lab_14_data_analysis_presentation_I

# Lab_14_data_analysis - Miramar College Biology 205 Microbiology Lab Exercise 14 Data Analysis Presentation I Background In Lab Exercise 10

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Lab Exercise 14: Data Analysis & Presentation I Page 1 of 14 Miramar College Biology 205 Microbiology Lab Exercise 14: Data Analysis & Presentation I Background In Lab Exercise 10: , you examined two ways of collecting data about the growth of a bacterial population. You measured the populations indirectly, using a spectrophotometer, and directly using serial dilutions and spread plating. The optical density (OD) readings you collected using the spectrophotometer can be used to graph the growth of a population over time without any further manipulation. The colony forming unit (CFU) data you collected, however, need a little explanation. You collected these data by counting the CFUs on your plate and then correcting for the dilution of the plate ( i.e ., 10 -4 , 10 -5 , 10 -6 , 10 -7 ). For instance, a 10 -5 with 230 colonies on it would be expressed as 230 × 10 5 = 2.3 ×10 7 (remember to take the reciprocal of the dilution to yield the dilution factor or DF ). What that notation represents is the number 23,000,000, which is large and cumbersome and so expressing these numbers is scientific notation is preferable. It is important to note, though, that although numbers written in scientific notation may seem close to one another, each number change for the 10 is a ten-fold change in the amount you’re talking about. If you need a refresher on this concept, re-read the Background information from Lab Exercise 2: The . Scientific notation allows numbers who are magnitudes different from one another to be compared easily, by counting the zeros separately. For instance, if your CFU count is 230 on a plate that was diluted to 10 -5 , you have 230 × 10 -5 CFUs/ml, or more correctly 2.3 × 10 -7 CFUs/ml. What this means is that there were 23,000,000 CFUs/ml in the original culture. Let’s say that at the next 30 minute reading, you count a total of 1.1 × 10 -9 CFUs/ml. These two numbers may not seem very different from one another, but a glance at Table 1 will show you how different they are. As you can see, the change in the actual digit between 10 -5 and 10 -5 is quite a bit larger than it looks at first glance. time plate count dilution CFU/ml (scientific notation) natural number mantissa 90 230 10 -5 230 × 10 -5 = 2.3 ×10 7 23,000,000 7.36 120 115 10 -7 115 × 10 -7 = 1.1 × 10 9 1,100,000,000 9.04 Table 1: A comparison of data as noted in scientific notation; natural numbers and the mantissa (result of the common log of the natural number). If you tried to graph the two natural numbers in Table 1, your X axis would be too large to fit on a piece of paper. In order to graph large numbers, one of two things must be done. Large numbers that are expressed in scientific notation can easily be graphed using logarithmic or semi-logarithmic graph paper . Logarithmic graphs have cycles of 10 whose digits vary in distance from one another in order to accommodate the wide data set. Semi-logarithmic graphs have one

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## This note was uploaded on 12/23/2009 for the course BIO 205 taught by Professor Murphy during the Fall '09 term at Miramar College.

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Lab_14_data_analysis - Miramar College Biology 205 Microbiology Lab Exercise 14 Data Analysis Presentation I Background In Lab Exercise 10

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