Effect of Zone of Proximal Development on the Performance of Learners in Stoichiometry in Selected Secondary Schools in the Zambezi Region, Namibia

This study investigated the effect of the Zone of Proximal Development (ZPD) on the performance of secondary school learners in stoichiometry in three selected schools currently doing Physical Science at Higher and Ordinary levels in the Zambezi Region, Namibia. Structured questionnaires were used to collect information bothering on learners’ knowledge of stoichiometry contents, perceived factors affecting learners’ performance in stoichiometry and strategies for improvingperformance in stoichiometry. A total of 83 participants from four secondary schools were randomly selected to fill the questionnaires. The results obtained showed that only 29.25% of the participants indicated that they have good knowledge of stoichiometry to solve related problems while 55.50% disagreed and 15.25% were undecided. On the perceived factors affecting learners’ performance in stoichiometry, it was found that only 28.25% of the participants indicated that they understand the principles of stoichiometry while majority indicated lack of understanding of the principles such as reactant-reactant pair and reactant-product pair needed to effectively plan solution to stoichiometry problem. There is also lack of peer-assisted learning as indicated by the participants. Peer-assisted learning is a very helpful approach to solving general academic problems as learners could easily discover useful tips through exchanging of ideas. On the strategies for improving performance in stoichiometry, only 13.00% of the participants indicated that they do meet their science teachers for help when solving stoichiometry problems but majority do not and are also not aware of any tutorial class to help week learners in stoichiometry.However, the majority (55.75%) of the participants disagreed with the idea whether stoichiometry should be removed from secondary school syllabus. Considering the challenges learners faced in stoichiometry in the study area and majority are still willing to have it on their syllabus, we recommend that further indepth research be carried out to identify specific challenges responsible for learners’ poor performances in stoichiometry in the study area and devise remediation measures. There is also need to institute proper strategies that will support learners understanding of stoichiometry taught in secondary schools in the region

Some Heavy Metals Content of Cabbage and Soil Cultivated in the Bezi Bar Farm Area of Katima Mulilo, Namibia

Abstract The accumulation of heavy metals in agricultural soils is of increasing concern due to food safety and potential health risks. This study determined the concentrations of chromium, cadmium, cobalt, lead, nickel and arsenic in the cabbage and soil obtained from the Bezi bar farm area of Katima Mulilo and compare the results with regulatory limits. Samples of the cabbage and soil were randomly collected from the same points in the farm during mid-October, 2013; 4 Months After Planting (4MAP). The samples were digested using EPA methods 3052 (cabbage) and 3050B (soil) followed by ICP-OES (ICP: Perkin Elmer Optima 7000 DV) analyses. The heavy metals concentrations in the cabbage varied between 2.00 mg/kg -0.05 mg/kg while in the farm soil, the result varied between 3.60 mg/kg -0.2 mg/kg. The soil-cabbage transfer factors of the heavy metals showed the following bio-accumulation trend: Ni (1.25) > Cd (0.40) > Pb (0.23) > Cr (0.20) > Co (0.04) > As (0.03). There were very high positive correlations between the cabbage and soil heavy metals which suggest common source of input. Although, the present levels of the heavy metals were lower than their regulatory limits in vegetable and agricultural soil; continuous accumulation is a concern to the produce safety and quality because of chronic human exposure. The soil properties revealed poor nutrient status resulting to the high usage of chemical fertilizer in order to improve cabbage yield and this pose threat to the produce quality and safety. Therefore, it becomes imperative for the farmer to consider using organic manure in enhancing the soil fertility in order to limit accumulations of residual chemicals in the soil and crop