Browsing by Author "Wesso, Iona"

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    An investigation of the effects of donor age on some haematological characteristics of the Wistar rat (Rattus Norwegicus)
    (University of the Western Cape, 1986) Wesso, Iona; Van der Horst, G.
    Knowledge of haematological 'normdata', of experimental animals, and the biological variables that affect it is essential in order to recognise variations from the normal. In addition, the haemopoietic system may be regarded in principle as good material for studies of the cellular events associated with ageing. These considerations, together with the well documented effects of age on various physiological processes, prompted an investigation into the effects of donor age on several blood parameters. Review of the literature revealed that age-related changes in blood parameters have been reported for several species, but the documentation thereof is incomplete, inconsistent and inconclusive in many respects. Blood samples from male Wistar rats of nine different biological ages, ranging from birth to 96 weeks of age, were analysed for haematological and biochemical parameters. These included the blood cell counts, erythrocytic indices, haemoglobin concentration, haematocrit, erythrocytic 2,3-diphosphoglycerate and adenosine triphosphate levels, and erythrocytic glucose 6-phosphate dehydrogenase and pyruvate kinase activities. Data was obtained which demonstrates that all blood parameters measured underwent significant, although not al~ays regular, age-related changes. These changes were found to be more marked during the first month of life than at any other period. Evidence is also presented to show that the depressed haemoglobin concentration during the early postnatal life may not imply a condition of 'physiologic anaemia' as was previously thought. Since the blood profile exhibits only slight changes from about 24 weeks of age, it does not seem that the haemopoietic system of the old rat deteriorates significantly as to constitute a limiting factor for the animal's life. However, the importance of taking an animal's age into account when blood parameters constitute experimental results is emphasised. The second phase of this study involved a detailed investigation of the effect of the animal's age on erythrocytes in particular. These cells have limited life-spans, and are often used as models in studies of cellular ageing. Special emphasis was therefore placed on comparing the relative effects of host and cellular ageing on the properties of these cells. Erythrocytes from rats between one and 48 weeks of age were separated into two populations by a modification of the conventional density gradient centrifugation technique. The two populations were assumed to differ in mean cell age and were analysed for erythrocytic indices, phosphate ester concentrations and the activities of glucose 6-phosphate dehydrogenase and pyruvate kinase. Evidence is presented to show that ageing rat erythrocytes exhibit a decrease in volume, phosphate ester content and enzyme activities while the cellular haemoglobin concentration increases. Differences in the mean cell age however, does not seem to account for the donor-age-related effects observed in the whole blood parameters. Rather, the significant differences found in the characteristics of similarly aged red cells, between variously aged donors, demonstrate that the biological age of the organism influences the red cells and probably the ageing thereof in vivo. The contribution of the changing status of the erythrocyte's environment of progressively older animals, to alterations which take place in the ageing red cell is discussed.
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    Science text: Facilitating access to physiology through cognition-based reading intervention
    (University of the Western Cape, 1995) Wesso, Iona; Sinclair, A. J. L.
    Reading and understanding science text is the principal means by which students at tertiary level access scientific information and attain scientific literacy. However, understanding and learning from science texts require cognitive processing abilities which students mayor may not have. If students fail to understand scientific text, their acquisition of subject knowledge and expertise will be impeded and they will fail to develop into thinking and independent learners, so crucial for academic progress and achievement. A major assumption in this study is thus that in order to increase access to science subjects there is a need to explicitly teach the thinking abilities involved in learning science from text. A review of the literature showed that while reading to learn from scientific text poses special challenges to students faced with this unfamiliar genre, little is known about reading (and thinking) for science learning. A synthesis of current research which describes the neglected interface between science learning, science reading and cognition is given in the literature review of this study. This synthesis highlights, in particular, the parallel developments in research into science learning and reading; the lack of integration of research in these areas; the absence of investigations on science reading located within the cognitive domain; and the absence of research into reading as it affects cognition and cognition as it affects reading in subject-specific areas such as physiology Possibilities for improving students' cognitive performance in reading to learn through intervention were considered from a cognitive perspective. From this perspective, students' observable intellectual performance can be attributed to their underlying knowledge, behaviour, and thought processes. Accordingly, the mental processes involved in comprehending scientific concepts from text and the cognitive processes which the students bring to the learning situation become highly relevant to efforts to improve cognitive skills for learning science Key questions which were identified to serve as a basis for intervention included: a) What cognitive abilities are needed for competent reading comprehension as demanded by physiology text?; b) How adequate is the cognitive repertoire of students in dealing with physiology text? With regard to these questions a catalogue of cognitive functions as formulated by Feuerstein et al (1980) was identified as optimally suited for establishing the cognitive match between reading tasks and students. Micro-analyses of the cognitive demands of students' textbook material and the cognitive make-up of second-year university students revealed a profound mismatch between students and their learning material. Students lacked both comprehension fostering and comprehension monitoring abilities appropriate to the demands of the learning task. The explication of the cognitive requirements which physiology text demands served as a basis for systematically designing instruction whereby appropriate intellectual performance for scientific comprehension from text may be attained Subsequent intervention was based on the explicit teaching of thinking abilities within the context of domain-specific (physiology) knowledge. An instructional framework was developed that integrated cognitive learning theories and instructional prescriptions to achieve an effective learning environment and improve students' cognitive abilities to employ and extend their knowledge. The objective was that the instructional model and resultant instructional methods would ensure that students learn not only the desired kinds of knowledge by conceptual change, but also the thought processes embedded and required by reading scientific material for appropriate conceptual change to take place. Micro-analysis of the cognitive processes intrinsic to understanding physiology text illuminated cognitive demands such as, for example, the ability to: transform linearly presented material into structural patterns which illuminate physiological relationships; analyse conceptually dense text rich in "paradoxical jargon"; activate and retrieve extensive amounts of topic-specific and subject-specific prior knowledge; to visualise events; and contextualise concepts by establishing an application for it. Within the above instructional setting, the study shows that the notion of explicitly teaching the cognitive processes intrinsic to physiology text is possible. By translating the cognitive processes into cognitive strategies such as assessing the situation, planning, processing, organisation, elaboration, monitoring and reflective responses, the heuristic approach effectively served to guide students through various phases of learning from text. Systematic and deliberate methods of thought that would enhance students problem-solving and thinking abilities were taught. One very successful strategy for learning from physiology text was the ability to reorganise the linearly presented information into a different text structure by means of the construction of graphic organisers. The latter allowed students to read systematically, establish relationships between concepts, identify important ideas, summarise passages, readily retrieve information from memory, go beyond the given textual information and very effectively monitor and evaluate their understanding In addition to teaching appropriate cognitive strategies as demanded by physiology text, this programme also facilitated an awareness of expository text conventions, the nature of physiological understanding, the value of active strategic involvement in constructing knowledge and the value of metacognitive awareness. Also, since the intervention was executed within the context of physiology content, the acquisition of content-specific information took place quite readily. This overcame the problem of transfer, so often experienced with "content-free" programmes. In conclusion, this study makes specific recommendations to improve science education. Inparticular, the notion of teaching the appropriate cognitive behaviour and thought processes as demanded by academic tasks such as reading to learn physiology seems to be a particularly fruitful area into which science educational research should develop and be encouraged.