A Photometric Method for Determining the Growth Rate of Yeast ( Saccharomyces cereviciae )

Methods are described for the induction and identification of respiratory deficient (RD) mutants in yeast. Practical schemes are given to enable students to obtain dose-response information for physical and chemical mutagens such as heat, ultraviolet light, or acriflavine. A simple test for environmental mutagens is described. Mutagens are characterized by their ability to increase the frequency of RD mutants in yeast populations. Results from class experiments are presented and discussed.

Section: Discussionmentioning

confidence: 50%

Some experiments with respiratory deficient mutants of yeast (iSaccharomyces cerevisiae)

Freeland

1978

“…Second, it is not necessary to smash the yeast cells in order to release the enzyme complement since most of the active enzyme is bound to the cell-surface membrane or cell wall. These advantages add weight to the view expressed in earlier papers (Freeland, 1971(Freeland, , 1973, that yeasts have many uses in the school laboratory, both for specific experimental projects and for illustrating broader biological principles.…”

Section: Discussionmentioning

confidence: 80%

Some aspects of catalase induction in baker's yeast (Saccharomyces cerevisiae)

Freeland

1974

Self Cite

Yeasts grown in anaerobic liquid media produced catalase in response to the presence of H,O s in the growth medium. The fact that some of the induced enzyme was active at the cell surface, bound either to the cell wall or cell-surface membrane, eliminated the need to crush cells in order to release the enzyme complement. Instead, catalase production was moni tored by using H,0,-reagent strips to detect changes in the level of H a O, in the growth medium. In addi tion, catalase induction in yeasts was found to be temperature-sensitive.It is suggested that biology teachers in schools might find the following experiments useful for demonstrat ing essential features of substrate-induced enzyme synthesis, based on the Jacob-Monod model, and for showing that the activity of certain genes can be modified by environmental temperature.

“…Perhaps the only difficulty is that of counting the cells 91 or otherwise estimating the population density, though the means for this, whether haemacytometer or simple photometric device, should now be available in most secondary schools, or could be purchased or constructed (for example see Freeland, 1971) at relatively little expense.…”

Section: Discussionmentioning

confidence: 99%

An experimental system usingChlorella vulgarisfor population studies in secondary-school biology

Gipps

Linke

1976

The development of an experimental system which can be used for demonstrating population studies in Chlorella vulgaris, and which is appropriate for use in secondary schools, is described. A culture medium was prepared on the basis of established inorganic nutrient requirements, and several cultures were set up to test the effects of variations in nutrient compo sition, temperature, pH, light and aeration. A satis factory system was eventually found which produced an ideal (sigmoidal) population-growth curve within three weeks. A similar pattern of results, though with different growth rates and maximum population levels, was obtained both for controlled and ambient con ditions of light and temperature, and for aerated tube and non-aerated flask cultures. Non-aerated tube cultures were relatively ineffective. Two methods were used, the counting of cells and the measurement of optical density, for estimating population density, and comparative results were obtained for serial dilutions of a standard culture.