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microbiology ph and temperature effect on bacterial culture

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Aim of this experiment is to investigate the effect of pH and temperature on bacteria growth. Apparatus: 4 universal bottles at different pH's, Escherichia coli, micrococcus luteus, pipettes, incubator, 4 test tubes, colorimeter. Method of pH Four bottles where used which contained nutrient growth at pH 5, 6, 7, 8. By using aseptic techniques, a pipette is used as each nutrient broth is inoculated with one drop of culture Escherichia coli. After this each of the nutrient broth was incubated at a temperature of 25 degrees for 3 days. After 3 days the contents within each of the bottle are mixed and their contents are transferred into a test tube. At first each pH condition is set to absorbance to zero by using a nutrient broth without any bacterial culture. After this was done the nutrient broth which contained the bacteria is measured to find out it's absorbance by using a colorimeter. This procedure is done with the micrococcus luteus bacteria. These results are shown in a table below of the effect of growth of bacteria Escherichia coli pH range pH4 pH5 pH6 pH7 Absorbance group 1 -0.05 1.57 1.41 0.88 Absorbance group 2 0.08 0.97 2 1.14 Absorbance group 3 0.06 0.7 0.3 0.83 Absorbance group 4 0.14 1.77 1.77 1.09 Absorbance group 5 0.04 1.24 1.09 0.63 Absorbance group 6 0.04 1.9 1.08 1.61 Absorbance group 7 0.06 1.03 1.04 1.5 Absorbance group 8 -0.04 1.16 0.94 1.62 Mean 0.04 1.29 1.20 1.16 The mean of each pH are represented on a bar chart below Conclusion From looking at the bar ...read more.


Temperature range (degrees) 4 20 35 60 Absorbance group 1 -0.05 1.34 0.78 -0.04 Absorbance group 2 0.01 1.26 0.96 -0.05 Absorbance group 3 0.04 0.94 1.25 0.09 Absorbance group 4 -0.06 0.86 0.95 -0.05 Absorbance group 5 0.06 1.27 1.13 0.02 Absorbance group 6 N/a N/a N/a N/a Absorbance group 7 N/a N/a N/a N/a Absorbance Group 8 0.01 1.19 1.1 0.02 Absorbance group 8 0.04 0.74 0.78 0.12 Absorbance group 9 0 0.74 0.45 -0.02 Mean 0.01 1.04 0.93 0.01 The mean of each Escherichia coli bacteria at certain temperatures are represented on a bar chart below. From looking at the bar chart above at the different temperatures I conclude that 20 degrees is the best temperature for which the bacteria Escherichia coli to grow in. Discussion of results From looking at the mean results at 20 degrees it had a mean value of 1.04 which this was the highest mean value compared to the other values. The second degree in which the E.coli can grow in is at 35 degrees as there is a 0.12 difference between the 20 degrees but more E.coli growth is produced than in 35 degrees. At 4 and 60 degrees they values came out to be 0.01 which are the same as these temperatures are to extreme or unsuitable for which the E.coli bacteria can grow in. At 4 degrees it is too cold for the bacteria to grow and slowed down their reactivity therefore making no production of growth and at 60 degrees the temperature is too high for the growth of the bacteria which they would of become killed or denatured this mean no growth of bacteria. ...read more.


Each tube had the same amount of nutrient broth volume for which the bacteria was able to grow in. These bacteria's were controlled at certain times as they were incubated for three days therefore a total of 72 hours. The same instrument was used to measure the absorbance of both bacteria and the same colour filter with was green at a wavelength of 250nm. There were some variables within the experiment one of them was the temperature. For the bacteria's of pH experiment all four bottles were incubated at 24 degrees as for the bacteria of the temperature experiment each bottle was incubated at different temperatures of 4, 35, 60 and room temperure which these temperature were not controlled therefore would give different results but however the pH of the nutrient broth of the bacteria from the temperature experiment was the same. Another variable in the experiment was the absorbance of each nutrient broth since both experiments pH and temperatures were at different values to see which pH and temperature value best to grow in so these were not kept control. When measuring the absorbance of each nutrient broth, the test tubes are needed to be the same thickness but not thick as this can cause errors with the results. Once the colorimeter had read the absorbency and gives a positive reading this shows that within the nutrient broth there is no growth of bacteria therefore this would give a less absorbance reading. This need to be controlled to give accurate results if not it is account as a variable. ?? ?? ?? ?? ...read more.

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