Chemistry textbooks and teachers frequently use a variety of metaphors, analogies and models to describe atomic and molecular structures and processes. While it is widely believed that multiple analogical models encourage students to construct appropriate mental models of chemical phenomena, uncritical use of multiple analogical models may actually be responsible for a number of alternative conceptions in chemistry. Students hear and read about electron clouds and shells, atoms that are like miniature solar systems and balls, and molecules that are simultaneously represented by balls-and-sticks, joined spheres, electron-dot and structural diagrams. A strong case has been made that students try to integrate these diverse analogical models resulting in the generation of unscientific synthetic models. Conceptual change research programs also propose that carefully designed teaching and learning activities can stimulate students to exchange their intuitive and synthetic conceptions for more scientific conceptions.This thesis investigates the occurrence of students' intuitive and synthetic mental models of atoms and molecules at both a general and specific level. The investigations consisted in the first phase of semi-structured interviews with 48 Year 8-10 science students. While the data were predominantly qualitative the interviews also generated simple quantitative data. The second phase was wholly qualitative and involved the researcher as teacher' in the Year 11 class. Portfolios were compiled for each student in the class and six portfolios were interpreted to produce a set of case studies describing the students' learning about atoms, molecules and bonds. These data were derived from transcripts of class discussions and individual interviews; pre-tests, formative tests and post-tests; student essays and worksheets and analogical teaching events. The data were ++ / interpreted from a constructivist viewpoint with attention given to credibility, viability and transferability, and dependability. The desire to collect every piece of useful data was constrained by the ethical need to minimise the disruptive effect of the research on the students' normal learning.The first or general phase of this study investigated the question: With what models of atoms and molecules are lower secondary science students familiar? The interviews about atomic and molecular conceptions held by the Year 8-10 students found, for example, that some students confused atoms with cells because both have a nucleus, while others believed that electron shells enclose and protect the atom. All but two students visualised atoms with large nuclei and close static electrons. A majority of this student sample were confused by ball-and- stick molecular models and had a strong preference for space-filling molecular models because they were more 'real'.The second or specific phase of this study consisted of an in-depth study of the development of mental models of atoms, molecules and bonds by six Year 11 chemistry students over 40 weeks of instruction. This study investigated the question: Do systematically presented multiple analogical models help students change their conceptions of atoms, molecules and bonds in favour of the scientific view? The students' prior mental models of an atom were dominated by a solar system model with the electrons in simple shells. A variety of metaphors, analogical models and explanations emphasising the diffuse spaciousness of atoms helped three students restructure their conceptions in favour of the scientific concept. Students also were encouraged to identify the shared and unshared attributes of familiar molecular models and, in time, three students became competent multiple modellers. It is claimed that these three students ++ / changed their conceptions of atoms and molecules in the sense that they realised that models are thinking and communicative tools, not reality itself. The significant change in these students' thinking was their recognition that atomic and molecular analogical models are context-dependent.The phase two study's pre-occupation with conceptual change or knowledge restructuring raised an important methodological question: Is a multi-dimensional approach a better way to interpret conceptual change learning? or, are the various theoretical perspectives on conceptual change complementary? The study's theoretical framework found that conceptual change learning can be interpreted from epistemological, ontological, motivational, holistic explanatory and developmental perspectives. The collection and analysis of the data showed that student modelling ability and Perry's model of intellectual development were powerful interpretive tools when data needed to be examined from multiple perspectives. The six case studies support the assertion that multi-dimensional interpretive frameworks have superior credibility and viability compared to uni-dimensional studies.Finally, the research raised several questions requiring further investigation. No direct support was found for the claim that dissatisfaction is central to conceptual change. This issue needs much more study due to the popularity of discrepant event teaching. While a multi-dimensional conceptual change model has been synthesised, this model needs further refinement as does the issue of how to monitor the status of students' conceptions. A most promising line of pedagogical research is the value of teaching scientific modelling through the use of multiple systematic analogical models.

L'adhésion cellulaire est un phénomène important en biologie. Le but de ce travail est le développement d'un modèle mécanique décrivant des phénomènes d'adhésion cellulaire à différentes échelles. La première échelle, microscopique, a pour objet la description des phénomènes cinétiques moléculaires durant le rolling. La seconde échelle, mésoscopique, est relative à la modélisation des déformations actives de la cellule durant la motilité. La troisième échelle, dite macroscopique, concerne la description de l'évolution dans le temps de l'adhésion d'une population de cellules. Les simulations réalisées mettent en évidence le rolling, et la déformation active de la cellule / Cell adhesion is an important phenomenon in biology, especially in the immune defence and tissue growth.We focus in this work on the development of a mechanical model for the description of the cell adhesion in a multiscal context. The first one is microscopic scale, which describes the molecular rupture and adhesion kinetics.At the mesoscopic scale, we model the active deformation of the cell during the motility phenomenon. At the macroscopic scale, we model the time evolution of the adhesion of cell population, under the action of the fluid. Numerical simulations emphasize the rolling phenomenon and the active deformation of a cell

Le mémoire vise à proposer une épistémologie pragmatique de la science scolaire à l’école primaire. Un défaut de compréhension de la nature de la science pourrait en effet justifier en partie les difficultés de l'enseignement des sciences par démarche d'investigation. Une étude des représentations de la science chez les enseignants et futurs enseignants confirme qu’ils n‘en ont pour la plupart qu‘une vision assez floue, relevant majoritairement d'une forme d'empirisme naïf. Un jeu opératoire de critères de scientificité adapté au contexte de l’école est développé dans une approche "bottom-up" partant des pratiques de classe effectives. Sa capacité à discriminer pratiques scientifiques et non scientifiques est discutée, de même que les implications didactiques et épistémologiques de son utilisation. Il est en particulier possible d‘en déduire des définitions évolutives d‘une science scolaire normative mais subsidiaire par rapport à la “science des scientifiques”. Cet outil épistémologique s’avère bien reçu par les enseignants auxquels il a été présenté. Le test en situation de différentes stratégies pédagogiques fait apparaître que les plus efficaces pour l'appropriation de critères de scientificité ajoutent à la démarche d’investigation une composante épistémologique explicite. Certains éléments de méthode scientifique peuvent être travaillés dès la Grande Section de maternelle (5-6 ans) : des élèves ayant vécu des démarches d’investigation s’avèrent capables de revendiquer la primauté de l’expérience, mais aussi de mettre en œuvre des tests relatifs à plusieurs critères de scientificité et de s‘approprier les rudiments de la modélisation scientifique. / The purpose of this thesis is to propose a pragmatic epistemology of school science in primary school. Indeed, some of the difficulties encountered by inquiry-based science education may be attributed to a lack of understanding of the very nature of science. A survey on the perception of science by incumbent teachers and teachers in training confirms that most of them have a relatively vague vision grounded in a form of naive empiricism. A practical set of criteria of scientificity adapted to the school context is developed through a “bottom-up” approach based on actual classroom practices. Its efficiency at discriminating scientific and non-scientific practices is discussed, as well as the didactical and epistemological implications of its use. It is thus possible to deduce evolutive definitions of a school science that is normative yet subordinated to the “science of scientists”. Teachers responded positively to this epistemological tool when it was presented to them. Among the different teaching strategies tested in a classroom, the most efficient for the acquisition of criteria of scientificity were those which supplemented the inquiry process with an explicit epistemological component. Some elements of scientific method can be introduced as early as kindergarten (5-6 y.o) : after experimenting with inquiry processes, pupils have proved able not only to claim the primacy of experiment but also to run tests related to different criteria of scientificity and acquire the basics of scientific modeling.