Advan. Physiol. Edu. 32: 225-230, 2008;
doi:10.1152/advan.00050.2007
1043-4046/08 $8.00
ADV PHYSIOL EDUC 32:225-230, 2008
© 2008 American Physiological Society
HOW WE TEACH
Glucose as the sole metabolic fuel: a study on the possible influence of teachers' knowledge on the establishment of a misconception among Brazilian high school students
Maurício Roberto Motta Pinto da Luz
Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, and Colégio de Aplicação, Setor de Biologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
Address for reprint requests and other correspondence: M. R. M. P. da Luz, Fundação Oswaldo Cruz, Instituto Oswaldo Cruz, Pavilhão Arthur Neiva, Avenida Brasil 4365, Manguinhos, Rio de Janeiro 21040-360, Brazil (e-mail: mauluz{at}ioc.fiocruz.br)
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Abstract
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In the present work, I investigated the origin of the misconception that glucose is the sole metabolic fuel previously described among Brazilian high school students. The results of a multiple-choice test composed of 24 questions about a broad range of biology subjects were analyzed. The test was part of a contest and was answered by a sample composed of undergraduate students as well as biologists and practicing biology teachers. The majority of the responders had difficulties in recognizing the existence of gluconeogenesis and the possibility of ATP production using other fuels other than carbohydrates. Biology teachers and biologists seemed to either lack the knowledge or present the misconception regarding energy-yielding metabolism found among students. I argue that in both cases, biology teachers are likely to teach metabolism-related subjects in a manner that may contribute to the appearance of the misconception among high school students.
Key words: metabolism teaching; physiology teaching; biochemistry teaching
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Introduction
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THE OCCURRENCE of a misconception related to energy-yielding metabolism (EYM) among Brazilian students has been previously reported (12). The students seemed to have contradictory conceptions regarding ATP production by human cells. They seemed to believe in that glucose is the sole metabolic fuel in formal situations but admitted that lipids could also be used for energy production when answering more informal questions. Nevertheless, students seldom considered that other nutrients such as proteins could be oxidized for ATP production in animal cells.
In Brazil, high school students must pass typical entrance exams (generally known in the country as "vestibular exams") to gain access to most of the university courses. Those entrance exams are extremely competitive due to the high candidate-to-place ratios. Briefly, the entrance exams consist of sets of written tests to be answered by students. The general features of the exams (multiple-choice and/or discursive questions) as well as the formulas used to calculate students' final grades vary depending on the institution. Students with the highest final grades take the places available. In general, students from low-income families are outperformed by those from families of higher incomes, which usually study in high-performing private high schools (9, 10, 14). Brazilian public universities, on the other hand, concentrate most of Brazilian growing research activities and are considered the best when research and teaching are considered (7, 8, 11). In recent years, preparatory courses have been offered by governmental and nongovernmental organizations to improve the opportunities for low-income students to enter Brazilian public universities. Public contests to select teachers for one of those preparatory courses occur yearly in the Brazilian State of Rio de Janeiro. In the present work, I analyzed the answers of candidates in that selective contest to investigate biologists and biology teachers' knowledge about EYM. The data obtained suggest that there may be an influence of teachers' knowledge on the establishment of misconceptions among high school students.
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MATERIALS AND METHODS
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Contest.
The contest aimed to select teachers for an outreach program designed to improve the skills and knowledge of low-income high school students prior to entrance exams. The contest consisted of 25 questions on biology and 10 questions on basic Portuguese. The key was posted on the internet immediately after the end of the written exam, and a period of 24 h was left for candidates to appeal. Appeals led to the cancellation of one question of the biology test. Question 3 mentioned only one cell type (red blood cells) but, due to a typing mistake, the candidates were asked to identify processes not occurring in "both cell types." That was considered misleading in a great number of appeals, and the question was thus cancelled. Weighed averages of each candidates' grades in the biology and Portuguese tests were used to calculate candidates' final grades. Only the candidates with the best grades proceeded to the didactic exam. The didactic exam occurred about 1 wk after the written tests and consisted of a 15-min introductory class on 1 of 10 predetermined biology subjects. The 10 biology subjects were made available for the candidates at the moment of their enrollment in the contest (
2 mo before the didactic test). The subject to be presented by each candidate was chosen by drawing immediately before the start of his or her didactic exam. They were supposed to teach a lesson at the high school level. A panel of three biologists (practicing teachers at public universities and/or high schools) evaluated the classes. The panel could pose questions to the candidates during and/or immediately after the class.
Sample.
A total of 402 individuals performed the biology test and are referred to herein as candidates. The sample was composed of approximately equal proportions of undergraduate students and graduated professionals (Table 1). Due to legal restrictions to scholarships, only students from the six public universities of the State of Rio de Janeiro could participate in the contest. Undergraduate candidates were nearly evenly distributed among the six public universities of the State of Rio de Janeiro (none accounted for >29.7% of the candidates). Graduate candidates graduated from 51 different institutions, but 56.7% of them had graduated from 1 of 6 aforementioned public universities. The remaining 43.3% were graduates from one of the remaining 45 institutions (the most represented of which accounted for <5.0% of the candidates).
Biology test.
The test consisted of 25 multiple-choice questions related to a broad range of biology subjects. A single alternative was considered correct for each question. The general features of the 24 valid questions are shown in Table 2 (the original numbering of the questions was maintained).
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RESULTS
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The candidates' profiles are shown in Table 1. The majority of the undergraduate candidates came from biology courses (84.4%), and 86.7% of them had finished at least the fourth semester of their courses (not shown). The majority of the graduated candidates came from public universities (Table 1). The sample of graduated candidates was composed mostly of biologists (89.3%) and recently graduated professionals (84.6%). Nearly one-fourth of all candidates were either graduating as teachers or identified themselves as practicing teachers. Although the mean ages of undergraduate and graduated candidates were significantly different (P < 0.001 by t-test), both groups were composed of relatively young individuals, as the mean age was <30 yr old for both groups.
Among the 24 valid questions, there were two questions (questions 23 and 24) related to EYM (APPENDIX). Question 23 demanded the analysis of a line graph showing a simplified version of the changes in blood levels of glucose (glycemia) of a human subject after a meal (adapted from Ref. 1). The graph was divided in three main sections as follows: glycemia rose in section I, fell to the initial level in section II, and reached a steady level in section III. Question 24 presented a table depicting the nutritional facts (except calories/portion) of three hypothetic cereal bars. The questions will be dealt with in detail later.
The proportions of correct answers to the two EYM-related questions were the lowest of the whole test (4.5% and 10.2% for questions 23 and 24, respectively). As shown in Fig. 1, the mean proportion of correct answers (7.4% for questions 23 and 24) to the two EYM-related questions was nearly eight times smaller than the averages obtained for the other six general physiology but EYM-unrelated questions (59.9% for general physiology). These results show that physiology itself was not a subject intrinsically difficult for the candidates. The proportion of correct answers to EYM-related questions was also much smaller than that obtained for the 16 questions dealing with biology subjects others than physiology (Fig. 1, 50.2% for general biology), corroborating the idea that EYM was a difficult subject for candidates. The proportions of correct answers to EYM-related questions were nearly identical for undergraduate and graduated candidates (not shown), indicating that the difficulties were not restricted to students but were also found among practicing biologists and teachers. It is remarkable that only one candidate answered correctly to both EYM-related questions and that 92% of the 62 candidates who answered correctly to any one of the two EYM-related questions studied in public universities. Taken together, these later results suggest that even the candidates with the best educational backgrounds have a fragmented knowledge of EYM.
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Fig. 1. Percentages of correct answers of candidates (n = 402) to the 24 valid questions of the biology test. The categories were general biology (questions dealing with subjects unrelated to physiology, n = 16), physiology (n = 6), and energy-yielding metabolism (EYM; n = 2). The features and subjects of each question are described in detail in Table 2. Horizontal lines indicate averages.
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I at first considered the possibility that some features of the EYM-related questions could have posed difficulties regardless of the candidates' knowledge of the subject itself. EYM-unrelated questions containing any kind of graphs (e.g., column graphs) or those containing only line graphs had mean proportions of right answers (60.2% and 59.8%, respectively) closer to the average of the whole test. Those proportions were much higher than the one obtained for EYM-related question 23, which featured a line graph (4.5%). In addition, question 22 demanded the analysis of the same graph of question 23 but had a much higher proportion of correct answers (52.5%). The presence of graphs is thus unlikely to be the cause of errors. Difficulties in analyzing tables are also unlikely to be an explanation for the errors, since the proportion of correct answers (10.2%) to the EYM-related question that contained a table (question 24) was much lower than that (51.5%) of the EYM-unrelated question that also featured a table (question 25). It seems reasonable to conclude that the candidates' difficulties with the EYM-related questions are due to difficulty in dealing with the subject itself.
The candidates' answers for each of the two EYM related questions were not randomly distributed among the five alternatives available in each question (x2 = 381.281, 4 degrees of freedom, P < 0.001 for question 23 and x2 = 432.905, 4 degrees of freedom, P < 0.001 for question 24; the null hypothesis being the equal distribution of choices among all 5 alternatives). I decided to analyze the alternatives chosen by the candidates in each of the EYM-related questions to seek explanations for the causes of the low proportions of correct answers.
The first EYM-related question (question 23) demanded students to properly identify the processes responsible for the near stabilization of blood levels of glucose in section III of the graph. Four affirmatives were available, and each alternative comprised combinations of them. The majority of candidates (55.2%) chose the alternative in which only affirmative II was considered correct, indicating that they recognized only another carbohydrate (glycogen) as the source for glucose production. Only 4.5% of candidates chose the correct answer (alternative E), indicating that most of them were also unaware that amino acids can be used to generate glucose molecules in animal cells. The fact that 19.0% of candidates chose alternative D indicates that they are more prone to admit that fatty acids rather than amino acids can be used for glucose production.
The great proportion of candidates (79.8%) that chose alternative D (affirmatives III, IV, and V), which excluded affirmative I, shows that the majority of them did not admit that glucose consumption could stop. That could be due to a proper knowledge of EYM. However, if that was true, one should expect a greater proportion of correct answers to question 23, higher than the mere 4.5% actually found. I speculate that the candidates might not admit the interruption of glucose consumption simply because they were unable to recognize that other molecules beside carbohydrates can be oxidized for ATP production. Consequently, the consumption of the cells' sole fuel could not stop. I believe that this hypothesis was further corroborated in two ways. First, only two candidates appealed against the contents of question 23, but none presented consistent arguments (one wrongly addressed the possibility of glucose synthesis from fatty acids and another assumed that glycogen breakdown was the sole source of glucose). Second, only 1 of the 11 candidates given the subject of "ATP production in animal cells" for their didactic exam spontaneously mentioned the oxidation of fatty acids or amino acids. Six of the ten remaining candidates were questioned by the examining panel about other metabolic fuels for ATP production, but only three of them mentioned fatty acids and none mentioned amino acid oxidation in their answers. Moreover, two of those six candidates explicitly stated that fatty acids could be used in glucose synthesis. These results are in fair agreement with the idea that candidates consider glucose as the main or sole energy source for human cells and thus its consumption could not cease. The analysis of the second EYM-related question (number 24) shed more light on this issue.
The amounts of fat in the three hypothetical cereal bars shown in question 24 were identical. The sums of the amounts of carbohydrates and proteins were also equal, although the relative proportions of each of these two nutrients varied. The only other relevant difference between the three bars was that the amount of sodium in bar 3 was 50 or 100 times greater than those found in bars 1 or 2, respectively.
The alternatives that excluded affirmative I were chosen by only 25.2% of candidates, suggesting that the role of sodium in hypertension was well recognized by them. The majority of candidates (59.0%) chose the alternative that not only admitted that affirmative I was correct but also that bar 2 was the most caloric among then (alternative D). In addition, the correct alternative, which was the one stating that all three bars were equally caloric (and also that affirmative I was correct) was chosen by only 10.2% of candidates. These results should be analyzed cautiously, since equal caloric values can be obtained for the three bars only by using standard conversion factors. However, the fact that no appeal regarding this question was received suggests that candidates were not considering detailed biochemical pathways of carbohydrate or amino acid oxidation while answering the question. Together, these results may indicate that students do not recognize proteins (and therefore amino acids) as potential metabolic fuels or at least consider them to contain fewer calories than carbohydrates. The results regarding the didactic test already mentioned do corroborate the former conclusion rather than the latter.
Question 22 also deserves consideration. It dealt with the same line graph as in question 23 but specifically asked candidates to identify the hormones responsible for the variations in blood glucose levels shown in the three sections highlighted in the line graph. The majority of students (52.5%) chose the correct alternative, which stated that there was an increase in glucagon secretion in section III of the curve. The proportion of right answers to this question was much higher than those obtained for the two EYM-related questions.
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DISCUSSION
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In a previous report, it has been described that a misconception regarding EYM was widespread among high-achieving students from a broad number of Brazilian schools (12). Those students were said to be high achieving because they were following the first year of their courses in one of Brazil's most recognized public university.
The existence of a widespread misconception among high-achieving students was by itself an impressive finding. It raised my attention to its possible causes. I took advantage of the occurrence of a contest for selecting teachers to obtain information on the EYM knowledge of biology teachers and biologists. The sample analyzed in the present study was composed of both graduated and undergraduate candidates. Candidates of both groups came mostly from main universities in the State of Rio de Janeiro, but those coming from other universities represented nearly one-fourth of the graduated group. I believe that the results obtained with such a broad and diversified sample represent a fair picture of the general knowledge of the teachers and biologists of the State of Rio de Janeiro.
The disciplines related to EYM (e.g., biochemistry, physiology, and cell biology) are usually taught during the first four semesters of biology courses. It is then very likely that most of the undergraduate candidates had already attended those courses. The great proportion of candidates in both groups that studies or graduated from public universities ensures that they had access to some of the best educational resources available in the country. It is also important to highlight that Brazilian biology students can graduate first as biologists and later as biology teachers (and vice versa). The majority of the undergraduate candidates came from biology courses and could thus choose to graduate as teachers in the near future. In addition, I believe that the proportion of graduate candidates that were already practicing teachers is likely to be underestimated. This belief is based on the facts that providing information on teaching activities in the inscription form was not mandatory and that contests for teaching activities are likely to attract practicing teachers. Anyway, there is no reason to believe that students training to graduate or professionals (biology teachers and those studying or already graduated in other biology fields) should differ in their knowledge about EYM because all of them usually follow the same EYM-related disciplines that are taught during the initial four semesters of all biology courses. It seems plausible, therefore, to assume that the results obtained reflect the knowledge of biologists and biology teachers as well.
We have analyzed the performance of undergraduate students and graduate Biologists and Biology teachers in two multiple choice questions related to the EYM. The test and the questions were not designed for research purposes, so their analysis faced limitations inherent to the structure of the questions (e.g., the alternatives available). The fact that candidates were applying for scholarships is reassuring about their seriousness when answering the questions. The high proportions of wrong answers to the two EYM-related questions called our attention and were considered especially important because of the previous report on the existence of a misconception regarding the EYM among Brazilian students.
I am aware that the analysis of the multiple-choice test results must be made cautiously. The meaning of technical terms can sometimes be different for the examiners and examinees (13). Technical terms were mostly absent in the two EYM-related questions analyzed. In fact, when used, these terms were readily explained in parentheses (as it was the case of the expression "glycemic curve" in the text used for questions 22 and 23). Although the term "calories" (question 24) may sound somewhat technical, it is likely to have been understood by the candidates not only because it is printed on all Brazilian food packages but also because the question associated it with the word "energy," making the connection between both evident.
The alternatives available in multiple-choice questions have also been reported as possible sources of confusion for the examinees. A cueing effect of assertions of the "all the above are correct" type sometimes occurs (5). Question 23 presented an alternative considering all four affirmatives presented as correct (alternative A), but care was taken not to use the expression "all the above" so as to encourage the candidates to read all the sentences. In addition, one affirmative (the interruption of glucose consumption) was clearly contradictory to all the others (glucose synthesis from three different precursors), and only 3.1% of the candidates chose alternative A, showing that it clearly was not acting as an attractor for wrong answers. I believe that the features of the EYM-related questions were not the cause of errors but that an underlying educational problem regarding the candidates' knowledge of EYM does exist.
The analysis of the pattern of answers to the two EYM-related questions seems to support the hypothesis that the problem (the high proportion of errors) is related to the presence of a misconception among undergraduate students, biologists, and biology teachers. It seems clear that candidates had fewer difficulties in identifying the hormones involved in the physiological processes for controlling the blood levels of glucose (question 22) than in identifying the biochemical pathways (question 23) underlying this phenomenon. The fact that no candidates appealed against question 23 makes it unlikely that any feature of the question (e.g., the time scale) misled the candidates. The results obtained for question 23 also indicate that most of the candidates seemed unaware of the pathways that use amino acids as precursors for the formation of glucose (gluconeogenesis). Moreover, the results obtained for question 24 and didactic tests strongly suggest that candidates also lack the knowledge that proteins (and thus amino acids) can be used to produce ATP and pay less attention to lipids than to carbohydrates as metabolic fuels. These results are consistent with the misconception described above, in which carbohydrates are considered as the sole energy sources for human metabolism when students deal with formal situations (such as that presented in question 23).
The lack of integration (as well as the need for the reversal of this situation) in the teaching of different subjects within a single discipline has been the subject of discussion in the case of chemistry (3, 4). The pattern of answers obtained for the two questions suggests that undergraduate students, graduate biologists, and practicing teachers fail to integrate concepts of the two closely related disciplines of physiology (homeostasis and control of blood levels of glucose) and biochemistry (gluconeogenesis and oxidation of lipids and amino acids).
The results obtained from graduate candidates show that these professionals also lack the knowledge or are at some level unaware of some metabolic pathways crucial for an integrated understanding of human metabolism. This could be a consequence of the disconnection between related disciplines, as argued in the case of chemistry and biology (16). From the educational point of view, the lack of knowledge and misconceptions held by professionals are different problems, but both could lead to the same consequence, that is, the establishment of a misconception among pupils of those professionals both in high schools and universities. In the present case, the findings are especially worrying for three main reasons. First, it seems that graduating in biology or closely related fields does not lead to an integrated view of the physiological and biochemical processes involved in ATP synthesis and in the control of blood levels of glucose. Second, misconceptions about physiology (and probably those regarding other disciplines) that survive until university are difficult to remedy and demand very specific teaching approaches to do so (2). It would be important to identify the early sources of the misconception to remedy them in the best moment along formal education. Finally, practicing teachers are unlikely to teach the concepts of biochemistry that underlie physiological processes both if they lack the knowledge of the processes of ATP synthesis from alternative fuels or if they consider those concepts less important. In that sense, it is remarkable that nearly all the candidates who presented introductory classes about EYM in their didactic tests simply did not mention fat acids or amino acid oxidation and rather focused solely on carbohydrates as fuels for ATP synthesis. Such way of teaching EYM could indeed help to consolidate the misconception described previously among high school students (11).
In Brazil, introductory concepts of both EYM and human physiology are taught at high school within the discipline of biology in the 10th and 11th grades, respectively. A similar problem of lack of integration in the teaching of those two subjects in high school could contribute to explain the results obtained previously with high school students (11) as well as those obtained with the undergraduate candidates at early years of their courses presented here.
I consider that a deeper understanding of how the teaching of introductory concepts of physiology and biochemistry occurs in Brazilian high schools and universities is strongly needed. One must also have in mind that the results reported here were obtained with samples of highly achieving students. Therefore, even if there are huge educational differences between countries, it is still possible that similar problems occur in developed countries as well. Finally, an integrated understanding of EYM and its relations with other aspects of human physiology is extremely important, since both are subjects connected to daily experiences and relevant health problems such as the increasing obesity rates among young individuals in developed and developing countries, including Brazil (6, 15).
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APPENDIX
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The following are multiple-choice EYM-related questions (with the correct choice for each question shown in bold).
Question 23.
Use the following text and graph (Fig. A1) to answer question 23.
The following affirmatives can be made about section III of the graph: - Glucose consumption by the cells ceases.
- Glucose is being produced from glycogen breakdown and released in the blood.
- Glucose is being produced from fatty acids and released in the blood.
- Glucose is being produced from amino acids and released in the blood.
Mark the correct option:
- Affirmatives I, II, III, and IV are correct.
- Only affirmative I is correct.
- Only affirmative II is correct.
- Only affirmatives II, III, and IV are correct.
- Only affirmatives II and IV are correct.
Question 24.
A food factory produces three bars of cereals marketed as "energy supplements." The ingredients present in the three bars are rigorously the same; only the proportions of each one of them varies. The nutritional facts of the three bars are shown in Table A1.
The following affirmatives can be made about the bars: - Bar 3 is less recommended for persons with arterial hypertension.
- Bar 2 has the highest caloric content of the three bars.
- The three bars are equally caloric.
Mark the option that lists only the correct affirmative(s):
- Affirmative I is correct.
- Affirmative II is correct.
- Affirmative III is correct.
- Affirmatives I and II are correct.
- Affirmatives I and III are correct.
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GRANTS
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This work was supported by grants from the Conselho Nacional de Desenvolvimento Cientifico e Techologico and Filho de Amparo À Pesquisa do Estado do Rio de Janeiro.
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Acknowledgments
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The author thanks B. Lages and C. N. Spiegel for reviewing the manuscript.
Received for publication July 11, 2007.
Accepted for publication June 25, 2008.
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Copyright © 2008 by the American Physiological Society.
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Abstract
Introduction
