The Effects of Various Factors on the Growth Rate of E. coli
There are times in our lives (as human beings) when people do not feel well. A doctor might diagnose them with a disease or an infection. There are also times when people do not feel clean. This could be a person's feeling after exercising, sweating, or maybe he/she had not taken a shower in a couple days. In any of the preceding scenarios, bacteria most likely played a major role in initiating a person's feeling of illness or squalor. "Sickness" can be caused from bacteria. Someone may be sick because they ate food contaminated with bacteria or they could have easily taken a sip from the cup of a friend and shared some sort of bacterial disease. Bacteria surrounds us everyday, every second. It is difficult for people to accept this fact because they want to believe they are clean, after they shower. In relative terms, a washed person is clean, but they are not free of bacteria. "Clean" is simply an image, because bacteria are covering all substances and objects tha!t you use to be clean; toothbrushes, soap, and even toilet paper. We live in a world of bacteria, maybe even a world that evolved from bacteria. These microscopic organisms reproduce quickly, sometimes even exponentially. In the experiment
Gregg, G., Hooke, A.M., McClure, J., Solomon, N.G. 2001. Laboratory Experiences for The last tests will be done to find out the effects of aeration on the growth of bacteria. Different types of bacteria can live in environments with oxygen, and some without. In this lab, we will be making our conclusion based three flasks containing the E.coli. One flask will be a control flask, which will sit still and be exposed to the atmosphere. Another flask will be placed in a moving water bath. The water bath is used to mix different amounts of the atmosphere with E. coli. The third and final flask will be a "baffled" flask, which will be placed in a trembling water bath. A "baffled" flask is irregular shaped and therefore may accept different amounts of oxygen. I predict that the baffled flask will have the greatest growth rate, and that the control flask will have the lowest growth rate because the baffled flask has a greater chance of the air reacting with the E. coli. Table 1 provides each culture condition and treatment for each category. First our class split up into three groups, one to observe the effects of aeration on the growth of E-coli, one to observe the effects of temperature, and another to observe the effects of nutrients. Each group followed the directions in the procedures section of the lab manual (Laboratory Experiences, Spring 2001). Using the results of the tests, we made graphs to determine the mean generation time. Every 15 minutes, my fellow students and I measured the light absorbency (at 600nm) of the growing E. coli and it's varied conditions. From these findings, we were able to calculate the mean generation time (MGT), by graphing our spectrophotometer results and deduced an approximate time that correlated with the doubled initial absorbency. For example, the flask with the temperature of 37 degrees Celsius had an initial absorbency of .13. After doubling this number (.26), we looked at our growth curve (Figure 1.) and found at what time would the growth curve of 37 degrees reach an absorbency of .26. In this example, the mean generation time (MGT) was approximately 73 minutes. In simpler terms, for the growth of E. coli to double it's initial population, at the given temperature of 37 degrees Celsius, it would take 73 minutes. Our results of all spectrophotometer readings are listed in Tables 2 through 4. Table 2 displays the outcome of the effects of different types of a! Figure 3 represents the effect of aeration on the growth of E. coli and I hypothesized that the baffled flask would have the highest growth rate and that the "control" flask would have the lowest growth rate. As scene in Table 5, the MGT for the normal flask in the shaky water bath was about 43 minutes. For the baffled flask, the MGT was about 50 minutes. Surprisingly, the control flask, the stationary flask, does not have a MGT because its population is still growing.
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