Lab Results

Result

 As seen in figure 1; there's a decrease in the distance for the saline agar plates from week 1 to 3, with the values being 51.27±0.81mm, 44.96±1.90mm, 30.36±2.33mm for weeks 1,2 and 3 respectively. For the control plates the distance remained fairly constant from week 1 to 2 and decreased at week 3, with the values being 0.66±0.15mm, 0.74±0.24mm, 0.22±0.07, for weeks 1, 2 and 3 respectively.

 For the saline agar plates, there's a negative correlation between the distance and the percentage of NaCl (i.e. with increasing distance there's decreasing % of NaCl ), the values for % of NaCl is 7.70±0.20%, 9.21±0.46%, 12.72±0.56%

There is a large difference between the means of the percentage of NaCl for the saline agar plates, for weeks 1 and 3. The statistical test (t-test) showed that the difference was 8.44.

Discussion Section

The bacterium that was used was Enterobacter aerogenes. My null hypothesis is; the presence of salt doesn't cause any changes in the bacteria. My alternate hypothesis is; the presence of salt causes evolution by natural selection in the bacteria. The result that I got agrees with my alternate hypothesis, and not my null hypothesis, this is because in week 1 the bacteria could only survive 7.70±0.20% of NaCl and then increased to 12.72±0.56% of NaCl by week 3. The statistical test that I used was the t-test, I used it because I was comparing the mean salinity at which the bacterial population was able to grow at week 1 and at week 3. Due to the t-value i.e. 8.44 that I got, I rejected my null hypothesis, because the value is larger than the  table t-value i.e. 1.96 (which I found using the degree of freedom which was 361 with the standard probability of 5%).