Students' perceptions of a blended learning experience in dental education.

INTRODUCTION: "Flipped" instructional sequencing is a new instructional method where online instruction precedes the group meeting, allowing for more sophisticated learning through discussion and critical thinking during the in-person class session; a novel approach studied in this research. PURPOSE: The purpose of this study was to document dental students' perceptions of flipped-based blended learning and to apply a new method of displaying their perceptions based on Likert-scale data analysis using a network diagramming method known as an item correlation network diagram (ICND). In addition, this article aimed to encourage institutions or course directors to consider self-regulated learning and social constructivism as a theoretical framework when blended learning is incorporated in dental curricula. MATERIALS AND METHODS: Twenty (second year) dental students at a Northeastern Regional Dental School in the United States participated in this study. A Likert scale was administered before and after the learning experience to obtain evidence of their perceptions of its quality and educational merits. Item correlation network diagrams, based on the intercorrelations amongst the responses to the Likert-scale items, were constructed to display students' changes in perceptions before and after the learning experience. RESULTS: Students reported positive perceptions of the blended learning, and the ICND analysis of their responses before and after the learning experience provided insights into their social (group-based) cognition about the learning experience. The ICNDs are considered evidence of social or group-based cognition, because they are constructed from evidence obtained using intercorrelations of the total group responses to the Likert-scale items. CONCLUSIONS: The students positively received blended learning in dental education, and the ICND analyses demonstrated marked changes in their social cognition of the learning experience based on the pre- and post-Likert survey data. Self-regulated learning and social constructivism are encouraged as useful theoretical frameworks for a blended learning approach.

Bacterial and heterotrophic nanoflagellate densities and C-biomass estimates along an Alaskan tundra transect with prediction of respiratory CO2 efflux.

Although tundra terrestrial ecology is significantly affected by global warming, we know relatively little about how eukaryotic microbial communities respond and how much microbial respiratory CO(2) may be released due to available organic nutrient sources in the permafrost melt. Prior research has shown a strong positive correlation between bacteria and fungi in some Arctic locales; this research focused on the relationships of terrestrial bacteria and heterotrophic nanoflagellates. The densities and estimated C-biomass of bacteria and heterotrophic nanoflagellates (a major occurring group of protozoa) were assessed in 14 samples obtained along a 10 km transect in northwest AK during the summer of 2012. Two samples were taken, one at the top and one near the base of seven hummocks along the transect. Densities (no./g soil) of bacteria varied from 2.7-16 × 10(9), and nanoflagellates 0.7-7.9 × 10(7). C-biomass (µg/g soil) of bacteria varied from 358 to 2,114, and nanoflagellates 12-37. Additionally, the rate of respiration was analyzed in the laboratory for each soil sample. A linear relationship between soil respiration and bacterial densities was obtained (20 °C): R(s) = 12.32 + 14.07 Bd (p ≪ 0.01); where R(s) is soil respiration (nmol/min/g soil) and B(d) = bacterial density (no. × 10(9) /g soil).

The fate of organic sources of carbon in moss-rich tundra soil microbial communities: a laboratory experimental study.

Effects of glucose-carbon supplementation on soil respiration and bacterial and protist biomass were investigated in laboratory studies of three soil samples from Alaskan tundra: spring tussock sample 1 (thin surface moss), spring tussock sample 2 (thick surface moss), and a summer tundra open field sample. Addition of 1% (w/v) glucose solution produced an immediate, pronounced two to three fold increase in respiration above basal rate, which declined over 4 h to baseline levels. Less than 1% (w/w) of glucose-C supplement was respired during the respiratory spike, relative to the 89 µg/g added. A more substantial amount of the glucose-C became incorporated in microbial biomass. The total difference in microbial carbon (µg/g) between the experimental treatments and controls without glucose after 1 wk was as follows: spring sample 1 (8), spring sample 2 (31), and summer sample (70). The percent (w/w) of glucose-C incorporated was: spring sample 1 (5%), spring sample 2 (17%), and summer sample (39%), most attributed to biomass of bacteria and heterotrophic nanoflagellates. Although respiratory response to pulsed glucose-C was minimal, the overall mean basal rate after 1 wk ranged between 4 and 6 nmol/min/g soil, indicating a significant assimilation and respiration of constituent soil organic carbon.

Element patterns in albatrosses and petrels: influence of trophic position, foraging range, and prey type.

We investigated the concentrations of 22 essential and non-essential elements among a community of Procellariiformes (and their prey) to identify the extent to which trophic position and foraging range governed element accumulation. Stable isotope analysis (SIA) was used to characterise trophic (delta(15)N) and spatial patterns (delta(13)C) among species. Few consistent patterns were observed in element distributions among species and diet appeared to be highly influential in some instances. Arsenic levels in seabird red blood cells correlated with delta(15)N and delta(13)C, demonstrating the importance of trophic position and foraging range for arsenic distribution. Arsenic concentrations in prey varied significantly across taxa, and in the strength of association with delta(15)N values (trophic level). In most instances, element patterns in Procellariiformes showed the clearest separation among species, indicating that a combination of prey selection and other complex species-specific characteristics (e.g. moult patterns) were generally more important determining factors than trophic level per se.

Plant growth in elevated CO2 alters mitochondrial number and chloroplast fine structure.

With increasing interest in the effects of elevated atmospheric CO(2) on plant growth and the global carbon balance, there is a need for greater understanding of how plants respond to variations in atmospheric partial pressure of CO(2). Our research shows that elevated CO(2) produces significant fine structural changes in major cellular organelles that appear to be an important component of the metabolic responses of plants to this global change. Nine species (representing seven plant families) in several experimental facilities with different CO(2)-dosing technologies were examined. Growth in elevated CO(2) increased numbers of mitochondria per unit cell area by 1.3-2.4 times the number in control plants grown in lower CO(2) and produced a statistically significant increase in the amount of chloroplast stroma (nonappressed) thylakoid membranes compared with those in lower CO(2) treatments. There was no observable change in size of the mitochondria. However, in contrast to the CO(2) effect on mitochondrial number, elevated CO(2) promoted a decrease in the rate of mass-based dark respiration. These changes may reflect a major shift in plant metabolism and energy balance that may help to explain enhanced plant productivity in response to elevated atmospheric CO(2) concentrations.

Naked Amoebas and Bacteria in an Oil-Impacted Salt Marsh Community.

Populations of soil amoebas were monitored in two salt marshes in Staten Island, NY for 2 years. One site, Gulfport Reach on the Arthur Kill, has been highly impacted by numerous oil spills. In particular, in 1990 a massive no. 2 fuel oil spill from a ruptured pipe flooded the area; its sediments had total petroleum hydrocarbon (TPH) concentrations in the range 800-46,000 ppm. A reference site 11 km away, on the Atlantic coast, had low TPH levels. Amoeba population densities were in general higher in the impacted sediments. In laboratory microcosm experiments, sediment samples from unimpacted sites were treated with added fresh (unweathered) hydrocarbons (no. 2 fuel oil) and cultured; these also yielded higher amoeba numbers than untreated controls. Four distinct amoeba morphotypes were monitored. Changes in population levels of total amoebas were correlated in the two sites, particularly for morphotype 2 (r = 0.83). The ratios of total amoebas to total bacterial numbers were also correlated (r = 0.85) between the sites. This suggests the amoebas may function as generalists, and that their trophic relation to bacterial prey is not much affected by the presence of petroleum hydrocarbons, but rather may reflect regional parameters such as ambient temperature or other physical factors.

Platyamoeba pseudovannellida n. sp., a naked amoeba with wide salt tolerance isolated from the Salton Sea, California.

A new species of naked amoeba, Platyamoeba pseudovannellida n.sp., is described on the basis of light microscopic and fine structural features. The amoeba was isolated from the Salton Sea, California, from water at a salinity of ca. 44%. Locomotive amoebae occasionally had a spatulate outline and floating cells had radiating pseudopodia, sometimes with pointed tips. Both these features are reminiscent of the genus Vannella. However, the surface coat (glycocalyx) as revealed by TEM indicates that this is a species of Platyamoeba. Although salinity was not used as a diagnostic feature, this species was found to have remarkable tolerance to fluctuating salinity levels, even when changes were rapid. Amoebae survived over the range 0 per thousand to 150 per thousand salt and grew within the range 0 per thousand to 138 per thousand salt. The generation time of cells averaged 29 h and was not markedly affected by salt concentration. This is longer than expected for an amoeba of this size and suggests a high energetic cost of coping with salinity changes. The morphology of cells changed with increasing salinity: at 0 per thousand cells were flattened and active and at the other extreme (138 per thousand) amoebae were wrinkled and domed and cell movement was very slow. At the ultrastructural level, the cytoplasm of cells grown at high salinity (98 per thousand was considerably denser than that of cells reared at 0 per thousand.

Abundance of terrestrial gymnamoebae at a northeastern U. S. site: a four-year study, including the El Niño winter of 1997-1998.

The abundance, sizes, and when appropriate, diversity of gymnamoebae were documented at approximately monthly intervals for four years (1995-1998) at a grassy, terrestrial site slightly upslope from a freshwater pond. Soil samples were analyzed for viable gymnamoebae using a standard laboratory culturing protocol. The mean density of gymnamoebae based on the total data set was ca. 1,600/g (s.e.+/-190). Minimum densities of gymnamoebae (156/g) occurred in January 1995, and a maximum for the sampling period (5,838/g) occurred in July 1997, when a rainy period followed an extended period of drought. Among the environmental variables monitored (precipitation, soil moisture, organic content, and temperature) only precipitation correlated significantly with abundance of gymnamoebae (r = 0.34, p = 0.02). During the mild, moist El Niño winter of 1997-1998, a larger than usual number of gymnamoebae was recorded at the site (approximately 3,800/g) compared to a mean density of approximately 900/g for comparable periods in preceding years. The mean sizes were also larger. Since gymnamoebae are increasingly recognized as major members of soil microbial communities enhancing soil fertility through nutrient mineralization, it is important to document environmental variables that influence their abundance and activity in terrestrial ecosystems.

A survey of flagellate diversity at four deep-sea hydrothermal vents in the Eastern Pacific Ocean using structural and molecular approaches.

Eighteen strains of flagellated protists representing nine species were isolated and cultured from four deep-sea hydrothermal vents: Juan de Fuca Ridge (2,200 m), Guaymas Basin (2,000 m), 21 degrees N (2,550 m) and 9 degrees N (2,000 m). Light and electron microscopy were used to identify flagellates to genus and, when possible, species. The small subunit ribosomal RNA genes of each vent species and related strains from shallow-waters and the American Type Culture Collection were sequenced then used for comparative analysis with database sequences to place taxa in an rDNA tree. The hydrothermal vent flagellates belonged to six different taxonomic orders: the Ancyromonadida, Bicosoecida, Cercomonadida, Choanoflagellida, Chrysomonadida, and Kinetoplastida. Comparative analysis of vent isolate and database sequences resolved systematic placement of some well-known species with previously uncertain taxonomic affinities, such as Ancyromonas sigmoides, Caecitellus parvulus, and Massisteria marina. Many of these vent isolates are ubiquitous members of marine, freshwater, and terrestrial ecosystems worldwide, suggesting a global distribution of these flagellate species.

Insights on the diversity within a "species" of Thalassicolla (Spumellarida) based on 16S-like ribosomal RNA gene sequencing.

We compared 16S-like ribosomal RNA (rRNA) coding regions of samples of the solitary spumellarian radiolarian Thalassicolla nucleata collected from the Sargasso Sea and the Pacific Ocean. Sequences derived from these locations showed variability in both length and base-pair composition. This level of sequence variability is similar to the degree of variability reported in the literature for species- or even genus-level distinctions. Explanations for our results include multiple alleles for the rRNA gene, or the existence of multiple species of Thalassicolla that are morphologically indistinguishable. The seven existing descriptions of Thalassicolla species, including T. nucleata, are discussed in view of these molecular findings and with reference to our current understanding of the physiology and life cycle of the spumellarian radiolaria.

Fine structure observations of phagotrophic activity by plasmodia of Physarum polycephalum.

Scanning electron microscopic observations of feeding plasmodia show three characteristic features: 1) extension of multilobed pseudopodia protruding from the leading edge of the plasmodium as it advances onto the surface of a food particle, 2) confluence of the lobes to form a sheath-like pseudopodium attached to the surface of the food particle, and 3) protrusion of small nodules with thin lamellar projections from the leading edge of the plasmodium. Sections through freeze-dried preparations of the feeding plasmodium exhibit a highly convoluted under surface in contact with loosened starch grains that appear to be released by extracellular digestion. The cytoplasm, viewed by transmission electron microscopy, contains branched, internally penetrating canals (ca. 2 microns wide) enclosing engulfed starch grains. Starch grains in the deeper part of the canals are more electron dense and appear to be digested. Micropseudopodia (70-80 nm dia.), projecting from the surface of the canals, protrude toward and into the ingested starch grains. Digestive marker enzyme (acid phosphatase) activity was detected cytochemically in food particles penetrated by micropseudopodia indicating a digestive role for these structures not reported previously.

Light and electron microscopic observations of feeding behavior, nutrition, and reproduction in laboratory cultures of Thalassicolla nucleata.

T. nucleata is a skeletonless, single-celled radiolarian commonly found in ocean surface water. Specimens were cultured in the laboratory in a seawater--antibiotic medium. Feeding experiments show that T. nucleata is omnivorous with preference for crustacea, colorless flagellates, and occasional diatoms. Pigmented algae bearing organic thecae are occasionally consumed, but Dunaliella sp. is rejected. Rhizopodial activity during algal predation is compared to activity during crustacean predation, and evidence for differentiation of function among rhizopodia is presented. Electron microscopic observations and evidence from cytochalasin B treatment support the hypothesis that microfilaments mediate organized rhizopodial streaming. Reproduction is by isospores which resemble those in other spumellarian Radiolaria. Survival time in laboratory culture indicates that T. nucleata has a life span of at least 3 weeks. These findings are discussed in relation to the unique requirements imposed by a pelagic habitat on survival of a single-celled floating organism.

Gametogenesis in planktonic foraminifera.

Gametogenesis in Globigerinella aequilateralis and Globigerinoides sacculifer in culture is preceded by sinking of the organism and loss of its spines. Hundreds of thousands of flagellated gametes, about 5 micrometers in diameter, are produced within the parent shell and released within a period of 13 hours.

Ultrastructure of a colonial radiolarian collozoum inerme and a cytochemical determination of the role of its zooxanthellae.

Collozoum inerme (Müller) is a colonial Radiolarian containing numerous cells bound in a common gelatinous matrix. The cells do not posses a skeleton as observed in many unicellular Radiolaria, but the cytoplasmic organization is similar. The cells are multinucleate and a complex system of cellular processes containing mitochondria, Golgi, and numerous vacuoles radiate out from the nuclear region. The endoplasm is connected to the ectoplasm across a double membrane boundary by thin cytoplasmic strands called fusules whose structure resemble those in unicellular Radiolaria. The ectoplasm contains a lacy network of vacuoles containing an osmiophilic substance. Rhizopodia emerge from the ectoplasmic sheath. Some are thin and densely granular. Larger diameter rhizopodia, containing less dense cytoplasm, sequester the zooxanthellae which present a typical dinoflagellate fine structure. Some of the zooxanthellae are apparently cultivated since they are sometimes observed dividing and persist in large numbers when colonies are cultivated under illumination for several weeks in the laboratory. However, colonies maintained in the dark have a decline in number of zooxanthellae and light microscopic examination shows they are being drawn into the ectoplasm of the radiolarian cells. Electron microscopic examination of zooxanthellae drawn into the ectoplasm sheath indicates they are digested. C. inerme is a remarkable example of a simple cellular aggregate that has exploited its colonial habit to culture algae and use them as food thus possibly enhancing the viability of the colony.

Photocontrol of Anthocyanin Synthesis: III. The Action of Streptomycin on the Synthesis of Chlorophyll and Anthocyanin.

Streptomycin enhances the synthesis of anthocyanins and inhibits the synthesis of chlorophylls and the development of chloroplasts in dark-grown seedlings of cabbage (Brassica oleracea), mustard (Sinapis alba), tomato (Lycopersicon esculentum), and turnip (Brassica rapa) exposed to prolonged periods of irradiation in various spectral regions. These results suggest that the contribution of photosynthesis to light-dependent high irradiance reaction anthocyanin synthesis in seedlings of cabbage, mustard, tomato, and turnip is minimal, if any at all. So far, phytochrome is the only photoreceptor whose action in the control of light-dependent anthocyanin synthesis in seedlings of cabbage, mustard, tomato, and turnip has been satisfactorily demonstrated.