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With the absorbance values, we can deduce the cell concentrations from the following steps: As a result, the difference in absorbance values obtained is identical to the difference cell concentration values at each respective hour. Samples were extracted from the bioreactor for 10 hours at every hour from 9am (first hour) to 6pm (last hour). Phase (1): The lag phase Phase (2): The exponential phase As a result of the deduction, the exponential phase started at 0.8 hours until the 5th hour whereby graph rose steadily after lag phase. This was logarithmic phase, the period where the cells were expected to grow exponentially. This phase happened after the cells had adapted to the environment already. Hence, they started to grow and divided at the maximum rate. Phase (3): The stationary phase Phase (4): The death phase
Day 3, Part II: Growth Graph
Discussion for Cell Growth
By plotting the cell growth curve, we can actually determine the:
1) Different stages of E.coli cell growth (lag, log, stationary, death)
2) Duration of the growth stages
3) Specific growth rate at a specific timing
To plot the curve, it is necessary to determine the cell concentration. On the other hand, to determine the cell concentration, the absorbance of the samples at every hour must be measured using a laboratory equipment known as the spectrophotometer ( refer to further questions for the principle of the machine).
Samples were extracted from the bioreactor 10 hours at every hour from 9am to 6pm (excluding the control sample) and the absorbance was taken.
The Beer-Lambert Law states that the absorbance of a material in solution is directly dependent on the concentration of that material.A α c The material in this case is the cell concentration (x). 
By comparing the two equations above, we can see that the efficient coefficient (ε) and the path length of the cuvette (l) are identical. Thus, the two equations can be combined into the equation below and the ε and l can be eliminated. 
From the cell concentration values, the values of Log (c/c0) or Log (x/x0) that we are required to find can be calculated so that the cell growth graph can be plotted.
From the graph plotted, only the exponential and the stationary phases could be observed. However, the lag phase and the death phase could not be seen and were not known. The slope of the exponential phase = μmax, which is the maximum cell growth rate. The slope of other parts of the curve = μ, which is the specific cell growth rate.
For the absence of the lag phase observed, one possible reason to support the observation would be due to the fact that the absorbance of the first fraction taken was right after the lag phase. Therefore the lag phase was not captured in this graph.
However, the lag phase can be deduced from the history plot (refer to the next page History Plot) which is 0.8 hours from the start (9am instead of 8.30am from the history plot).
Stationary phase, also called the idiophase, happened when cell growth was equal to cell death. This occurs at the 5th hour to the 17.5th hour (observed from the history plot) on the graph whereby the slope equals to zero. This phase occurred because the rate of cell growth is more or less equal to the rate of cell death, and can be triggered by the exhaustion of a particular critical nutrient essential for maintaining cell growth, or the accumulation of toxic metabolic products.
Finally, the death phase was not detected and could not be observed from the graph. It refers to the period of exponential decay and it occurs either due to the depletion of cellular reserves of energy or accumulation of toxic waste products.
Please refer to the History Plot for further details!
There are four sections to Day 3:
Part I (Procedures)
You are Here: Part II (Growth Graph)
Part III (History Plot)
Part IV (Futher Questions)
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