A general challenge in science education is the abstract character of the content and the use of a specialised language, including terminology, that many students in primary school perceive as challenging. This also applies to biology and chemistry, especially at a subcellular or molecular level (Tibell & Rundgren, 2010). Therefore, the teacher has an important role to clarify and discuss terminology in connection with explanations of scientific phenomena. One way of promoting students’ learning in science is by “unpacking” the scientific terms by alternately using everyday language and the discourse of science in a wavelike manner, including subject specific terminology (Nygård Larsson, 2018). Furthermore, abstract scientific concepts generally need to be learned indirectly as they cannot be directly experienced by our senses. An example of this is nutrient uptake. Metaphors can act as bridges between students’ everyday experiences and the scientific concepts. Hence, researchers in science education have identified metaphors as important for scientific learning (Duit, 1991; Aubusson et al., 2006; Ogborn, Kress & Martins, 1996). With this study we seek to contribute to the research field about the role of metaphors in meaning-making in the upper primary science classroom.

A metaphoric expression implies the description of something more or less unfamiliar in the ‘target domain’ (in our case, science, and in particular, nutrient uptake) in terms of something more familiar in the ‘source domain’ (e.g., everyday life) (Gentner & Gentner, 1982; Lakoff & Johnson, 1980). In science, a concept can be presented as similar to a different one, from a distant domain (metaphor), e.g., ‘melting’ as a metaphor for food digestion. It can also be presented as if it functions in some respect in parallel to another concept (analogy). One such example is that the partly degraded food becomes like a ‘soup’. Both metaphor and analogy build on a perceived similarity between the concepts and domains involved, and it is not always easy to draw a sharp dividing line between their means of conceptualising scientific ideas. Therefore, in line with, for instance, Cameron (2002), we do not distinguish between metaphors and analogies, and hereafter ‘metaphor’ (or ‘metaphoric expression’) may refer to either ‘metaphor’ or ‘analogy’. In this article we use a social semiotic perspective on metaphors. Therefore, unlike Gentner and Gentner (1982) and Lakoff and Johnson (1980), for example, we do not equate people’s utterances with their cognition. Rather, we consider metaphors as semiotic resources that people may use as kinds of models when interacting about and making meaning of abstract phenomena. Since all social interaction is multimodal (Kress, 2010), and meaning-making in classrooms involves various modes that collectively communicate a meaningful offer to the students (Kress et al., 2001), we take into consideration all the resources used to communicate subject content, such as spoken and written words, gestures, and images.

Despite metaphors’ promotion as tools for teaching and learning, research also indicates that metaphors can be challenging for students (Danielsson et al., 2018), partly because the reach of the metaphor may be unclear (Haglund, 2013). In addition, many metaphors are expressed through everyday language, which can lead to students’ scientific language being disadvantaged. Furthermore, metaphors may be interpreted literally (Danielsson et al., 2018). Nevertheless, students’ use of metaphors may also manifest (and/or facilitate) initiation of deeper scientific understanding that provides foundations for the development of scientific language (Rundgren, 2006). Because metaphorical expressions are common in science, teachers need to support their students to “unpack” the metaphors (Danielsson & Selander, 2021) and preferably discuss the metaphorical expressions explicitly with them (Danielsson et al., 2018; Rundgren et al., 2012).

In science education, as in other subject areas, metaphors are commonly used, both to describe concepts developed within the disciplines (e.g., ‘cell’ and ‘magnetic field’) and for pedagogical reasons, such as describing enzymes as functioning like ‘scissors’. Metaphors can be particularly useful didactic tools for subject content concerning structures and processes that are not visible, for example molecules, internal organs, and processes involving phenomena at multiple scales, such as diffusion or digestion (Tibell & Rundgren, 2010); the latter is the focus of the present study.

Even though students commonly regard the human body as an interesting subject area, research has shown that understanding degradation of food and nutrient uptake poses challenges to students (Teixeira, 2000; Reiss & Tunnicliffe, 2001). Previous research based on interviews with students (Cakici, 2005; Rowlands, 2004) has revealed that students use metaphors to explain food digestion, potentially with mixed results. In his study, Cakici (2005) considered students’ use of metaphors as incorrect descriptions. In contrast, when interviewing 10-year-old students in two classes about their ideas of digestion and nutrition, Rowland (2004) introduced analogies to support students who initially appeared to find talking about those concepts challenging, supposedly because they did not want to risk answering incorrectly. Also, research concerning students’ meaning-making about chemical and biological processes in the human body indicate that students initially express themselves metaphorically, but later replace the metaphors with science terminology. For instance, studies have shown that students express that nutrients “jump” into organs and that receptors on the cell surface of molecules are described as “flags” (Olander et al., 2018; Rundgren, 2006). Olander and colleagues argue that the students’ use of “jump” is an example of a temporary expression that contributes to students’ further concept development. In contrast to previous studies focussing specifically on metaphors, which have often been based on interviews (e.g., Rundgren, 2006; Cakici, 2005; Rowland, 2004), in this study, we investigate how metaphors are developed in classroom interaction through a design that enables us to study how metaphors are developed from an animation used in classrooms, to whole class and small group discussions.

In the chemistry of the human body, organs, tissues, and cells, the relationship between structure and function is fundamental. Visual representations of these phenomena often aim to emphasize structural features with functional roles (Rundgren & Tibell, 2010). However, if students are unaware of this intent or the functions associated with visually represented phenomena, they may overlook the connection between structure and function. Metaphors, acting as a form of internal visualization (Danielsson & Selander, 2021), often relying on perceived structural similarities, such as comparing a large sports arena to the atom and its parts (Danielsson et al., 2018). Yet, metaphors can also be based on function, like describing noble gases as ‘content’ or ‘lazy’ due to their relative stability (ibid.). Thus, metaphors may aid students in making meaning not only about the structures but also the functions within human (or other organisms’) bodies.

Aim and Research Questions

The study aims to enhance the understanding of metaphors’ role in meaning-making within the upper primary science classroom. This will be achieved through an exploratory case study, investigating the potential of metaphors related to nutrient uptake in classrooms utilising an animation. Our specific research questions are as follows:

  1. 1.

    What aspects of the content are expressed metaphorically in the classroom interaction, including the animation?

  2. 2.

    How are metaphors established and transformed in the classroom interaction?

  3. 3.

    What characterises teaching in which metaphor use appears to be successful for students’ meaning-making about nutrient uptake?

Theoretical Framework

The present study is theoretically grounded in multimodal perspectives of social semiotics (Halliday, 1978, Jewitt et al., 2016). An important premise in such perspectives is that content and form are inseparable: the choice of resource, or ‘sign’ (Kress, 2010), such as lexicogrammatical choices and choice of gestures, also contribute to what content is possible to express. The choice of sign in social interaction is also regarded as tightly connected to the context, including historically developed conventions (e.g., science education), participants (e.g., grade 5 students), and available resources for meaning-making. Further, multimodal theories stress that all social interaction is multimodal and that meaning-making involves integrating multiple resources into a meaningful whole (Jewitt et al., 2016). Thus, in the present study, the analysed data derive from a variety of semiotic resources, such as speech, gestures, writing, and both still and moving images. When analysing the use of metaphors, we have considered all of these resources. Since metaphors are typically expressed through words, however, we have largely focused on speech and writing, while treating other resources as parts of ‘multimodal ensembles’ (Jewitt, 2011) in metaphoric reasoning, e.g., combinations of speech, image, gesture, and bodily action. It should be noted that in multimodal theories, ‘the whole’ in such ensembles is considered to be more than the sum of the parts (Jewitt et al., 2016: 39).

In the following analysis of students’ use of metaphors in classroom conversation and their texts, we sometimes refer to the concepts ‘transformation’ and ‘transduction’ (Bezemer & Kress, 2008; Kress, 2010). When content is converted within a certain semiotic mode, for instance when a drawn image is based on an image, this is referred to as transformation. In contrast, when a conversion is made between different semiotic modes, such as when an image is described in words, this is referred to as transduction. As commented on below, different semiotic modes have different affordances (Kress, 2010), so transductions always involve changes in the content expressed. We argue that since all social interaction is multimodal, a transduction process might involve a multimodal ensemble that is transduced into another multimodal ensemble, for instance transduction of spoken words and images into spoken words combined with gestures or bodily action. Use of metaphors can also be regarded as a kind of transduction, e.g., from words into a kind of inner visualisation. For instance, we cannot see how enzymes degrade molecules, but with the frequently used metaphor describing enzymes as “cutting” nutrients into smaller pieces, we can make that process visible to our inner eye.

The concept of affordance (Jewitt et al., 2016; Kress, 2010), mentioned above, concerns different resources’ potential for meaning-making. Regarding different semiotic modes, images are especially apt for showing spatial properties, e.g., relative size and position, while words are more apt for reasoning about causes and consequences. Such differences are connected to modal affordance (Jewitt et al., 2016, pp. 72ff). However, specific resources can also have different pedagogical affordances, that is “the aptness of a semiotic resource for teaching some educational content” (Airey & Eriksson, 2019, p. 99–100). In contrast to pedagogical affordances, disciplinary affordance concerns “the agreed meaning making functions that a semiotic resource fulfils for a particular disciplinary community” (Airey, 2015, p.103).

A specific visual representation, or disciplinary specific terminology, with high disciplinary affordance might have low pedagogical affordance in a science classroom. Hence, a statement such as “membrane proteins are substance specific” is an example of an expression with high disciplinary affordance (cf. Airey & Eriksson, 2019). Science teachers are aware that membrane proteins interact with specific substances. However, for students not yet familiar with the content, some kind of support might be needed to facilitate their meaning-making. Therefore, to contribute to students’ meaning-making, teachers need to choose appropriate resources with high pedagogical affordance for the specific students. A well-chosen metaphor can serve as such a resource, while other metaphors may not be functional for the given content or the specific student group. Consequently, different metaphors are presumed to have varying potentials as pedagogical resources when students engage in meaning-making about nutrient uptake.

To identify metaphors in the classroom interaction, we employed an analysis according to systemic-functional grammar (SFG) (Halliday & Matthiessen, 2014), grounded in social semiotic theory. SFG-analysis can involve analysis of verbal utterances (or visual representations) according to three so-called metafunctions. These are: ideational (how we construct and represent our ideas and experiences of the world), interpersonal (through which we enact our relationship and stance with others and our experiences), and textual (how we organise and connect parts of a textFootnote 1 into a coherent whole). The analysis conducted in this study focuses on the ideational metafunction, specifically employing transitivity analysis, as elaborated in greater detail in the Analytical Procedures section below.

Methods

This section describes: the data collection methods, the context of the study, and the animation used by the teacher as an introduction to the subject content; the teaching and learning sessions we followed; and the applied analytical procedures.

Data and Context

Data were collected by the first author in three mixed gender grade 5 (age 10–11) classes in a school located in a medium-sized municipality in Sweden. They all had the same teacher, specialised in science for upper primary school. The language of instruction was Swedish. The teacher was not asked to use metaphors, nor did she know that the study would focus on metaphorical expressions. We followed teaching and learning sessions on the theme of digestion and nutrition, which is part of a larger theme in the learning resource NTA-digitalFootnote 2 called ‘the human body’ which in turn consists of a digital platform with an interactive, three-dimensional model of the human body with integrated factual content and several animations (Fig. 1). The animation presenting nutrient uptake is eight minutes long with a narration commenting on and explaining the visual images. It is non-interactive, serving as a short movie to illustrate biological processes and concepts.

Fig. 1
figure 1

Screenshot from the digital platform NTA-digital about digestion and nutrition

Full size image

We followed two lessons in each of the three classes. The data collected included the animation, video recordings of the teacher’s whole class reviews, the students’ group discussions and the multimodal texts they created in connection to their group discussions. The design of the lesson was similar in all three classrooms. The teacher started by showing the animation, which encompasses three main areas or aspects of nutrient uptake: (i) the surface enlargement of the small intestine, (ii) the cell membrane and the function of membrane proteins, and (iii) enzymes. The students watched the animation in the whole class. Afterward, the teacher explained six concepts (nutrient, villi, microvilli, amino acids, enzymes, cell membranes) that she had written on the whiteboard. She then asked the students to tell her what they remembered about these concepts from the animation, and she also developed their answers. She then divided the class into groups of 2–4 students, who discussed the concepts and created multimodal text to describe how nutrients from food can be distributed to all the cells in the body.

We transcribed the narration of the animation and the conversations between the students and the teacher. The quotations in the results section have been adjusted to writing conventions and translated by the authors from Swedish into English. This was done with an aim to preserve linguistic choices in Swedish, sometimes resulting in unidiomatic English expressions. Omitted parts of the quotations are marked with slashes and dots (/…/). The study adheres to the ethical guidelines formulated by the Swedish Research Council (2017) regarding, e.g., informed consent, the right to withdraw from the study without giving a reason, and participants’ anonymity. To ensure the participants’ anonymity, the teacher is called ‘the teacher’, the three classes are referred to as Class 1, 2, and 3, and students have been given fictitious names. There were significant similarities between the classes regarding metaphor use and activities, and examples in the results section are taken from all of them.

Analytical Procedures

Identifying metaphors in educational discourse poses numerous challenges (Cameron, 2002), and various approaches can be employed. Consistent with one of our prior studies (Jahic Pettersson et al., 2020), we utilized transitivity analysis, a method linked to the ideational metafunction in SFG (Halliday & Matthiessen, 2014). The procedure is outlined in more depth in Jahic Pettersson et al. (2020). Here, we provide an overview.

Transitivity analysis concerns the identification of three main linguistic constituents in a clause, with different functional roles: processes, participants, and circumstances. The identification of the process (corresponding to ‘verb’ in traditional grammar) is the starting point. The following process types are identified: material, verbal, mental, and relational.Footnote 3,Footnote 4 Depending on process type (bold), the participants in processes take on different roles. The main participant (italicised) in material processes has the role of an Actor, who performs an action (“the enzymes cut the nutrients”)Footnote 5. In mental processes, the main participant has the role of a Senser who thinks or feels something (“the body feels exhausted”) and for verbal processes, the main participant has the role of a Sayer who says something (“the brain tells the body what to do”). Relational processes are of another type. Through them, participants are related to one another, for instance as carrier and attribute (“The cells are satisfied”). The processes can be described in terms of circumstances (underlined), such as time, manner, and place (“Different nutrients passthrough different gates”). As our examples indicate, all of these functions may be part of metaphoric reasoning:

  1. 1)

    Metaphors building on process types that imply anthropomorphisms (expressions that attribute human characteristics to non-human entities), such as material doing processes and mental processes, with organs or chemical entities involved in nutrition being acting or sensing participants;

  2. 2)

    Metaphors where participants such as organs are substituted with concepts from everyday life or other domains (e.g. microvilli being substituted by ‘lint’), or circumstances of the same type;

  3. 3)

    Metaphors building on relational processes where participants such as organs are given attributes or identified as a concept taken from everyday life, or vice versa.

In contrast to our previous study (Jahic Pettersson et al., 2020), we do not focus here on students’ use of scientific expressions with a metaphoric origin, such as “cell”, or less obvious metaphors for which there is no scientific term that could replace them, such as “pass through”, “transport”, etc. After identifying metaphors in the data, they were categorised as structural or functional and the transformations and transductions that the metaphors were subject to were tracked. Further, we related the way the students used different metaphors concerning the science content and the metaphors’ potential to describe the content adequately. Furthermore, we evaluated whether a certain metaphor (structural or functional) used by the students led to adequate explanations in relation to the science content or not, hence, whether the metaphor was successful or not.

Results

In the following, the first research question is answered by giving an overview of the subject content described metaphorically in the animation and in the classroom interaction. The second research question is answered by describing how metaphors were established and transformed in the classroom interaction. Finally, the third research question, what characterises metaphors that appear to be successful in students’ meaning-making of nutrient uptake, is answered, mainly with focus on structural and functional similarity.

Before delving into the results related to the specific research questions, we provide an overview of the occurrence of metaphoric expressions used in the classrooms (Table 1). Notably, it is interesting to observe that the students employed a greater number of functional metaphors during their group work compared to the instances in the whole-class setting, despite the overall similarity in the total number of metaphoric expressions uttered by the students in both contexts.

Table 1 Cumulative use of metaphoric expressions in the three classes (whole class and small group work including student texts) and in the animation. The metaphoric expressions are classified as either structural or functional
Full size table

Structural metaphors were often part of expressions with a relational process connecting two participants where one was a scientific concept (or a pronoun referring to a previously mentioned scientific concept) and the other was an everyday word. Examples are “microvilli was dust on dust” and “the small intestine is like a fluffy carpet”, where the latter example makes the metaphoric expression explicit (“is like”), while the former identifies the science concept, microvilli, as an everyday object, dust, hence resulting in an implicit metaphor.

Functional metaphors were often parts of expressions with a material process with a participant in the form of a scientific concept which had the function of an Actor. This usually led to anthropomorphisms, in examples like “the enzymes cut the food”. Occasionally, functional metaphors were introduced similarly to structural metaphors, where a relational process linked a scientific concept with an everyday word, such as “the enzymes are like scissors”. A recurring subtype of functional metaphor involved dramatisations based on material processes with participants represented by scientific concepts (e.g., enzymes), doing things like knocking on doors, resulting in anthropomorphisms.

Content Expressed Metaphorically in the Animation and in Classroom Interaction

Three central aspects of the subject content were addressed by use of metaphors in the teaching and learning activities, including the animation: (i) the surface enlargement of the small intestine, (ii) the cell membrane and the function of membrane proteins, and (iii) enzymes. This was done both in the animation and in the classroom interaction. In the animation, the function of membrane proteins was highlighted as a crucial aspect of nutrient uptake. Furthermore, the spoken narration of the animation includes several metaphors while none of the images are metaphorical.

The surface enlargement of the small intestine was described metaphorically in terms of a carpet, for instance when the narrative voice in the animation talks about “a velvet-soft, moist and brown-pink fuzzy carpet” while showing a zoom-in of the small intestine showing villi, or when the teacher talked about ‘carpet’ in the classroom interaction. This metaphor highlights a structural similarity between the source (carpet) and the target (enlargement of the small intestine) based on the fact that the surface of the small intestine is full of small folds or protrusions called villi (tarmludd in Swedish). However, the metaphor has potential to also be developed into a metaphor based on function, as the structure of the small intestine results in the vital surface enlargement.

Few metaphors were used to describe the structure of the cell membrane. In the animation, the proteins are described in much more detail than the cell membrane, probably due to their key role in nutrient uptake, which is also the focal process of the animation. When describing the cell membrane in the animation, metaphors were mainly used to describe the function of membrane proteins. One example is when the narrator, using an anthropomorphism, comments that the cell membrane is made of fat molecules but that “fat and water do not get along together”, which relates to the characteristics (consisting of water soluble ‘heads’ pointing outwards and fat soluble ‘tails’ pointing inwards) of phospholipids. When discussing in whole-class, the students used the metaphor cotton swabs to describe the structure of those molecules. The membrane proteins were described, e.g., in terms of lumps, channels, tolls, doors, and further metaphors based on these. Taken together, membrane proteins were talked about through a great number of metaphors, both based on structural (e.g., lumps) and functional (e.g., tolls, doors) similarity. More examples are given in the next section.

Enzymes were described metaphorically in the animation, by the teacher and by the students in the classroom interaction. All of these metaphors were based on function. When the narrative voice in the animation describes the enzymes’ function, such as degrading substances, enzymes are repeatedly compared with scissors. For instance, the chemical decomposition in the stomach is explained as partly dependent on hydrochloric acid and partly on digestive enzymes “that function as tiny, tiny scissors that gradually cut the molecules in the food into smaller and smaller pieces.” In the classroom interaction, ‘cut’ and ‘scissors’ were also used to describe the function of enzymes, both between the teacher and the students, and between students.

Furthermore, some metaphors were used for other aspects of the content than the three central aspects mentioned above. For example, when fatty acid molecules were described in terms of French fries (see below), or when the microvilli were described in terms of a dust bunny. Both of these are based on structural similarity and they did not lead to discussions connected to function.

Establishment and Transformations of Metaphors in the Classroom Interaction

In the classroom interaction, both the teacher and the students re-used or developed metaphors from the animation, and they also introduced and developed new metaphors. A number of metaphors from the animation were picked up by the teacher in whole class discussions, such as the carpet metaphor for the cell membrane based on structure, and the scissors and cutting metaphors for the function of enzymes:

Teacher: Enzyme, that was what they said were like scissors.

Student: The scissors cut the food.

Teacher: Yes, because when we eat a hamburger this hamburger doesn’t get into the blood /…/ but we eat the hamburger to get all the nutrients and then the body needs to cut it into pieces.

However, other metaphors were introduced by the teacher or by students, often on the basis of the metaphors mentioned in the narration or on the appearance of phenomena visualised in the animation. One example was when a student related the fatty acid molecules to “French fries” based on the visual appearance of these molecules in the animation (see Fig. 1), hence a metaphor based on structural similarity. At times a metaphor led to chains of new metaphors, as when the teacher connected the metaphors to chemical and biological structures and processes, unpacking or further concretising them through gestures, dramatisation, and so on.

Metaphorical expressions combined with gestures can be a way to discuss and explain abstract processes with a focus on creating meaning about the functions that take place in the processes, in this case concerning nutrient absorption. The structural metaphors used in the classroom can be regarded as potential steps to making connections to functional metaphors that actually relate to the chemical/biological processes taking place. In the following, we give some illustrating examples, focusing in particular on a chain of metaphors that were all linked to the carpet metaphor for the surface enlargement of the small intestine. The reason for this choice is that the carpet metaphor, based on structural similarity, gave rise to a chain of metaphors connected not only to the surface enlargement of the small intestine, but also to the function of membrane proteins.

As mentioned, in the animation, the carpet metaphor is used for highlighting structural similarity between the cell membrane and a fluffy carpet. It was re-used and developed in all three classes by both the teacher and the students. Based on this metaphor, a student in Class 1 introduced the metaphor “cotton swabs” in relation to the phospholipids of the cell membrane, since he thought that the cell membrane in the animation looked like cotton swabs (Fig. 2, right image), hence another metaphor based on structural similarity. When he had commented that the cell membrane looked like cotton swabs, the teacher took up the metaphor, also focusing on structural similarity. She referred to an image of membrane proteins taken from the animation that she had projected on the whiteboard combining spoken words with gestures (Fig. 2, top images), hence, an example of a transduction of a spoken metaphor into a multimodal ensemble:

Teacher: Exactly, yes, they do look a bit like cotton swabs, exactly, that they are sort of small (points at the projected image) … a long thing in the middle and then two tops at the ends, great! (visualises the top and bottom of cotton swabs with iconic gestures) (whole class discussion, Class 1).

Fig. 2
figure 2

Top images: The teacher refers to an image of phospholipids from the animation connecting to the cotton swab metaphor in spoken words and gestures. Bottom images (left): The teacher explains with spoken words and gestures how the cell membrane lets through different substances. Class 1

Full size image

She then continued by reconnecting to the “black lumps” in the depiction of membrane proteins in the animation (right image, Fig. 2) that another student in the class had mentioned. When doing so, she also introduced a metaphor based on functional similarity to the target: “the thing that you said is black is like a gate, you can say”. She verbalised what was seen in the picture/animation i.e., the black lumps, and explained their function using a gate as a functional metaphor. She also said that there is a specific gate that just lets through proteins and a gate for fat and sugar, moving her hands up and down (bottom images, Fig. 2). This is an example of a successful metaphor since it also led to a student’s introduction of another metaphor based on functional similarity to the target, namely, a ‘toll barrier’:

Student: the cell membrane was probably the thing made of fat molecules, the protein which only lets sugar through like a toll barrier.

Teacher: Like a toll barrier, yes! Yes, exactly, or as a door that you must have the key to. (whole class discussion, Class 1)

In this case, the function of the cell membrane (to be correct, membrane proteins) was expressed by the student in terms of a toll barrier. The teacher further connected that metaphor to a door, dramatising the membrane proteins’ function by knocking on students’ desks while anthropomorphically giving the students the roles of different membrane proteins. The students subsequently used several metaphoric expressions to describe this specificity, such as ‘VIP members.’ The dramatisation as a whole functioned as metaphoric reasoning in a multimodal orchestration, with several metaphors based on functional similarity uttered verbally, combined with bodily action. As demonstrated in the following interaction, the dramatisation, coupled with metaphoric reasoning based on function, appears to effectively elucidate the specificity of membrane proteins:

Teacher: If I was one of those sugars and I came to Tina, who lets through fat for example, if I go there and knock, can I come in then?

Students: No!

Teacher: No, I have to go to the one who’s for sugar, who’s sitting here (goes to another student) and then I knock, can I come in?

Students: Yes.

Students: You must be a VIP member!

Teacher: Yes, I have to be a VIP member for exactly the protein I usually run into, quite right! (whole class discussion, Class 1)

Later, the teacher re-used the cotton swab metaphor in the two other classrooms, mentioning that a student had thought that the cell membrane in the animation looked like cotton swabs. She also did similar dramatisations of the specialisation of membrane proteins in the other classrooms, hence going from the metaphor based on structural similarity to a chain of metaphors based on functional similarity.

Metaphors introduced in the animation or in whole class discussions were at times transformed into and further developed in the small group discussions. One such example was the gate metaphor to talk about the function of membrane proteins. One student group developed this metaphor in their reasoning about the function of membrane proteins in terms of doors or gates that only allow entry of specific kinds of people or animals:

Imagine as you said a gate or a door. In this door or gate there is a wall where only one kind of person enters, if another person comes and sneaks behind, then they don’t open the doors. Hey, they are geniuses /…/ Here is one and here and here /…/ Sheep can only go in there and elephants there /…/ they can’t sneak in a sheep with the giraffe, then you would notice it (small group discussion, Class 1).

Another student group combined the door metaphor with scientific terminology:

It was like doors as [teacher name] said … Sugar molecules /…/ come through these doors /…/ The membrane proteins open the doors, sugar molecules enter here maybe, fat molecules enter through this one, so everyone enters different [doors]. (small group discussion, Class 2)

The channel metaphor given in the animation was also transformed and used in a small group discussion, in this case connecting that metaphor to two new metaphors, tunnel and gate, to describe the function of membrane proteins:

Through those tunnels, there were like gates and these gates they can only let in one kind, here we have one gate for water and one gate for fat, one for sugar (small group discussion, Class 1).

The scissors metaphor for the function of enzymes that the teacher picked up from the animation was not further developed into new metaphors, like the ones for membrane proteins. However, in one small group discussion, a student transduced this metaphor into a multimodal ensemble while referring to an image of enzymes from the animation. He then made an iconic gesture with his index and middle fingers to mimic scissors cutting, at the same time as he commented in words: “An enzyme is the one that cuts the food”.

The cotton swab metaphor was also later transformed into students’ small group discussions, and in a number of cases it was also transduced into images in group texts. An interesting finding is that the metaphor appears to have affected students’ drawings since in some of the drawings, the membrane proteins looked more like cotton swabs than they did in the animation. Examples include the drawing in Fig. 3, produced by one of the student groups.

Fig. 3
figure 3

Student texts from Class 3

Full size image

Characteristics of Metaphors that Appear to be Successful in Students’ Meaning-making of Nutrient Uptake

As mentioned, we consider metaphors to be successful in classroom interaction when they are used to explain nutrient uptake adequately. A general pattern that we noted was that metaphors that were successful for such explanations were characterised by being based on functional rather than structural similarity with the target domain. Interestingly, the structural metaphors were more common in the whole class discussion with the teacher, while the functional metaphors were more common in the students’ small group discussions (see Table 1), where the students were supposed to explain the content. In the following, we revisit some of the examples given above to illustrate the finding that metaphors based on function appear to be more successful than those based on structural similarity. Successful metaphors were predominantly found in regard to the specialisation of the membrane proteins. Successful metaphors were also found in conjunction with the function of enzymes.

Examples of discussions containing successful metaphors in the classroom interaction are for instance when membrane proteins were talked about in terms of ‘doors’, ‘gates’ and ‘channel’, which are all based on function. They gave rise to both whole-class and small-group discussions focussing on the chemical and biological function of membrane proteins. The subject specific term, ‘membrane proteins’ is not mentioned explicitly, though the metaphors building on function seem to be successful in students’ meaning-making about membrane proteins: “they open the doors, sugar molecules enter here maybe, fat molecules enter through this one, so everyone enters different [doors].” In this way, the concept of membrane proteins and their function is unpacked through metaphors connected to everyday experiences.

In general, students predominantly employed metaphoric reasoning rooted in everyday experiences to elucidate the transfer of various nutrient molecules through specific membrane proteins. They conceptualised this process by envisioning a gate or door within the cell membrane, allowing only a particular type of person or animal to enter. Their descriptions suggested that attempting to sneak in someone else would result in the doors remaining closed. Within their reasoning, students demonstrated a capacity for meaning making related to the intricate scientific concept of ‘substance-specific membrane proteins,’ articulating the functions of these proteins through accessible everyday metaphors.

During a group discussion, one student, using a paused animation displayed on a tablet, pointed to different membrane proteins, stating, “Here is one, and another here.” Simultaneously, other students exemplified which entities could enter through various membrane proteins, pointing and elaborating, “Sheep can only go in there, and elephants there /…/ it is not possible to sneak in a sheep with the giraffe; then you would notice it.” In summary, the findings suggest that metaphors can effectively support students in constructing scientific meaning, even in the absence of explicit use of scientific terminology.

Discussion

Previous studies have shown that metaphors can play an important role in increasing the accessibility of abstract knowledge for students in science classrooms (e.g., Aubusson et al., 2006; Rundgren, 2006). Research has also pointed to students’ challenges in understanding processes at cellular and sub-cellular levels, especially when connecting these organisational levels (e.g., Jahic Pettersson et al., 2022). This study indicates that teachers can support students to talk about these processes by using metaphors in a creative way, through a teaching design highlighting key functional aspects, and fostering a classroom environment in which students feel allowed to use expressions other than science terminology. The study gives a special contribution to the field of how metaphors are developed in the classroom through the design of the study, which enabled us to study how the metaphors were developed from the animation through the discussion in the whole class with teacher and students together and in the end to the group discussions. Other studies (e.g., Cakici, 2005; Rowlands, 2004) about children’s use of metaphors in relation to food digestion have been based on interviews, while the data collected for the present study derives from one teacher’s regular teaching. Further, in contrast to Cakici’s (2005) interpretation of students’ metaphorical expressions, we claim that students participating in our study often gave scientifically valid descriptions of digestive processes by using metaphors. Another important contribution of the study, through the application of the SFG-analysis, is the characterisation of metaphors based on structural and functional similarity respectively. Moreover, the result from our study also implies that if metaphors are to be functional tools for meaning making in science education, the teacher has an important role to play in (i) choosing relevant metaphors, (ii) developing metaphorical reasoning in relevant ways, and (iii) explicitly connecting the metaphors to scientific concepts.

Metaphors relating to the function of membrane proteins dominated in the classroom discussion. The reasons for this could relate to this being a central focus in the animation. Furthermore, the teacher made this content into a teaching focus through her dramatisation, hence transducing the content from speech into multimodal orchestration. In addition to this, the function of membrane proteins can be regarded as an example of a process connecting different organisational levels, which has been characterised as both especially challenging to grasp, and, simultaneously, central to understanding nutrient uptake (Jahic Pettersson et al., 2022). The results show that the number of metaphors used are increased from the animation to the whole class discussions and to the group discussions. A sign of the success of the teaching is that in their small group discussions, the students use a larger number of functional metaphors related to adequate descriptions of central processes, mainly the specificity of membrane proteins. Furthermore, we did not identify any metaphors in this study which were misleading for the students’ understanding, which has been noted in other studies (e.g., Haglund, 2013; Danielsson et al., 2018).

In this study, the teacher specifically utilised functional metaphors to elucidate related processes, making metaphorical expressions a shared semiotic resource with distinct pedagogical affordances (Airey & Eriksson, 2019; Jahic Pettersson et al., 2022). Metaphorical expressions facilitated the exploration of processes involving different organisational levels. By linking biomolecular processes, such as cell membrane transport, to familiar scenarios like knocking on doors, the teacher bridged everyday language and experiences with complex disciplinary concepts. The use of metaphors, coupled with dramatisation and bodily engagement, likely contributed to students employing functional metaphors in their meaning making about processes related to nutrient uptake.

When students proposed metaphors like ‘passing through a toll barrier,’ the teacher validated these expressions as legitimate ways to convey content. Students expanded on these metaphors by relating different molecules to VIP members or various animals, illustrating the flexibility of metaphorical language in expressing scientific concepts. Taken together, in this study, the teacher effectively rendered scientific concepts accessible to students through metaphors, integrating them into the broader pool of semiotic resources for shared meaning making in the classroom (cf. Jewitt, 2008).

Figure 4 presents a model applying metaphorical expressions to Airey and Eriksson’s (2019) framework regarding resources’ disciplinary and pedagogical affordances. Our application of the model illustrates how metaphorical expressions can serve as bridges between everyday language and intricate disciplinary terms (depicted as a double-headed arrow on the right side of Fig. 4). Notable examples, such as using ‘doors’ or ‘gates’ as metaphors for membrane proteins, highlight the pedagogical affordance of these metaphors. They specify the meaning making of membrane proteins in a way that the term alone might not do.

Fig. 4
figure 4

The affordances of metaphorical expressions (developed from Airey & Eriksson, 2019). The arrow indicates the important role of the teacher in supporting students from using everyday expressions to the use of disciplinary terms when using metaphorical expressions as a stepping stone

Full size image

Researchers have previously promoted teachers’ movement between everyday language and scientific terminology as a way of supporting students’ meaning making in science (e.g., Nygård Larsson, 2018). Consistent with this perspective, we propose that supporting students in utilising complex disciplinary terms can be facilitated by employing metaphorical expressions as stepping stones (see the double-headed arrow, Fig. 4). In the observed classrooms, the teacher consistently initiated discussions by introducing a scientific term and then regularly utilised metaphors as explanatory tools, representing a movement from the upper left corner to the lower right in Fig. 4. Conversely, movements from metaphors to scientific terms were infrequent. Despite this, students in these classrooms demonstrated a clear understanding of the content. Notably, the previously mentioned metaphors for membrane proteins, initiated through dramatisations, proved effective in fostering students’ meaning-making. A logical progression could involve “making an upwards tour” along the double-headed arrow in Fig. 4, allowing students access to and utilisation of the language specific to the discipline.

So far, we have highlighted functional metaphors for their potential to be successful. Initially in the animation and in the classroom interaction, some metaphors relied on structural similarities, such as comparing the small intestine to a fluffy carpet. This metaphor was subsequently expanded to establish a connection to function, as the ’fluff’ on the inner surface of the intestine, when understood, served as a starting point for discussing the role of microvilli in nutrient uptake. However, the explicit link between structure and function was not emphasised in the classroom, so the potential of that structural metaphor was not fully utilised.

Similarly, the pedagogical potential of the cotton swabs metaphor, which could aid in understanding the relationship between the function of phospholipids (the main constituents of the cell membrane) and their structure (comprising fat-soluble ‘tails’ and water-soluble ‘heads), went untapped by both students and the teacher, as well as in the animation. However, despite not explicitly connecting structure to function, the teacher utilised the cotton swab metaphor as a foundation to introduce the previously mentioned ‘gate’ metaphor, emphasising functional similarity. Subsequently, she employed dramatisation to elucidate the function of membrane proteins, likening it to knocking on ‘different gates.’ Based on the results of the present study, we suggest that this kind of transformation of metaphors based on structural similarity into functional similarity could serve as a valuable tool for enhancing meaning making in science education.

Implications for science education

The present study underscores the significant role of metaphorical expressions in scientific meaning making, allowing students and teachers to grasp scientific processes and functions before delving into specific terminology. Moreover, certain metaphors explicitly articulate functions that scientific terms might not encapsulate, such as using ‘tolls’ or ‘gates’ to represent membrane proteins. Therefore, metaphors serve as a crucial bridge or stepping stone toward utilising the language specific for the discipline, including the scientific vocabulary. However, for this facilitation to occur, teachers must carefully guide and discuss with the students regarding the choice of metaphors with the potential to elucidate scientific content.

In this study, a notable example is the metaphorical depiction of ‘gates’ allowing, for instance, elephants but not giraffes, symbolising substance-specific membrane proteins. We posit that metaphors grounded in functional similarity offer a valuable affordance for comprehending intricate processes like nutrient uptake. In contrast, metaphors based on structural similarity lack the same pedagogical affordance but can serve as initial points for teachers to highlight structural similarities before linking them to potential functional similarities (Rundgren & Tibell, 2010).

Additionally, teachers may find it beneficial to explicitly discuss metaphors and their affordances, aligning them with various aspects of the content to enhance students’ meaning making. By seamlessly connecting metaphors to scientific expressions, teachers can provide students with gradual opportunities to use the special language of the discipline including its terminology. To further support this transition, teachers may need to navigate between everyday language and the corresponding scientific terms.