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This feature is designed to point CBE---Life Sciences Education readers to current articles of interest in life sciences education as well as more general and noteworthy publications in education research.This feature is designed to point CBE—Life Sciences Education readers to current articles of interest in life sciences education as well as more general and noteworthy publications in education research. URLs are provided for the abstracts or full text of articles. For articles listed as “Abstract available,” full text may be accessible at the indicated URL for readers whose institutions subscribe to the corresponding journal.
  • 1. Freeman S, Eddy SL, McDonough M, Smith MK, Okoroafor N, Jordt H, Wenderoth MP (2014). Active learning increases student performance in science, engineering, and mathematics. Proc Natl Acad Sci USA 111, 8410–8415. [Abstract available at www.pnas.org/content/111/23/8410.abstract]
Online publication of this meta-analysis last spring no doubt launched a legion of local and national conversations about how science is best taught—as the authors state the essential issue, “Should we ask or should we tell?” To assess the relative effectiveness of active-learning (asking) versus lecture-based (telling) methods in college-level science, technology, engineering, and mathematics (STEM) classes, the authors scoured the published and unpublished literature for studies that performed a side-by-side comparison of the two general types of methods. Using five predetermined criteria for admission to the study (described fully in the materials and methods section), at least two independent coders examined each potentially eligible paper to winnow down the number of eligible studies from 642 to 225. The working definition of what constitutes active learning (used to determine potential eligibility) was obtained from distilling definitions written by 338 seminar attendees; what constitutes lecture was defined as “continuous exposition by the teacher” (quoted from Bligh, 2000 ). The eligible studies were situated in introductory and upper-division courses from a full range of enrollment sizes and multiple STEM disciplines and included majors and nonmajors as participants. The frequency of use and types of active-learning methodologies described in the 225 eligible studies varied widely.Quantitative analysis of the eligible studies focused on comparison of two outcome variables: 1) scores on identical or formally equivalent examinations and 2) failure rates (receipt of a “D” or “F” grade or withdrawal from the course). Major findings were that student performance on exams and other assessments (such as concept inventories) was nearly half an SD higher in active-learning versus lecture courses, with an effect size (standardized mean weighted difference) of 0.47. Analyses also revealed that average failure rates were 55% higher for students in the lecture courses than in courses with active learning. Heterogeneity analyses indicated that 1) there were no statistically significant differences in outcomes with respect to disciplines; 2) effect sizes were lower when instructor-generated exams were used versus concept inventories with both types of courses (perhaps because concept inventories tend to require more higher-order thinking skills); 3) effect sizes were not significantly different in nonmajors versus majors courses or in lower versus upper-division courses; and 4) although active learning had the greatest positive effect in smaller-enrollment courses, effect sizes were higher with active learning at all enrollment sizes. Two types of analyses, calculation of fail-safe numbers and funnel plots, supported a lack of publication bias (tendency to not publish studies with low effect sizes). Finally, the authors demonstrated that there were no statistically significant differences in effect sizes despite variation in the quality of the controls on instructor and student equivalence, supporting the important conclusion that the differences in effectiveness between the two methods were not instructor dependent.In one of the more compelling sections of this meta-analysis, the authors translated the relatively dry numbers resulting from statistical comparisons to potential impacts on the lives of the students taking STEM courses. For example, for the 29,300 students reported for the lecture treatments across all students, the average difference in failure rates (21.8% in active learning vs. 33.8% with lecture) suggests that 3516 fewer students would have failed if enrolled in an active-learning course. This and other implications for the more beneficial impact of active learning on STEM students led the authors to state, “If the experiments analyzed here had been conducted as randomized controlled trials of medical interventions, they may have been stopped for benefit.” That is, the control group condition would have been halted because of the clear, beneficial effects of the treatment. The authors conclude by suggesting additional important implications for future undergraduate STEM education research. It may no longer be justified to conduct more “first-generation” research comparing active-learning approaches with traditional lecture; rather, for greater impact on course design, second-generation researchers should focus on what types and intensities of exposure to active learning are most effective for different students, instructors, and topics.This provocative commentary by Carl Weiman highlights the major findings reported in the Proceedings of the National Academy of Sciences by Freeman et al. (2014) and underscores the implications. The graphical representations displaying the key data on effect sizes and failure rates presented in the Freeman et al. meta-analysis are redrawn in the commentary in a way that is likely to be more familiar to the typical reader, making the differences in outcomes for active learning versus lecture appear more striking. Weiman concludes by elaborating on the important implications of the meta-analysis for college-level STEM educators and administrators, suggesting that it “makes a powerful case that any college or university that is teaching its STEM courses by traditional lectures is providing an inferior education to its students. One hopes that it will inspire administrators to start paying attention to the teaching methods used in their classrooms … establishing accountability for using active-learning methods.”National societies, committee reports, and accrediting bodies recommend that engineering curricula be designed to prepare future engineers for the complex interdisciplinary nature of the field and for the multitude of skills and perspectives they will need to be successful practitioners. The authors posit that case-based instruction, with its emphasis on honing skills in solving authentic, interdisciplinary, and ill-defined problems, aligns well with these recommendations. However, the methodology is still relatively underutilized, and its effectiveness is underexamined. This article describes a study designed to advance these issues by comparing lecture- and case-based methods within the same offering of a 72-student, upper-level, required course in mechanical engineering.The study used a within-subjects, posttest only, A-B-A-B research design across four key course topics. That is, two lecture-based modules (the A or baseline phases) alternated with case-based modules (the B or treatment phases). Following each module, students responded to open-response quiz questions and a survey about learning and engagement (adapted from the Student Assessment of Learning Gains instrument). The quiz questions assessed ability to apply knowledge to problem solving (so-called “traditional” questions) and ability to explain the concepts that were used (“conceptual” questions). This study design had the advantage that the same students experienced both the baseline and treatment conditions twice. The authors describe in detail the pedagogical approaches used in both sets of the A and B phases.The quizzes were scored by independent raters (with high interrater reliability) on a 0–3 scale; scores were analyzed using appropriate statistical methods. Survey items were analyzed using a principal-components factor analysis; composite scores were generated for a learning confidence factor and an engagement–connections factor. Analyses revealed that the two pedagogical approaches had similar outcomes with respect to the traditional questions, but conceptual understanding scores (indicating better understanding of the concepts that were applied to problem solving) were significantly higher for the case-based modules. Students reported that they appreciated how cases were better than lecture in helping them make connections to real-world concerns and see the relevance of what they were learning, but there were no significant differences in students’ perceptions of their learning gains in the case-based versus the lecture modules. The authors note that many studies have likewise demonstrated that students’ perceptions of their learning gains in more learner-centered courses are often not accurate reflections of the actual learning outcomes.The authors conclude that while these results are promising indications of the effectiveness of case-based instruction in engineering curricula, the studies need to be replicated across a number of semesters and in different engineering disciplines and extended to assess the long-term effect of case-based instruction on students’ ability to remember and apply their knowledge.Although this study was limited to an engineering context, the case-based methodologies and research design seem well-suited for use in action research in other disciplines.Well-documented challenges to conceptual change faced by students of evolution include the necessity of unseating existing naïve theories (such as natural selection having purposiveness), having the ability to view the complex and emergent nature of evolutionary processes through systems-type thinking, and being able to see the connections between evolutionary content learned in the classroom and everyday life events that can facilitate appreciation of its importance and motivate learning. To help students meet these challenges, the authors adapted a pedagogical model called Teaching for Transformative Experiences in Science (TTES) in the course of instruction on six major concepts in evolutionary biology. This article reports on a comparison of the effectiveness of TTES approaches in fostering conceptual change and positive affect with that of instruction enhanced with use of refutational texts (RT). Use of RTs to promote conceptual change, a strategy with documented effectiveness, entails first stating a misconception (the term used by the authors), then explicitly refuting it by elaborating on a scientific explanation. By contrast, the TTES model promotes teaching that fosters transformative learning experiences—teaching in which instructors 1) place the content in a context allows the students to see its utility or experiential value; 2) model their own transformative experiences in learning course concepts; and 3) scaffold a process that allows students to rethink or “resee” a concept from the perspective of their previous, related life experiences.The authors designed the study to address three questions relevant to the comparison of the two approaches: would the TTES group (vs. the RT group) demonstrate or report 1) greater conceptual change, 2) higher levels of transformative experience, and 3) differences in topic emotions (more positive affect) related to learning about evolution? The study used three survey instruments, one that measured the types and depth of students’ transformative experiences (the Transformative Experience Survey, adapted from Pugh et al., 2010 ), another that assessed conceptual knowledge (Evolutionary Reasoning Scale; Shulman, 2006 ), and a third that evaluated the emotional reactions of students to the evolution content they were learning (Evolution Emotions Survey, derived from Broughton et al., 2011 ). In addition to Likert-scale items, the Transformative Experience Survey contained three open-ended response questions; the responses were scored by two independent raters using a coding scheme for degree of out-of-school engagement. The authors provide additional detail about the nuances of what these instruments were designed to measure and their scoring schemes and include the instruments in the appendices. The Evolutionary Reasoning Scale and the Evolution Emotions survey were administered as both pre- and posttests, and the Transformative Experience survey was administered only at the end of the intervention. The treatment (TTES, n = 28) and comparison (RT, n = 27) groups were not significantly different with respect to all measured demographic variables and the number of high school or college-level science courses taken.Briefly, the evolutionary biology learning experience that participants were exposed to was 3 d in duration for both the treatment and comparison groups. On day 1, the instructor (the same person for both groups) gave a PowerPoint lecture on the same six evolutionary concepts, with illustrative examples. For the treatment group only, the instructor drew from his own transformative experiences in connection with the illustrative examples, describing how he used the concepts, what their value was to him, and how each had expanded his understanding and perception of evolution. On days 2 and 3 for the treatment group, the students and instructor engaged in whole-class discussions about their everyday experiences with evolution concepts (and related misconceptions) and their usefulness; the instructor scaffolded various “reseeing” experiences throughout the discussions. For the comparison group, misconceptions and refutations were addressed in the course of the day 1 lecture, and on days 2 and 3, the participants read refutational texts and then took part in discussions of the texts led by the instructor.Survey results and accompanying statistical analyses indicated that both groups exhibited gains (with significant t statistics) in understanding of the evolution concepts as measured by the Evolutionary Reasoning Scale (Shulman, 2006 ). However, the gains were greater for the treatment (TTES) group: effect size, reported as a value for eta-squared, η2, equaled 0.29. The authors point out by way of context for this outcome that use of RTs, along with follow-up discussions that contrast misconceptions with scientific explanations, has been previously shown to be effective in promoting conceptual change; thus, the comparison was with a well-regarded methodology. Additionally, the Transformation Experience survey findings indicated higher levels of transformative experience for the TTES group participants; they more extensively reported that the concepts had everyday value and meaning and expanded their perspectives. The TTES group alone showed pre- to posttest gains in enjoyment while learning about evolution, a positive emotion that may have classroom implications in terms of receptivity to learning about evolution and willingness to continue study in this and related fields.The authors conclude that the TTES model can effectively engage students in transformative experiences in ways that can facilitate conceptual change in content areas in which that change is difficult to achieve. In discussing possible limitations of the study, they note in particular that the predominance of female study participants (71% of the total) argues for its replication with a more diverse sample.I invite readers to suggest current themes or articles of interest in life sciences education, as well as influential papers published in the more distant past or in the broader field of education research, to be featured in Current Insights. Please send any suggestions to Deborah Allen (ude.ledu@nellaed).  相似文献   

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At the close of the Society for the Advancement of Biology Education Research conference in July 2012, one of the organizers made the comment: “Misconceptions are so yesterday.” Within the community of learning sciences, misconceptions are yesterday''s news, because the term has been aligned with eradication and/or replacement of conceptions, and our knowledge about how people learn has progressed past this idea. This essay provides an overview of the discussion within the learning sciences community surrounding the term “misconceptions” and how the education community''s thinking has evolved with respect to students’ conceptions. Using examples of students’ incorrect ideas about evolution and ecology, we show that students’ naïve ideas can provide the resources from which to build scientific understanding. We conclude by advocating that biology education researchers use one or more appropriate alternatives in place of the term misconception whenever possible.  相似文献   

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The scale and importance of Vision and Change in Undergraduate Biology Education: A Call to Action challenges us to ask fundamental questions about widespread transformation of college biology instruction. I propose that we have clarified the “vision” but lack research-based models and evidence needed to guide the “change.” To support this claim, I focus on several key topics, including evidence about effective use of active-teaching pedagogy by typical faculty and whether certain programs improve students’ understanding of the Vision and Change core concepts. Program evaluation is especially problematic. While current education research and theory should inform evaluation, several prominent biology faculty–development programs continue to rely on self-reporting by faculty and students. Science, technology, engineering, and mathematics (STEM) faculty-development overviews can guide program design. Such studies highlight viewing faculty members as collaborators, embedding rewards faculty value, and characteristics of effective faculty-development learning communities. A recent National Research Council report on discipline-based STEM education research emphasizes the need for long-term faculty development and deep conceptual change in teaching and learning as the basis for genuine transformation of college instruction. Despite the progress evident in Vision and Change, forward momentum will likely be limited, because we lack evidence-based, reliable models for actually realizing the desired “change.”
All members of the biology academic community should be committed to creating, using, assessing, and disseminating effective practices in teaching and learning and in building a true community of scholars. (American Association for the Advancement of Science [AAAS], 2011 , p. 49)
Realizing the “vision” in Vision and Change in Undergraduate Biology Education (Vision and Change; AAAS, 2011 ) is an enormous undertaking for the biology education community, and the scale and critical importance of this challenge prompts us to ask fundamental questions about widespread transformation of college biology teaching and learning. For example, Vision and Change reflects the consensus that active teaching enhances the learning of biology. However, what is known about widespread application of effective active-teaching pedagogy and how it may differ across institutional and classroom settings or with the depth of pedagogical understanding a biology faculty member may have? More broadly, what is the research base concerning higher education biology faculty–development programs, especially designs that lead to real change in classroom teaching? Has the develop-and-disseminate approach favored by the National Science Foundation''s (NSF) Division of Undergraduate Education (Dancy and Henderson, 2007 ) been generally effective? Can we directly apply outcomes from faculty-development programs in other science, technology, engineering, and mathematics (STEM) disciplines or is teaching college biology unique in important ways? In other words, if we intend to use Vision and Change as the basis for widespread transformation of biology instruction, is there a good deal of scholarly literature about how to help faculty make the endorsed changes or is this research base lacking?In the context of Vision and Change, in this essay I focus on a few key topics relevant to broad-scale faculty development, highlighting the extent and quality of the research base for it. My intention is to reveal numerous issues that may well inhibit forward momentum toward real transformation of college-level biology teaching and learning. Some are quite fundamental, such as ongoing dependence on less reliable assessment approaches for professional-development programs and mixed success of active-learning pedagogy by broad populations of biology faculty. I also offer specific suggestions to improve and build on identified issues.At the center of my inquiry is the faculty member. Following the definition used by the Professional and Organizational Development Network in Higher Education (www.podnetwork.org), I use “faculty development” to indicate programs that emphasize the individual faculty member as teacher (e.g., his or her skill in the classroom), scholar/professional (publishing, college/university service), and person (time constraints, self-confidence). Of course, faculty members work within particular departments and institutions, and these environments are clearly critical as well (Stark et al., 2002 ). Consequently, in addition to focusing on the individual, faculty-development programs may also consider organizational structure (such as administrators and criteria for reappointment and tenure) and instructional development (the overall curriculum, who teaches particular courses). In fact, Diamond (2002) emphasizes that the three areas of effort (individual, organizational, instructional) should complement one another in faculty-development programs. The scope of the numerous factors impacting higher education biology instruction is a realistic reminder about the complexity and challenge of the second half of the Vision and Change endeavor.This essay is organized around specific topics meant to be representative and to illustrate the state of the art of widespread (beyond a limited number of courses and institutions) professional development for biology faculty. The first two sections focus on active teaching and biology students’ conceptual understanding, respectively. The third section concerns important elements that have been identified as critical for effective STEM faculty-development programs.  相似文献   

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A Year of Firsts     
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In educational research, investigators in one field are often ignorant of similar research in other fields. Physics education in particular has undergone dramatic reforms in recent years, all based on insights gained from conducting educational research. Often, pedagogical methods resulting from research in one field can be revised and transferred to another. This paper demonstrates that many methods used in physics and other science programmes<fnr rid="b"> <fn id="b">Throughout this paper, programme will refer to the curricular concept and program will refer to computer programs.</fn> can be adapted to teaching computer science. The author has pursued action research in computer science and implemented ideas from science education, especially from physics education, in teaching computer science classes at a small religious secondary school in the southwestern United States. This paper presents ideas and teaching strategies with the hope of building bridges between computer science education research and other science education research.  相似文献   

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This paper considers thought experiment as a special scientific tool that mediates between theory and experiment by mental simulation. To clarify the meaning of thought experiment, as required in teaching science, we followed the relevant episodes throughout the history of science paying attention to the epistemological status of the performed activity. A definition of thought experiment is suggested and its meaning is analyzed using two-dimensional conceptual variation. This method allows one to represent thought experiment in comparison with the congenerous conceptual constructs also defined. A similar approach is used to classify the uses of thought experiments, mainly for the purpose of science curriculum.
Igal GaliliEmail:
Igal Galili   is professor of science education at the Hebrew University of Jerusalem, Israel. Educated in physics, he turned to the area of physics education where his research addresses students’ knowledge of physics and its structure, the nature of physics concepts to be taught, physics knowledge structure and the ways of its representation in teaching. This orientation implies addressing the history and philosophy of science, both by teachers and students, as providing conceptual framework of the meaningful and cultural knowledge of the subject. Within this effort, a special framework of discipline-culture was developed and suggested for teaching science. The same framework was used to explain students’ conceptual change, the structure of science curriculum, as well as of scientific revolutions.  相似文献   

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A response to Maskiewicz and Lineback''s essay in the September 2013 issue of CBE-Life Sciences Education.Dear Editor:Maskiewicz and Lineback (2013) have written a provocative essay about how the term misconceptions is used in biology education and the learning sciences in general. Their historical perspective highlights the logic and utility of the constructivist theory of learning. They emphasize that students’ preliminary ideas are resources to be built upon, not errors to be eradicated. Furthermore, Maskiewicz and Lineback argue that the term misconception has been largely abandoned by educational researchers, because it is not consistent with constructivist theory. Instead, they conclude, members of the biology education community should speak of preconceptions, naïve conceptions, commonsense conceptions, or alternative conceptions.We respectfully disagree. Our objections encompass both the semantics of the term misconception and the more general issue of constructivist theory and practice. We now address each of these in turn. (For additional discussion, please see Leonard, Andrews, and Kalinowski , “Misconceptions Yesterday, Today, and Tomorrow,” CBE—Life Sciences Education [LSE], in press, 2014.)Is misconception suitable for use in scholarly discussions? The answer depends partly on the intended audience. We avoid using the term misconception with students, because it could be perceived as pejorative. However, connotations of disapproval are less of a concern for the primary audience of LSE and similar journals, that is, learning scientists, discipline-based education researchers, and classroom teachers.An additional consideration is whether misconception is still used in learning sciences outside biology education. Maskiewicz and Lineback claim that misconception is rarely used in journals such as Cognition and Instruction, Journal of the Learning Sciences, Journal of Research in Science Teaching, and Science Education, yet the term appears in about a quarter of the articles published by these journals in 2013 (National Research Council, 2012 ).

Table 1.

Use of the term misconception in selected education research journals in 2013
Journal (total articles published in 2013a)Articles using misconception (“nondisapproving” articles/total articles)Articles using other terms
LSE (59)23/24Alternative conception (4)
Commonsense conception (2)
Naïve conception (1)
Preconception (4)
Cognition and Instruction (16)3/3None
Journal of the Learning Sciences (17)4/4Commonsense science knowledge (1)
Naïve conception (1)
Prior conception (1)
Journal of Research in Science Teaching (49)11/13Commonsense idea (1)
Naïve conception (1)
Preconception (5)
Science Education (36)10/11Naïve conception (1)
Open in a separate windowaAs of November 25, 2013. Does not include very short editorials, commentaries, corrections, or prepublication online versions.A final consideration is whether any of the possible alternatives to misconception are preferable. We feel that the alternatives suggested by Maskiewicz and Lineback are problematic in their own ways. For example, naïve conception sounds more strongly pejorative to us than misconception. Naïve conception and preconception also imply that conceptual challenges occur only at the very beginning stages of learning, even though multiple rounds of conceptual revisions are sometimes necessary (e.g., see figure 1 of Andrews et al., 2012 ) as students move through learning progressions. Moreover, the terms preferred by Maskiewicz and Lineback are used infrequently (Smith et al. (1993) that they object to statements that misconceptions should be actively confronted, challenged, overcome, corrected, and/or replaced (Smith et al. (1993) argue on theoretical grounds that confrontation does not allow refinement of students’ pre-existing, imperfect ideas; instead, the students must simply choose among discrete prepackaged ideas. From Maskiewicz and Lineback''s perspective, the papers listed in Maskiewicz and Lineback (2013) as using outdated views of misconceptionsa
ArticleExample of constructivist languageExample of language suggesting confrontation
Andrews et al., 2011 “Constructivist theory argues that individuals construct new understanding based on what they already know and believe.… We can expect students to retain serious misconceptions if instruction is not specifically designed to elicit and address the prior knowledge students bring to class” (p. 400).Instructors were scored for “explaining to students why misconceptions were incorrect” and “making a substantial effort toward correcting misconceptions” (p. 399). “Misconceptions must be confronted before students can learn natural selection” (p. 399). “Instructors need to elicit misconceptions, create situations that challenge misconceptions.” (p. 403).
Baumler et al., 2012 “The last pair [of students]''s response invoked introns, an informative answer, in that it revealed a misconception grounded in a basic understanding of the Central Dogma” (p. 89; acknowledges students’ useful prior knowledge).No relevant text found
Cox-Paulson et al., 2012 No relevant text foundThis paper barely mentions misconceptions, but cites sources (Phillips et al., 2008 ; Robertson and Phillips, 2008 ) that refer to “exposing,” “uncovering,” and “correcting” misconceptions.
Crowther, 2012 “Prewritten songs may explain concepts in new ways that clash with students’ mental models and force revision of those models” (p. 28; emphasis added).“Songs can be particularly useful for countering … conceptual misunderstandings.… Prewritten songs may explain concepts in new ways that clash with students’ mental models and force revision of those models” (p. 28).
Kalinowski et al., 2010 “Several different instructional approaches for helping students to change misconceptions … agree that instructors must take students’ prior knowledge into account and help students integrate new knowledge with their existing knowledge” (p. 88).“One strategy for correcting misconceptions is to challenge them directly by ‘creating cognitive conflict,’ presenting students with new ideas that conflict with their pre-existing ideas about a phenomenon… In addition, study of multiple examples increases the chance of students identifying and overcoming persistent misconceptions” (p. 89).
Open in a separate windowaWhile these papers do not adhere to Smith et al.''s (1993) version of constructivism, they do adhere to the constructivist approach that advocates cognitive dissonance.Our own stance differs from that of Maskiewicz and Lineback, reflecting a lack of consensus within constructivist theory. We agree with those who argue that, not only are confrontations compatible with constructivist learning, they are a central part of it (e.g., Gilbert and Watts, 1983 ; Hammer, 1996 ). We note that Baviskar et al. (2009) list “creating cognitive dissonance” as one of the four main tenets of constructivist teaching. Their work is consistent with research showing that focusing students on conflicting ideas improves understanding more than approaches that do not highlight conflicts (e.g., Kowalski and Taylor, 2009 ; Gadgil et al., 2012 ). Similarly, the Discipline-Based Education Research report (National Research Council, 2012 , p. 70) advocates “bridging analogies,” a form of confrontation, to guide students toward more accurate ways of thinking. Therefore, we do not share Maskiewicz and Lineback''s concerns about the papers listed in Price, 2012 ). We embrace collegial disagreement.Maskiewicz and Lineback imply that labeling students’ ideas as misconceptions essentially classifies these ideas as either right or wrong, with no intermediate stages for constructivist refinement. In fact, a primary goal of creating concept inventories, which use the term misconception profusely (e.g., Morris et al., 2012 ; Prince et al., 2012 ), is to demonstrate that learning is a complex composite of scientifically valid and invalid ideas (e.g., Andrews et al., 2012 ). A researcher or instructor who uses the word misconceptions can agree wholeheartedly with Maskiewicz and Lineback''s point that misconceptions can be a good starting point from which to develop expertise.As we have seen, misconception is itself fraught with misconceptions. The term now embodies the evolution of our understanding of how people learn. We support the continued use of the term, agreeing with Maskiewicz and Lineback that authors should define it carefully. For example, in our own work, we define misconceptions as inaccurate ideas that can predate or emerge from instruction (e.g., Andrews et al., 2012 ). We encourage instructors to view misconceptions as opportunities for cognitive dissonance that students encounter as they progress in their learning.  相似文献   

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Thanks!     
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Plant Behavior     
Plants are a huge and diverse group of organisms ranging from microscopic marine phytoplankton to enormous terrestrial trees. Stunning, and yet some of us take plants for granted. In this plant issue of LSE, WWW.Life Sciences Education focuses on a botanical topic that most people, even biologists, do not think about—plant behavior.Plants are a huge and diverse group of organisms (Figure 1), ranging from microscopic marine phytoplankton (see http://oceandatacenter.ucsc.edu/PhytoGallery/phytolist.html for beautiful images of many species) to enormous terrestrial trees epitomized by the giant sequoia: 300 feet tall, living 3000 years, and weighing as much as 3000 tons (visit the Arkive website, www.arkive.org/giant-sequoia/sequoiadendron-giganteum, for photos and basic information). Stunning, and yet some of us take plants for granted, like a side salad. We may see plants as a focal point during the blooming season or as a nice backdrop for all the interesting things animals do. For this plant issue of CBE—Life Sciences Education, I am going to focus on a botanical topic that most people, even biologists, do not think about—plant behavior.Open in a separate windowFigure 1.Plants are very diverse, ranging in size from microscopic plankton (left, courtesy of University of California–Santa Cruz Ocean Data Center) to the biggest organisms on our planet (right, courtesy Arkive.org).Before digging into plant behavior, let us define what a plant is. All plants evolved from the eukaryotic cell that acquired a photosynthetic cyanobacterium as an endosymbiont ∼1.6 billion years ago. This event gave the lineage its defining trait of being a eukaryote that can directly harvest sunlight for energy. The cyanobacteria had been photosynthesizing on their own for a long time already, but this new “plant cell” gave rise to a huge and diverse line of unicellular and multicellular species. Genome sequences have shed light on the birth and evolution of plants, and John Bowman and colleagues published an excellent review titled “Green Genes” several years ago in Cell (www.sciencedirect.com/science/article/pii/S0092867407004618#; Bowman et al., 2007 ). The article has concise information on the origin and evolution of plant groups, including helpful graphics (Figure 2). Of course, plants were classified and subdivided long before DNA analysis was possible. The Encyclopedia of Earth (EOE) is a good website for exploring biological diversity and has an article on plants (www.eoearth.org/view/article/155261) that lays out the major plant groups and their characteristics. It states that there are more than 400,000 described species, a fraction of the estimated total number.Open in a separate windowFigure 2.Genomic analysis has illuminated the relationship among the many species of plants, as illustrated in this phylogeny of three major plant groups from Bowman et al. (2007 , p. 129).The venerable Kew Gardens has an excellent website (Figure 3) that includes extensive pages under the tab Science and Conservation (www.kew.org/science-conservation). It is a beautifully organized website for exploring plant diversity and burrowing into the science of plants, and includes an excellent blog. Ever wonder how many different kinds of flowers there are? You can find out by visiting their feature titled, “How Many Flowering Plants Are There in the World?” There is an interesting video feature on coffee, which describes how only two species out of more than a hundred have come to dominate coffee production for drinking. As the monoculture in Ireland led to the potato blight, a lack of genetic diversity in today''s coffee plants is threatening the world''s coffee supply with the onset of climate change. The possibility of life without coffee is a call to action if ever I have heard one.Open in a separate windowFigure 3.Kew Gardens has a large and informative website that should appeal to gardeners and flower lovers, as well as more serious botanists and ecologists.Classification of plants is challenging for students and teachers alike. Perhaps understandable, given that plants constitute an entire kingdom of life. For an overview, have students read the EOE article as well as the Bowman Cell article to appreciate the enormity and diversity of the organisms we call plants. The EOE article is reproduced on the Encyclopedia of Life website (http://eol.org/info/449), an excellent context for further exploration of diverse plant species. As we probe the topic of plant behavior, the examples will be drawn from the vascular plants that include the many familiar plants commonly called trees, shrubs, flowers, vegetables, and weeds.Plants do respond to changes in their environment, but is it fruitful or scientifically valid to say that they have behavior? They lack muscles and nerves, do not have mouths or digestive systems, and are often literally rooted in place. A growing number of plant biologists have embraced the term behavior, as demonstrated by the journal devoted to the subject, Plant Behavior. Their resources page (www.plantbehavior.org/resources.html) is a good place to get oriented to the field.As in so many things, Darwin anticipated important questions concerning the movement of plants, despite the difficulties in observing plant behavior, and in 1880 he published The Power of Movement in Plants. The Darwin Correspondence Project website has a good treatment of Darwin''s work on plants, with interesting anecdotes relating to how he collaborated with his son Francis on this work late in his career (www.darwinproject.ac.uk/power-of-movement-in-plants). You can download Chapter 9 of the book and some of the correspondence between Darwin and his son. The entire book is available at http://darwin-online.org.uk/content/frameset?itemID=F1325&viewtype=text&pageseq=1, or in various e-reader formats at the Project Gutenberg website (http://www.gutenberg.org/ebooks/5605). The PBS NOVA website, has a feature covering several of Darwin''s “predictions,” including one in which he noted the importance of plant and animal interactions. He famously predicted that a Madagascar orchid (Angraecum sesquipedale), which has a long narrow passage to its nectar stash, must have a long-tongued pollinator. In 1903, biologists identified the giant hawkmoth, with a 12-inch-long proboscis, as the pollinator predicted by Darwin (www.pbs.org/wgbh/nova/id/pred-nf.html).Darwin recognized that plants mostly do things on a timescale that is hard for us to observe, so he devised clever ways to record their movements. Placing a plant behind a pane of glass, he marked the plant''s position on the glass over time using a stationary reference grid placed behind the plant. Darwin transferred the drawing to a sheet of paper before cleaning the glass for the next experiment (Figure 4). By varying the distance between the plant, the reference points, and the glass, he magnified apparent distances to detect even small plant movements over periods as short as minutes. High-definition time-lapse photography and other modern techniques have extended Darwin''s observations in some compelling directions.Open in a separate windowFigure 4.One of Darwin''s drawings that can be found on the Darwin Correspondence Project Web pages devoted to his book The Power of Movement in Plants. For this figure, the position of the cotyledons of a Brassica was marked on a glass plate about every 30 min over a period of more than 10 h.A recent episode of the PBS Nature series, “What Plants Talk About,” epitomizes the increased interest in plant behavior and, unfortunately, some of the hyperbole associated with the field. The time-lapse video sequences and associated science are fascinating, and the entire program can be viewed on the PBS website at http://video.pbs.org/video/2338524490. The home page for the program (Figure 5; www.pbs.org/wnet/nature/episodes/what-plants-talk-about/introduction/8228) has two short video clips that are interesting. The video titled “Dodder Vine Sniffs Out Its Prey” is nicely filmed and features some interesting experiments involving plant signaling. It might be instructive to ask students to respond to the vocabulary used in the narration, which unfortunately tries to impart intent and mindfulness to the plant''s activities, and to make sensible experimental results somehow seem shocking. The “Plant Self-Defense” video is a compelling “poison pill” story that needs no narrative embellishment. A plant responds to caterpillars feeding on it by producing a substance that tags them for increased attention from predators. Increased predation reduces the number of caterpillars feeding on the plants. The story offers a remarkable series of complex interactions and evolutionary adaptations. Another documentary, In the Mind of Plants (www.youtube.com/watch?v=HU859ziUoPc), was originally produced in French. Perhaps some experimental interpretations were mangled in translation, but the camera work is consistently excellent.Open in a separate windowFigure 5.The Nature pages of the PBS website have video clips and a short article, as well as the entire hour-long program “What Plants Talk About.” The program features fantastic camera work and solid science, but some questionable narration.Skepticism is part and parcel of scientific thinking, but particular caution may be warranted in the field of plant behavior because of the 1970s book and documentary called The Secret Life of Plants (www.youtube.com/watch?v=sGl4btrsiHk). The Secret Life of Plants was a sensation at the time and was largely responsible for the persistent myths that talking to your plants makes them healthier, that plants have auras, and that plants grow better when played classical music rather than rock. While the program woke people up to the notion that plants indeed do fascinating things, the conclusions based on bad science or no science at all were in the end more destructive than helpful to this aspect of plant science. Michael Pollan, author of The Botany of Desire and other excellent plant books, addresses some of the controversy that dogs the field of plant behavior in an interview on the public radio program Science Friday (http://sciencefriday.com/segment/01/03/2014/can-plants-think.html). His article “The Intelligent Plant” in the New Yorker (www.newyorker.com/reporting/2013/12/23/131223fa_fact_pollan?currentPage=all), covers similar ground.The excellently understated Plants in Motion website (http://plantsinmotion.bio.indiana.edu/plantmotion) is a welcome antidote to some of the filmic excesses. The site features dozens of low-definition, time-lapse videos of plants moving, accompanied by straightforward explanations of the experimental conditions and some background on the plants. The lack of narration conveys a refreshing cinema verité quality, and you can choose your own music to play while you watch. Highlights include corn shoots growing toward a light bulb, the rapid response of a mimosa plant to a flame, vines twining, and pumpkins plumping at night. You may have driven past a field of sunflowers and heard the remark that the heads follow the sun, but that is a partial truth. The young buds of the early plants do track the sun, but once they bloom, the tall plants stiffen and every head in the field permanently faces … east! The creators of Plants in Motion curated an exhibit at the Chicago Botanic Gardens called sLowlife (Figure 6). The accompanying video and “essay” (http://plantsinmotion.bio.indiana.edu/usbg/toc.htm) are excellent, featuring many interesting aspects of plant biology.Open in a separate windowFigure 6.sLowlife is an evocative multimedia essay designed to accompany an exhibit installed at the Chicago Botanic Gardens. It features text and video that reveal interesting aspects of plant biology.High-definition time-lapse photography is far from the only tool available to reveal hard-to-observe activities of plants. Greg Asner and colleagues at the Carnegie Airborne Observatory are using informatics to study the dynamic lives of plants at the community ecology level. The Airborne Observatory uses several impressive computer- and laser-enabled techniques (http://cao.stanford.edu/?page=cao_systems) to scan the landscape at the resolution of single leaves on trees and in modalities that can yield information at the molecular level. These techniques can yield insights into how forests respond to heat or water stress or the introduction of a new species. The site has a gallery of projects that are best started at this page: http://cao.stanford.edu/?page=research&pag=5. Here, they are documenting the effect of the Amazon megadrought on the rain forest. The very simple navigation at the top right consists of 15 numbered squares for the different projects. Each project is worth paging through to understand how versatile these aerial-mapping techniques are. They also have six buttons of video pages (http://cao.stanford.edu/?page=videos) that give you a feel for what it might be like to be in the air while collecting the data (Figure 7).Open in a separate windowFigure 7.The Carnegie Airborne Observatory is a flying lab that can collect real-time aerial data on forests at resolutions smaller than a single leaf on a tree.If this Feature seems to have been too conservative about whether plants have behavior, visit the LINV blog (www.linv.org/blog/category/plant-behavior) of the International Laboratory for Plant Neurobiology. The term “plant neurobiology” may be going too far, but the website presents some interesting science. Another fascinating dimension of plant “behavior” is seed dispersal, from seeds that can burrow, to seeds that “fly,” to seeds that are shot like bullets. A couple of websites have some good information and photos of the myriad designs that have evolved to take advantage of air currents for seed dispersal; see http://waynesword.palomar.edu/plfeb99.htm and http://theseedsite.co.uk/sdwind.html. The previously mentioned PBS Nature series also produced a program on seeds, “The Seedy Side of Plants,” which you can view at www.pbs.org/wnet/nature/episodes/the-seedy-side-of-plants/introduction/1268. ChloroFilms, a worldwide competition for plant videos, is now in its fourth season, with some really good videos (www.chlorofilms.org). If you love plants, work with plants, or have insights into plant biology, you should consider submitting a video!  相似文献   

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The National Institutes of Health publishes a series of science curriculum supplements for K–12 education that are available from their Web site free of charge (http://science.education.nih.gov/supplements). In this feature, we review two of the high school supplements, Human Genetic Variation and Cell Biology and Cancer. Overall, we find that they are both excellent resources that engage students in learning science content while emphasizing the impact of scientific breakthroughs on personal and public health. In this review, we highlight the many strong features of the curricula and point out instances in which teachers may wish to seek out supplemental, updated information.  相似文献   

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We have designed, developed, and validated a 17-question Meiosis Concept Inventory (Meiosis CI) to diagnose student misconceptions on meiosis, which is a fundamental concept in genetics. We targeted large introductory biology and genetics courses and used published methodology for question development, which included the validation of questions by student interviews (n = 28), in-class testing of the questions by students (n = 193), and expert (n = 8) consensus on the correct answers. Our item analysis showed that the questions’ difficulty and discrimination indices were in agreement with published recommended standards and discriminated effectively between high- and low-scoring students. We foresee other institutions using the Meiosis CI as both a diagnostic tool and an instrument to assess teaching effectiveness and student progress, and invite instructors to visit http://q4b.biology.ubc.ca for more information.  相似文献   

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This feature is designed to point CBE—Life Sciences Education readers to current articles of interest in life sciences education as well as more general and noteworthy publications in education research.This feature is designed to point CBE—Life Sciences Education readers to current articles of interest in life sciences education, as well as more general and noteworthy publications in education research. URLs are provided for the abstracts or full text of articles. For articles listed as “Abstract available,” full text may be accessible at the indicated URL for readers whose institutions subscribe to the corresponding journal. This themed issue focuses on recent studies of concepts and conceptualization—from how textbook images and students’ attitudes and levels of acceptance can influence their understandings to design of tools that educators can use to understand what their students know.1. Novick LR, Stull AT, Catley KM (2012). Reading phylogenetic trees: the effects of tree orientation and text processing on comprehension. BioScience 62, 757–764.[Abstract available: www.jstor.org/stable/10.1525/bio.2012.62.8.8]Cladograms—branching, nested hierarchical diagrams drawn in a variety of formats—are commonly used to depict how organisms might be related. Although differently formatted cladograms can convey the same information, informationally equivalent cladograms are not necessarily equivalent “computationally,” that is, with respect to the ease with which observers interpret and use them. Because diagonal cladograms with a slanting up-to-the-right (UR) orientation are most commonly used in college-level textbooks, the authors explored whether a diagonal cladogram drawn with a UR backbone line is computationally equivalent to its informationally equivalent mirror-image, drawn in a slanting down-to-the-right (DR) orientation. Drawing from existing studies on the influence of processing biases and prior experience on directional scanning of visual materials, the authors hypothesized that the direction of the slant influences students’ processing of the cladogram and that the more commonly used UR format is harder for students to understand.They tested this hypothesis with a study population of 19 upper-division students majoring in biology or biology-related subjects. The subjects processed a series of 24 diagonal cladograms, each paired with a rectangular-format cladogram. The diagonal cladograms varied in one of three ways: 1) UR or DR orientation, 2) forward or reverse alphabetical order of taxa labeling, and 3) the taxon topology (branching pattern). The subjects initially viewed a diagonal cladogram presented on the center of a computer screen, and their eye movements were tracked electronically. When they indicated that they understood the diagonal cladogram, they were presented with a rectangular cladogram, and then were asked whether the evolutionary relationships depicted in the two cladograms were the same. The authors used rectangular cladograms for comparison, because information about how students interpret them was available from a previous study (Novick and Catley, 2007 ). Incorrect rectangular cladograms could therefore be modeled after common types of interpretation and translation errors observed in this earlier study.Analysis of the results indicated that, for both the UR and DR orientations, the subjects tended to scan the cladograms from left to right (upward for the UR cladograms and downward for the DRs); that is, most used the processing direction that they use to read text. There was a significant effect of cladogram orientation on the accuracy of translation to the rectangular format. As predicted, the subjects were more successful at translating the diagonal cladogram to the rectangular format when the DR orientation was used. As a possible explanation for this finding, the authors suggest that people generally encounter the branching points in an order that reflects the nesting pattern when reading from left to right in the DR orientation. Thus, in this study, informationally equivalent UR and DR cladogram formats were not computationally equivalent for students.The authors conclude by discussing the implications for instruction. They suggest that if textbook diagrams do not change, students could benefit from instruction and practice in how to change their processing strategies to successfully interpret the computationally more difficult UR-oriented cladograms.2. Liben LS, Kastens K, Christensen AE (2011). Spatial foundations of science education: the illustrative case of instruction on introductory geological concepts. Cogn Instr 29, 45–87.[Abstract available: www.tandfonline.com/doi/abs/10.1080/07370008.2010.533596]The concepts of strike and dip, used to describe planar features such as the orientation of layers of rock, are notoriously difficult aspects of spatial thinking for novice learners of geology to grasp. The “strike” of a planar surface (such as a fault, bed, or other type of geologic formation) refers to the compass direction of a line of intersection of the planar surface with a horizontal plane; the latter is often referenced to the surface of a still body of water. The “dip” is the angle of tilt of the surface from the horizontal. Textbook illustrations of the strike and dip of geologic features often attempt to make the concepts more accessible by using water level and falling water to help students understand these concepts. However, educators are becoming increasingly aware that, for some students, these illustrations may convey insufficient information about three-dimensional spatial relationships. In this study, the authors used various tasks related to strike and dip to explore the nature of students’ underlying difficulties. In doing so, they anticipated that performance on stripe and dip tasks would shed light on broader issues related to spatial perception and how it influences science learning.The study population consisted of 125 college students (roughly equal numbers of males and females) who had completed a pencil-and-paper water-level test in which they drew lines of predicted water levels on diagrams of straight-sided empty bottles tilted at different angles. Participants were assigned to high-, medium-, and low-scoring water-level groups (WLG) based on their test scores. Each WLG was then assigned a series of additional field and laboratory tasks. Field tasks included estimating and recording (on a campus map) the strike and dip of an artificial rock outcrop, indicating the location of a wooden rod placed on the ground on a campus map, and additional tasks that assessed sense of direction. Laboratory tasks consisted of a series of three-dimensional horizontality (shoreline) and verticality (drop) tasks. Both sets of tasks used plastic models with paper-covered planar surfaces of different shapes attached to clear Plexiglas pillars; the dip of the surfaces varied, but the strike was held constant In the shoreline task, subjects were asked to imagine that the whole model was covered in water up to the midpoint of the paper-covered surface and to then draw on the paper how the water would look. In verticality tasks, the subjects were asked to imagine that a drop of water had fallen on the paper surface, were then asked to draw the path of the drop along the paper after it fell. Participants were asked to supply information about their level of confidence in their performance on all tasks, and observations were made of their behaviors and the strategies they used.The authors determined the variance of the absolute values by which scores on the directional responses to field and laboratory tasks deviated from the correct scores, with WLG and participant gender as between-subject factors. Although they found that students in the low WLG generally had the lowest task scores, the entire study population appeared to be challenged by the tasks. The authors used multiple regression analysis, in which confidence served as the criterion variable to determine whether the water-level “pretest,” actual performance on the field and laboratory tasks, and being female were predictive of participants’ confidence level. They found that low water-level scores and being female were predictive of low confidence scores, and performance on tasks was generally predictive of participants’ confidence ratings. In groups of students with similar scores on the water-level test, females scored lower than males on a number of the tasks. The authors speculate that the water-level test may not have identified all key components of spatial skill needed to complete the tasks, because the gender differences were most pronounced when participants had to orient in relation to a larger, more distal environment and were absent when more local frames of reference for orientation could be used. Finally, observations of the participants’ task performance indicated that they often did not use strategies that educators might assume are too basic to warrant mentioning in the course of instruction.The authors conclude that, in fact, strike and dip are difficult geological concepts to teach, and the difficulty may lie in part with underdevelopment of students’ “Euclidean conceptual system” (p. 81). They suggest the need for more research to inform the design of instructional programs that would foster development of specific foundational spatial concepts and skills.3. Fulop RM, Tanner KD (2012). Investigating high school students’ conceptualizations of the biological basis of learning. Adv Physiol Educ 36, 131–142.[Full text available: http://advan.physiology.org/content/36/2/131.long]This study sets the stage for increasing the amount and relevance of high school neuroscience education by exploring what students already know about the biological basis of learning. Recent studies (e.g., Blackwell et al., 2007 ) suggest that the nature of students’ understandings about this area of cognitive neuroscience—the biological basis of learning—has implications for their academic success.High school juniors (n = 339) enrolled in chemistry classes in a large urban high school participated in the study, which used a mixed-methods design consisting of written assessments (both multiple-choice and open-ended assessment prompts) and interviews. Although all participants were invited to participate in the interviews, only a few (n = 15) actually did so. Most of the 19 “yes/no/I don''t know” multiple-choice assessment prompts were taken from the literature, and all were demonstrated to elicit agreement from neuroscientists (>90%) on the answer. The first of the two open-ended prompts was designed to determine whether students would place the process of learning within a biological or some other framework; the second was designed to explicitly elicit responses of a biological nature. Two independent observers analyzed the interview responses by: 1) sorting them into one of three categories (nonbiological, minimally biological, or primarily biological) using a rubric; 2) scoring for the level of understanding they revealed about neural structures, mechanisms of learning, and plasticity of the nervous system using a second rubric; and then 3) coding them for emergent conceptual themes.The findings indicated a low level of knowledge about the biological basis for learning in this set of high school juniors: <70% of the students agreed with the neuroscientists’ responses to the majority of the multiple-choice prompts; 75% of the responses to the first open-ended assessment exhibited a nonbiological framework; and 67% of the interviewed subjects revealed misconceptions during the interview. The authors provide numerous quotes from students to illustrate these conclusions. Fewer than half of the interview subjects reported having had prior (albeit minimal) instruction about neuroscience, a topic that is included in the National Science Education Standards. However, the majority thought that understanding how people learn was of value to their own learning.The authors conclude by underscoring the importance to the general public of teaching about the biology of the brain, particularly since high school biology represents the last opportunity for formal education to reshape preconceptions of the >70% of the U.S. population that will not go on to college. Although the teaching of neuroscience in high school is not yet prevalent, in the words of the authors, the good news is that “students appear to be ready, willing and able to learn about their own brains” (p. 139).4. Nadelson LS, Southerland S (2012). A more fine-grained measure of students’ acceptance of evolution: development of the inventory of student evolution acceptance: I-SEA. Int J Sci Educ 34, 1637–1666.[Abstract available: www.tandfonline.com/doi/abs/10.1080/09500693.2012.702235]Science, technology, engineering, and mathematics educators and education researchers are becomingly increasingly aware of the potential role that affective constructs, such as learning dispositions, self-efficacy, beliefs, and motivation, can play in shaping the learning process. This study is based on a premise that, for emotionally charged topics such as evolution, the affective perceptions of belief and acceptance can interfere with conceptual understanding. The authors have developed an instrument for measuring students’ acceptance of biological evolution in a way that avoids blending acceptance with belief or understanding of specific content. They report having taken particular care in designing the instrument to distinguish acceptance of evolution—based on the validity of the evidence supporting it and its plausibility and utility as an explanatory paradigm—from beliefs about evolution based on feelings, personal convictions, or faith.The article guides the reader through the processes of instrument design, item and scale development, and field-testing (with groups of high school and college students) of an initial 49-item Likert-scale instrument: the Inventory of Student Evolution Acceptance (I-SEA). The instrument has three subscales designed to differentiate between areas of evolution that are perceived differently by the general public: microevolution (the results of evolution in the short term), macroevolution (long term), and human evolution. After field-testing, the authors performed statistical analyses to determine instrument and subscale reliability, as well as an exploratory factor analysis to guide instrument refinement. They conducted a refined analysis of the resulting 24-item instrument as a whole and for each of the three subscales. Ten postsecondary biology faculty contributed to the process of expert validation and final refinement of the items. The authors point out the potential usefulness of the instrument, as well as its possible limitations, in making curricular decisions and assessing their subsequent impact on student perceptions. Appendices include the items from both the field-tested and final versions of the I-SEA.I invite readers to suggest current themes or articles of interest in life science education, as well as influential papers published in the more distant past or in the broader field of education research, to be featured in Current Insights. Please send any suggestions to Deborah Allen (ude.ledu@nellaed).  相似文献   

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A standard genetic/bioinformatic activity in the genomics era is the identification within DNA sequences of an "open reading frame" (ORF) that encodes a polypeptide sequence. As an educational introduction to such a search, we provide a webapp that composes, displays for solution, and then solves short DNA exemplars with a single ORFTo the Editor: We wish to bring a new Web resource to the attention of CBE—Life Sciences Education readers.When being introduced to the central dogma of nucleic acid transactions, students are often required to identify the 5′→3′ DNA template strand in a double-stranded DNA (dsDNA) molecule; transcribe an antiparallel, complementary 5′→3′ mRNA; and then translate the mRNA codons 5′→3′ into an amino acid polypeptide by means of the genetic code table. Although this algorithm replicates the molecular genetic process of protein synthesis, experience shows that the series of left/right, antiparallel, and/or 5′→3′ reversals is confusing to many students when worked by hand. Students may also obtain the “right” answer for the “wrong” reasons, as when the “wrong” DNA strand is transcribed in the “wrong” 3′→5′ direction, so as to produce a string of letters that “translates correctly.”In genetics and bioinformatics education, we have found it more intuitively appealing to demonstrate and emphasize the equivalence of the mRNA to the DNA sense strand complement of the template strand. The sense strand is oriented in the same 5′→3′ direction and has a sequence identical to the mRNA, except for substitution of thymidine in the DNA for uracil in the mRNA. It is thus more computationally efficient to “read” the polypeptide sequence directly from this strand, with mental substitution of thymidine in the triplets of the genetic code table. (By definition, “codons” occur only in mRNA: the equivalent three-letter words in the DNA sense strand may be designated “triplets.”) This is the same logic used in DNA “translation” software programs.A further constraint often imposed on dsDNA teaching exemplars is that five of the six possible reading frames are “closed” by the occurrence of one or more “stop” triplets, and only one is an open reading frame (ORF) that encodes an uninterrupted polypeptide. We designate this the “5&1” condition. The task for the student is to identify the ORF and “translate” it correctly. Other considerations include correct labeling of the sense and template DNA strands, their 5′ and 3′ ends (and of the mRNA as required), and the amino (N) and carboxyl (C) termini of the polypeptide.Thus, instructors face the logistical challenge of creating dsDNA sequences that satisfy the “5&1” condition for homework and exam questions. Instructors must compose sequences with one or more “stops” in the three overlapping read frames of one strand, while simultaneously creating two “stopped” frames and one ORF in the other. We have explored these constraints as an algorithmic and computational challenge (Carr et al., 2014 ). There are no “5&1” exemplars of length L ≤ 10, and the proportion of exemplars of length L ≥ 11 is very small relative to the 4L possible sequences (e.g., 0.0023% for L = 11, 0.048% for L = 15, 0.89% for L = 25). This makes random exploration for such exemplars inefficient.We therefore developed a two-stage recursive search algorithm that samples 4L space randomly to generate “5&1” exemplars of any specified length L from 11 ≤ L ≤ 100. The algorithm has been implemented as a Web application (“RandomORF,” available at www.ucs.mun.ca/~donald/orf/randomorf). Figure 1 shows a screen capture of the successive stages of the presentation. The application requires JavaScript on the computer used to run the Web browser.Open in a separate windowFigure 1.Successive screen captures of the webapp RandomORF. First panel: the Length parameter is the desired number of base pairs. Second panel: Clicking the “Generate dsDNA” button shows the dsDNA sequence to be solved, with labeled 5′ and 3′ ends. The button changes to “Show ORF.” Third panel: A second click shows the six reading frames, with the ORF highlighted. Here, the ORF is in the sixth reading frame on the bottom (sense) strand. The polypeptide sequence, read right to left, is N–EITHLRL–C, where N and C are the amino and carboxyl termini, respectively. The conventional IUPAC single-letter abbreviations for amino acids are centered over the middle base of the triplet; stop triplets are indicated by asterisks (*).The webapp provides a means for students to practice identifying ORFs by efficiently generating many examples with unique solutions (Supplemental Material); this can take the place of the more standard offering of a small number of set examples with an answer key. The two-stage display makes it possible for problems to be worked “cold,” with the correct ORF identified only afterward. For examinations, any exemplar may be presented in any of four ways, by transposing the top and bottom strands and/or reversing the direction of the strands left to right. Presentation of the 5′ end of the sense strand at the lower left or upper or lower right tests student recognition that sense strands are always read in the 5′→3′ direction, irrespective of the “natural” left-to-right and/or top-then-bottom order. We intend to modify the webapp to include other features of pedagogical value, including constraints on [G+C] composition and the type, number, and distribution of stop triplets. We welcome suggestions from readers.  相似文献   

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