Using the US national sample from the Third International Mathematics and Science Study (TIMSS) and the Rasch modeling method, this study identified the conceptual progression sequence of various matter concept aspects, and compared students' latent abilities against the sequence. We found that the four matter aspects, i.e. conservation, physical properties and change, chemical properties and change, and structure and composition, are interrelated. Although they differ in overall difficulty with an increased difficulty from conservation to physical properties and change to chemical properties and change and to structure and composition, the difference among them is not statistically significant at the 0.05 level. Elementary school students (3rd and 4th grades) have an average latent ability below the average difficulty of items on the conservation aspect; 7th graders' average latent ability is above the average difficulty level of the conservation and physical properties and change aspects; 8th and 12th grade students' average latent ability is above the average difficulty level of all the aspects except for structure and composition; and 12th grade science specialization students' average latent ability is above the average difficulty level of all the four aspects. We proposed a dynamic overlapping wave model of matter concept development to make sense the above-identified progression patterns.

Adopting a neo‐Piagetian conceptual framework and a phenomenographic approach, we identified students' conceptual progression pattern on matter from elementary to high school. We interviewed 54 students from Grade 1 to Grade 10 chemistry on their conceptions of substances (i.e., water, vinegar, and baking soda) and the combining of the substances. We found that progression of students' conceptions on matter from elementary to high school is multifaceted. For any aspect we examined, from spontaneous description of substances to chemical reaction of baking soda with vinegar, there was a unique progression pattern. Different conceptual progression patterns existed for different substances (i.e., water, baking soda, and vinegar) as well. Further, there is no clear conceptual leap between different grade levels in conceptual progression; that is, there is tremendous overlap in conceptions among students of different grades. © 2006 Wiley Periodicals, Inc. J Res Sci Teach 43: 320–347, 2006

The unidirectional fluxes of 20, 100, 500, and 2,000 microM rho-aminohippurate (PAH) were measured under open- and short-circuit conditions in canine tracheal epithelium mounted as flat sheets in Ussing chambers. In tissues pretreated with mucosal indomethacin (10(-6) M) and amiloride (10(-4) M), unidirectional PAH fluxes under short-circuit conditions increased with increasing bath concentrations but there was no significant net PAH transport. After stimulation of chloride secretion by mucosal cyclic adenosine 3',5' -cyclic monophosphate (cAMP 10(-3) M), there was a significant increase in the secretory flux of PAH and a significant decrease in the absorptive flux of PAH. This resulted in net PAH secretion that demonstrated saturation kinetics with an apparent Michaelis-Menten constant of 754 microM by Lineweaver-Burk analysis. Intracellular concentrations of PAH were 0.4-1.2 times bath concentrations after pretreatment with indomethacin and amiloride and increased to 2.6-3.3 times bath concentrations after cAMP. Under open-circuit conditions, secretory PAH flux decreased and absorptive flux increased resulting in net PAH absorption. We conclude from these early studies that the canine tracheal epithelium possesses a specialized system for the transport of organic anions in the airways and that this transport system may share many similarities with organic anion transport in the kidney.

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