Food systems need to produce enough of the essential trace element Se to provide regular adult intakes of at least 40 microg/d to support the maximal expression of the Se enzymes, and perhaps as much as 300 microg/d to reduce risks of cancer. Deprivation of Se is associated with impairments in antioxidant protection, redox regulation and energy production as consequences of suboptimal expression of one or more of the Se-containing enzymes. These impairments may not cause deficiency signs in the classical sense, but instead contribute to health problems caused by physiological and environmental oxidative stresses and infections. At the same time, supranutritional intakes of Se, i.e. intakes greater than those required for selenocysteine enzyme expression, appear to reduce cancer risk. The lower, nutritional, level is greater than the typical intakes of many people in several parts of the world, and few populations have intakes approaching the latter, supranutritional, level. Accordingly, low Se status is likely to contribute to morbidity and mortality due to infectious as well as chronic diseases, and increasing Se intakes in all parts of the world can be expected to reduce cancer rates.

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Selenium in global food systems.

The applications of ultrasound as auxiliary energy for accelerating leaching processes are reviewed to alert analysts to its advantages. The widely used batch systems are compared with dynamic systems, the use of which is still very rare. Comparison of ultrasound-assisted leaching with other sorts of leaching, such as Soxhlet, microwave-assisted and supercritical fluid extraction, shows the potential of ultrasound for leaching in a number of areas.

Ultrasound: a powerful tool for leaching

This paper summarizes case studies developed by a group of collaborating educators. We investigated ways of speaking that encourage students to (a) formulate insightful questions about science topics and (b) express their own ideas during reflective discussions. The authors include elementary, high school, and college faculty. Subject-matter contexts included phases of the moon, motion, electricity, light, and waves. In developing case studies, we documented and interpreted student and teacher questions during the three ways of speaking we value most: guided discussions, student-generated inquiry discussions, and peer collaborations. Student questions occurred when we set up discourse structures that explicitly elicited student questions, engaged students in conversations about familiar contexts in which they had made many observations over a long time period, created comfortable discourse environments in which students could try to understand one another's thinking, and established small groups where students were collaborating with one another. Typically we elicited student thinking by asking questions that develop conceptual understanding. These included questions to help students clarify their meanings, explore various points of view in a neutral and respectful manner, and monitor the discussion and their own thinking. We also elicited student thinking by practicing quietness through long wait times, attentive silence, and reticence. © 2001 John Wiley & Sons, Inc. J Res Sci Teach 38: 159–190, 2001

Student and teacher questioning during conversations about science

The metalloid Se is ubiquitous in soils, but exists mainly in insoluble forms in high-Fe, low-pH and certain leached soils, and hence is often of limited availability to plants. Consequently, it is often supplied by plants to animals and human consumers at levels too low for optimum health. Se deficiency and suboptimality are manifested in populations as increased rates of thyroid dysfunction, cancer, severe viral diseases, cardiovascular disease and various inflammatory conditions. Se deficiency probably affects at least a billion individuals. Optimal cancer protection appears to require a supra-nutritional Se intake, and involves several mechanisms, which include promotion of apoptosis and inhibition of neo-angiogenesis. Evidence suggests that in some regions Se is declining in the food chain, and new strategies to increase its intake are required. These could include education to increase consumption of higher-Se foods, individual supplementation, food fortification, supplementation of livestock, Se fertilisation of crops and plant breeding for enhanced Se accumulation. Se levels in Australian residents and wheat appear to be above the global estimated mean. Wheat is estimated to supply nearly half the Se utilised by most Australians. Increasing the Se content of wheat represents a food systems approach that would increase population intake, with consequent probable improvement in public health and large health cost savings. The strategies that show most promise to achieve this are biofortification by Se fertilisation and breeding wheat varieties that are more efficient at increasing grain Se density. Research is needed in Australia to determine the most cost-effective fertilisation methods, and to determine the extent of genetic variability for grain Se accumulation. Before recommending large-scale fortification of the food supply with Se, it will be necessary to await the results of current intervention studies with Se on cancer, HIV and AIDS, and asthma.

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High-selenium wheat: biofortification for better health.

Soil type influences crop mineral composition in Malawi.

As an important subject in the curriculum, many students find chemistry concepts difficult to learn and understand. Chemical bonding especially is important in understanding the compositions of chemical compounds and related concepts and research has shown that students struggle with this concept. In this theoretical paper based on analysis of relevant science education research, textbooks, and our classroom observations and teaching experiences, the authors argue that the difficulty in learning chemical bonding concepts is associated with the sequence (ionic, covalent and polar covalent bonding) in which students are taught because this sequence receives little support from constructivist theories of learning. Consequently, the paper proposes a sequence to teach chemical bonding (covalent, polar covalent and ionic bonding) for effective and sustainable learning. In this sequence, the concepts are developed with minimum reorganisation of previously learned information, using a format which is claimed to be easy for students to learn. For teaching these concepts, the use of electronegativity and the overlap of atomic orbitals for all types of bonding have also been stressed. The proposed sequence and emphasis on electronegativity and atomic orbital overlap meets the criteria for teaching and learning of concepts based on the psychology of learning including the theory of constructivism necessitating the construction of new knowledge using related prior knowledge. It also provides a better linkage between the bonding concepts learned at secondary and tertiary levels. Considering these proposed advantages for teaching, this sequence is recommended for further research into effective and sustainable teaching.

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Prospective pedagogy for teaching chemical bonding for smart and sustainable learning

A novel method for sample preparation by ultrasound-accelerated solid-liquid extraction prior to selenium determination in the phosphate-rich biological samples by electrothermal atomization atomic absorption spectrometry (ETAAS) with continuum-source background correction and nickel nitrate as a chemical modifier was established and compared with the results of conventional sample wet decomposition (however, this last item was not the object of this study). Diluted (4%) nitric acid was used as an extraction medium. The evaluation of the analytical results for biological Certified Reference Materials indicates that the results of a selenium determination after wet acid digestion (HNO3+HCl+H2O2) agreed well with the certified values, whereas the proposed solid-liquid extraction procedure can be used for simple and rapid control of the selenium levels.

Ultrasound Accelerated Solid-Liquid Extraction for the Determination of Selenium in Biological Samples by Electrothermal Atomization Atomic Absorption Spectrometry

Selenium is essential for humans because it protects the heart against cardiomyopathy. It may also reduce ischaemic heart disease owing to its antioxidant activity. It is known that Indian migrants in a number of countries have high incidences of ischaemic heart disease. In this study, fasting plasma selenium concentrations of Sikh migrants in Sydney (Australia) were measured to investigate whether selenium concentration is reduced in this community. The mean concentration of selenium in plasma (91.8 ± 15.0 ng ml–1, n = 196) was within the normal range. A significantly higher plasma selenium concentration was demonstrated in males than in females (p < 0.01). This was mainly due to the difference in mean selenium concentrations between genders in vegetarians because no significant difference was observed in non-vegetarian males versus females. The mean concentration of selenium in teetotal males was similar to those who consumed alcohol. Despite significant variations with gender and diet, the selenium concentrations were within the normal range. The results suggest that selenium status is adequate in this Sikh community even though vegetarian diet is common and alcohol use is condoned in males.

Plasma selenium concentrations in a Sikh population in Sydney, Australia†

A model of the effects of rate of teacher communication on student acquisition of information

Students who study science in single-sex and coeducational schools have attracted lots of attention from the education community. However, changes to students’ attitudes toward science as they progress to higher grades in these schools are not clearly understood. The aim of this study was to compare the changes in attitudes toward science among lower secondary students (Grade 7 to Grade 9) in single-sex and coeducational schools in Brunei. A cross-sectional survey design was used to collect data from 1,034 students. Despite a significant nonlinear decline in attitudes toward science from Grade 7 to Grade 9, the attitudes remained positive. This decline in attitudes toward science was at a minimum for students in the coeducational school, and it followed the following order: single-sex boys > single-sex girls > coeducational students. The decline was independent of the initial perceived values of the students’ attitudes, and it followed different trends when the data of the same-sex students from single-sex and coeducational schools were compared. Male students from the SSB school had more chances for significant decline as they progressed from Year 7 to Year 9. Brunei and countries with similar intentions to expand single-sex and coeducation school systems can target communication between single-sex and coeducation schools so they may learn from each other to improve the effectiveness of science teaching and learning processes. We expect that academics and administrators can benefit from the results of this study to guide their secondary science education policies, curriculum reforms, and teaching practices.

Harkirat S. Dhindsa

Papers

Prospective pedagogy for teaching chemical bonding for smart and sustainable learning

Ultrasound Accelerated Solid-Liquid Extraction for the Determination of Selenium in Biological Samples by Electrothermal Atomization Atomic Absorption Spectrometry

Plasma selenium concentrations in a Sikh population in Sydney, Australia†

A model of the effects of rate of teacher communication on student acquisition of information

Affective Domain Progression in Single-Sex and Coeducational Schools