School-based assessment of practical competence in science: Some issues from English experience

Teacher-conducted assessments of practical skills are a compulsory component of GCSE examinations in science in England and Wales. The paper presents some of the findings of a research project that investigated this aspect of a science teacher's work. The project was concerned principally with the ways in which science teachers interpreted and operationalised the policy decision of central government and examination boards that teachers assume responsibility for the internal assessment of the practical competence of pupils aged 14–16 preparing for GCSE examinations in science. Specializations: the social history and politics of school science education     

Insulator-based dielectrophoresis of mitochondria

Isolated mitochondria display a wide range of sizes plausibly resulting from the coexistence of subpopulations, some of which may be associated with disease or aging. Strategies to separate subpopulations are needed to study the importance of these organelles in cellular functions. Here, insulator-based dielectrophoresis (iDEP) was exploited to provide a new dimension of organelle separation. The dielectrophoretic properties of isolated Fischer 344 (F344) rat semimembranosus muscle mitochondria and C57BL/6 mouse hepatic mitochondria in low conductivity buffer (0.025–0.030 S/m) at physiological pH (7.2–7.4) were studied using polydimethylsiloxane (PDMS) microfluidic devices. First, direct current (DC) and alternating current (AC) of 0–50 kHz with potentials of 0–3000 V applied over a channel length of 1 cm were separately employed to generate inhomogeneous electric fields and establish that mitochondria exhibit negative DEP (nDEP). DEP trapping potential thresholds at 0–50 kHz were also determined to be weakly dependent on applied frequency and were generally above 200 V. Second, we demonstrated a separation scheme using DC potentials <100 V to perform the first size-based iDEP sorting of mitochondria. Samples of isolated mitochondria with heterogeneous sizes (150 nm–2 μm diameters) were successfully separated into sub-micron fractions, indicating the ability to isolate mitochondria into populations based on their size.     

Magnetic compass orientation in C57BL/6J mice

We report evidence for a robust magnetic compass response in C57BL/6J mice. Mice were trained to build their nests in one of four magnetic directions by creating a light gradient along the long axis of a rectangular cage and positioning a nest box at the opposite (dark) end. The mice were then tested overnight in a circular, visually symmetrical arena in one of four magnetic field alignments. The positions of the nests built in the test arena showed strong unimodal orientation in the magnetic direction coinciding with the dark end of the training cage.