The aims of this study were to measure the concentrations of nutrients and pollutants in peri-urban wetlands, to analyze the plant morphology of the most representative macrophyte species, and to determine their potential use as biomonitors. Four wetlands in the Middle Paraná River floodplain evidencing contamination or anthropogenic impact were studied. The studied species were Typha domingensis Pers., Eichhornia crassipes (Mart.) Solms., Alternanthera philoxeroides (Mart.) Griseb., and Pistia stratiotes L. Besides, the same plant species from an uncontaminated wetland considered as control were studied. A. philoxeroides showed the highest total phosphorus (TP) concentration in leaves throughout the study, while the other species showed a higher TP concentration in roots than in leaves. Since metal concentration in A. philoxeroides tissues was always higher than in sediment, further studies focused on its phytoremediation capacity should be carried out. T. domingensis exhibited the highest Zn concentrations in roots followed by Pb, and E. crassipes presented the highest values of Pb concentrations in roots. The aerial part height of the plants from peri-urban wetlands was significantly higher than that of the plants from the control, while the root length was significantly lower. The root length of P. stratiotes showed a negative correlation with soluble reactive phosphorus (SRP) concentration in water. All the root anatomical parameters of T. domingensis and E. crassipes showed a positive correlation with nitrate and ammonium concentrations in water. The studied macrophytes evidenced a high tolerance, enabling them to grow and survive in peri-urban wetlands that receive pollution from different sources. The use of aquatic and wetland plants as contaminant bioindicators and bioaccumulators in the Middle Paraná River floodplain is completely feasible.
In the present work we carried out a qualitative educational research to assess the perceptions of a group of students that attended (weekly and non-mandatory) complementary classes of a physics course during 2017. In these classes the teaching method called peer instruction (PI) was implemented, which involves collaborative learning among students. From the students' responses to a simple questionnaire we assessed some basic aspects of these classes from which we can conclude that, in the first place, students considered that PI had positively influenced their comprehension of physical concepts and that, secondly, they positively valued the activities performed and the dynamics of these classes. These results, which are part of a series of previous works that have been published elsewhere, are relevant in a context were active and collaborative learning strategies are practically non-existent and push us to continue and broaden the implementation of this and other active learning methods in physics courses.
Realizamos un estudio comparativo entre dos diseños didácticos constructivistas para la enseñanza del tema Calor en estudiantes de carreras en ciencias naturales. Uno con un enfoque de ciencia integrada y el otro con un enfoque no integrador. En el primer diseño el alumno construye su propio conocimiento resolviendo situaciones problemáticas relacionadas a la biología y el medio-ambiente, que le permite analizar y relacionar los conceptos involucrados, mientras que en el segundo construye su conocimiento a través de la resolución de situaciones problemáicas físicas pero no biológicas. Concluimos que el primer diseño favorece en los alumnos la construcción de una estructura cognitiva del tipo integrada, que les facilita internalizar y transferir los conceptos físicos a problemas concretos de su especialidad.
ResumenEn la enseñanza de la Física, al abordar los temas de Mecánica, son numerosas las situaciones tratadas que involucran masas vinculadas a través de resortes en las que, con fines simplificadores, se idealizan a los resortes asignándoles masa despreciable. Se presenta un estudio sobre las conceptualizaciones, desde los puntos de vista dinámico y energético, logradas por estudiantes universitarios que cursan carreras científico-tecnológicas, acerca de dicha modelización. A partir de resultados obtenidos con relación a las conceptualizaciones, se indagó sobre el tratamiento que de esta idealización presentan los libros de texto de física usados frecuentemente en el ciclo inicial. En estos últimos se investigó, si se explican adecuadamente las consecuencias físicas derivadas de considerar a los resortes sin masa. Del estudio realizado se desprende, por un lado, que no es inmediato para los estudiantes establecer nexos entre esta modelización, y la aplicación de las leyes y principios físicos, al abordar situaciones problemáticas; y por otro, que no todos los autores de los libros de Mecánica frecuentemente utilizados presentan análisis detallados acerca de la misma. Se destacan recomendaciones para ser consideradas por docentes.Palabras claves: Mecánica introductoria; Enseñanza y aprendizaje; Libros de texto; Resortes; Modelizaciones. AbstractIn Physics teaching, especially when the topics of Mechanics are addressed, there are several situations about masses linked by springs, in which springs are considered to have negligible mass with simplifying purposes. We present a study on the conceptualizations, from the dynamic and energetic points of view, achieved by university students who study scientific and technological careers, about this modelling. From the unpromising results obtained, we inquired, about the treatment of this idealization in Physics textbooks frequently used in the initial cycle, in which we researched if the physical consequences of considering springs massless are properly explained by the authors. From the results achieved we consider that establishing links between this idealization, and applying laws and physical principles when addressing problem situations may not be immediate for students; and, on the other hand, we found that not all the authors presented sufficient explanations about this simplifying assumption. Recommendations for teachers are mentioned.
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