Thesis (M.S.)--University of Wisconsin--Madison, 1961. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 63-65).

Thesis--Wisconsin. / Vita. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1942. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf [62]).

The occurrence of the ϐ-carboxylatlon pathway of photosynthesis Is correlated with the presence of two chlorophyllous tissues, within a leaf, which function co-operatively. It is postulated that: (a) Carbon dioxide fixation by ϐ-carboxylation is confined to the leaf mesophyll tissue. (b) The carboxyl transfer and the subsequent reactions leading to the synthesis of starch are confined to the bundle sheath tissue. (c) The carboxyl transfer reaction proceeds by decarboxylation of a C₄-acid coupled with RuDP carboxylase catalyzed synthesis of 3-PGA. (d) Cooperation between the two chlorophyllous tissues is made possible by the transport of metabolites between the tissues. Two plants Gomphrena globosa and Zea mays were used to test these postulates. These plants were found to form labelled aspartate and malate as early products of photosynthesis. Studies of the redistribution of ¹⁴C in pulse and chase type feedings of ¹⁴C0₂ and ¹²C0₂ indicate that nearly all labelled phosphorylated compounds may be formed from the C₄-aclds by a carboxyl transfer reaction. The location of some photosynthetic enzymes was studied by differential removal of enzymes from the two tissues. P-enolpyruvate carboxylase which is probably responsible for CO₂ fixation was found to occur predominantly in the mesophyll cells. "Malic" enzyme which will decarboxylate malic acid and RuDP carboxylase were found predominantly in the cells of the bundle sheath. Microradioautographs of thin sections of a Gomphrena globosa leaf indicate that ¹⁴C labelled C₄-acids rapidly appear in the cells of the bundle sheath. This apparently precedes the carboxyl transfer step. Studies of the location of labelled compounds within leaf cells by nonaqueous fractionation indicate that a portion of the C₄-acids are present in the cytoplasm and could be transported by cytoplasmic bridges. P-enolpyruvate carboxylase, "malic” enzyme, and RuDP carboxylase are present in extracts of these leaves in activities which approach or exceed the in vivo photosynthetic rate. These data suggest that the reactions of ϐ-carboxylation photosynthesis proceed as postulated. This mechanism involves CO₂ as a free intermediate as well as a substrate. An unusual C0₂ evolving process was detected at the onset of photosynthesis in Zea leaves after a short dark period. Feedings of ¹⁴CO₂ suggest that the C0₂2 evolved in this burst may be the result of a light stimulated decarboxylation of a C₄-acid. Studies of the kinetic properties of "malic" enzyme indicate that it would not be activated by light induced changes in the pH and Mg²⁺ concentrations, or in the adenylate pool. / Science, Faculty of / Botany, Department of / Graduate

Certain aspects of CO₂ exchange by wheat (Triticum aestivum L.), corn (Zea mays L.) and the grain Amaranth (Amaranthus edulis Speg.) were investigated. The effects of O₂ concentration on apparent photosynthesis of juvenile wheat and corn shoots were measured at different temperatures, CO₂ concentrations and light intensities using infra-red CO₂ analysis and both open and closed gas-flow systems. The only condition in which apparent photosynthesis of wheat was not inhibited by O₂ was in 20.8% O₂ when the CO₂ concentration was saturating and the temperature was 30° C or less. The degree of inhibition increased with increasing O₂ concentration, increasing temperature, and decreasing CO₂ concentration and was independent of the light intensity. During some of the growing season in temperate regions, the effect of atmospheric O₂ on the photosynthetic productivity of wheat may be negligible. The effect of O₂ on wheat was ascribed to both a stimulation of photorespiration and an inhibition of photosynthesis by O₂. In corn, which apparently lacks photorespiration, photosynthesis was also inhibited by 99% O₂- No inhibition occurred at 20.8% O₂, however, and the stability and reversibility of the inhibition observed at 99% O₂ differed from that found with wheat. These differences between wheat and corn are correlated with differences in leaf anatomy and photosynthetic carbon metabolism and with differences in the response of apparent photosynthesis and the CO₂ compensation point to environmental conditions. Many of the gas exchange characteristics of corn and similar plants seem to be advantageous for the warm dry areas they often inhabit. Initially high rates of CO₂ production are exhibited by wheat immediately following illumination, and it has been suggested that this post-illumination CO₂ burst is an extension of photorespiration into the dark period. In accord with this, CO₂ concentration was found to influence both the post-illumination CO₂ burst and the inhibition of apparent photosynthesis by O₂ in a similar way. Except for Amaranthus edulis, plants which lack photorespiration also lack significant post-illumination CO₂ bursts. On the basis of its response to O₂ concentration, however, the burst of Amaranthus edulis is concluded to be unrelated to photorespiration. Measurements of ¹²CO₂ and ¹⁴CO₂ exchange were used to estimate the quantity of carbon in wheat and corn shoots which was in free exchange with atmospheric CO₂. The free exchange pool size was found to be very small and it cannot be an important factor in the CO₂ concentration response of photosynthesis or in the post-illumination CO₂ burst. / Science, Faculty of / Botany, Department of / Graduate

Submitted to the faculty of Education in fulfilment of the requirements for the degree of Master of Education in the Department of Mathematics, Science and Technology of Education, University of Zululand, 2010. / The purpose of this study was to investigate possible reasons for the high failure rate in Biology, particularly under the topic “Photosynthesis”. Photosynthesis is a biological process which is critical for producing food for all living organisms. A test was used as a tool for collecting data. The test consisted of six questions taken from previous grade twelve final examination papers. The questions were analysed to determine the cognitive demands according to Blooms taxonomy. The questions were found to be integrated and tested lower and higher order cognitive levels according to Bloom’s taxonomy. The learners achievement scores showed that the test discriminated well among those learners who studied well and those who did not know their work. The sample was drawn from six high schools of Mthunzini circuit, in northern KwaZulu-Natal. To test whether there were significant differences in achievement scores among the six schools, a statistical Package for Social Sciences was used. Poor performance in the structured questions showed that language was a major barrier in expressing the learners ideas. Examples of incoherent sentences written by learners were captured in the main study. English as a medium of instruction affects the ability of the learners to answer questions. Looking at the learners responses, it is evident that language is a barrier to those students who cannot discuss in the target language (TL) of instruction which is English. Some students with better English competence were able to express themselves in the instructional language, and this gave them a chance of explaining their observations clearly and accurately. The poor performance at the level of 29% in lower order questions, showed how poorly the learners are mastering their work. Question 5 an application level question was the most poorly done with 66% learners achieving between 0-10%. The learners failed completely to plot a graph, they failed to use information given to identify correct axes on which to plot the independent and dependent variables. There was therefore also a problem of mathematical literacy which should make sure that every learner can handle a simple graph question. Learners who had chosen careers for which Biology is a requirement, performed better than their peers. Career choices seemed to be a factor in motivating learners to strive to do well. There were no significant differences in the achievement scores between boys and girls at 95 confidence levels. In one of the more conceptual questions the girls did better than boys at the range of 61-70% while at the range 71-80% only the girls featured. The efforts by the government to encourage girl children to do well may be beginning to pay off. It is also an achievement that the overall study showed the girls performing as well as the boys. The study provides a window which shows what is happening in our Black schools and a challenge for the government to look for ways of assisting, in particular, poverty stricken schools and also supplying such schools with well qualified teachers. The schools may also need to spend more time on task instead of allowing learners to mill around doing nothing.

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