Lag Phase cell synthesizing new components e.g., to replenish spent materials e.g., to adapt to new medium or other conditions varies in length in some cases can be very short or even absent Exponential Phase also called log phase rate of growth is constant population is most uniform in terms of chemical and physical properties during this phase Stationary Phase total number of viable cells remains constant may occur because metabolically active cells stop reproducing may occur because reproductive rate is balanced by death rate Possible Reasons for Entry into Stationary Phase nutrient limitation limited oxygen availability toxic waste accumulation critical population density reached Death Phase two alternative hypotheses Cells are Viable But Not Culturable (VBNC) Cells alive, but dormant programmed cell death Fraction of the population genetically programmed to die (commit suicide) Prokaryotic growth vs. Eukaryotic Growth Prokaryote Vibrio natrigens Generation time (g) = 10minutes Eukaryote Saccharomyces cerevisiae Generation time (g) YEPD = 90 ? 100 minutes YNB = 200 minutes Generation Time Length of time for one cell to divide into two Affected by?. Physical growth factors Microbial characteristics Media (nutrient availability) Mean Generation Time The mean generation time (g) is the average time required for all the components of the culture to double Same as doubling time g = t ? t0 n Number of generations in time t n = (log10 N ? log10 N0) log102 Timepoint (minutes) CFU per ml 0 77,000,000 10 93,000,000 20 71,000,000 30 320,000,000 40 125,000,000 50 3,000,000,000 60 10,500,000,000 70 10,800,000,000 80 10,000,000,000 90 13,700,000,000 100 6,300,000,000 110 1,220,000,000 120 146,000,000 Number of generations n = (log10 N ? log10 N0) log102 n = (log10 6,300,000,000) ? (log10 125,000,000) .301 n = (9.79934) ? (8.09691) .301 Generation time g = _ t - t0 n g = (100 ? 40) 5.6559 g = 10.6 minutes Generation (g) = t ? t0 time n K : Mean growth rate constant K = n/t (number of generations per unit time) Also, K= 1/g What to Include in your Report Title Introduction Studying microbial growth Factors that affect growth Phases of growth curve Differences/similarities prokaryote vs. eukaryotes Purpose of experiments Materials and Methods Site lab manual and online exercise ?Exercises were performed as described in?.. Tell me your time point(s) for eukaryotes and prokaryotes Results Graphs: Eukaryote Cell number (hemocytometer) vs time CFUs/ml vs time Absorbance vs time Prokaryote CFU/ml vs time Absorbance vs time Results Generation time + mean growth rate constant Eukaryote in YNB Eukaryote in YEPD Prokaryote * Show calculations* * Use your best looking graph Discussion Mutations in S. cerevisiae that made it more fastidious Media requirements Refer to graphs Differences between growth in YNB vs YEPD Differences between eukaryote vs prokaryote Discussion Refer to generation times YNB vs YEPD Prokaryote vs eukaryote Physiological cellular differences Were the results what you expected? Calculated generation time vs known generation time Conclusions
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