LAB 1 â Biology Lab Skills

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AP Biology—Lab 01 In Procedures 1-8, you should have calculated the percent error for each volumetric instrument. The mean of the percent error can be related to the accuracy of each volumetric instrument. Therefore, the lesser the mean is of the percent error, the more accurate the measuring device. Inversely, the greater the mean is of the percent error, the more accurate the measuring device. However, we cannot determine precision from the above. To determine precision, we must look at the variance that exists in the set. We can get this by looking at the standard deviation. The formulas for mean, standard deviation (SD), and standard error of the mean (SEM) are listed below and are also supplied in Appendix A (Lab 00 – Equations). SD The standard deviation (SD) describes the variability between individuals in a sample; the standard error of the mean (SEM) describes the uncertainty of how the sample mean represents the overall population mean. If normally distributed (a bell curve – more on that later), the study sample can be described entirely by two parameters: the mean and the standard deviation. The SD represents the variability within the sample; the larger the SD, the higher the variability within the sample. Although the SD and the SEM are related (see formulas), they give two very different types of information. Whereas the SD estimates the variability in the study sample, the SEM estimates the precision and uncertainty of how the study sample represents the underlying population. In other words, the SD tells us the distribution of individual data points around the mean, and the SEM informs us how precise our estimate of the mean is. In Table 9 below, for each volumetric device, fill in your calculated mean, the standard deviation (SD), and the standard error of the mean (SEM) for each set of percent error values. Table 9: Mean, standard deviation, and standard error of the volumetric devices measuring a known quantity of water. Volumetric device Mean percent error Standard deviation Standard Error of the mean 100 mL beaker 100 mL graduated cylinder 50 mL graduated cylinder 25 mL graduated cylinder 25 mL Erlenmeyer flask 50 mL volumetric flask 10 mL glass pipette 100 L – 1000 L micropipette Page 16 of 39
AP Biology—Lab 01 Using Excel It is important to not only be able to correctly collect data, but also present it visually – often in chart and graph form. Data tables and visual representations of data are integral parts of the results section of the lab write-ups and mini-posters that you will be producing this year. For general graphing help, refer to Appendix B (Lab 00 – Making Graphs) in your Lab Manual. For help with Excel, refer to the summer assignment that was given. If you still need help, make sure you get it – from the teacher or other students in the class. You will have to know how to do this, so make sure you understand the steps to construct a useful graph. Using Excel, create a series of 5 graphs (use scatter plot with trendlines) that show the relationship of total calculated mass versus total measured mass of the water samples measured for each volumetric device in Procedures 1 through 5. For each graph, also include a line that shows a direct correlation – you will need to plot a line that is ‗perfect‘ – (0,0), (20,20), (40,40), (60,60), (80,80), (100,100). Note: Make sure that you label all axes, complete a reasonable figure caption, have a key/legend of points/lines, etc. These graphs (and linked data tables used to construct it) will also be collected. Also using Excel, put all 6 of these lines on one graph (these include the 5 from procedures 1 -5 and the ‗perfect‘ line) on one grid. Do your best make this multi-line graph easy to interpret – you will need a properly formatted graph with all the bells and whistles (legend, caption, etc.) Compare the lines on the above graph with the mean percent error that you calculated for each volumetric device. Which would you say is the most accurate based on both your calculations and on the graphical representation of the data? HINT: compare each trendline for the calculated data with the ‗perfectly correlated [R 2 = 1.000] line. _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ Page 17 of 39
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LAB 1 â Biology Lab Skills

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LAB 1 â Biology Lab Skills