A morphometric method for correcting phytoplankton cell volume estimates

Cell volume calculations are often used to estimate biomass of natural phytoplankton assemblages. Such estimates may be questioned due to morphological differences in the organisms present. Morphometric analysis of 8 species representative of phytoplankton types found in the Great Lakes shows significant differences in cell constituent volumes. Volume of physiologically inert wall material ranges from nil, in some flagellates, to over 20% of the total cell volume in certain diatoms. Likewise, “empty” vacuole may comprise more than 40% of the total cell volume of some diatoms, but less than 3% of the volume of some flagellates. In the organisms investigated, the total carbon containing cytoplasm ranged from 52% to 98% of the total cell volume and the metabolizing biovolume ranged from 30% to 82%. Although these differences complicate direct biomass estimation, morphometric analysis at the ultrastructural level may provide ecologically valuable insights.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41732/1/709_2005_Article_BF01275650.pd

Making sense of shared sense-making in an inquiry-based science classroom: Toward a sociocultural theory of mind.

Despite considerable exploration of inquiry and reflection in the literatures of science education and teacher education/teacher professional development over the past century, few theoretical or analytical tools exist to characterize these processes within a naturalistic classroom context. In addition, little is known regarding possible developmental trajectories for inquiry or reflection---for teachers or students---as these processes develop within a classroom context over time. In the dissertation, I use a sociocultural lens to explore these issues with an eye to the ways in which teachers and students develop shared sense-making, rather than from the more traditional perspective of individual teacher activity or student learning. The study includes both theoretical and empirical components. Theoretically, I explore the elaborations of sociocultural theory needed to characterize teacher-student shared sense-making as it develops within a classroom context, and, in particular, the role of inquiry and reflection in that sense-making. I develop a sociocultural model of shared sense-making that attempts to represent the dialectic between the individual and the social, through an elaboration of existing sociocultural and psychological constructs, including Vygotsky's zone of proximal development and theory of mind. Using this model as an interpretive framework, I develop a case study that explores teacher-student shared sense-making within a middle-school science classroom across a year of scaffolded introduction to inquiry-based science instruction. The empirical study serves not only as a test case for the theoretical model, but also informs our understanding regarding possible developmental trajectories and important mechanisms supporting and constraining shared sense-making within inquiry-based science classrooms. Theoretical and empirical findings provide support for the idea that perspectival shifts---that is, shifts of point-of-view that alter relationships and proximities of elements within the interaction space---play an important role in shared sense-making. Findings further suggest that the mutually constitutive interaction of inquiry and reflection plays a key role in flexible shared sense-making. Finally, findings lend support to the idea of a dialectical relationship between human models of shared sense-making and human systems of shared sense-making; that is, the ways in which human minds are coordinated is a work in progress, shaping and shaped by human culture.Ph.D.EducationEducational psychologyScience educationUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125799/2/3224667.pd

Intracisternal fibers in the liver cells of starved frogs

Fibers observed within the cisternae of endoplasmic reticulum of liver cells of Rana pipiens are described. Fibers were observed only in animals subjected to starvation, but the frequency of fiber occurrence was found to vary widely from animal to animal and from cell to cell within the same animal. It is, therefore, suggested that starvation is important in, but not solely responsible for, the process of fiber formation. Some characteristic morphological changes observed in fiber-containing cells are described, and a tentative theory outlining a possible sequence of steps involved in fiber formation is presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33871/1/0000132.pd

Quantitative ultrastructural studies of hepatocytes from fed and starved frogs

Stereological analysis of liver tissue excised from mature female Rana pipiens starved for 59 days and from a fed control group was conducted both at the light and electron microscopy levels. Average cellular volume decreased by more than a factor of 4 following prolonged fasting. Nuclear volume was not significantly decreased. Mitochondrial volume per cell showed a slight, though not statistically significant, decrease from 540 Μm 3 to 420 Μm 3 . Rough endoplasmic reticulum decreased in absolute surface area per cell from 13,600 Μm 2 /cell to 3,000 Μm 2 /cell after starvation, but its surface density in the cytoplasm remained relatively constant. Lipid decreased from 650 Μm 3 per cell to less than 1 Μm 3 per cell after fasting. Glycogen decreased from 49% of hepatocyte cytoplasmic volume to less than 15%, a decrease in absolute volume from 4,000–240 Μm 3 per cell. Glycogen changed from the Α to the Β-configuration during fasting. Condensed cross-banded fibers or sheets formed within the rough endoplasmic reticulum cisternae of some fasted animals. The significance of these results relative to the energy metabolism of poikilotherms is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38085/1/1402100304_ftp.pd

Synergistic effects of nutrients and lead on the quantitative ultrastructure of Cyclotella (Bacillariophyceae)

A four-way completely crossed factorial enrichment experiment (2T×2Si×2Pb×2P) was used to analyze the short (2 hr) and long (48 hr) term effects of nutrients and lead on the quantitative ultrastructure of Cyclotella , a diatom. Some of the cytological modifications that have been reported to occur in other algae as a result of heavy metal exposure occurred in Cyclotella , but were mediated in some cases by the addition of low levels of nutrients. While it is extremely difficult to simulate the natural environment where a variety of parameters may be changing simultaneously, it is suggested that factorial design experiments approximate it more closely. Furthermore, environmental factors that may change the availability of metals may also change the physiological state of the cells, which may also either amplify or mitigate the metal effects.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48062/1/244_2005_Article_BF01061106.pd