-class readings and after the lesson, the seven questions included three pairs of two-tiered questions: the first tier asks for analysis or prediction, and the second tier probes the reasoning for the answer to the first tier. In testing the lesson, we administered the quantitative assessment only in the upper-level course; in future, we intend to administer it in both courses.

The Institutional Review Board (IRB) approved and exempted from continuing review the protocol for collecting the qualitative data (IRB exemptions 16 June 2023 and 19 October 2023). The IRB confirmed that the protocol for collecting the quantitative data did not warrant IRB oversight (IRB letter dated 22 March 2024).

Inclusive Teaching

In topic and orchestration, the lesson fosters inclusion. Use of lubricants is common across sexualities. With a representative sample of U.S. women (n = 1559, based on gender identification), Herbenick et al. (23) found that 66.2% heterosexual, 63.6% homosexual, 66.0% bisexual, and 44.4% asexual women reported having used lubricant. Similarly, in a companion study with a representative sample of U.S. men (n = 1510), Reece et al. (49) found that 69.2% heterosexual, 98.4% homosexual, 68.8% bisexual, and 60.0% asexual men reported having used lubricant. Use of lubricant is common regardless of relationship status, too, for women (23) and for men (49). We were unsuccessful in finding research on lubricant use by persons identifying as non-binary or gender-fluid.

With their orbits, the small-group dialogues give equal voice to all participants, who seek to build on one another’s ideas. The dialogues center on different forms of data—tabulated, graphical, photographical—and thereby create opportunities for students who might differ in analytical strengths to contribute. Moreover, the dialogues’ ORID scaffolding accommodates students who might differ in preferred mental process in problem solving. For example, the zig-zag model of problem-solving (50) envisages four sequential processes, each aligned with a personality-type preference: (i) gathering facts (aligns with Myers-Briggs type S, sensing), (ii) imagining the future (aligns with N, intuition), (iii) evaluating trade-offs (aligns with T, thinking), and (iv) considering impact and acceptance (aligns with F, feeling). These processes map well to ORID’s stages: the first (gathering the facts) to ORID’s observational stage, the second to ORID’s reflective, the third to ORID’s interpretative, and the fourth to ORID’s decisional. Thus, in orchestration, the lesson offers varied intellectual tasks. In so doing, the lesson invites participation of students differing in competencies and preferences, thereby promoting engagement and ultimately well-being (51, 52).

Lesson Plan

Context and Overview

We place this lesson (Table 1) at the point at which our courses—an introductory one on organismal biology and an upper-level one on medical physiology—transition in topic from nerve and muscle function to circulatory systems. The lesson includes a small amount of pre- and post-class homework for students, spans 48 minutes in class, and comprises 11 PowerPoint frames or slides (Supporting File S1). For implementing the lesson, we transfer the frames to a collaborative digital whiteboard (e.g., Google Slides or Lucid’s Lucidspark) accessible by students working with their laptops. We shepherd the class through Frames 1–4, as well as Frames 10 and 11. Student teams pace themselves through Frames 5–9.

Table 1. Osmosis lesson timeline.

Pre-Class Preparation

We prepare students for the lesson by assigning as homework two items, collectively taking about 20 minutes to complete. The first item is an anonymous, online assessment comprising seven published questions about osmosis and diffusion, as noted in Assessment: questions 11a and 11b of the Diffusion and Osmosis Diagnostic Test (DODT; [4]); questions 3, 4, 13, and 14 of the Osmosis and Diffusion Conceptual Assessment (ODCA; [5]); and question R5 of the Molecular Randomness Concept Inventory (MRCI; [6]). We place the questions in a Qualtrics survey and provide students with the survey’s URL. Questions alternatively could be administered in a Google form or on paper. The assessment is repeated after the lesson. We report scores and correct answers after the post-lesson assessment. Although anonymous, the assessment asks each respondent to generate an identification code, allowing the respondent to compare answers given before and after the lesson. To generate the code, the survey includes the following text:

To link your anonymous data between initial and final surveys, we would like you to create a private personal identification code consisting of the following pieces of information:

The second letter of your last name (e.g., a for Gates)

The last number in your birth year (e.g., 4 for 2004)

The first letter of your high school’s name (e.g., L for Lakeside)

The first letter of your mother’s name (e.g., C for Carolyn)

The number of your siblings (e.g., 0 for zero brothers and sisters)

The first letter of the city in which you were born (e.g., S for Seattle)

The second pre-lesson item is meant to be done after the assessment and comprises two preparatory readings, one defining epithelia and the other osmosis. We have used pages from Principles of Life, third edition (53):

(i) on osmosis, sub-section “Osmosis is the movement of water across membranes”—textbook pages 75 and 76, in section 4.2. (Note that the Figure 4.3 title incorrectly defines osmosis as net movement of water from a region of high to low solute concentration; we scanned the two pages, redacted the figure title in Adobe Acrobat, and made the redacted version available to students.);

(ii) on epithelia, section 28.4, along with Figure 28.19 (in the printed text, extreme bottom right of page 695 through upper left of page 696).

Beginning of Class

Students sit in a manner that allows collaboration in teams of approximately four. Our classroom has tables seating four, so the formation of teams occurs naturally.

The frames for this lesson can be found in Supporting File S1.

Frame 1

We introduce students to the lesson by concisely stating the central problem and learning goals. The central problem is the World Health Organization’s need for a scientific recommendation on the bulk procurement of lubricant for male and female condoms. The learning goals are (i) to deepen understanding of osmosis, diffusion, and sexual physiology and (ii) to practice collaboratively analyzing, evaluating, synthesizing, and making decisions with biological data. We remind class members that our strategy for making sense of data progresses through observational, reflective, interpretative, and decisional stages. Also, we remind students of the value of task conflict (differences of perspectives and insights) and psychological safety in teams.

Frame 2

Frame 2 provides the in-class time allocations. We ask teams to designate a time-keeper to ensure timely progression through the ORID-based orbits and a recorder to report the team’s reasoning when requested.

Frame 3

Students are then directed to Frame 3, which presents on its left Perrin’s traces of three diffusing particles and on its right two questions, loosely related to Perrin’s data (54). We allow teams four minutes to formulate answers to the questions. We then call on a team to explain its reasoning; if necessary, by soliciting elaboration from other teams, we shepherd the class to a shared understanding of thermally-induced random motion and diffusion.

Frame 4

We then state that osmosis differs from diffusion: in osmosis, solvent is forced from a region of low impermeant solute concentration to a region of higher impermeant solute concentration because of a difference of energy (or pressure, since, in units, pressure is energy per volume) between the two regions. We note, too, that the difference of energy stems from the differing concentration of impermeant solutes. We remind students of the solute potential in the equation of water potential, as well as oncotic pressure (i.e., colloid osmotic pressure) in the expression for capillary filtration; both terms depend on concentration of impermeant solute. In prior course studies, students have seen Ohm’s Law, so we relate osmosis to Ohm’s Law, with flow per time determined by an energy difference between two spaces and by the conductance to flow between the spaces. We then note that the next five frames present key pieces of information for teams to consider on their own, with number of orbits, stage of ORID, and allocation of time (pacing) suggested on each frame.

As teams consider Frames 5 through 9, we move through the classroom and socratically guide visibly adrift teams. Particularly for Frames 7 and 8, while we move through the room, we ensure that teams are using orbits. Also for Frames 7 and 8, we ensure that teams are fully observing, i.e., taking a visual inventory, rather than jumping to interpretation. If a team were jumping to interpretation, we would ask questions along the lines of the following, which are drawn from Housen’s Visual Thinking Strategies (28): “What is going on in this image? What more can you find? What makes you think or say that? How does this image compare with that one?”

Frame 5

This frame lists considerations drawn from World Health Organization (22) and Edwards and Panay (26).

Frame 6

This frame succinctly notes two kinds of experimental data depicted in subsequent frames: microscopy of vaginal epithelial cells exposed to lubricants as an assay of cellular shape and viability, and mucus production by slugs exposed to lubricants as an assay of irritation.

Frame 7

This frame presents selected images from Panel A of Figure 1 of Wilkinson et al. (27) and asks for observational and reflective stages of ORID. The images juxtapose crystal violet staining with fluorescent marking of cell membrane and DNA for cultured vaginal epithelial cells that were either untreated or exposed to lubricants with 270, 2243, and 10300 mOsm/kg. Copyright permission to adapt and publish these images was obtained through the Copyright Clearance Center (Order License ID 1478376-1); copyright permission is unnecessary for instructors’ use of images with attribution in classroom. The key observation is that survival of cells, contact among cells, and size of cells diminish as the osmolality of the lubricant increases.

Students with color vision deficiency will differ from other students in perception of the stains’ colors. In the case of protanopia (red blindness), crystal violet appears bluish, and fluorescent wheat germ agglutinin (WGA) appears yellow-greenish. With deuteranopia (green blindness), crystal violet appears blue-grayish, and WGA mustard-ish. For tritanopia (blue blindness), crystal violet appears brownish, and DNA-staining DAPI greenish. For instructors wishing for a visual illustration of the differences, we recommend viewing the image with Coblis - Color Blindness Simulator prior to the lesson.

Frame 8

This frame depicts the relation between mucus production by slugs and osmolality of lubricant to which slugs were exposed. We generated the graph by using regression coefficients reported by Adriaens and Remon (42). For use in the classroom, instructors may simply use with attribution Figure 1 of Adriaens and Remon (42). The key observation is that mucus production—a sign of irritation—increased as the osmolality of the lubricant to which slugs were exposed increased. The frame prompts for three orbits: observations, reflections, and interpretations.

Frame 9

This frame lists osmolality, pH, and selected ingredients of eleven lubricants. We chose these eleven to offer teams a range of lubricants from which to draw for a recommendation on bulk sourcing. The list could be expanded by inclusion of additional lubricants noted in World Health Organization (22), Edwards and Panay (26), and Alba (55). This frame prompts each team to craft a recommendation regarding osmolality, pH, and ingredients of lubricant for bulk procurement. The recommendation is added to the next frame.

Frame 10, then 11

Frame 10 serves as a white board on which teams write their recommendation and reasoning within a text box. The frame can be duplicated if additional space is needed. After teams have added their recommendation, we allow a couple of minutes for class-members individually to read the recommendations (i.e., we allow a two-minute, quiet “gallery walk”), and we then call on two or three teams to elaborate their thinking to the class.

Then, we thank the teams for serving on the expert scientific review panel. We also indicate that Frame 11 states the primary recommendation from the actual panel (22). Regarding osmolality, the ideal lubricant would not exceed 380 mOsm/kg; yet, given the scarcity of lubricants that currently meet this specification, bulk procurement would necessitate raising the upper limit to 1200 mOsm/kg. The ideal pH depends on use: lubricant should have pH near 4.5 for vulvovaginal use or in range of 5.5 to 7 if intended for anal (with or without vulvovaginal) use.

Post-Lesson Assessment

We include as post-lesson homework two items assessing the lesson. One is a repetition of the seven-question quantitative assessment done prior to the lesson. After all students have completed the repetition, we make available to students a spreadsheet containing their answers and an indication of the scientifically accurate (correct) ones.

The second post-lesson homework item asks students to reflect anonymously on their learning within a day of completing the activity. Administered via Qualtrics survey, the prompt asks students to compose several sentences addressing one or more of the following about the learning activity: “What surprised you?, Where did you struggle?, What was the insight that you gained?, In which ways are the lesson and insight relevant for society and/or you?” The reflection alternatively could be done via Google form or on paper. After the course ended, we thematically analyzed the reflections.

Teaching Discussion

Prior to implementing the lesson, we wondered whether the in-class, scaffolded discussion would be sufficient to prompt conceptual shifts regarding osmosis and diffusion. Quantitative assessment data showed that students shifted toward accurate conceptions. We collected these assessment data from students in the upper-level physiology course. On the 7-item assessment, students correctly answered 3.7 items before the lesson and 5.3 after the lesson. In paired analysis for pre to post, the mean gain was 1.6 correct items (standard deviation 2.1, n = 19; two-tailed p by Wilcoxon Signed-Rank Test = 0.008). Table 2 shows that students shifted toward scientifically accurate views regarding the three assessed concepts or knowledge propositions: that molecules move randomly and do so because of thermal energy and collisions; that osmosis and diffusion can occur in living and non-living systems alike; and that osmosis involves movement of solvent from a region of lower impermeant solute concentration to one of higher.

Table 2. Quantitative assessment of understanding of osmosis and diffusion prior and after the lesson in the upper-level course (n = 19 students). We used questions 11a and 11b of the Diffusion and Osmosis Diagnostic Test (DODT; [4]), questions 3, 4, 13, and 14 of the Osmosis and Diffusion Conceptual Assessment (ODCA; [5]), and question R5 of the Molecular Randomness Concept Inventory (MRCI; [6]). The seven questions included three pairs of two-tiered questions: the first tier asks for analysis or prediction, and the second tier probes the reasoning for the answer to the first tier. We administered the quantitative assessment only in the upper-level course. As noted in the Assessment section, the correct answer to question 14 of ODCA was re-worded to be scientifically accurate.

Student Reactions in Both Courses

The occurrence of conceptual shifts suggests that the lesson created cognitive impasses and productive dialogue. We wondered whether positive or negative academic emotions were elicited. Thus, we did thematic analysis with 79 metacognitive reflections composed by students after the lesson in the two courses. Table 3 presents the extracted themes; their generalizability to other demographic contexts was not studied. Amongst the 79 collected student reflections only 3% (i.e., 2 of 79) conveyed negative references to the topic (Theme 12). One student complained about excessive attention to the vagina. A potential remedy might be elaborating at the lesson’s start the instructor’s motivation for increasing knowledge of sexual physiology and health. The other student who offered a complaint felt that transgender and intersex persons would be harmed by conflation of having vaginal tissue with being a woman. As suggested by the student, a potential remedy would be the instructor’s reminding self and class members to refer to “persons with vaginas” rather than to “women.”

Table 3. Thematic analysis of students’ meta-cognitive reflections after the lesson in both courses (introductory and upper-level). We inductively coded the reflections and then sorted into categories and themes. The coding scheme was formulated with a randomly chosen subset of reflections from the introductory course, found to apply successfully to a randomly chosen subset of reflections from the upper-level course, and then applied to all of reflections (N = 79; n = 63 from introductory course; n = 16 from upper-level). Interrater agreement measured by percent agreement was 92% and by Cohen’s kappa was 0.80.

Also expressed was another potentially negative emotion: the struggle inherent in making sense of graphs, figures, and topic (Themes 7 and 8). Nineteen percent of reflections from the two classes remarked on struggling without any mention of knowledge gains (Theme 7). Disaggregated by course, the percentages were 21 for the introductory class and 13 for the upper-level. The difference suggests that the introductory students struggled more than the upper-level ones. In our context, the extent of struggle was acceptable, but other instructors might choose to provide instruction on making sense of the images and graph (Frames 7 and 8 of Supporting File S1), e.g., by guiding students through a panel. In our case, we are uncertain whether inclusion of additional instruction and guidance would be beneficial or, instead, would detract from the social constructivist underpinnings of the lesson and the potential for increasing self-efficacy. Speaking to such self-efficacy, Theme 8 was revealed in reflections noting an initial struggle giving way to understanding or learning. Disaggregated by course, 16% of the introductory students’ reflections and 19% of the upper-level students’ reflections evidenced Theme 8.

Notwithstanding the two students’ complaints and the struggles of some others, the most prevalent themes in the students’ reflections highlighted insights gained from the lesson and positive academic emotions toward it. For example, 27% of the reflections gave evidence for the theme of positive feelings (Theme 4), as signaled by in vivo codes such as “enjoyed,” “important,” and “engaging.” Relatedly, 47% of the reflections noted the personal relevance of the lesson (Theme 1). The reflections supported that students advanced in their understanding of sexual physiology: 33% of reflections noted increased knowledge about lubricants (Theme 3), and 23% commented on learning about vaginal health (Theme 5). The reflections also conveyed surprise. We discerned in the data three sources of surprise and report them here separately, since they speak to distinct facets that captured attention. Thirty-four percent of the reflections expressed surprise at the composition and risks of lubricant (Theme 2). Sixteen percent expressed surprise at the topic and its real-world application (Theme 9), and 11% at the data (Theme 10). Collectively among these three facets, the extent of surprise emphasizes to us that the lesson engaged and motivated learners (56).

Adaptations

We wish to draw attention to two additional themes extracted from the meta-cognitive reflections and reported in Table 3: Theme 6 (Unsettled by the consequences of pharmaceutical companies’ overlooking women’s physiology; conveyed in 23% of reflections) and Theme 11 (Alarmed by the general lack of awareness of women’s health; 11%). They both suggest ways to expand or to adapt the lesson. One expansion could involve consideration of the socio-cultural embeddedness of science, for example, as revealed in the historical centering of medicine on males (e.g., 57). Another expansion could consider arousal non-concordance, i.e., the important distinction between vaginal sweating (lubrication) and sexual desire (e.g., see chapter 6 of [24]).

Depending on student composition and nature of the course in which the lesson is implemented, other adaptations and expansions can be envisioned. These include considering the following: potential endocrine disruptors such as parabens in products applied to skin (e.g., 58), cardiovascular and pulmonary responses during coitus (e.g., 59–61), and efforts to replace, refine, and reduce animal research (e.g., 62).

Supporting Materials

• S1. Osmosis Lesson – Frames

Acknowledgments

The images of vaginal epithelial cells (Frame 6 of Supporting File S1) are taken from Wilkinson et al. (40). Copyright permission to use these images in this publication was obtained through the Copyright Clearance Center (Order License ID 1478376-1). Documentation of the copyright permission will be provided if requested. Copyright permission is not needed for instructors’ use of the images in class provided attribution is given. We thank the students in Organismal Biology and Physiology courses at Oberlin College for engaging in the lesson and its assessments. For introducing us to Visual Thinking Strategies we thank Drs Liliana Milkova, Colette Crossman, and Stephanie Wiles (all formerly of Allen Memorial Art Museum, Oberlin College). For introducing us to ORID, we thank members of the IDEAL Center, Science Museum of Minnesota.

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