Chew, Shit Fun

In order to refine teaching styles and methods of assessing students' learning, it is important to realise the perceptions different schools hold about teaching and learning. Thus, this study was undertaken to compare students in the Bachelor of Science with Diploma in Education (Secondary) programme (PGDE) on their perceptions of the desirable characteristics of a "good" lecturer, their preferences of teaching methods and student assessment, their motives for taking the course and their learning styles employed. The results indicate that both groups of students were genuinely interested in the courses they enrolled in. Although there was a high degree of unanimity among students in their conception of a "good" lecturer and their preferred learning styles, the PGDE students preferred lecturers who were more expressive. In addition, the PGDE students were more independent in their learning than the BSC students. The findings of the present study may serve to kindle some genuine ideas among lecturers on how to improve the quality of teaching and learning in the University.

Giant clams generally harbor phototrophic Symbiodiniaceae dinoflagellates of genera Symbiodinium, Cladocopium, and Durusdinium. The coccoid symbiotic dinoflagellates (zooxanthellae) reside extracellularly inside the lumen of zooxanthellal tubules in the colorful outer mantle. They obtain from the host inorganic carbon (Ci) for photosynthesis and supply photosynthate to the host. The outer mantle has a host-derived carbon concentration mechanism (CCM) to facilitate the transport of Ci from the hemolymph into the luminal fluid. To regulate Ci uptake, the symbionts probably possess their own CCMs that comprise an extracellular alpha carbonic anhydrase (αCA) and a proton transporter. Indeed, we obtained from the outer mantle of the giant clam, Tridacna squamosa, three complete cDNA coding sequences of a membrane-associated αCA derived from Symbiodinium (Symb-αCA), Cladocopium (Clad-αCA), and Durusdinium (Duru-αCA), which consisted of 2808, 2847, and 2829 bp, respectively. The respective encoded proteins had 935 (104.7 kDa), 948 (106.1 kDa), and 942 (105 kDa) amino acids, each containing a transmembrane domain. The outer mantle had the highest level of Duru-αCA transcripts. Phenogramic analyses denoted Duru-αCA as an extracellular CA closely associated with human CA4 and had a dinoflagellate-origin. Using an antibody that could react comprehensively with zooxanthellae-αCAs (Zoox-αCA) derived from all three genera of dinoflagellate, immunofluorescence microscopy revealed immuno-labeling at the dinoflagellate’s plasma membrane. As Symb-αCA, Clad-αCA, and Duru-αCA possessed extracellular catalytic domains, they could catalyze the dehydration of HCO3− to CO2 in the luminal fluid. Importantly, illumination led to significant increases in the gene and protein expression levels of Zoox-αCA/Zoox-αCA in the outer mantle of T. squamosa. Taken together, Zoox-αCA could be part of the symbiont’s light-enhanced external CCM to promote and regulate the acquisition of Ci from the host for photosynthesis. Our results also suggested that the potentials of generating CO2 adjacent to the symbionts’ plasma membrane could differ among different phylotypes of Symbiodinium and Cladocopium.

Giant clams harbor three genera of symbiotic dinoflagellates (Symbiodinium, Cladocopium, Durusdinium) as extracellular symbionts (zooxanthellae). While symbiotic dinoflagellates can synthesize amino acids to benefit the host, they are nitrogen‐deficient. Hence, the host must supply them with nitrogen including urea, which can be degraded to ammonia and carbon dioxide by urease (URE). Here, we report three complete coding cDNA sequences of URE, one for each genus of dinoflagellate, obtained from the colorful outer mantle of the giant clam, Tridacna squamosa. The outer mantle had higher transcript level of Tridacna squamosa zooxanthellae URE (TSZURE) than the whitish inner mantle, foot muscle, hepatopancreas and ctenidium. TSZURE was immunolocalized strongly and atypically in the plastid, moderately in the cytoplasm, and weakly in the cell wall and plasma membrane of symbiotic dinoflagellates. In the outer mantle, illumination upregulated the protein abundance of TSZURE, which could enhance urea degradation in photosynthesizing dinoflagellates. The urea‐nitrogen released could then augment syntheses of amino acids to be shared with the host for its general needs. Illumination also enhanced gene and protein expression levels of TSZURE/TSZURE in the inner mantle and foot muscle, which contain only small quantities of symbiotic dinoflagellate, have no iridocyte, and lack direct exposure to light. With low phototrophic potential, dinoflagellates in the inner mantle and foot muscle might need to absorb carbohydrates in order to assimilate the urea‐nitrogen into amino acids. Amino acids donated by dinoflagellates to the inner mantle and the foot muscle could be used especially for syntheses of organic matrix needed for light‐enhanced shell formation and muscle protein, respectively.

The objective of this study was to determine the effects of 12h of exposure to light, as compared with 12h of exposure to darkness (control) on enzymatic activities of transporters involved in the transport of NH+4 or H+, and activities of enzymes involved in converting NH+4 to glutamate/glutamine in inner mantle, outer mantle, and ctenidia of the giant clam, Tridacna squamosal. Exposure to light resulted in a significant increase in the effectiveness of NH+4 in substitution for K+ to activate NA+/K+-ATPase(NKA), manifested as a significant increase in the NA+/NH+4-activated-NKA activity in the inner mantle. However, similar phenomena were not observed in the extensible outer mantle, which contained abundant symbiotic zooxanthellae. Hence, during light-enhanced calcification, H+ released from CaCO3 deposition could react with NH3 to form NH+4 in the extrapallial fluid, and NH+4 could probably be transported into the shell-facing inner mantle epithelium through NKA. Light also induced an increase in the activity of glutamine synthetase , which converts NH+4 and glutamate to glutamine, in the inner mantle. Taken together, these results explained observations reported elsewhere that light induced a significant increase in pH and a significant decrease in ammonia concentration in the extrapallial fluid, as well as a significant increase in the glutamine concentration in the inner mantle, of T. squamosa. Exposure of T. squamosa to light also led to a significant decrease in the N-ethylmaleimide (NEM)-sensitive-V-H+-ATPase (VATPase) in the inner mantle, and significant increases in the NA+/K+-activated-NKA, H+/NH+4-activated-H+/K+-ATPase, and NEM-sensitive-VATPase activities in ctenidia, indicating that light-enhanced calcification might perturb Na+ homeostasis and acid/base balance in the hemolymph , and might involve the active uptake of NH+4 from the environment. This is the first report on light having direct enhancing effects on activities of certain transporters/enzymes related to light-enhanced calcification in the inner mantle and ctenidia of T. squamosa.

Suspended animation has long fascinated scientists because of its great application potentials in fields ranging from medicine to space travel. Animals become inactive during suspended animation, with absolutely no intake of food and water, and hence producing minimal or no urine and faecal materials, for an extended period. They enter into a state of torpor, possibly slowing down the biological time in relation to the clock time. If suspended animation can be achieved in humans, surgeons would have more time to operate on patients during critical moments when the blood circulation stops, and the dream of long distance space travel can be realized. In nature, suspended animation is expressed in some adult animals undergoing hibernation or aestivation. ‘Aestivation’ is a loose term that signifies little more than an animal undergoing a state of torpor to survive arid conditions (except for aquatic aestivators like certain sponges and sea cucumbers) at high temperature, in many cases during summer. The term has been used to describe the listless state of endotherms, like ground squirrels and cactus mouse at the height of summer heat, and ectotherms, like amphibians and African lungfishes that make cocoons to encase themselves for weeks to more than a year during the hot dry season.

African lungfishes are obligatory air-breathers with exceptionally high environmental ammonia tolerance. They can lower the pH of the external medium during exposure to ammonia-loading conditions. This study aimed to demonstrate the possible involvement of branchial vacuolar-type H+-ATPase (Vha) in the ammonia-induced acidification of the external medium by the West African lungfish, Protopterus annectens, and to examine whether its capacity to acidify the medium could be augmented after exposure to 100 mmol l−1 NH4Cl for six days. Two full coding cDNA sequences of Vha subunit B (atp6v1b), atp6v1b1 and atp6v1b2, were obtained from the internal gills of P. annectens. The sequence of atp6v1b1 comprised 1548 bp, encoding 515 amino acids (57.4 kDa), while that of atp6v1b2 comprised 1536 bp, encoding 511 amino acids (56.6 kDa). Using a custom-made antibody reactive to both isoforms, immunofluorescence microscopy revealed the collective localization of Atp6v1b (atp6v1b1 and atp6v1b2) at the apical or the basolateral membrane of two different types of branchial Na+/K+-ATPase-immunoreactive ionocyte. The ionocytes labelled apically with Atp6v1b presumably expressed Atp6v1b1 containing a PDZ-binding domain, indicating that the apical Vha was positioned to transport H+ to the external medium. The expression of Atp6v1b was regulated post-transcriptionally, as the protein abundance of Atp6v1b and Vha activity increased significantly in the gills of fish exposed to 100 mmol l−1 NH4Cl for six days. Correspondingly, the fish exposed to ammonia had a greater capacity to acidify the external medium, presumably to decrease the ratio of [NH3] to [NH4+] in order to reduce the influx of exogenous NH3.

In light, giant clams can increase rates of shell formation and growth due to their symbiotic relationship with phototrophic zooxanthellae residing extracellularly in a tubular system. Light-enhanced shell formation necessitates increase in the uptake of Ca2+ from the ambient seawater and the supply of Ca2+ through the hemolymph to the extrapallial fluid, where calcification occurs. In this study, the complete coding cDNA sequence of a homolog of voltage-gated calcium channel subunit α1 (CACNA1), which is the pore-forming subunit of L-type voltage-gated calcium channels (VGCCs), was obtained from the ctenidium (gill) of the giant clam, Tridacna squamosa. It consisted of 6081 bp and encoded a 223 kDa polypeptide with 2027 amino acids, which was characterized as the α1D subunit of L-type VGCC. Immunofluorescence microscopy demonstrated that CACNA1 had an apical localization in the epithelial cells of filaments and tertiary water channels in the ctenidium of T. squamosa, indicating that it was well positioned to absorb exogenous Ca2+. Additionally, there was a significant increase in the protein abundance of CACNA1 in the ctenidium of individuals exposed to light for 12 h. With more pore-forming CACNA1, there could be an increase in the permeation of exogenous Ca2+ into the ctenidial epithelial cells through the apical membrane. Taken together, these results denote that VGCC could augment exogenous Ca2+ uptake through the ctenidium to support light-enhanced shell formation in T. squamosa. Furthermore, they support the proposition that light-enhanced phenomena in giant clams are attributable primarily to the direct responses of the host’s transporters/enzymes to light, in alignment with the symbionts’ phototrophic activity.

This study aimed to obtain the coding cDNA sequences of Na+/K+-ATPase α (nkaα) isoforms from, and to quantify their mRNA expression in, the skeletal muscle (SM), the main electric organ (EO), the Hunter’s EO and the Sach’s EO of the electric eel, Electrophorus electricus. Four nkaα isoforms (nkaα1c1, nkaα1c2, nkaα2 and nkaα3) were obtained from the SM and the EOs of E. electricus. Based on mRNA expression levels, the major nkaα expressed in the SM and the three EOs of juvenile and adult E. electricus were nkaα1c1 and nkaα2, respectively. Molecular characterization of the deduced Nkaα1c1 and Nkaα2 sequences indicates that they probably have different affinities to Na+ and K+. Western blotting demonstrated that the protein abundance of Nkaα was barely detectable in the SM, but strongly detected in the main and Hunter’s EOs and weakly in the Sach’s EO of juvenile and adult E. electricus. These results corroborate the fact that the main EO and Hunter’s EO have high densities of Na+ channels and produce high voltage discharges while the Sach’s EO produces low voltage discharges. More importantly, there were significant differences in kinetic properties of Nka among the three EOs of juvenile E. electricus. The highest and lowest Vmax of Nka were detected in the main EO and the Sach’s EO, respectively, with the Hunter’s EO having a Vmax value intermediate between the two, indicating that the metabolic costs of EO discharge could be the highest in the main EO. Furthermore, the Nka from the main EO had the lowest Km (or highest affinity) for Na+ and K+ among the three EOs, suggesting that the Nka of the main EO was more effective than those of the other two EOs in maintaining intracellular Na+ and K+ homeostasis and in clearing extracellular K+ after EO discharge.