Digestion - Children's understanding of what happens to the food that they eat

 Featured article

Teixeira, F. (2000). What happens to the food we eat? Children’s conceptions of the structure and function of the digestive system. International Journal of Science Education, 22 (5), pp.507–520

The children (aged 4 to 10) taking part in this study were each given a bar of chocolate and an outline, on paper, of a human body. They were asked to eat the chocolate and draw on the paper the parts of the body this food will pass through. The children were then asked to name any organs that they had drawn and to describe what happened to the food as it passed through each organ. They were also asked what the food would look like at each stage.

[AI generated impression of a child's drawing]

The study took place a private primary school in Brazil and the paper specifies that none of the children had had formal education about the digestive system. Clearly the outcomes may be different for children who have received scientific teaching about this during their primary years. However, the approach taken by the researcher and the outcomes still provoke some interesting questions about what children understand about what happens inside their bodies and how they build these ideas based on daily experiences.

The researcher analysed children’s drawings and explanations in terms of understanding of both structure and function. Clearly biologically these are linked as the structures inside the body all have a function. However, this distinction was designed to find out how much the children understood about the internal structure of their own bodies and how much awareness they had about the function of these parts.

The researchers categorised the responses based on three different broad ways of thinking about the path of food through the body:

1.  All food that has been ingested (eaten) remains in the body.

2. All the food that has been ingested eventually leaves the body.

3. Part of what has been ingested stays in the body but the rest leaves.

Broadly speaking number 1 was the predominant way of thinking of the four-year-olds in the study, number 2 was the more common thought process of the 6- to 8-year-olds and only for the oldest children (age 10) was number 3 the majority view.

At age four the most commonly used body part name was “tummy”. For children aged 4, 11% of children left the abdominal area in the drawing as empty space. The authors later comment that for a child that thinks all their food remains in the body this is not unexpected. There is no need for any other structures or compartments because the body is perceived as being simply a container. Interestingly for some of these children the only way food could leave their tummy was through moving down into their legs (or their arms if they bended). It was even suggested that the accumulation of food results in a stretching of the body. The children were aware (probably due to experience of chewing) that the food was broken into smaller pieces.

The children who thought that all the food that has been ingested leaves the body appeared to have some concept of physical change to the food but did not give any evidence of awareness that the identity of the food changed.

The oldest children showed some awareness of the limitations of the body realising that the body cannot absorb everything that is ingested. They also appeared to have some awareness of the idea that parts of food that are useful to the body are kept inside but other parts, which are not useful, leave the body.

Only six children (all older than 8) indicated that there maybe substances in the body that could modify others. This enabled them to conceive of the possibility that ingested food could be changed into something different to what it was. The idea of chemical transformation (change) was noted to be a complex one but difficulty with the idea was acknowledged to limit children’s explanations of the function of the digestive system.

Reflective questions

Primary (age 5-11)

The research suggests that even young children form ideas about what happens to the food they eat. What everyday discussion about food and eating may influence children’s reasoning?

e.g. An adult asking, “Is your tummy full?”

In what ways could the researcher’s approach of asking children to draw and then discuss what they think is inside their bodies be used in the classroom? How could the idea be extended to other topics?

What explanation of what happens to food when you eat do you think is acceptable for children aged 10 to 11 and what should be left for later learning?

Secondary (age 11-16)

In what ways could the researcher’s approach of asking the children to draw and discuss what they think is inside of them be used in a secondary context?

What chemistry learning is needed to support the development of biological understanding about digestion?

To what extent/ how do you build connections between the two subjects in your teaching?

 

 

The particle model

Featured article

Johnson, P. (1998). Progression in children’s understanding of a ‘basic’ particle theory: A longitudinal study. International Journal of Science Education, 20 (4), pp.393–412.

Very often students will get asked to label a particle diagram or to draw the particle diagram for a given state, however this paper suggests that even if answering ‘correctly’ students may hold a range of misconceptions.

The particle model under discussion in this paper is described as a model with sufficient detail to account for the characteristic properties of the three states of matter. It is not, the author specifies, a model that distinguishes between the types of particle (atoms, molecules and ions). 

The author summarises the common findings of the existing literature about student understanding of the particle model, identifying five areas of difficulty:

1. The relative spacing between particles in the three states.

Showing the spacing between particles in the liquid state as intermediate between the solid and gas states.Typical diagrams for the gas state underrepresent the relative spacing of particles.

2. The intrinsic motion of particles

Many students showed little appreciation of the intrinsic motion of particles.

3. Ideas of forces of attraction between particles

Very few students used the idea of forces of attraction between particles.

4. The ‘space’ between particles

The idea that there is ‘nothing’ between particles seemed to cause a lot of difficulties for students. Some preferred to think that something must be there (often referring to this as ‘air’).

5. The nature of the particles themselves

Many students were found to give particles the same properties as the bulk material. For example, a copper atom was thought to have the same properties as copper metal.

The paper reports on a three-year longitudinal study following a cohort of pupils in a non-selective English secondary school as they moved from year 7-9 (ages 11 to14). Students were periodically interviewed following teaching of four planned unit designed to develop the idea of a chemical substance.

The responses were used to identify four distinct particle models held by the students.

Model X: Substances are continuous (and not made of particles).

Model A: Particles are found in the continuous substance.

Model B: Particles are the substances, but with the macroscopic character of the bulk substance.

Model C: Particles are the substance and the properties of the substance in a given state are a collective property of those particles.

The interview questions enabled the author to identify the model of thinking held by students at the time of the interview. Whilst there were some students were inconsistent and applied different models in different circumstances, the majority had complete models of either X, A, B or C. This method of categorisation enabled the author to explore how student thinking about the particle model changed over time.

In general, many students were found to progress in the model that they were using. The author identified two different ‘dimensions’ of this progression: a continuous to particulate dimension and a macroscopic to collective properties dimension.

BEST Diagnostic question

Imagine you could see the particles in a jar of methane gas.

Which diagram best matches what you would see?

 

The correct answer is C.

Reflective questions

When teaching the particle model, do you teach what is between the particles? How do/could you explain the concept of ‘nothing’ to students?

It is not uncommon to refer to the ‘particles in a solid’. To what extend could this language reinforce existing misconceptions and how could the language be changed to avoid this?

An atom is often defined as ‘the smallest particle of an element’. To what extent could that reinforce earlier misconceptions about the particle model? How could this be mitigated?

Useful links

BEST Topic 1 Key concept 1: Particle model for the solid, liquid and gas states

Diagnostic questions to check for student misconceptions about the particle model as part of a five-part progression (and including response activities)

University of York Science Education Group

Developing understanding: States of matter

A ramped student worksheet that aims to help students to deepen their understanding of the particle model and to strengthen their mental models.

Royal Society of Chemistry

Acknowledgements

The example BEST diagnostic question was developed by Helen Harden (UYSEG), from an idea by Andrew Hunt selected from a collection of ASK items devised for research by Philip Johnson (Durham University).

The particle model image is from the RSC Johnstone's Triangle Resource: States of Matter

 

 

 

 

 

Compounds: The importance of emergent thinking

 

Featured article

Talanquer, V. (2008). Students’ predictions about the sensory properties of chemical compounds: Additive versus emergent frameworks. In: Science Education. 92 (1). January 2008. pp.96–114.

This research investigated the reasoning used by students to predict the properties (colour, smell or taste) of the compound formed from the reaction of two substances, each with their own given properties. 

The opening of the paper introduces the idea of "commonsense reasoning" that can result in naïve explanations by novice learners.  The author shares findings from the research literature relating to the use of this “intuitive thinking”. It is suggested that an intuitive thinker is more likely to create an explanation based on a single mechanistic cause that produces a linear progression of events.

This study was carried out in the U.S. with over 400 students in their first year of a general introductory chemistry course for science and engineering majors. These first-year student participants were still regarded as “novices” for the purposes of the study.

The focus of the study was on the properties of compounds and so it is still potentially highly relevant to those teaching younger students as the properties of elements and compounds commonly features in the school chemistry curriculum for students aged 11 to 14. 

The paper describes one way of reasoning about the predicted properties of a compound (from given information on the properties of the reacting substances) as an additive framework. Using this framework, the properties of a compound are thought of as a linear combination of the original properties of each component.

This is to be contrasted with the use of emergent framework of thinking in which the properties of a complex system result from an interaction of its parts. This is the framework of thinking that should be applied to the properties of compounds. The properties of a compound arise (or "emerge") from the arrangement of atoms (or ions) and not from the addition of the properties of the substances from which it is formed. 

The author devised a series of questionnaires using multiple choice questions and black and white particle diagrams. The questions asked students to select the answer that best predicted the colour, taste or smell of the compound resulting from a reaction between the two substances depicted. Some students also took part in follow-up interviews to determine the reasons for their answers.

The researchers used a range of examples in the multiple-choice questionnaires including:

• varied ratios of reacting substance particles
• different sizes of reacting substance particles
• reacting substances with no property (e.g. no colour)
• the answer options of “other” and “more information needed to make a prediction”

A student who was confident in using an emergent framework for their thinking would be expected to consistently answer “other” or “more information needed” across all questions.

Less than 3% of students were found to consistently respond in this way.

In the initial question in which a blue substance reacted with a yellow substance with a 1:1 ratio of particles, 90.4% of participants selected the answer “green” as being the property of the final compound.  This suggests that the vast majority of students in the study were applying additive rather than emergent thinking.

The questions which included a non 1:1 ratio of reacting substance particles provided further evidence of this additive thinking. In a similar question to above (but with a 4:1 ratio of particles), 79.6% of students answered blue (rather than green).

The interviews revealed that even when some students did select “other” it was not necessarily due to emergent thinking. Sometimes students said that there was a need for more information on the “dominance” of a particular property. For example, if a blue substance reacted with yellow substance (in a 1:1 ratio of particles) might the blue dominate over the yellow rather than answering “green”?

If additive thinking is indeed present in other educational contexts, then this raises questions about the teaching of this topic. The reflective questions below raise some points to consider about the way in which this topic is commonly taught which could inadvertently encourage additive thinking.

The final recommendation of the author of the paper is that “helping students recognise the existence of emergent properties in chemical systems is crucical if we want them to develop meaningful understandings of a variety of topics”. This  raises questions regarding curriculum priorities and the importance of getting the earlier years (age 11-4) right to provide a sound foundation for later chemistry learning.

BEST Question

A compound Is made up of a combination of atoms from a blue substance and a yellow substance.

What colour is the compound?

A blue

B yellow

C green

D other

The expected answer is D "other". 

The colour of the compound is not related to the colour of substances made from its constituent atoms. This information is not sufficient to predict the colour of the compound.

Students who are using an additive approach are likely to predict that the compound is green (option C). A prediction of blue (option A) may mean that the student thinks that a darker colour may overwhelm the yellow.

Useful links

BEST Topic 2 Key concept 1: Atoms and molecules

Diagnostic questions to check for student misconceptions about the atomic model as part of a five-part progression (and including response activities)

University of York Science Education Group

Reflective questions

This study was undertaken with students in their first year of a general chemistry course in the U.S. To what extent do you think an additive framework of thinking is applied by students in your school context?

Look at some particle diagrams that you use to teacher elements and compounds. To what extent could these reinforce additive thinking and what adjustments to the diagrams or your use of the diagrams could better emphasise the need for emergent thinking?

A compound is often defined as “a substance formed when two or more different elements are chemically bonded together”. To what extent could this reinforce additive thinking and what adjustments in the phrasing of the definition, or clarification when teaching, could reduce this?