Students’ ability to solve process-diagram problems in secondary biology education

Process diagrams are important tools in biology for explaining processes such as protein synthesis, compound cycles and the like. The aim of the present study was to measure the ability to solve process-diagram problems in biology and its relationship with prior knowledge, spatial ability and working memory. For this purpose, we developed a test that represents process diagrams and adjacent tasks used in secondary education biology. Results show that the ability to solve process-diagram problems is correlated to prior knowledge, spatial abilities and visuospatial working memory capacity. A difference in impact of spatial skills was demonstrated for the level of cognitive demand when solving process-diagram problems

Participation of diatoms in the amino acid cycle of coastal waters; uptake and excretion in cultures

Micro-algae are thought to be involved in the turnover of pools of dissolved free amino acids (DFAA) in seawater either by their excretion or by the uptake of these compounds. Our study showed that, in vitro, 3 benthic diatom species were able to deplete small additions of individual Lamino acids down to concentrations below 10 to 40 nmol I-', as determined by HPLC. When nitrogen was limited, all test species scavenged their media for 10 or 11 amino acids added but Amphiprora cf. paludosa assimilated 3 amino acids also inthe presence of surplus nitrate. Navicula salinarum took up all 10 amino acids supplied, whereas Nitzschia closterium assimilated none of them, when nitrate was present. Excretion of DFAA could not be detected in the medium of growingnitrate-sufficient cultures; N. clostenum, N. saljnaium and A. cf. paludosa excreted respectively less than 0.03, 0.05 and 0.1 Oh of the cellular nitrogen as amino acids. Only silicate deprivation induced A. cf. paludosa to excrete 1 % cellular nitrogen as DFAA. The results show that benthic diatom populations may act as net consumers of DFAA, even when the concentrations are as low as 100 to 1,000 nmol I-', the range reported for nearshore seawater and the porewater of mudflat