${session.getAttribute("locale")} 5 Synthetic and physical organic studies of chromone derivatives Wed 12 May 2021 23:59:48 SAST ]]> Determination of the optimum environmental requirements of juvenile marine fish : the development of a protocol Wed 12 May 2021 23:02:40 SAST ]]> Detached harmonies : a study in/on developing social processes of environmental education in eastern southern Africa Wed 12 May 2021 22:39:22 SAST ]]> Ecological interaction between the introduced and native rock-dwelling cichlid fishes of Lake Malawi National Park, Malawi Wed 12 May 2021 20:24:26 SAST ]]> Breaking the karmic complex: the role of transpersonal phenomena in psychotherapy with an adult survivor of child abuse : a clinical case study Wed 12 May 2021 20:17:02 SAST ]]> Share-net: a case study of environmental education resource material development in a risk society Wed 12 May 2021 19:42:06 SAST ]]> Modelling parallel and distributed virtual reality systems for performance analysis and comparison Wed 12 May 2021 19:36:59 SAST ]]> Regulation of tryptophan-2,3-dioxygenase and pineal indoleamines by selected tryptophan derivatives and antidepressants Wed 12 May 2021 18:40:54 SAST ]]> Radio observation of the Gum Nebula Region Wed 12 May 2021 18:37:47 SAST ]]> Theories of exchange rates and the methodology of economics Wed 12 May 2021 18:18:15 SAST ]]> The effect of elevated CO₂ on Phaseolus vulgaris L. cv Contender Wed 12 May 2021 16:35:01 SAST ]]> Studies of the biology and ecology of the high shore South African limpet, Helcion pectunculus (Mollusca : patellogastropoda) 22 mm were generally female. Helcion pectunculus grows allometrically, increasing in height faster than length, which is expected of a high shore gastropod mollusc attempting to reduce evaporative water loss. Growth rates were similar on both east and west coasts regardless of the differing oceanographic conditions. The theoretical values of Lmax were also similar being 30.86 mm and 30.71 mm respectively. Micro-growth bands are laid down within its' shell which have the same periodicity as the tidal cycle and these enabled age estimates to be made. Younger individuals were male whilst older animals were female, suggesting that H pectunculus is a protandrous hermaphrodite. Histological examination proved, unequivocally, that this limpet undergoes a protandric sex change, changing from male to female when they are about 2 years old. Both east and west coast popUlations had a marked reproductive cycle, exhibiting two spawning periods a year, one in April and another in November. The possibility that the reproductive pattern exhibited is now phylogeneticallyconstrained is discussed. It is suggested that H pectunculus has evolved a reproductive cycle which will allow its planktonic larvae to utilise the valuable phytoplankton bloom food source whilst using onshore winds to ensure that larvae are not transported out to sea and lost. The number of foraging excursions carried out by individuals of H pectunculus was found to have a significant effect on Gonad Index and hence potential reproductive output. The activity pattern of H pectunculus varied depending upon micro-habitat; animals inhabiting both east and west facing rock surfaces are active during nocturnal low tides whilst animals on west facing rock surfaces are also active during daytime low tides whilst in the shade. Limpets travel further during foraging excursions in winter (X = 85.53 cm) than in either spring (x = 55.7 cm) or summer (X = 48.8 cm) and also during spring low tides (x = 89.8 cm) compared with neaps (x = 40.9 cm). This limpet exhibits rigid homing to a fixed scar within a-crevice and feeding excursions were found to of three distinct phases, a rapid outward phase, a slower foraging phase and a rapid homeward phase. Foraging was always highly directional, with a mean vector which took limpets onto an area of the rockface with the highest microalgal biomass and also the smoothest rock surface. Helcion pectunculus exhibits a free-running endogenous rhythm of locomotor activity with both circadian and circatidal components and it is suggested that this rhythm plays a role in allowing the limpet to avoid unfavourable environmental conditions. The exogenous entrainment factor of this endogenous rhythm was the time of exposure to air in the field. There was found to be an organized distribution of limpets within crevices with smaller, younger limpets being towards the back of the crevice and larger, older limpets towards the crevice mouth. It is hypothesized that juvenile limpets of this species actively select and settle at the backs of crevices responding to chemical cues of adult conspecifics. The crevice refuge supplies the limpets with a stable and buffered environment with higher relative humidities (X = 72.3%) and lower rock surface temperatures (X = 19.7°C) than adjacent exposed rock surfaces (X = 64.5%; x = 22.9°C). Limpet body temperatures were significantly lower in crevic~refuges compared to limpets on exposed rock surfaces. Body temperatures never exceeded the rock surface temperatures. It is suggested that this is the result of morphological adaptations such as shell ornamentation and allometric growth. Light levels above 1000 J.1E.m-2.s-1 inhibited foraging activity in H. pectunculuswhilst limpets subjected to 30-50% shade foraged even during daytime lowtides. This limpet is one of the least tenacious (2.75 ± 0.13 ) of all South African limpets and the possibility that wave activity governs both the activity patterns and homing behaviour of this limpet is discussed. Limpets deprived of a crevice refuge experienced extremely high mortalities, with 45% of the limpets being lost during the first high tide period. A hypothetical model of the hierarchy of exogenous factors controlling limpet foraging activity is introduced and discussed in relation to the results of this study. Finally, it is suggested that in addition to the "migratory" and "non-migratory" groups of limpets present on southern African shores a third group of limpets seem to be present which may be classed as "specialized non-migratory" species. These are species that do not migrate, garden or aggressively fight off like conspecifics. They have overcome the competition for space and food on intertidal rocky shores by adapting to a particular habitat which is exclusive to them alone. From the combined results of these studies, it can be stated that H. pectunculus has adapted physiologically, morphologically and behaviourally to successfully survive the extreme conditions in the upper Balanoid zone.]]> Wed 12 May 2021 16:34:32 SAST ]]> Urban agriculture: advocacy and practice: a discursive study with particular reference to three Eastern Cape centres Wed 12 May 2021 16:17:51 SAST ]]> Metabolic responses in melanoma cells to combined nutrient supplementation Wed 12 May 2021 16:13:35 SAST ]]> Biologically active natural products from South African marine invertebrates Wed 12 May 2021 15:53:48 SAST ]]> Environmental education : a strategy for primary teacher education Wed 12 May 2021 15:50:07 SAST ]]> A phenomenological investigation into educational leaders' perceptions of themselves, their followers, and their organisational contexts Wed 05 Apr 2023 08:16:17 SAST ]]> Design, synthesis and evaluation of novel, metal complexing agents Thu 13 May 2021 08:49:15 SAST ]]> Parasitism and invasive species : an ecological study of mussel populations Thu 13 May 2021 08:19:42 SAST ]]> Grouping complex systems for classification and parallel simulation Thu 13 May 2021 06:54:07 SAST ]]> Solid state thermal decomposition of amide complexes of nickel(II) chloride Thu 13 May 2021 05:56:24 SAST ]]> Healing stories of the unconscious: past-life imagery in transpersonal psychotherapy Thu 13 May 2021 04:01:47 SAST ]]> Vitamin E supplementation and secondary metabolites interactions and effects on melanoma growth Thu 13 May 2021 03:57:00 SAST ]]> Bioaccumulation of heavy metals by the yeast S. cerevisiae and the bioremediation of industrial waste water chitin> glucan > intact cell walls exists. However, these components differ in their affinities for metal ions. Storage of metal ions within the cell occurs predominantly in the vacuole. The present study concluded that metal accumulation by the vacuole could be related to size. Metal accumulation occurred in the order of Cu2+ > Co2+ > Cd2+ with a corresponding decrease in atomic radii of Cd2+ > C02+ > Cu2+. Vacuolar ion deposition occurs at an early stage during the internalization of metal ions within the yeast cells. At the onset of vacuolar saturation, depositions of metal ions as granules within the cytosol occurs. In the presence of heavy metal cations viable yeast cells can be shown to exhibit two types of cellular responses. Uptake of Cu2+ and Cd2+ causes the loss of intracellular physiological cations from within the yeast cell. In comparison, uptake of Co2+ into the cell does not have this effect. All three heavy metal cations initiate plasma cell membrane permeability, thus the Cu2+ and Cd2+ induced loss of the intracellular cations, occurs. ~ a result of ion-exchange mechanisms and not due to cation leakage brought about by membrane permeabilization. Uptake of heavy metals by viable yeasts appears to be generally non-selective though the amount of metals accumulated are largely affected by the ratio of ambient metal concentration to biomass quantity. In addition, the energy dependent nature of internalization necessitates the availability of an external energy source for metal uptake by viable yeast cells. For these reasons metal removal from industrial waste water was investigated using non-viable biomass. By immobilizing the yeast cells additional mechanical integrity and stability was conferred apon the biomass. The three types of biomass preparations developed in this study, viz. polyvinyl alcohol (PV A) Na-alginate, PV A Na-orthophosphate and alkali treated polyethylenimine (PEI):glutaraldehyde (GA) biomass pellets, all fulfilled the necessary physical requirements. However, the superior metal accumulating properties of the PEI:GA biomass determined its selection as a biosorbent for bioremediation purposes. Biosorption of heavy metals by PEI:GA biomass is of a competitive nature, with the amount of metal accumulated influenced by the availability of the metal ions. This availability is largely determined by the solution pH. At low pH values the affinity of the biomass for metals decreases, whilst enhanced metal biosorption occurs at higher pHs, ego pH 4.5 - 6.0. PEI:GA biomass pellets can be implemented -as a biosorbent for the bi9remediaiton of high concentration, low-volume metal containing industrial waste. Several options regarding the bioremediation system are available. Depending on the concentration of the metals in the effluent, the bioremediation process can either be used independently or as part of a biphasic remediation system for the treatment of waste water. Initial phase chemical modification may be required, whilst two types of biological systems can be implemented as 'part of the second phase. The PEI:GA biomass can either be contained within continuous-flow fixed bed tanks or continuous-flow stirred bioreactor tanks. Due to the simplicity of the process and the ease with which scale-up is facilitated, the second type of system shows greater application potential for the treatment of this type of industrial waste water than the fixed-bed systems.]]> Thu 13 May 2021 02:58:09 SAST ]]> A comparative study of the Grey-headed Sparrow (Passer griseus L) and the House Sparrow (Passer domesticus L) in Malawi Thu 13 May 2021 02:32:42 SAST ]]> Termination of psychotherapy : a phenomenological exploration of the therapist's and the patient's experience Thu 13 May 2021 01:49:03 SAST ]]> The oral-style South African short story in English A.W. Drayson to H.C. Bosman Thu 13 May 2021 01:48:03 SAST ]]> Regional and local economic development strategies in the Eastern Cape and guidelines for future development Thu 13 May 2021 01:19:01 SAST ]]>