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DOI: 10.1039/C2RP20035J (Paper) Chem. Educ. Res. Pract., 2012, 13, 447-461

Learning goals and conceptual difficulties in cell metabolism—an explorative study of university lecturers' views

Mari Stadig Degerman and Lena A. E. Tibell *
Linköping University, Department of Science and Technology (ITN), Sweden

Received 18th March 2012 , Accepted 20th June 2012

First published on 15th August 2012

Abstract

The rapid development and increasing inter- and multi-disciplinarity of life sciences invokes revisions of life science course curricula, recognizing (inter alia) the need to compromise between covering specific phenomena and general processes/principles. For these reasons there have been several initiatives to standardize curricula, and various authors have assessed general curricular requirements. The results have shown that teacher preferences strongly influence both topic arrangement and course content, and that generating consensus among scientists and lecturers is challenging. Applying a somewhat different approach, we have focused on a limited part of the curriculum (cell metabolism). Using Delphi methodology, in four rounds of surveys we investigated phenomena that 15 experienced, practising lecturers consider to be central aspects for students to learn in the cell metabolism module of an introductory university course. The overall aim was to identify learning goals of special concern, i.e., aspects considered by the teachers to be both central and difficult for students to understand. Our informants emphasized learning goals of overarching and principal type, e.g. to be able to couple different system levels (from molecules to cells to organisms) and grasp the interactions between them. However, the teachers also expect students to retain detailed knowledge, e.g. to know the structure of central biomolecules and metabolites. The main result of the study is a ranked list of learning goals of special concern in cell metabolism. We also identified both important learning goals and difficulties that have not been previously reported (even though they are covered by most textbooks), e.g. the necessity of proximity and common intermediates for coupled reactions and that energy production occurs in well-regulated steps.

Introduction

Learning and teaching are always about something (Marton et al., 2004). Teachers always have to select the content they wish the students to learn, and to achieve intended learning goals it is important for students to be able to discern the selected content. However, selecting content is not always straightforward, for various reasons. Notably, in molecular life (and other) sciences the recent explosive increase of relevant information has greatly complicated the selection of the most important and pertinent scientific content (Bell, 2001), not least for fundamental undergraduate courses. The increasing inter- and multi-disciplinarity of life sciences has added further educational complications (Wright and Hamilton, 2008; Anderson, 2007). High value is generally attached to integrative thinking, but most students are not given opportunities for higher-level learning. Indeed, most introductory courses are content-driven and do not include elements of active learning (Wolfson et al., 2008). Consequently, the core of the subject seems to be obscured by rote learning of detailed content, and many teachers perceive students' learning to be superficial. Several authors, e.g., Bobich (2006), have thus called for a revision of life science course curricula to clarify the key learning goals and accommodate more focus on processes and principles. However, compromises between covering specific phenomena and general processes/principles are essential, since general processes cannot be understood without sufficient fundamental knowledge, given the massive wealth of information and time limitations. Further, generating consensus among scientists and lecturers about the most important concepts in molecular life science education has been persistently challenging (Bailey et al., 2010; Smith and Tanner, 2010; Michael et al., 2008; Garvin-Doxas and Klymkowsky, 2007), due largely to variations in teacher preferences, class composition, and textbooks' contents and rationale. Teacher preferences strongly influence both topic arrangement and course content (Bobich, 2006). This situation has prompted several initiatives to introduce at least some standardization. For example, the American Society of Biochemistry and Molecular Biology (ASBMB) has launched a five-year project (ASBMB, 2010) with the following main aims: to identify core biochemistry and molecular biology concepts and skills, to construct appropriate assessment tools, to learn what and how students learn, and to find effective pedagogical approaches (Bailey et al., 2010; Rowland et al., 2011).

Our investigation presented here takes a narrower and somewhat different approach. We focus on only one of the central topics in the biochemistry/cell biology curriculum—cell metabolism—and investigate what experienced practising lecturers, who are not involved in concept inventory projects or science education research, consider to be central aspects for students to learn.

Cell metabolism

Cell metabolism encompasses thousands of enzyme-catalyzed reactions, connected in a coordinated, web-like structure. In other words, thousands of compounds, enzymes, reactions, nutrients, energy inputs and transformations, and regulatory mechanisms are involved. The coordination involves various levels of organization, at temporal and spatial scales ranging from invisible, imperceptible and near-instantaneous gargantuan and to geological (when societal, evolutionary and wide-scale adaptive responses are considered). All these aspects raise challenges for both teachers and learners, which have become increasingly severe as massively increasing amounts of information about metabolic processes, at every level, have been acquired. However, embedded in the mass of metabolic details and complexity there are important patterns. Notably, there are relatively few central metabolic pathways, and “standard solutions” to common problems have emerged in cell systems. For example: the chemi-osmotic potential across membranes provides the driving force for both ATP-production and nerve signaling; many of the steps in glycolysis are common to steps in gluconeogenesis; and reaction steps in the tricarboxylic acid (TCA) cycle are branch points in other metabolic pathways. From this perspective the challenge for the learner is to discover these similarities, and here the students need help and guidance.

Concept inventories

Concept inventories are lists of core concepts of given topics that can facilitate assessments of the degree to which students have grasped those core concepts (Adams and Wieman, 2011). Since the increasing multidisciplinarity and information explosion in molecular life science have complicated the selection of content and pedagogic practice in teaching the domain, attempts have also been made to develop biological concept inventories. Thus, to inform our search for central concepts associated with cell metabolism we initially consulted pertinent concept inventories that have recently been, or are currently being, compiled.

In 2003 recommendations for standard biochemistry curricula for use in the USA were drafted by the ASBMB and tested in various settings in various American universities (Boyer, 2003). Other examples include the Biology Concept Inventory (BCI, http://bioliteracy.net) presented by Klymkowsky et al. (2003) and Garvin-Doxas et al. (2007). The results have been published in a mini series in BAMBED (Bobich, 2004; Bell, 2003; Boyle, 2003; Gunn, 2003; Zimmerman, 2003). One of the general conclusions was that overlapping molecular chemistry with molecular biology is important (Voet et al., 2003). However, according to Cheesman et al. (2007) these inventory efforts have had very little effect on life science courses in practice since 1992, when the ASBMB first attempted to develop an undergraduate biochemistry and molecular biology curriculum. In a recent paper, Rowland et al. (2011) report a new approach to present the key concepts using four conceptual lenses, organized in teaching modules. This teaching approach was reported to stimulate the students but challenge the teachers.

In an effort to bridge the gap between scientific knowledge and what is taught in schools and universities, an international project was initiated by the International Union of Biochemistry and Molecular Biology (IUBMB) to scrutinize the core concepts in biochemistry and create a concept inventory for the Life Sciences (Howit et al., 2008; Wright and Hamilton, 2008). This project is ongoing and its development is described on the Internet.†

Central learning goals in cell metabolism

One identified difficulty when constructing concept inventories in biology and molecular life science has been to define what constitutes a concept (Bailey, 2010). For example, are sphingolipids, coupled reactions, conservation of matter and glycolysis concepts? And what are the relations between facts, concepts, processes, principles, topics and “big ideas”? In this paper the term concept embraces everything that students may need to learn about cell metabolism, ranging from the names of biomolecules and cell components, through the networks of reactions that occur in cells, to the complex physio-chemical systems associated with various cellular processes, and principles such as regulation and adaptation. Hence, learning goal refers to an intention for students to acquire knowledge and/or understanding of any one of these concepts.

However, there are defined core concepts in biology education to which we can relate our work. Based on the BCI, Khodor et al. (2004) constructed a hierarchical Biology Concept Framework (BCF), including 18 Top Level Concepts they identified, which serves as an umbrella for the detailed and complex concepts (http://web.mit.edu/bioedgroup/HBCF/CBE-Summer2004.htm). We identified the following “core concepts”/”top level concepts”/“big ideas” that are associated, to varying degrees, with cell metabolism: the core BCI areas Biomolecules – structure and function, Protein – structure and function, Allosteric regulation, Bioenergetics and Equilibrium (Voet et al., 2003); the BCF biology curriculum Top Level Concepts 4, 11, and 15, “All cells share many processes/mechanisms”, “Life processes are the result of regulated chemical reactions” and “All carbon-containing biomass is created from CO2”) and “Introduction to metabolism and concepts of compartmentalization” (Khodor et al., 2004); and the concept inventory for molecular life science “big ideas” “Compartmentalization”, “Regulation”, “Catalysis”, “Energy and organization” and “Complexity of molecular structure” (Howit et al., 2008). The most relevant of the conceptual lenses presented by Rowland et al. (2011) is “Thermodynamics and Energy”, and some of the concepts in “Regulation and Organization” and “Structure and Function of Biomolecules”. These conceptual frameworks provide guides for both classifying learning objectives and applying information obtained from inventories in curriculum design.

Students' difficulties related to cell metabolism

Learning difficulties are often divided into conceptual difficulties and reasoning difficulties (Grayson et al., 2001). Conceptual difficulties include preconceptions, alternative conceptions and misconceptions, while reasoning difficulties refer to students' problems grasping causal relationships and complex processes, which often span two or more conceptual domains. Both types of learning difficulties are associated with making meaning of various aspects of cell metabolism.

Students' difficulties and misconceptions have been intensively studied in physics, especially school level physics (Duit, 2009), but they have been much less thoroughly investigated in biology and molecular life science, particularly at the university level. However, there are some well-documented problems. The vast numbers of substances, reactions and processes involved in cellular metabolism and physiological processes present substantial obstacles for learners. A further key challenge for learners grappling with the metabolism of cells is the “invisibility” of these complex systems. Other documented difficulties are associated with the linguistic and visual representations used, dynamic flows, energy transformations and the complexity of the systems. However some of the most thoroughly documented difficulties are, in fact, associated with the multiple levels of organization, e.g., of the phenomena included in the scientific content of chemistry courses (Bahar et al., 1999; Johnstone, 1991). This also applies to learning molecular life science; there are documented difficulties in relating biochemical processes to the structures and functions of cells, and relating cellular processes, structures and functions to organisms' (and ecosystems') functions (e.g., Wilson et al., 2006). For example, to understand the process and roles of photosynthesis in plants, scientific meaning must be constructed at multiple system levels, simultaneously. The learner has to grasp how the absorption of light quanta, via the excitation of electrons in organic molecules in the inner membrane of the chloroplast, osmotic pumping of protons, energy capture in chemical bonds, synthesis of cell components, cell-division and cellulose production are inter-related and connected to the growth and development of all of the plant's tissues and organs. Photosynthetic responses to diurnal, seasonal and stochastic environmental variables add further layers of complexity that students must grasp to develop levels of understanding required for many university level courses, posing additional difficulties.

Furthermore, confusion introduced by some terminology and visual representations might be related to difficulties associated with the multiple levels of organization. Functional similarities between organelles in cells and organs in the human body also contribute to the confusion, particularly since illustrations of the connections are often shown on the same page in textbooks and the students sometimes misinterpret the pedagogical intentions. Other conceptual difficulties can be linked to the way the content is represented and the manner in which the symbolism is used (Schönborn and Anderson, 2006). For example, students sometimes interpret diagrams as realistic depictions of the illustrated events (Harrison and Treagust, 2000). In addition, the vivid linguistic and/or visual metaphors and analogies sometimes used as pedagogical tools can be sources of misconceptions for students (Tibell and Rundgren, 2010; Michael et al., 1999).

Widespread difficulties connected to students' conceptions of coupled reactions and inhibition of biochemical pathways have been identified (Schönborn and Anderson, 2003). Well documented sources of learning difficulties in both chemistry and molecular life studies are connected to the highly dynamic nature of the processes that involve numerous states such as (quasi-)equilibrium, (quasi-)steady state, variable mixtures of diffusion and active transport, and countless arrays of molecular interactions (Höst et al., submitted).

Regarding metabolic pathways, students have difficulties grasping the functioning of metabolic pathways and their connections (Anderson et al., 1999; Anderson and Grayson, 1994). Observed difficulties have been associated with glycolysis (e.g., Oliveira et al., 2003), respiration (e.g., Marmaroti and Galanopoulou, 2006; Wood-Robinson, 1991), the interactions between fat and carbohydrate metabolism during exercise (Morton et al., 2008), and many difficulties associated with photosynthesis (e.g., Eisen and Stavy, 1988). For example, students get confused between photosynthesis and respiration, believe that respiration occurs only when there is no photosynthesis (Amir and Tamir, 1994; Stavy et al., 1987), misconceive the need to harvest energy from the sun (Marmaroti and Galanopoulou, 2006), and have difficulty seeing the connection between light reactions and the Calvin Cycle (Hazel and Prosser, 1994). Students also have several difficulties understanding the role of photosynthesis in ecosystems and tracing matter and energy flows through dynamic systems (e.g., Lonergan, 2000; Eisen and Stavy, 1988, Stavy et al. 1987). Students may very well know about the laws of conservation of matter and energy, but get confused by transformations of matter and energy in biological systems (Wilson et al., 2006, Lin and Hu, 2003).

However, some of the most thoroughly investigated and documented sources of students' difficulties relate to energy, ATP formation, energy transformations and thermodynamic concepts (Waheed and Lucas, 1992). Galley (2004) claims these difficulties are associated with the coupling between hydrolysis of ATP to ADP and energy metabolism, i.e., how energy released in the exothermic breakage of bonds between phosphate-groups in ATP is used to drive other metabolic reactions and processes. Students have also been found to have problems grasping that biological substances can be oxidized, and that oxidation can be coupled to the loss of hydrogens (Anderson et al., 1999; Morton et al., 2008). Common illustrative misconceptions are that glucose is the only metabolic fuel used to produce ATP in human cells and that ATP production is independent of the electron transport in oxidative phosphorylation (Luz et al., 2008; Oliveira et al., 2003). Further sources of problems for students are the causal relations between the elements in complex processes such as photosynthesis and oxidative phosphorylation (Nerdel et al., 2002).

Motivation and aim

The selection of appropriate content and clear guidance are critical for successful teaching and learning about cell metabolism, particularly at university foundation levels, since there is so much information that could be included, but time is inevitably limited. However, in Sweden, as in many other countries, no common national curricula have been developed for university courses in chemistry, biology, molecular life science or numerous other subjects. Instead, curricula are usually expressed in very general terms (unpublished findings). This leaves considerable freedom and responsibility to the individual teacher to select content and examples. A key aim of most efforts to develop concept inventories (see above) has been to support teachers and educators in this task.

Thus, teachers must not only know their content (subject matter), but also be able to transform it into teaching subject matter (van Driel et al., 1998; de Jong and van Driel, 2004). Therefore another kind of content knowledge is content specific pedagogical knowledge, which goes beyond knowledge of the subject matter per se to the dimension of subject matter for teaching. Such knowledge includes; what makes the learning of specific topics easy or difficult; the conceptions and preconceptions of the students; known difficulties and their origin (Lederman et al., 1994); and strategies most likely to be fruitful in reorganizing the understanding of learners. This set of abilities is collectively often referred to as Pedagogic Content Knowledge (PCK) of a specific subject matter (Shulman, 1987).

Concept inventories are based on consensus developed in detailed discussions among selected panels of internationally recognized experts in the specific science concerned and science education. However, important issues are the degree of unity about the central concepts and learning goals among practising lecturers, the degree to which concept inventories coincide with the central concepts recognized by these lecturers, and to explore which learning difficulties they recognize in their practice.

The aim of the explorative study presented here was to determine empirically the extent of any consensus regarding core cell metabolism concepts, and learning difficulties using a four-stage Delphi questionnaire and a panel of 15 experienced, practising university lecturers. We asked the participants both what they consider to be central learning goals and what they considered to be difficult for students to understand and learn.

The overall aim of the study was to identify learning goals that are considered to be both central and difficult in the domain of cell metabolism in an introductory university level biochemistry course. The specific aims were to:

1. investigate the degree of consensus among the practising teachers regarding the learning goals and difficulties;

2. find concepts and principles that have not been previously identified as important to emphasize or learn;

3. identify potential problems that researchers have not yet discovered or investigated;

4. find out if there are any documented reasoning difficulties that the practising teachers are not aware of.

By comparing our results with previously published inventories and research on student difficulties we aimed to contribute to curriculum development. In addition, we were interested in the possibility of identifying learning goals that warrant further attention either because teachers consider them to be both important and difficult, or because they are goals that have not been previously reported.

Methodology

Cell biology and biochemistry courses are often obligatory components of university programs offered by a wide range of faculties. We used a modified Delphi method in our investigation. This seemed appropriate since we aimed to discern the degree (if any) of consensus among teachers across different programs, faculties and universities.

The Delphi method

The Delphi method is an iterative process, based on several rounds of questionnaires. It is considered a reliable method for finding group consensus among an expert panel without face-to-face interaction, and for obtaining unbiased general views of groups from large geographic areas, since the participants never meet (Murry and Hammons, 1995). Since the participants never meet, they cannot influence each other, and they need to draw their own conclusions. However, the informants always get feedback from the preceding round, thereby obtaining opportunities to make comments and amend their responses in the following rounds. By utilizing the knowledge of experts, combining it and redistributing it, the technique opens doors and promotes the emergence of new thought processes. The self-validation is also beneficial.

The Delphi method was first designed for applications such as forecasting new conflict strategies and technology during the cold war, but it has also been used to define, design and develop educational curricula (Linstone and Turoff, 1975), both undergraduate and postgraduate, and to reach consensus on what is important in other specialties. Notably, Osborne et al. (2003) used the method to find experts’ view of central concepts in the “nature of science” that should be taught in school, and most recently it was applied in an international study to identify common core content in technology education (Rossouw et al., 2010).

Panel selection and context

To ascertain views of practising lecturers, we recruited informants with diverse educational backgrounds who had extensive experience of teaching (5–35 years), and who were teaching students on various educational programs (including medical, science and engineering students, and student teacher). The chosen panel comprised 15 experienced lecturers/professors from seven universities in Sweden (nine biochemists, and six biologists or cell biologists) several of whom specialized in teaching, while others combined teaching with active research. Invitations were sent by e-mail to selected teachers who were known anecdotally by our colleagues to have good teaching practices.

Research design

The design of our study was inspired by the work of Osborne et al. (2003) and Rossouw et al. 2010. It included four consecutive rounds of sending questionnaires, analyzing the responses, providing feedback and amending the questionnaires, resulting in a validated system of categorized learning goals (expressed as statements regarding core concepts) that the informants considered to be highly important and/or particularly difficult to grasp. However, we found it necessary to supplement and deepen some aspects of the information provided, primarily because the responses to questions posed in the first round of the Delphi-questionnaires were often rather vague, hence there was a need to clarify which metabolic pathways and what aspects of the pathways should be defined as learning goals (Fig. 1). We therefore deviated from the strict Delphi format and added questions concerning metabolic pathways in Round 3 (cf.Rossouw et al., 2010). The added information was addressed following the Delphi method in the subsequent rounds. Round 1 responses were collected via email and post, while Rounds 2, 3 and 4 were collected with web-based questionnaires. The response rate was 100% in Rounds 1 and 2, then 80% in Rounds 3 and 4 (12 of 15).
Schematic diagram of the modified Delphi questionnaire-based study design. LG refers to Learning Goals.
Fig. 1 Schematic diagram of the modified Delphi questionnaire-based study design. LG refers to Learning Goals.

Round 1

In Round 1 we wanted our informants to freely generate ideas to construct a list of learning goals associated with cell metabolism. In this first round we therefore asked the panellists to list learning goals (concepts, processes and skills) in an open-ended survey sent by post and/or e-mail. In this first round their views were elicited by the following two questions, which were deliberately broad to permit the individual brainstorming that is a key element of the initial round of a Delphi study:

1. Which learning goals do you think are important and central in teaching cell metabolism?

2. Which learning goals, if any, do you think may be difficult for students to achieve when studying cell metabolism?

The responses resulted in over 200 different statements, from which two lists of learning goals were generated, one of goals considered to be central and one of goals expected to present difficulties for students. Some of the statements in Round 1 concerned learning goals outside the scope of cell metabolism, and were thus excluded from the following rounds. Statements expressing identical or very similar learning goals were fused into single statements, thereby reducing the number of statements to 99, of which 72 were considered to be of great importance and/or to pose major learning-difficulties (27). These statements were coded into categories, and compiled in a list of stated learning objectives (statements and identified learning goals are used synonymously hereafter), which were presented to the informants in the panel in Round 2.

Rounds 2 and 3

In Rounds 2 and 3 the informants were first presented with the summarized results from the previous round and given the opportunity to comment on them. The next task in Round 2 was to assess the importance and difficulty of each learning goal in the list of 99 statements compiled from Round 1 on a five-point scale from not important to very important and not difficult to very difficult, respectively. Learning goals expressed by statements with a mean score exceeding 3 were assessed as important or difficult for students’ meaning-making and those with mean scores of less than 2 were omitted from the list. However, this procedure only reduced the list to 78 statements for use in Round 3.

The stated learning goals ranged from general principles of cell metabolism to far more specific concepts, for example the definition of Gibbs free energy or specific enzyme reaction mechanisms. However, some of the 78 statements were very vaguely phrased, for example glycolysis, or the connection between nutrition and energy production in the cell, with no definition of the level of detail or understanding required. To gain a better insight into some aspects of the meaning of the stated learning goals an additional questionnaire, comprising sixteen metabolic processes, was constructed for use in Round 3 (Appendix 2). In this part of the questionnaire the informants were asked to rank the pathways according to their importance for the students to learn. In an attempt to elucidate the students' expected level of understanding (and detail) of the sixteen metabolic pathways we also asked the panellists to indicate the level of detail at which students were expected to learn the pathways (reaction steps, enzyme names, mechanisms and regulation) on a three-point scale (“not important”, “neutral” and “important”). It should be noted that the questionnaire did not provide possibilities for respondents to give the background and reasons why they considered learning specific pathways to be highly important, or less important, to learn.

Round 4

The aim of Round 4 was to identify the stated learning goals that were regarded as both highly important and difficult for students to achieve. Correlation analysis of the 78 statements from Round 3 identified thirteen statements/learning goals that the participants considered to be both important and pose difficulties or be challenging for the students to understand (see analysis section below). Those thirteen statements were selected for the fourth round. In addition, two further statements representing extremes were included as reference cases. One of the reference goals was the metabolic pathway “Nucleotide synthesis”, which had been previously considered as the least important (but difficult) metabolic pathway to learn, while the other, “The structure and function of the mitochondrion”, had been considered as important but easy to learn.

The panel was asked to rank the concepts from 1–15 in both importance and difficulty dimensions (1 being the most important/difficult) in a web-based questionnaire (following procedures suggested by previous authors, e.g., Jurgensen, 1978). The reference questions were included to validate the outcome of the ranking (see below).

Data analysis

The standard way to analyze Delphi-material is to use descriptive statistics to find consensus among the informants. Accordingly, the responses in Rounds 2 and 3 were analyzed by calculating the mean and standard deviation of the scores for each statement. There is little guidance in the literature to inform decisions about the minimum level of agreement that might constitute consensus. However, one way to assess the degree of consensus is to evaluate the divergence of individual responses around a median response, and to define stability or convergence as being reached when it becomes apparent that little further shifting of positions will occur (Brooks, 1979). This state will equate to full consensus if all panellists fully agree with the final statements and their rankings. In our case it was evident from the descriptive statistics that rankings of most of the final statements stabilized above the midpoints of the scales (i.e., as being both important and difficult), but in some cases there was substantial divergence. As a consequence it was difficult to reduce data between rounds and to discern clear patterns in the statistics. Therefore we also included analytical induction to identify themes among the highly ranked learning goals (see category system below). This categorization system helped us to detect convergence patterns and trends in our data, and emerging areas of consensus among our informants.

To identify learning objectives that were considered to be both highly important and difficult to achieve addition, correlation analysis was used in Round 3. This analysis resulted in the shortlist of 13 statements used in Round 4.

Developing a category system

The stated learning goals from Round 1 were generally formulated as statements, which were read to identify themes according to the method of analytical induction, and sorted into preliminary categories according to content analysis (Graneheim and Lundman, 2004). This analysis was systematic and performed in several rounds, by two researchers (the authors), who independently read the written responses several times, analyzed them iteratively and summarized them, then compared their findings. In the few cases of discrepancy, the researchers made a common assessment after discussion, and eventually both agreed with the categories. From the statements obtained in Round 1 we developed a preliminary category system comprising 30 sub-categories sorted into seven categories, which in turn were sorted into three themes. The category system was modified and validated according to the Delphi method in Rounds 2 and 3.

The statements in Rounds 2 and 3 were sorted according to the category system, then the number of statements in each category was counted, and is here expressed as a percentage of the total number of statements in all categories. The statements' categorization was visible to the informants. The category system is summarized in Table 1 and illustrated by the categories for statements sorted into Theme A in Table 2.

Table 1 Stated central and/or difficult learning goals divided into content-related and skill-related learning goals

Table 2 Illustrative categorization of statements under Theme A. The percentages show the proportions of representative statements that were coded into the Theme and each category in each of the rounds (R1–3 corresponds to rounds 1, 2 and 3 respectively)

Theme A includes a general understanding of patterns, principles and properties of cell metabolism, as well as the connections between cell metabolism, the host organism and the environment.

Category a relates to the links between nutrition, energy transformation and energy use in the cell. This category includes statements about: how nutrient molecules are converted into characteristic molecules and building blocks in the cell; how metabolism can be described as a complex network of coherent chains of reactions; and how reactions are catalyzed by enzymes and which often are highly regulated.

Category b concerns similarities and differences among different elements of cell metabolism and between the cell metabolism in various organisms, e.g., similarities and differences in catabolic and anabolic pathways, and between final electron acceptors in chemotropic and phototropic organisms.

Category c refers to the coupling between levels (micro, sub-micro and macro) of explanation of molecules and reactions, e.g., the connections between micro-level intra- and inter-cellular communication, within-organism communication systems through to environmental signaling or the biotechnological exploitation of cell metabolism.

Theme B relates to more detailed knowledge, often concerned with structure-function relationships.

Category d includes: knowledge of the structure of both macromolecules and central metabolites of the cell; cellular metabolic pathways, for which detailed knowledge is often expected (for example, knowledge of the successive reaction steps, the enzymes involved, the mechanisms of the enzymatic reactions and their regulation); and relationships between the structure and function of the enzymes and reacting components.

Category e refers to knowledge required to comprehend how energy is captured, converted and used in the cell, requiring coupling of thermodynamic knowledge to the chemistry of the reactions. Some of the stated learning-aims in this category overlap with those assigned to Categories b and d, but were assigned to a separate category since we wanted to gather all stated aims concerning bioenergetics into a common category, for example, recognition of the differences and similarities between photosynthesis and oxidative phosphorylation, and the roles of O2 and CO2 in those processes.

Category f relates to the structure of the cell, sites of different metabolic reactions, and the importance and functions of different components and compartments.

Theme C concerns a skill that is not directly coupled to knowledge of cell metabolism, but affects how the learner understands metabolism.

Category g refers to visual literacy, which includes the skills to create and interpret visual representations of various kinds (such as molecular models, animations, diagrams and graphs) and to connect multiple representations of the same process.

Possible limitations of the study

The members of the panel (lecturers) were all selected from Swedish universities; this is a potential limitation of the study. However, rather than making generalisations to a larger population the focus of this study was on describing and exploring learning goals that lecturers consider important and/or difficult for students to learn. Nevertheless, an expansion of the later part of the study to an international panel might strengthen the findings and claims.

The main disadvantage of Delphi studies is the length of the process. There a risk to lose informants, who give up and leave the panel, is common. In our study, however, we only lost three informants (originally 15) during the process. Another limitation of Delphi studies is that the investigators influence the responses via their formulation of questions (Murry and Hammons, 1995). It is important to recognize these disadvantages and take steps to minimize their effects. For these purposes very little guidance was given regarding the expected contents of responses in the first round (in which two very open questions were asked) and care was taken to ensure that the participants' original phrasing were used in the questionnaires in the second and third rounds (see above).

The open-ended nature of the first round in the Delphi study generated a plethora of suggestions of varying character, from vague to detailed, and from specific concepts to general principles. This is normal in a Delphi study, since the first round corresponds to a brainstorming session. Further, since the researchers process and categorize the responses between rounds their influence is potentially a limitation. However, giving participants the opportunity to respond to any possible misinterpretations by the researcher in each iteration, possible validity problems are overcome. A Delphi study is therefore in fact regarded to be self-validated (Murry and Hammons, 1995).

Results

In search of consensus

The difficulty to reduce data between rounds and to discern clear patterns in the statistics is an indication of that the lecturers considered most of the learning goals (statements) to be important (above the midpoint of the scale) and that there are also substantial disagreement concerning some of them. However, the application of the categorization system helped us to detect convergence patterns and trends.

From the content analysis seven categories, sorted into three themes, emerged for which there was both consensus and stable rating as important and/or difficult learning goals in the domain of cell metabolism. These categories, highlighted in Table 1, were: (a) General properties and principles of cell metabolism, (b) Similarities and differences in cell metabolism, (c) The coupling/connections between macro- micro- and sub-micro system levels, (d) Components, structures and mechanisms, (e) Bioenergetics, (f) Structure and function of the cell, and (g) Visual literacy.

Categories a-c are sorted under Theme A. In Round 1 over 62% of the learning goals considered to be important were classified in this theme, but in Rounds 2 and 3 the proportions of statements under Theme A tended to decrease and stabilize at 46 and 43%, respectively.

The proportion of important learning goals categorized under Theme B stayed approximately constant between rounds (43–46%). Visual literacy (category g, under Theme C) is a skill that affects students' possibilities to interpret representations of cell metabolism. The proportion of important learning goals in this theme/category increased considerably from Round 1 (0%) to Round 2 (9%) then stabilized in Round 3 (11%). The corresponding numbers for learning goals considered to be difficult in Rounds 1, 2 and 3 were 62%, 56% and 51% for Theme A, 30%, 35% and 39% for theme B, and 8%, 9%, and 12% for Theme C, respectively, indicating similar trends to those observed for the important learning goals.

Central and difficult learning goals—categories

In the following section we exemplify and clarify the important and difficult learning goals we have categorized in our system (Table 1), and illustrate the categorization using those assigned to Theme A in Table 2.
Theme A: properties, principles and connections of cell metabolism. The learning objectives under Theme A reflect a desire for the students to understand general patterns in the complexity of cell metabolism. The major category within Theme A was Flow and principles of cell metabolism (a), in which two thirds of the statements were classified. Statements concerning the link between nutrition, metabolic building blocks and energy generation and consumption, and the metabolic pathways are linked in complex networks, were most often mentioned as central learning goals. The remaining statements under the theme were evenly distributed among the categories b, Relationships in cell metabolism – meta-perspectives and c, The coupling between macro- micro- and sub-micro system levels. The learning goals considered to be important and those considered to be difficult showed similar patterns (Table 2).
Theme B: structure and function—in more detail. (Appendix 1). Over half of the stated learning goals in Theme B were assigned to the Bioenergetics category (e) (23%, 21% and 19% of the totals for learning goals in all themes, in Rounds 1–3, respectively). This category was also the most frequently cited as difficult under the theme (23%, 22% and 12% of the totals for learning goals in all themes, in Rounds 1–3, respectively). The theme emphasizes the importance of understanding the mechanisms underlying the processes involved in greater detail. Statements in the other categories assigned to the theme—Components, structures and mechanisms (d) and Structure and function of the cell (f)—were less often mentioned as being difficult for students to grasp, but the former more often (stable, at around 16%) than the latter (increasing from 4–10% from Round 1 to Round 3).
Theme C: skills affecting students' understanding of cell metabolism (Appendix 1). In Round 1 none of the statements regarded as being important were found under Theme C, this theme was only identified among the ‘difficult statements'. However, statements mentioned as difficulties in Round 1 (for example Visual literacy) also appeared on the importance scale in later Rounds. Approximately 10% of the statements were assigned to the Visual literacy category (g) in Rounds 2 and 3, but it was not considered to be a particularly difficult skill to achieve.

In summary, the learning-objective statements drawn from the open-ended questions in Round 1 resulted in a spontaneous emphasis on learning goals of a general and global character. When faced with the gathered statements from the whole group (in Rounds 2 and 3) more specific learning goals emerged as being equally desired. Interestingly, bioenergetics stands out as an objective that was stated as being one of the most central learning goals in all three rounds, while the importance of visual literacy was only suggested by a few informants in Round 1, but it gained ground over time (rounds) and finally emerged as one of the central goals.

Learning goals—metabolic pathways

Results obtained from Round 2 led us to suspect that a relatively high level of detail was expected in some content areas since the category Components, structures and mechanism increased in the difficulty rankings. Therefore, in an attempt to clarify the intended meaning of these general statements we added further questions concerning 16 metabolic pathways to Round 3 (see research design. For results see Appendix 2.1 and 2.2).

The pathways considered the most important for the students to learn were the electron transport chain, oxidative phosphorylation and photosynthesis, closely followed by glycolysis and the TCA cycle. These metabolic pathways are also emphasized in most textbooks. The majority of our informants' expected the reactions and enzymes involved in glycolysis, the TCA cycle and the photosynthesis dark reactions to be learned. Knowledge of the reaction mechanisms was also required for electron transport and oxidative phosphorylation, photosynthesis (light reactions), fatty acid breakdown and fatty acid synthesis, and both regulatory steps and mechanisms involved in pyruvate dehydrogenation and glycogen metabolism.

The largest disagreements between the participants regarded the fermentation reactions, Calvin cycle, pentose phosphate cycle and the transamination reaction mechanism. For example, some of them considered it highly important for students to learn the Calvin cycle in detail, while others only expected knowledge of the principle of the reactions. Some lecturers regarded detailed understanding of the mechanisms of transamination reactions as highly important, while others regarded it as redundant knowledge. The nucleotide synthesis was considered the least important pathway to learn. Surprisingly, given the critical role of fermentation in anaerobic metabolism and its connection to everyday phenomena such as brewing, baking and bread production, the panellists regarded fermentation as being only the tenth most important to learn of the 16 listed pathways.

Central learning goals that involve difficulties

In Round 4 the informants were presented with a list of 15 statements (see Research design) drawn from Round 3. The informants were asked to rank the statements with respect to both their importance and difficulty relative to the other statements (here, a low number corresponds to high importance or difficulty, respectively. For example the most important/most difficult statements were ranked 1). Table 3 summarizes the results.
Table 3 Importance and difficulty rankings (Rank Imp and Rank Diff, respectively), and categories, of 15 statements drawn from Round 3. The asterisked statements (*) are reference statements, included to verify the rankings, since they ranked lowest in importance and difficulty, respectively
Statement Rank Imp. Rank Diff. Category
To have an overview of cell metabolism and be able to see principles, similarities and differences in networks of reaction pathways. 1 5 a
To be able to couple different system levels (from molecules to cells to organisms) and grasp the interactions. 2 3 c
To be able to see the different sources of energy and nutrients different organisms use for generating metabolic building blocks, and the energy transformations involved. 3 14 a
Oxidative phosphorylation. 4 9 e
To see the complexity and great numbers of molecules, reactions and participating enzymes. 5 7 a
To see the connections between structures, properties and functions of molecules. 6 1 d
To understand the chemical fundaments of energy transformations in cell metabolism, for example how electron gradients are used. 7 10 e
To understand fundamental thermodynamic concepts, such as ΔG. 8 2 e
To understand the principles of electron donors and acceptors and redox-reactions. 9 8 e
To link different visualizations to different aspects of processes. 10 12 g
* The structure and function of the mitochondrion. 11* 15* f
To understand the principles of coupled reactions. 12 4 a
To be able to use and create graphs, diagrams and other visualizations. 13 11 g
To understand the difference between oxidative phosphorylation and phosphorylation at the substrate level. 14 13 b
* To know the reactions in the nucleotide synthesis pathway. 15* 6* d

Discussion and implications

The overall aim of this study was to identify concepts that are important learning goals in cell metabolism, particularly those that are also problematic, since they must be of special concern. Most literature on conceptual and learning difficulties focuses on students' understanding of concepts in relation to current scientific views or definitions. In contrast, teachers' observations and understanding of students' perceptions of core concepts and processes, and their difficulties in grasping them, have received limited attention. However, the opinions of this group are clearly crucial, because they ultimately decide what is actually taught in the classroom. Thus, they were the target group of our study.

We investigated (i) the extent of consensus among the teachers on the most important learning goals and difficulties. We also investigated the overlap of their views with recent findings on learning difficulties and concept inventories. Thereby, we could explore the possibilities that (ii) we had identified important cell metabolism concepts or principles that previous researchers have not identified as being important learning goals, (iii) that there are potential problems not earlier described, and (iv) important and difficult learning goals that the teachers in our study might not be aware of as important or to be connected to reasoning difficulties. In the following sections we discuss our results and their implications with respect to these issues.

General observations

Our informants in Round 1 generated a high number of learning goals, perhaps reflecting the challenges associated with teaching and learning cell metabolism. Similar to Rowland et al. (2011), many of the responses could be considered as content or domains rather than concepts. Several of the learning goals that were considered to be important and/or difficult have been previously identified in the research literature, but we also found goals and difficulties that, to our knowledge, have not been previously reported. Another general observation was that the informants were often more explicit when describing difficulties than when stating important learning goals. For example, they considered it important for students to be able to see the link between nutrition, metabolic building blocks and energy generation and consumption—an all-inclusive goal—while they reported difficulties for students to understand that coupled reactions require physical proximity and common intermediates—a general, but more clearly specified, principle.

Concerning detail and depth the stated learning goals were often imprecisely expressed, for example, “It is important that students know the central metabolic pathways”. The supplemental questions about the metabolic pathways in Round 3 were added in an attempt to make the informants specify such statements. The results show that glycolysis, the TCA cycle and oxidative phosphorylation are considered the most central pathways. These metabolic pathways are also emphasized in most textbooks. However, there were some disagreements between participants regarding a couple of processes, which could often be linked to the informants' background and teaching assignments. The most surprising observation was the low rank of fermentation reactions. These reactions are fundamental for anaerobic metabolism and can easily be connected to everyday phenomena such as lactic acid production during physical activity, baking and bread production. We have no explanation for this observation.

There is no clear emphasis on knowledge of central metabolic pathways in the relevant concept inventories (e.g., Khodor et al., 2004; Garvin-Doxas et al., 2007), possibly because none of them specifically focus on cell metabolism, and aim to identify “Top level concepts” or “Big ideas” rather than specific content. However, cell metabolism comprises thousands of reactions, and the key pathways must be mirrored in the expected content knowledge of the students after an introductory course. In our study the informants expected detailed knowledge regarding glycolysis, the TCA cycle and oxidative phosphorylation (reaction mechanisms, enzymes and regulation). Most textbooks provide a multitude of such details, but there seems to be substantial consensus among the informants regarding the selection of details, suggesting that the selection is a widespread practice.

In conclusion, our panel strongly emphasize learning goals of overarching and principal type, but when asked to specify the level of knowledge they expect, they cite detailed knowledge of mechanisms and structures. To be able to see principles and patterns there must be some detailed examples for the students to reflect upon in more detail. Therefore it is not surprising that the teachers expect students to acquire detailed knowledge, depth of understanding and discernment of overarching principles, but it might be difficult for students to interpret the pedagogical intentions, particularly in an introductory cell metabolism course. The challenge for teachers is to find the balance between rote learning of reactions and understanding principles and patterns. This challenge can result in ambivalence and insecurity of the teachers’ choice of content and the learning goals to focus upon, as apparent in this quote: “I only reflected that where different metabolic pathways occur in the cell is sometimes considered important and sometimes not. Why is this so? Is it due to old teaching habits and traditions, or does the cellular site sometimes provide critical information about a certain process?” A critical issue is whether the teachers are aware of the students' need for guidance in navigating through the complex networks of reactions and grasping principles that are exemplified by detailed descriptions of certain mechanisms. The four lens conceptual map presented by Rowland et al. (2011) might be helpful in this regard.

Results verified in concept inventories and conceptual research

The highest proportions of statements were linked to learning goals assigned to the Flow and principles… (a) and Bioenergetics (e) categories; the largest in Themes A and B, respectively. The content emphasized under Theme A is of overarching and comprehensive type. Since learning goals identified in concept inventories often comprise general principles they could be expected to overlap with learning goals under Theme A, but no core concept or top-level concept directly corresponds to the Flow and principles category. However, two overlapping core or top-level concepts were identified; “life processes are the result of regulated chemical reactions”, and “all cells share many processes/mechanisms” (Khodor et al., 2004; Rowland et al., 2011). In addition, the Top-level concept “the principle of allosteric regulation” (Voet et al., 2003) overlaps with category (d), Components, structures and mechanisms, under our Theme B. The lack of direct correspondence might be at least partly due to the fact that none of the inventories is specifically focused on cell metabolism.

Grayson et al. (2001) created a framework for identifying and classifying students' conceptual and reasoning difficulties based on how much that is known about them by researchers. Level 1 corresponds to difficulties occurring unexpectedly in the analysis of empirical data; Level 2 are difficulties experienced by researchers in their teaching experience. Level 3 and 4 are difficulties established in at least one systematic investigation or repeatedly established in different contexts, respectively. Several of the learning difficulties identified are well known from the research literature and are therefore classified at level 3 or 4 in this four-level.

The largest number of problematic learning goals was found under Theme A (e.g., problems in getting an overview of metabolism, and understanding that metabolic reactions take place in “a common container”, that they are ordered and regulated, and that metabolites can take different routes in the metabolic network depending on the needs in the system). Many of these system-associated difficulties can be recognized from the research literature. For example Morton et al. (2008), Schönborn and Anderson (2003) and Anderson et al. (1999) report similar problems for students to grasp the functioning of metabolic pathways and their connections, coupled reactions, and the various routes carbohydrates may take in metabolic systems.

Regarding bioenergetics, it encompasses many learning goals considered to be very important in all the relevant concept inventories, and many of them are also well documented and investigated sources of students' difficulties and misconceptions (e.g., Marmaroti and Galanopoulou, 2006; Galley, 2004; Waheed and Lucas, 1992).

Documented difficulties lacking parallels in our material

Our informants highlighted, in Round 3, Visual literacy (Theme C, category g) as a core-learning goal for understanding cell metabolism. Visual literacy is not mentioned in the concept inventories of the domain. However, it is not a category of skills that are specific for cell metabolism. On the other hand, our informants appeared not to realize that the widely documented difficulties are associated with the interpretation of visualizations and representations (e.g., Schönborn and Anderson, 2006; Harrison and Treagust, 2000). Since these skills are seldom (if ever) tackled in the relevant textbooks or curricula this raises interesting questions about how often they are consciously fostered in general, and in association with cell metabolism education in particular.

Similarly, connecting macro-level phenomena to sub-micro explanations is considered to be particularly problematic in chemistry (Bahar et al., 1999; Johnstone, 1991), and could be expected to be so also in molecular life science. For example, to explain traits and disorders (e.g., diabetes) or photosynthesis on a molecular level, the scientific meaning has to be constructed at several system levels simultaneously. However, our informants appeared initially to consider these learning-goals to be less problematic or to be unaware of the difficulties. In Round 1 only 9% of the learning goals considered to be important are found in the category; The connections between, macro- micro- and sub-micro system levels in Round 1. This proportion rose to 17% in Round 3. But in the difficulty dimension the proportion of learning-goals in this category remained approximately constant (9–10%) from Round 1–3. Interestingly, in Round 4 the learning goals sorting under this category were among the top ranked goals in both dimensions.

Several other difficulties that have been emphasized in previous research were not mentioned at all by our informants. There is a multitude of reports on students' difficulties to understand the function of different metabolic pathways in the cell (e.g., Marmaroti and Galanopoulou, 2006; Olivera et al., 2003). Likewise, many relevant core concepts in chemistry, e.g., equilibrium, steady state, diffusion and the dynamic nature of molecular interactions, are well known to be problematic for students (e.g., Friedler et al., 1987; Odom and Kelly, 2001; Banerjee, 1995; Thomas and Schwenz, 1998). These are highly relevant for chemical reactions in the cell. However, none of the informants indicated that these concepts would be difficult. It is of course not possible to tell from our data if this was because the informants had not observed any such problems or if they simply did not think of them as typical for cell metabolism. However, our results described in this section probably also illustrate the gap between education practice and science education research. If teachers had a greater awareness of the knowledge available in the research literature they might be better equipped to avoid some of the educational problems.

Learning goals of special concern

The overall aim of the study was to identify learning goals that are considered to be both central and difficult in the domain of cell metabolism. These should be of special concern in teaching, and focal points of science education research and development. The five top-ranked learning goals in both importance and difficulty dimensions are:

• The ability to couple different system levels;

• The ability to see principles;

• Similarities and differences in networks of reaction pathways;

• Understanding the relation between structures and functions of molecules;

• Bioenergetics

Three of these learning goals fall in Theme A (Properties, principles and connections) and two in Theme B (Structure, function and detail). These learning goals are all complex in character. Seeing principles in this context (cell metabolism) often requires the ability to discern patterns and similarities/differences between pathways in the complex reactions. Many textbooks dedicate whole chapters to this issue, but the presentation is often general, including lists of examples. The same examples are presented in detail in their specific contexts in other chapters of the book, but are seldom linked back to the general principles in the other chapters. This also typically applies to descriptions of the coupling and connections between processes and system levels. In many cases the connections are at best implicit, and the students, and also teachers, have to make those links themselves. On the other hand, examples of structure-function relationships are often described in detail (e.g., those of hemoglobin, ATP-synthase, and the translation machinery). Learning goals in the bioenergetics category include various types of concepts and processes, which are treated separately. The fundamental thermodynamic concepts used to describe bioenergetics and redox processes are often described in separate, dedicated chapters. The energizing or energy-consuming reactions are then characterized, assuming that these concepts are understood. The dispersed treatment of these learning goals might explain part of the difficulties associated with them.

Conclusions

There was consensus among informants about learning goals, but the number of learning goals was high, and both detailed and holistic knowledge was requested. In other words, we confirmed “the selection problem” that has been earlier reported in the domain. Many of these learning goals and difficulties confirm earlier work in the field. We also identified a set of learning goals that, from the perspective of experienced practising teachers, were considered to be central and important and, at the same time, associated with problems for students to learn—learning goals of specific concern. The identification of these implies goals to focus in teaching, and could aid in future development of cell metabolism curricula. We also identified some “new” learning goals and difficulties, and our results also indicate that there might be well-established learning difficulties that our informants are not fully aware of.

Observations without parallels in research literature

We found three learning goals assigned to Theme A, category a, that have no clear reported parallels and warrant specific attention:

• That metabolic reactions occur in many “bite-sized” steps

• That energy production occurs in well regulated steps

• That metabolites can take different routes in the metabolic network depending on the needs in the system

We also found two difficulties under Theme B, category b, with no reported correspondence in science education research:

• The necessity of proximity and common intermediates for coupled reactions

• The ability to recognize similarities and differences between different pathways.

None of these have been addressed in the research literature or concept inventories, to our knowledge, but they are covered in most textbooks, some of them repeatedly, in most cases in connection to specific metabolic reactions, and often implicitly. These difficulties can therefore be classified as level 2 in the four-level framework of Grayson et al. (2001) and are obvious candidates for further investigation, and special attention in teaching. In addition, these new learning goals and difficulties can contribute to the present efforts in developments of biochemistry curricula and to the research as well as to the research and development of pedagogical content knowledge (PCK).

Appendix 1

Themes B and C

Illustrative categorization of statements under Themes B and C. The percentages show the proportions of representative statements that were coded into each theme and each category in each of the rounds. Table 4.
Table 4 Appendix 1

Appendix 2

Metabolic pathways – importance and detail

Results from Round 3. Metabolic pathways are listed according to importance, starting with the most important. x indicates mean score above neutral on what aspects that are considered to be most important for each metabolic pathway to learn. Table 5.
Table 5 Appendix 2
Metabolic Pathway Enzymes Reactions Spec. E/R Where reaction takes place Regulation Principles
Glycolysis x     x   x
Oxidative phosphorylation including electron transport chain     x x   x
Photosynthesis, Light   x   x    
Tricarboxylic acid cycle x x   x   x
Pyruvat dehydrogenase reactions x x x   x  
Photosynthesis, Dark   x   x   x
Transamination x x x      
Fatty acid breakdown x x       x
Fermentation   x        
Fatty acid synthesis x x x     x
Glycogen synthesis       x x x
Glycogen break down   x     x x
Urea cycle           x
Pentosphosphate pathway           x
Aminosyrasyntes            
Nukleotidsyntes            

Acknowledgements

The authors would like to thank the participating informants at seven universities in Sweden for taking part in this long run Delphi-study. We are also grateful to our colleagues at Linköping University for valuable input and discussions and to Dr John Blackwell for valuable suggestions and reviewing the manuscript. The Swedish Research Council (grant VR 2008:5077) supported this research.

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Footnote

† http://www.lifescinventory.edu.au/index.html?page=92512.
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