Chemistry is traditionally perceived as difficult to comprehend. Its mastery requires that a variety of concepts be linked to form an organized knowledge system. The connections need to be made not only between the concepts associated with the macroscopic level of the chemistry triplet but also between the submicroscopic and symbolic levels. Many factors influence a learner's success in bridging concepts between these levels. In this study, the aim was to identify and examine the changes in general chemistry students' knowledge structures by utilizing Word Association Tests. Although many studies have examined knowledge structures and aspects of the chemistry triplet, almost none has considered both at the same time. This study highlights the interconnectedness between the chemistry triplet and changing knowledge structures in overall student populations and in high-and low-achieving students. It provides insights on why students fail to understand chemistry and suggests ideas for future research as limiting factors were noted.

Success in chemistry requires not only the ability to recruit prior knowledge but also the ability to establish strong connections between new and existing concepts to form knowledge clusters around core principles. How these knowledge structures are organized can be used to understand the relationships between concepts within a student's mind. 618 undergraduate students in a general chemistry course participated in this study at a US institution. The purpose of this study was to determine the effect, if any, that prior knowledge in chemistry and mathematics and gender have on the formation of students' knowledge structures. In addition, the structures were analyzed to identify the hidden connections between macroscopic, submicroscopic, and symbolic representations of chemical knowledge. To visualize these structures, a word association test (WAT) was created to determine concept relatedness. Student response data was then transformed into a series of distances by a computer program called JPathfinder, which created visual representations of the knowledge structures in the Gephi platform. The meaning and implications of these structures were discussed to provide ideas for teaching interventions that focus on weakly associated basic general chemistry concepts. The potential uses of WAT were also shared to help educators identify student misconceptions.

This study aimed to examine the impact of years of experience and field of expertise on the development of chemistry knowledge structures from STEM experts comprising 103 professors, 10 postdocs, and 146 doctoral students. Of these participants, 127 were specialized in chemistry and the rest were from various science and engineering disciplines. Although most participants were part of a research university located in Northern California, the pool included a small group of experts from different universities and countries. The main source of the data was a Word Association Test generated with 17 keywords that refer to major topics or concepts commonly introduced in the general chemistry curricula. The knowledge structures were examined to determine if the contents and the orientations of the clusters varied between the expert groups. In addition, their analysis was enriched with the consideration of chemistry triplet designations and central terms identified by eccentricity values on each structure. The overall expert knowledge structure generated in this study was also compared to undergraduate structures determined by using the same instrument and methodology. The investigation of the structures revealed several differences between expert groups and provided insight into the transformation of novices into experts. The paper also presents practical suggestions for educators on how to utilize structures while teaching, informing their instructional practices, and reforming teaching materials.

Whether distantly related organisms evolve similar strategies to meet the demands of a shared ecological niche depends on their evolutionary history and the nature of form-function relationships. In fishes, the visual identification and consumption of microscopic zooplankters, selective zooplanktivory, is a distinct type of foraging often associated with a suite of morphological specialisations. Previous work has identified inconsistencies in the trajectory and magnitude of morphological change following transitions to selective zooplanktivory, alluding to the diversity and importance of ancestral effects. Here we investigate whether transitions to selective zooplanktivory have influenced the morphological evolution of marine butterflyfishes (family Chaetodontidae), a group of small-prey specialists well known for several types of high-precision benthivory. Using Bayesian ancestral state estimation, we inferred the recent evolution of zooplanktivory among benthivorous ancestors that hunted small invertebrates and browsed by picking or scraping coral polyps. Traits related to the capture of prey appear to be functionally versatile with little morphological distinction between species with benthivorous and planktivorous foraging modes. In contrast, multiple traits related to prey detection or swimming performance are evolving toward novel, zooplanktivore-specific optima. Despite a relatively short evolutionary history, general morphological indistinctiveness, and evidence of constraint on the evolution of body size, convergent evolution has closed a near significant amount of the morphological distance between zooplanktivorous species. Overall, our findings describe the extent to which the functional demands associated with selective zooplanktivory have led to generalisable morphological features among butterflyfishes and highlight the importance of ancestral effects in shaping patterns of morphological convergence.