Submicroscopic Level Research Articles

Teaching chemical change modeling to Tunisian students: an “expanded chemistry triplet” for analyzing teachers' discourse

Through a comparative analysis of the chemical content of three teachers' discourse; we propose to give answers to the question: “how is the connection between the experiential level and the generally accepted representation of the three levels of chemistry presented by teachers to Tunisian students, during their first contact with chemical change modeling”. We chose to perform the analysis using an “expanded chemistry triplet” to represent the different levels and their possible connections to the elements of knowledge taught. These elements of knowledge, called facets, included definitions, representations and rules used by the teachers to convey the meaning. While there was some difference in priorities between the three teachers with regard to teaching content, the connection between the experiential field and the three levels of representation of chemistry was only partially taught by all. It is the description, the interpretation and the representation of objects and events of the experiential field at the macroscopic level that are strongly in the majority. On the other hand, interest in the sub-microscopic level and clarification of the procedures to implement for the quantitative treatment of chemical reactions seems insufficient. The responsibility is thus left to the students to acquire a large amount of knowledge and expertise. These observations led us to formulate proposals for improving the teaching of chemical reactions and teacher training.

Representaciones macroscópicas, submicroscópicas y simbólicas sobre la materia

In this paper we present a review of the macro, micro and symbolic representations of matter. From this review, a questionnaire was adapted for application of 15-years, in the classification of the subject content. Data analysis shows that students have great difficulty in relating the macroscopic and sub-microscopic levels of matter, as well as to distinguish between mixtures and compounds.

Chromosomal Microarrays in Prenatal Diagnosis: Time for a Change of Policy?

Microarrays have replaced conventional karyotyping as a first-tier test for unbalanced chromosome anomalies in postnatal cytogenetics mainly due to their unprecedented resolution facilitating the detection of submicroscopic copy number changes at a rate of 10–20% depending on indication for testing. A number of studies have addressed the performance of microarrays for chromosome analyses in high risk pregnancies due to abnormal ultrasound findings and reported an excess detection rate between 5% and 10%. In low risk pregnancies, clear pathogenic copy number changes at the submicroscopic level were encountered in 1% or less. Variants of unclear clinical significance, unsolicited findings, and copy number changes with variable phenotypic consequences are the main issues of concern in the prenatal setting posing difficult management questions. The benefit of microarray testing may be limited in pregnancies with only moderately increased risks (advanced maternal age, positive first trimester test). It is suggested to not change the current policy of microarray application in prenatal diagnosis until more data on the clinical significance of copy number changes are available.

Development Of Minimal Residual Disease (MRD) Analysis In Childhood Acute Lymphoblastic Leukaemia (ALL) By Next Generation Sequencing (NGS)

Detection of sub-microscopic levels of disease (minimal residual disease; MRD) in childhood acute lymphoblastic leukaemia (ALL) during treatment is an important prognostic factor. Currently, stratification of therapy for the new frontline trial in childhood ALL (UKALL 2011) is provided by MRD analysis using real time quantitative PCR (RQ-PCR) to identify and quantitate the patient specific rearrangements of the immunoglobulin (Ig) and T-cell receptor (TCR) genes. The current methodology is expensive, time-consuming and complex to perform. Although MRD has proven to be a powerful and essential tool in stratification of ALL patients, 8% of individuals in the current UKALL 2011 trial do not have an informative MRD result. Recently, Next Generation Sequencing (NGS) has led to the opportunity to improve the sensitivity and specificity of Ig/TCR based MRD analysis.In this study, we focussed on the IgH locus using BIOMED 2 primers (van Dongen et al., 2003) modified to allow target identification and quantitation by deep sequencing on the Illumina MiSeq platform. We developed a novel pipeline to automate the clustering and classification of sequencing reads leading to characterisation of the clonal subtypes present. In a sample of 12 patients, the method correctly identified all the major clones revealed by current methodologies, and also detected many related and unrelated low-frequency clones. Additional targets were also identified in patients in which no IgH targets were detectable by current methodologies. These NGS-identified targets were subsequently used to monitor MRD by RQ-PCR to the desired quantitative range required for stratification of therapy according to UKALL 2011 guidelines (Figure 1). In addition, we were able to delineate patterns of IgH rearrangements in two patients previously shown to have oligoclonal (>2) rearrangements. Such patients represent a time consuming and technical challenge for current technologies as it is important that all targets at the locus are followed by RQ-PCR to provide an informative and robust MRD result. Furthermore, by clustering similar sequences, we identified diagnostic samples where multiple V regions are attached to the same N1-D-N2-J region. This may allow for the study of clonal evolution in follow-up samples. Altogether, NGS sequencing has the potential to significantly reduce false negative results, as multiple evolved clones can be identified. This methodology also represents a significant time saving (5-7 days) in comparison to established methods (3-4 weeks). [Display omitted] Having established NGS for identifying clonal targets in ALL, we are currently assessing the ability of the method and pipeline to quantify disease levels in end of induction and relapse samples, previously analysed by RQ-PCR, to determine the concordance between the methodologies. Indeed, logarithmic dilution series of patient DNA in a normal background revealed that stratification based on a clinical threshold of 1 in 1,000,000 is possible using this methodology. Further investigation into the clinical utility of NGS for MRD analysis will focus on analysing earlier time points in treatment and studying the potential use of blood rather than bone marrow. Altogether, this will further improve the predictive value and specificity of MRD testing. Disclosures:No relevant conflicts of interest to declare.

Submicroscopic Plasmodium falciparum malaria and low birth weight in an area of unstable malaria transmission in Central Sudan

BackgroundMalaria, which frequently occurs in pregnant women in the tropics, is a leading cause of maternal anaemia and low birth weight (LBW) in infants. Few data exist concerning malaria infections that are present at submicroscopic levels during pregnancy and their LBW delivery in babies.MethodsA case–control study (87 in each group) was conducted at the Medani Hospital, Central Sudan. Cases were women who had LBW deliveries where the infants weighed < 2,500 g. Controls were parturient women without having LBW babies. Obstetrical and medical characteristics were gathered from both groups through structured questionnaires. Both cases and controls were investigated for malaria using microscopic blood film analysis, placental histology and polymerase chain reaction (PCR). Microscopic and PCR analyses were conducted on maternal peripheral blood, placenta, and umbilical cord samples. Infant weights were recorded immediately after birth.ResultsPlasmodium falciparum-positive blood films were not obtained from any of the women (cases or controls). Twenty-seven (31.0%) versus 22 (25.3%) (P = 0.500) of the cases and controls, respectively, had placental malaria infections as determined by histological examination. In comparison to the controls, the submicroscopic malaria infection prevalence rates were significantly higher in the cases; 24 (27.6%) vs six (7.0%), P < 0.001. Multivariate analysis showed that while malaria infection of the placenta (based on histology) was not associated with LBW, submicroscopic P. falciparum infection (OR = 6.89, 95% CI = 2.2–20.8; P = 0.001), or a combination of histologically determined and submicroscopic infections (OR = 2.45, 95% CI = 1.2–4.9; P = 0.012), were significantly associated with LBW.ConclusionIn Central Sudan, pregnant women were at a higher risk of having an LBW delivery if they had submicroscopic infections rather than a histological diagnosis of placental malaria.

The Effect of Different Textual Narrations on Students’ Explanations at the Submicroscopic Level in Chemistry

The effect of different textual versions (macroscopic (control), submicroscopic, and guided imagery) of the explanation of a chemical phenomenon on students’ submicroscopic explanation of a related phenomenon was examined. The sample included 152 pre-service science teachers. The three textual versions of the explanation were distributed randomly to the participants. The results revealed that students who received the submicroscopic version and those who received the guided imagery version outperformed students who received the macroscopic version. These results indicated that students’ use of the submicroscopic understanding was not spontaneous and they needed to be cued to do so. Also, the submicroscopic mean scores of all three groups were low, and this might be an indication of a weak ability to: 1) translate between macroscopic and submicroscopic levels of chemistry, and 2) transfer a submicroscopic understanding of one phenomenon to another related one.

Research-based design and development of a simulation of liquid–vapor equilibrium

Helping learners to visualize the structures and dynamics of particles through the use of technology is challenging. Animations and simulations can be difficult for learners to interpret and can even lead to new misconceptions. A systematic approach to development based on the findings of cognitive science was used to design, develop, and evaluate a simulation of physical equilibrium that addresses learner needs and misconceptions. Findings from a research study involving 45 chemistry instructors and 94 students were used to design and develop a dynamic computer simulation of liquid–vapor equilibrium that can be viewed at both macroscopic and submicroscopic levels. In the first stage of the process, mental models of the instructors and students were elicited by an open-ended questionnaire. Next, a selected group of participants were interviewed while viewing two dynamic animations of physical equilibrium. Based on these research findings, a dynamic simulation of liquid–vapor equilibrium was designed and developed. The simulation underwent several evaluation and revision steps that involved both experts and students. The final version of the simulation was implemented with a new group of 191 students. It was found to be effective in improving students' understanding of dynamic equilibrium and was well received by them.

Differences in Alcohol‐Soluble Protein from Genetically Altered Wheat Using Capillary Zone Electrophoresis, One‐ and Two‐Dimensional Electrophoresis, and a Novel Gluten Matrix Association Factor Analysis

ABSTRACTWheat protein composition and organization play interrelated roles in determining physical properties for technological purposes. In prior research, a number of isogenic wheat lines of Bobwhite that have high levels of expression of the native Dx5 and/or Dy10 high‐molecular‐weight glutenin subunits (HMW‐GS) were examined vis‐à‐vis physical properties related to separation. In particular, these altered lines were characterized by poor mixing properties, the formation of mixtures in water that could not be separated by conventional mechanical methods, reduced water absorption, unique milling properties, and severely limited development of microscopic fibrils. These attributes suggested inherent organizational differences at submicroscopic and molecular levels among the various lines. Therefore, proteins were fractionated from whole meals using 70% ethanol to elucidate solubility characteristics and compositions and to infer structural properties. Capillary zone electrophoresis and one‐ and two‐dimensional SDS‐PAGE (2DE) revealed striking differences in the protein composition and solubility among these new lines and the Bobwhite from which they were derived. Generally, Bobwhite yielded soluble protein that included not only what would be considered as classical gliadins but also some of each of the HMW‐GS as monomers or polymers with low degrees of polymerization, whereas the genetically altered lines produced far less total soluble protein and very limited amounts of HMW‐GS. In the extreme, high levels of expression of Dx5 subunit not only led to reduced solubility of the HMW‐GS but also limited the solubility of the many other proteins that are normally soluble. In addition, a matrix association factor similar to the classical separation factor of analytical chemistry and chemical engineering was introduced and applied to 2DE data for insoluble and soluble protein to summarize and index relative involvement of specifically enhanced proteins in the insoluble gluten matrix after equilibration with ethanol. The highest relative association was determined for the HMW‐GS lines enriched in Dx5 or Dy10 protein and the lowest for Bobwhite. Greater association was indicated for Dx5 than for Dy10 protein in these lines. The value of the association factor was likely influenced by differences in glutamine‐to‐cysteine ratios and differences in altered glutenin chain configurations stemming from high levels of expression of a single or limited number of HMW‐GS.

Pediatrik B Hücreli Akut Lenfoblastik Lösemide Minimal Kalıt Hastalığının Akan Hücre Ölçer ile Saptanması

Objective: Improvements in the treatment of childhood acute lymphoblastic leukemia (ALL) provide a complete remission in many patients. Several study groups indicated that determining submicroscopic levels of leukemia cells in the bone marrow (minimal residual disease-MRD) on day 15 is affects the prognosis. Flow cytometry (FCM) is a fast and cheap approach when compared to other molecular methods. In this study, day 15 bone marrow MRD levels and demographic profile in B-ALL patients assessed in our laboratory between December 2010 and August 2011 were discussed. Material and Methods: Bone marrow samples obtained on treatment day 0 and 15 from patients diagnosed with ALL (n=45) and the expressions of CD10, CD11a, CD19, CD20, CD34, CD38, CD45 and CD58 have been determined using FACSCalibur according to the Associazione Italiana Ematologia Oncologia Pediatrica- Berlin Frankfurt Münster (AIEOP-BFM) protocol and evaluated by CELLQuest-Pro software. After determination of the number of nucleated cells with Syto16, the percentages of leukemic cells (blast-MRD percentage) detected in the nucleated CD19+ B cell population were classified as flow low (FLR), flow medium (FMR) and flow high (FHR) risk. Results: Six of the 45 cases (10 females, 35 males, 6.17±3.90 years) in our survey were MRD negative and 39 were positive. Eleven cases were determined as FLR (24.4%), 26 as FMR (57.8%) and 8 as FHR (17.8%) according to MRD risk. Conclusion: All of the evaluations were approved by an AIEOP-BFM partner (100%). Since 30 August 2011, our institute has become the first center in Turkey to evaluate its own cases with the qualifications of our AIEOP-BFM partner (Vienna). In the future, we plan to investigate correlation of MRD-FCM results with prognosis and relapse, and to compare these findings with the polymerase chain reaction results.

Student Conceptions of Ionic Bonding: Patterns of thinking across three European contexts

Previous research has reported that students commonly develop alternative conceptions in the core topic of chemical bonding. Research in England has reported that students there commonly demonstrate an alternative ‘molecular’ conceptual framework for thinking about ionic bonding: in terms of the formation of molecule-like ions pairs through electron transfer, which are internally bonded, but not bonded to other ions. The present study reports the use of translated versions of a diagnostic instrument to elicit the conceptions of bonding in NaCl (commonly used as the teaching example of an ionic compound) from two samples of students setting out on university courses in Greece and Turkey. The study reports that students in these two contexts displayed high levels of support for statements based upon the alternative conceptual framework identified in the English context. Students commonly develop similar alternative conceptions of ionic bonding in these three different educational contexts. The study also found some quite large differences in the specific response patterns across these three contexts, some of which could reflect specific features of the different curriculum contexts. The study reinforces the cross-national nature of the challenge of effectively teaching the abstract models of chemistry at the submicroscopic level. It also provides intriguing suggestions that a close study of the interactions between specific curriculum contexts and specific patterns in students' thinking offers much potential for identifying particular aspects of subject pedagogy that either support or impede the learning of accepted scientific models.

Has MRD monitoring superseded other prognostic factors in adult ALL?

Significant improvements have been made in the treatment of acute lymphoblastic leukemia (ALL) during the past 2 decades, and measurement of submicroscopic (minimal) levels of residual disease (MRD) is increasingly used to monitor treatment efficacy. For a better comparability of MRD data, there are ongoing efforts to standardize MRD quantification using real-time quantitative PCR of clonal immunoglobulin and T-cell receptor gene rearrangements, real-time quantitative-based detection of fusion gene transcripts or breakpoints, and multiparameter flow cytometric immunophenotyping. Several studies have demonstrated that MRD assessment in childhood and adult ALL significantly correlates with clinical outcome. MRD detection is particularly useful for evaluation of treatment response, but also for early assessment of an impending relapse. Therefore, MRD has gained a prominent position in many ALL treatment studies as a tool for tailoring therapy with growing evidence that MRD supersedes most conventional stratification criteria at least for Ph-negative ALL. Most study protocols on adult ALL follow a 2-step approach with a first classic pretherapeutic and a second MRD-based risk stratification. Here we discuss whether and how MRD is ready to be used as main decisive marker and whether pretherapeutic factors and MRD are really competing or complementary tools to individualize treatment.

Interfacial behavior and structural properties of a clinical lung surfactant from porcine source

Surfacen® is a clinical surfactant preparation of porcine origin, partly depleted of cholesterol, which is widely used in Cuba to treat pre-term babies at risk or already suffering neonatal respiratory distress. In the present study we have characterized the interfacial behavior of Surfacen in several in vitro functional models, including spreading and compression–expansion cycling isotherms in surface balances and in a captive bubble surfactometer, in comparison with the functional properties of whole native surfactant purified from porcine lungs and its reconstituted organic extract, the material from which Surfacen is derived. Surfacen exhibited similar properties to native porcine surfactant or its organic extract to efficiently form stable surface active films at the air–liquid interface, able to consistently reach surface tensions below 5mN/m upon repetitive compression–expansion cycling. Surfacen films, however, showed a substantially larger and stable compression-driven segregation of condensed lipid phases than exhibited by films formed by native surfactant or its organic extract. In spite of structural differences observed at microscopic level, Surfacen membranes showed a similar thermotropic behavior to membranes from native surfactant or its organic extract, characterized by calorimetry or fluorescence spectroscopy of samples doped with the Laurdan probe. On the other hand, analysis by atomic force microscopy of films formed by Surfacen or by the organic extract of native porcine surfactant revealed a similar network of interconnected condensed nanostructures, suggesting that the organization of the films at the submicroscopic level is the essential feature to support the proper stability and mechanical properties permitting the interfacial surfactant films to facilitate the work of breathing.

A comparison of secondary schools students’ levels of conception of qualitative and quantitative inorganic analysis

This study constructed a two tier multiple choice questions to assess the levels of conception of students in qualitative and quantitative inorganic analysis. The study is an ex-post facto. The population consisted of all S.S.S.3 students in Ibadan south-west local government area of Oyo state, Nigeria. The sample is made of five public and five private schools selected from the local government and a total of 500 students attempted the test. The data were analysed using Analysis Of Variance and Tukey to ascertain the direction of difference in the three levels of conception. Results showed that there was a significant difference in the three levels of conception by the secondary school students in Chemistry. More students were discovered to be at the macroscopic level which was the farthest from the meaningful learning of the concepts. Furthermore, very few were at the submicroscopic and symbolic levels of conception which was the closest to the meaning of those concepts in qualitative and quantitative analysis. Recommendations based on the importance of proper and high level of conception were made.

Acute Lymphoblastic Leukemia: Monitoring Minimal Residual Disease as a Therapeutic Principle

Measurement of submicroscopic (minimal) levels of residual disease (MRD) can be used to monitor treatment response much more precisely than morphological screening of bone marrow slides. Several studies have demonstrated that MRD assessment in childhood and adult acute lymphoblastic leukemia (ALL) significantly correlates with clinical outcome. MRD detection is particularly useful for evaluation of early treatment response, but also to monitor disease before and after stem cell transplantation, for early assessment of an impending relapse and in the setting of salvage treatment. Currently, three highly specific and sensitive methodologies for MRD detection are available, namely, real-time quantitative polymerase chain reaction (RQ-PCR) of fusion gene transcripts or breakpoints, RQ-PCR-based detection of clonal immunoglobulin and T-cell receptor (TCR) gene rearrangements, and multiparameter flow cytometric immunophenotyping. Assessment of MRD has gained a prominent position in many ALL treatment studies as a tool for tailoring therapy. Only the results of these studies will answer the question of whether MRD-based treatment intervention is associated with improved outcome.

The LBFGS quasi-Newtonian method for molecular modeling prion AGAAAAGA amyloid fibrils

Experimental X-ray crystallography, NMR (Nuclear Magnetic Resonance) spectroscopy, dual polarization interferometry, etc. are indeed very powerful tools to determine the 3-Dimensional structure of a protein (including the membrane protein); theoretical mathematical and physical computational approaches can also allow us to obtain a description of the protein 3D structure at a submicroscopic level for some unstable, noncrystalline and insoluble proteins. X-ray crystallography finds the X-ray final structure of a protein, which usually need refinements using theoretical protocols in order to produce a better structure. This means theoretical methods are also important in determinations of protein structures. Optimization is always needed in the computer-aided drug design, structure-based drug design, molecular dynamics, and quantum and molecular mechanics. This paper introduces some optimization algorithms used in these research fields and presents a new theoretical computational method—an improved LBFGS Quasi-Newtonian mathematical optimization method—to produce 3D structures of prion AGAAAAGA amyloid fibrils (which are unstable, noncrystalline and insoluble), from the potential energy minimization point of view. Because the NMR or X-ray structure of the hydrophobic region AGAAAAGA of prion proteins has not yet been determined, the model constructed by this paper can be used as a reference for experimental studies on this region, and may be useful in furthering the goals of medicinal chemistry in this field.

Association of sub-microscopic malaria parasite carriage with transmission intensity in north-eastern Tanzania

BackgroundIn malaria endemic areas, individuals are frequently asymptomatic and may be undetected by conventional microscopy or newer, rapid diagnostic tests. Molecular techniques allow a more accurate assessment of this asymptomatic parasite burden, the extent of which is important for malaria control. This study examines the relative prevalence of sub-microscopic level parasite carriage and clonal complexity of infections (multiplicity of infection) over a range of endemicities in a region of north-eastern Tanzania where altitude is an established proxy of malaria transmission. The PCR prevalence was then compared against other measures of transmission intensity collected in the same area.MethodsThis study used 1,121 blood samples collected from a previously conducted cross-sectional malario-metric survey during the short rainy season in 2001 from 13 villages (three at < 600 m, four at 600-1,200 m and six at > 1,200 m in altitude above sea level). Samples were analysed by PCR for carriage of parasites and multiplicity of infection. These data were compared with other measures of transmission intensity collected from the same area.ResultsParasite prevalence was 34.7% by PCR and 13.6% by microscopy; a 2.5-fold difference in line with other recent observations. This fold difference was relatively consistent at the different altitude bands despite a marked decrease in parasite prevalence with altitude: < 600 m 70.9 vs 28.6, 600-1,200 m 35.5 vs 9.9, > 1,200 m 15.8 vs 5.9. The difference between parasite prevalence by PCR was 3.2 in individuals aged between 15 and 45 years (34.5 vs 10.9) compared with 2.5 in those aged 1-5 (34.0 vs 13.5) though this was not statistically significant. Multiplicity of infection (MOI) ranged from 1.2 to 3.7 and was positively associated with parasite prevalence assessed by both PCR and microscopy. There was no association of MOI and age.Village level PCR parasite prevalence was strongly correlated with altitude, sero-conversion rate and predicted entomological inoculation rate.ConclusionsAsymptomatic, low density, multi-clone malaria infection was common in this study area. These infections are important as potential contributors to the infectious reservoir of parasites and need to be identified by control programmes especially in this era where malaria elimination is a focus. High throughput standardized PCR approaches are needed to identify individuals who are malaria carriers.

Genomic profiling in high hyperdiploid acute myeloid leukemia: a retrospective study of 19 cases

Among patients with acute myeloid leukemia (AML), the rare group of complex aberrant karyotypes characterized by high hyperdiploidy (HH) is a subset with poor prognosis. Because of their rarity, few conventional cytogenetic studies have specifically addressed these patients. To identify DNA copy number aberrations at the submicroscopic level, we applied array-based comparative genomic hybridization (aCGH) to samples from 19 AML patients with complex karyotypes characterized by HH (≥49 chromosomes). We found a total of 155 imbalances (average: 8.2 per patient), and a high proportion of these imbalances involved whole chromosomes (n = 75). The chromosomes most commonly gained were chromosomes 8 (58%), 21 (42%), and 19 (32%). We identified 80 segmental genomic aberrations, and losses (n = 47) were more frequent than gains (n = 33). We identified common deleted regions at 5q, 15q, 18p, and 19p. The tumor suppressor gene L3MBTL4 and zinc finger proteins reside within 18p and 19p, respectively. The aCGH analysis added new information to the karyotypic interpretations in 16 of the 19 HH AML cases (84%), leading to a significantly higher detection rate of abnormalities.

Assessment of electrochemical concepts: a comparative study involving senior high-school students in Indonesia and Japan

Background and purpose This study investigated Indonesian and Japanese senior high-school students’ understanding of electrochemistry concepts. Sample The questionnaire was administered to 244 Indonesian and 189 Japanese public senior high-school students. Design and methods An 18-item multiple-choice questionnaire relating to five conceptual categories (reactions occurring during electrolysis, differences between electrolytic and voltaic cells, movement of ions in voltaic cells, poles in voltaic cells, voltaic cell reactions) was administered. Results The findings of this study show that difficulties and alternative conceptions previously reported in the literature are held equally by students from a developing and developed country, Indonesian and Japan respectively. Conclusions Collectively, the findings suggest that students’ understanding of electrochemistry concepts is relatively weak. Students from both samples shared common difficulties and displayed several alternative conceptions dealing with electrolysis, electricity flow, the voltaic cell and the electrode reactions. Not surprisingly, the students displayed limited consistency in understanding of the concepts in the five categories. This study has implications for teaching and learning, particularly in classroom discussions using models and computer animations in order to reinforce understanding at the sub-microscopic level.

Compounding Confusion? When Illustrative Practical Work Falls Short of its Purpose—A Case Study

Illustrative practical work is commonly used in chemistry education to enrich students’ understandings of chemical phenomena. However, it is possible that such practical work may not serve to foster understanding but rather cause further confusion. This paper reports the struggles experienced by a group of senior (Year 12) secondary chemistry students as they sought to understand redox chemical concepts involved in the reactions occurring when steel wool is added to copper sulfate solution. The results showed that the students lacked the skills required to make accurate observations during the practical work. Nor were they able to link the observed phenomena with previously taught redox concepts. The paper also presents possible ways to overcome the difficulties encountered by students as they move between macroscopic and submicroscopic levels of representation of redox reactions.

University students' conceptions of bonding in melting and dissolving phenomena

Undergraduate and graduate students' predictions and submicroscopic level explanations for the melting of four materials (salt, chalk, sugar, and butter), and for the mixing of these solutes in two solvents (water and cooking oil) were collected. Twenty-three undergraduate students and seven graduate students participated in the study, and data were collected through individual semi-structured interviews. The purpose of the study was to investigate students' conceptions of how bonding is involved in both melting and dissolving processes, as well as to investigate students' ideas of specific bonds and forces involved in melting and dissolving. Three types of misconceptions about bond breaking in the process of melting were revealed, as well as three types of misconceptions about bond breaking and three types of misconceptions about bond forming in the process of dissolving. Analysis indicated that students viewed the dissolving process as occurring via a single-step mechanism or via a multi-step mechanism. Analysis also revealed that students viewed bond breaking similarly in melting and dissolving processes, likely resulting in confusion between these two processes.