Cambridge IGCSE Biology : workbook.

Libro de ejercicios para alumnos de enseñanza secundaria de segundo ciclo que estén preparando el examen Cambridge IGCSE (International General Certificate of Secondary Education) en el área de la Biología. Está desarrollado para ser usado junto al libro de texto del curso y sus contenidos están aprobados por la Universidad Cambridge International Examinations (CIE). Las materias que cubre son: clasificación, células, movimiento dentro y fuera de las células, sustancias químicas de la vida, encimas, nutrición de las plantas, nutrición de los animales, transporte, respiración, coordinación y respuesta, homeostasis y excreción, drogas, reproducción, herencia y evolución, organismos que viven en su entorno, el ser humano y el medio ambiente.

Cambridge IGCSE Biology: Teacher´s Resource.

Es un CD-ROM cuyos contenidos son de la asignatura de enseñanza secundaria biología para el examen IGCSE de la Universidad de Cambridge. El contenido ha sido revisado y escrito por un experimentado profesor, asegurando que su cobertura sea actualizada y exhaustiva. El CD-ROM contiene: sugerencias capítulo por capítulo sobre la manera de llevar el material de las lecciones, ideas para cada lección, los conceptos erróneos más comunes, hojas de trabajo organizadas capítulo por capítulo, notas para los profesores sobre practica y otras actividades, respuestas a preguntas y actividades del libro, respuestas a ejercicios del Workbook, respuestas a las preguntas de las hojas de trabajo.

Breeding Biology of Grassland Birds in Western New York: Conservation and Management Implications

Declining grassland breeding bird populations have led to increased efforts to assess habitat quality, typically by estimating density or relative abundance. Because some grassland habitats may function as ecological traps, a more appropriate metric for determining quality may be breeding success. Between 1994 and 2003 we gathered data on the nest fates of Eastern Meadowlarks (Sturnella magna), Bobolinks (Dolichonyx oryzivorous), and Savannah Sparrows (Passerculus sandwichensis) in a series of fallow fields and pastures/hayfields in western New York State. We calculated daily survival probabilities using the Mayfield method, and used the logistic-exposure method to model effects of predictor variables on nest success. Nest survival probabilities were 0.464 for Eastern Meadowlarks (n = 26), 0.483 for Bobolinks (n = 91), and 0.585 for Savannah Sparrows (n = 152). Fledge dates for first clutches ranged between 14 June and 23 July. Only one obligate grassland bird nest was parasitized by Brown-headed Cowbirds (Molothrus ater), for an overall brood parasitism rate of 0.004. Logistic-exposure models indicated that daily nest survival probabilities were higher in pastures/hayfields than in fallow fields. Our results, and those from other studies in the Northeast, suggest that properly managed cool season grassland habitats in the region may not act as ecological traps, and that obligate grassland birds in the region may have greater nest survival probabilities, and lower rates of Brown-headed Cowbird parasitism, than in many parts of the Midwest.

Pollen ultrastructure in anther cultures of Datura innoxia. III. Incomplete microspore division

During the microspore division in Datura innoxia, the mitotic spindle is oriented in planes both perpendicular (PE) and oblique (OB) to the spore wall against which the nucleus is situated. However, irrespective of polarity, the usual type of hemispherical wall is laid down at cytokinesis and isolates the generative cell from the rest of the pollen grain (type A). In PE spores the vegetative nucleus initially occupies a central position in the pollen grain, whereas in OB spores the vegetative nucleus lies at the periphery of the grain close to the generative cell. In anther cultures initiated just before the microspore division is due to take place, no marked change can be observed in either orientation or symmetry of the mitotic spindle when the spores divide. In some, however, cytokinesis is disrupted and deposition of the hemispherical wall arrested. In the absence of a complete wall, differentiation of the generative cell cannot take place and binucleate pollen grains are formed having 2 vegetative-type nuclei (type B). The 2 nuclei in the B pollens are always situated against the pollen-grain wall, suggesting that the disruption phenomenon is related to the OB spores. The incomplete wall always makes contact with the intine on the intine-side of the spindle. Wall material may be represented merely as short stubs projecting out from the intine into the cytoplasm, in which event the 2 nuclei lie close to each other and are separated by only a narrow zone of cytoplasm. In other grains the wall is partially developed between the nuclei and terminates at varying distances from the tonoplast; in these, the nuclei are separated by a wider zone of cytoplasm. The significance of these binucleate grains in pollen embryogenesis is discussed.