Class: BE210
Group: W4
Members: FACILITATOR
..
Jeff Byrnes
TIME & TASK KEEPER
Christie Snead
SCRIBES
.... Norman Cabanilla
Vikram Krishnan
PRESENTER . Marisa Kastner
Date: May, 2001
Abstract:
In an experiment to determine the effect of extracellular pH on the
growth rate of Saccharomyces cerevisiae, the yeast was grown in an aerobic
culture at 37 degrees Celsius, and appropriate amounts of acid and/or base
were added to attain and then keep the medium at a constant predetermined
pH for approximately an hour, having a standard deviation of no more than
±0.0935 pH units. These chosen pHs ranged from 2 to 8.
From absorbance readings taken every 10 minutes, plots of ln(absorbance)
versus time were made. The slopes of the ln(absorbance) versus time
plots were used to determine the growth rate constant, which was then plotted
against the previously recorded pH values. All of these plots were
used to determine the correlation between growth rate constant and pH.
The results of the growth rate constants for each pH 2-8 are 0.001316,
0.002763, 0.003542, 0.002744, 0.003549, 0.003089, and 0.002627 (all in
min-1) respectively. Statistical analysis has shown that the 95%
confidence limits of the growth constant at each pH do not overlap with
those of the pH directly above and below it. Also, the plot of growth
rate constant versus pH shows a second order relationship having an optimal
maximum growth rate at a pH level between 4 and 6. This shows that
pH does affect the growth rate constant. Because some pHs were evaluated
right after another pH was observed, some other variables besides pH that
come about near the end of the growth phase, such as toxic products of
cell growth, might have effected the value of the growth rate of yeast.
Performing multiple trials of the same pH, as well as observing growth
rate for each pH for an extended period of time, would have produced more
accurate data for better analysis.