Smaller Classes Promote Equitable Student Participation in STEM

As science, technology, engineering, and mathematics (STEM) classrooms in higher education transition from lecturing to active learning, the frequency of student interactions in class increases. Previous research documents a gender bias in participation, with women participating less than would be expected on the basis of their numeric proportions. In the present study, we asked which attributes of the learning environment contribute to decreased female participation: the abundance of in-class interactions, the diversity of interactions, the proportion of women in class, the instructor's gender, the class size, and whether the course targeted lower division (first and second year) or upper division (third or fourth year) students. We calculated likelihood ratios of female participation from over 5300 student–instructor interactions observed across multiple institutions. We falsified several alternative hypotheses and demonstrate that increasing class size has the largest negative effect. We also found that when the instructors used a diverse range of teaching strategies, the women were more likely to participate after small-group discussions.

"Is This Class Hard?" Defining and Analyzing Academic Rigor from a Learner's Perspective

Despite its value in higher education, academic rigor is a challenging construct to define for instructor and students alike. How do students perceive academic rigor in their biology course work? Using qualitative surveys, we asked students to identify "easy" or "hard" courses and define which aspects of these learning experiences contributed to their perceptions of academic rigor. The 100-level students defined hard courses primarily in affective terms, responding to stressors such as fast pacing, high workload, unclear relevance to their life or careers, and low faculty support. In contrast, 300-level students identified cognitive complexity as a contributor to course rigor, but course design elements-alignment between instruction and assessments, faculty support, active pedagogy-contributed to the ease of the learning process. Overwhelmingly, all students identified high faculty support, learner-centered course design, adequate prior knowledge, and active, well-scaffolded pedagogy as significant contributors to a course feeling easy. Active-learning courses in this study were identified as both easy and hard for the very reasons they are effective: they simultaneously challenge and support student learning. Implications for the design and instruction of rigorous active-learning college biology experiences are discussed.

Chemically imaging bacteria with super-resolution SERS on ultra-thin silver substrates

Plasmonic hotspots generate a blinking Surface Enhanced Raman Spectroscopy (SERS) effect that can be processed using Stochastic Optical Reconstruction Microscopy (STORM) algorithms for super-resolved imaging. Furthermore, by imaging through a diffraction grating, STORM algorithms can be modified to extract a full SERS spectrum, thereby capturing spectral as well as spatial content simultaneously. Here we demonstrate SERS and STORM combined in this way for super-resolved chemical imaging using an ultra-thin silver substrate. Images of gram-positive and gram-negative bacteria taken with this technique show excellent agreement with scanning electron microscope images, high spatial resolution at <50 nm, and spectral SERS content that can be correlated to different regions. This may be used to identify unique chemical signatures of various cells. Finally, because we image through as-deposited, ultra-thin silver films, this technique requires no nanofabrication beyond a single deposition and looks at the cell samples from below. This allows direct imaging of the cell/substrate interface of thick specimens or imaging samples in turbid or opaque liquids since the optical path doesn’t pass through the sample. These results show promise that super-resolution chemical imaging may be used to differentiate chemical signatures from cells and could be applied to other biological structures of interest.

Define Your Goals Before You Design a CURE: A Call to Use Backward Design in Planning Course-Based Undergraduate Research Experiences

We recommend using backward design to develop course-based undergraduate research experiences (CUREs). The defining hallmark of CUREs is that students in a formal lab course explore research questions with unknown answers that are broadly relevant outside the course. Because CUREs lead to novel research findings, they represent a unique course design challenge, as the dual nature of these courses requires course designers to consider two distinct, but complementary, sets of goals for the CURE: 1) scientific discovery milestones (i.e., research goals) and 2) student learning in cognitive, psychomotor, and affective domains (i.e., pedagogical goals). As more undergraduate laboratory courses are re-imagined as CUREs, how do we thoughtfully design these courses to effectively meet both sets of goals? In this Perspectives article, we explore this question and outline recommendations for using backward design in CURE development.

A Call to Develop Course-Based Undergraduate Research Experiences (CUREs) for Nonmajors Courses

Course-based undergraduate research experiences (CUREs) for non-science majors (nonmajors) are potentially distinct from CUREs for developing scientists in their goals, learning objectives, and assessment strategies. While national calls to improve science, technology, engineering, and mathematics education have led to an increase in research revealing the positive effects of CUREs for science majors, less work has specifically examined whether nonmajors are impacted in the same way. To address this gap in our understanding, a working group focused on nonmajors CUREs was convened to discuss the following questions: 1) What are our laboratory-learning goals for nonmajors? 2) What are our research priorities to determine best practices for nonmajors CUREs? 3) How can we collaborate to define and disseminate best practices for nonmajors in CUREs? We defined three broad student outcomes of prime importance to the nonmajors CURE: improvement of scientific literacy skills, proscience attitudes, and evidence-based decision making. We evaluated the state of knowledge of best practices for nonmajors, and identified research priorities for the future. The report that follows is a summary of the conclusions and future directions from our discussion.

A SCALE-UP Mock-Up: Comparison of Student Learning Gains in High- and Low-Tech Active-Learning Environments

Student-centered learning environments with upside-down pedagogies (SCALE-UP) are widely implemented at institutions across the country, and learning gains from these classrooms have been well documented. This study investigates the specific design feature(s) of the SCALE-UP classroom most conducive to teaching and learning. Using pilot survey data from instructors and students to prioritize the most salient SCALE-UP classroom features, we created a low-tech "Mock-up" version of this classroom and tested the impact of these features on student learning, attitudes, and satisfaction using a quasi--experimental setup. The same instructor taught two sections of an introductory biology course in the SCALE-UP and Mock-up rooms. Although students in both sections were equivalent in terms of gender, grade point average, incoming ACT, and drop/fail/withdraw rate, the Mock-up classroom enrolled significantly more freshmen. Controlling for class standing, multiple regression modeling revealed no significant differences in exam, in-class, preclass, and Introduction to Molecular and Cellular Biology Concept Inventory scores between the SCALE-UP and Mock-up classrooms. Thematic analysis of student comments highlighted that collaboration and whiteboards enhanced the learning experience, but technology was not important. Student satisfaction and attitudes were comparable. These results suggest that the benefits of a SCALE-UP experience can be achieved at lower cost without technology features.

Choosing orientation: influence of cargo geometry and ActA polarization on actin comet tails

Networks of polymerizing actin filaments can propel intracellular pathogens and drive movement of artificial particles in reconstituted systems. While biochemical mechanisms activating actin network assembly have been well characterized, it remains unclear how particle geometry and large-scale force balance affect emergent properties of movement. We reconstituted actin-based motility using ellipsoidal beads resembling the geometry of Listeria monocytogenes. Beads coated uniformly with the L. monocytogenes ActA protein migrated equally well in either of two distinct orientations, with their long axes parallel or perpendicular to the direction of motion, while intermediate orientations were unstable. When beads were coated with a fluid lipid bilayer rendering ActA laterally mobile, beads predominantly migrated with their long axes parallel to the direction of motion, mimicking the orientation of motile L. monocytogenes. Generating an accurate biophysical model to account for our observations required the combination of elastic-propulsion and tethered-ratchet actin-polymerization theories. Our results indicate that the characteristic orientation of L. monocytogenes must be due to polarized ActA rather than intrinsic actin network forces. Furthermore, viscoelastic stresses, forces, and torques produced by individual actin filaments and lateral movement of molecular complexes must all be incorporated to correctly predict large-scale behavior in the actin-based movement of nonspherical particles.