This lab experiment involves investigating the effects of various environmental conditions, antibiotics, antiseptics, disinfectants, and hand soaps on bacterial growth. Students will conduct experiments to determine how these substances impact bacterial growth. The results must be written up in a formal lab report following IB Internal Assessment guidelines, with attention to properly describing the problem, variables, methodology, data collection and processing, and conclusions. The report will be considered for inclusion in the student's IB portfolio, so careful and thorough work is required.

1. Introductory Microbiology Lab
Controlling bacterial growth: antibiotics, antiseptics/disinfectants & hand soaps
In this lab, you will be given the opportunity to investigate the affects of several different environmental
conditions, antibiotics, antiseptics & disinfectants, or hand soaps on bacterial growth.
You may use this lab as a final IA. You may submit an entire IA (D, DCP, CE) or you may submit any of
the three components you wish to have considered for your portfolio. Keep in mind that your IB lab is
28% of your IB score. If you have a 3 or less on any aspect (D, DCP or CE) I strongly suggest you take
advantage of this lab.
Use the IA guidelines for you r IA lab report. IA lab reports must be turned in by Wednesday April 6th.
No labs turned in after April 6th will be considered for IA submission.
You may refer to this lab guide in the design of your IA. Be sure to provide a citation
IntroMicro/2011 IntroMicroLab7.pdf [class handout]. IB Biology, South Lakes High School, Reston, VA
Citation in text: (Intro Micro 2011)
LOGISTICS
 Lab typed or neatly hand written  Clear spelling, grammar, and flow of the
 Title of lab is clear and relevant writing
 1.5 line spacing  Past tense throughout the paper
 Logical order, with clear headings  References correctly cited
DO NOT COPY this lab procedure in aspect 3. Put in your own words.
IB DESIGN ASPECT 1: problem and variables
 Relevant contextual information is provided
 Accurate biology background information is included
 Sources are cited
 Scientific name of organism is provided or explained why unknown
 Scientific name is always italicized or underlined
 Problem question is stated with a clear MV and RV
 Manipulated variable correctly identified (or describe why no MV)
 Levels of the MV are listed
 Unit for the MV is provided
 Responding variable is correctly identified
 Quantitative RV provided
 Qualitative RV provided (or explain why none)
 Unit for the RV is provided
 Hypothesis concerns effect of MV on RV
 Hypothesis explanation is valid
IB DESIGN ASPECT 2: Control of Variables
 At least three relevant controlled variables are identified
 Controlled variables are not validity measures

2.  There is a clear explanation why each variable needs to be controlled
IB DESIGN ASPECT 3: Method for Collection of Data
 The major apparatus used are listed, including size and graduation
 There is a picture or diagram of the set up
 Diagram is titled and labeled
 Procedure includes enough detail to follow instructions
 Procedure includes a few validity measures
 Procedure describes how the manipulated variable was varied
 Sample size is at least 5 for each level of the MV
 Explanation of how and why you sampled data
 Indication that data was pooled, with reference to IB subject guide
 Procedure describes how the controlled variables were kept constant
 Directions about how to collect measurement data (with tool listed)
 Safety precautions are provided
IB DATA ASPECT 1: Recording Raw Data
 Relevant quantitative data are collected
 Relevant qualitative data are collected
 All measurements are in metric units
 Final data is organized into a easy to read table
 Manipulated variable is in the left column of the data table
 Table has clearly labeled title and column headings (with units)
 Table(s) labeled sequentially as Table 1… Table 2…
 Measurement uncertainty is noted and correct
 Data is measured to a consistent, correct precision for the tool used
 Decimal points align down a column
IB DATA ASPECT 2: Processing Raw Data
 Correct mean(s) is calculated for each level of the MV
 Correct standard deviation(s) is calculated for each level of the MV
 At least one example calculation for mean, SD and T-test
 Correct t-value(s) calculated (if in excel, correct P value is given)
 Use of the mean in explained
 Use of the SD is explained
 Use of the t-test is explained
IB DATA ASPECT 3: Processed Data Presentation
 Processed data is summarized into an easy to understand table
 Table has clear title and column headings (with units)
 Processed data has correct precision
 Processed data has correct unit
 Processed data has decimal points align
 T-test significance level is provided (0.06)
 Results summarized in a graph with RV on the Y axis
 Correct type of graph is used for the type of data collected
 Graph includes the mean and the SD, labeled as such
 If needed, smooth lines or curves are added

3.  Graph has clear title and labeled axis
 Graphs titled as sequential Figures
 “Series” boxes are deleted from graphs created in Excel
IB CONCLUSION ASPECT 1: Concluding
 Correct conclusion is drawn
 Conclusion relates to the problem / purpose
 Conclusion refers to hypothesis (without using the word “proves”)
 Reference to data to support conclusion (mean, SD and T)
 Refer directly to figures and tables
 Correct t-test significance
 Compare with literature or accepted values (if possible)
IB CONCLUSION ASPECT 2: Evaluating Procedure
 Confidence in results is stated
 Positive aspects of lab design are mentioned
 Appropriateness of MV range and levels
 Anomalous data points explained (if appropriate)
 At least 3 errors / limitations that actually effected data
 Description of how errors / limitations may have impacted results
 Limitations to procedure and conclusion are provided
IB CONCLUSION ASPECT 3: Improving the Investigation
 At least 3 improvements to procedure are provided
 Improvements are based in errors / limitations described
 Suggestions are not vague (“be more careful” is unacceptable)
 Suggestions reduce errors or improve control of variables
 Address modifications to technique and range

8. 13. Development of possible Antibiotic Resistance within the (originally) antibiotic-susceptible
bacterial population.
After recording the results for antibiotic resistance, susceptibility, zones of inhibition,
Be sure to dispose of plates by autoclave technique. You may look up this procedure and add it to
your design with a proper citation.