Lesson 5 – Data Analysis for the Halo Salinity Experiment

Description: An increase in salinity allows for an increase in halobacteria population size. The reliability of data increases with an increase in the size of the data pool/set. To draw reliable conclusions, multiple trials/replicates should be performed.




Course:  Life Science, Integrated Science, STEM

Unit:  Ecological Networks Part 1- Network interactions

What Students Learn:

  • An increase in salinity allows for an increase in halobacteria population size
  • The reliability of data increases with an increase in the size of the data pool/set
  • To draw reliable conclusions, multiple trials/replicates should be performed

What Students Do:

  • Students analyze lab results of the Halo salinity lab to determine the optimal salinity for halobacteria growth
  • Students interpret their experimental data to make conclusions about the observed pattern of halobacteria growth in the north arm of the Great Salt Lake.
  • Students discuss/identify possible errors/sources of variation in their results.
  • Students plan an appropriate investigation from the list of potential hypotheses


  1. Warm-up:
    1. Are all 3 data points within a relatively close range?
    2. What are some initial reactions/comments that you have?

    Students begin this lesson AFTER they have entered their group’s data into the Excel sheet (tab 1 {data-class}) and a Molarity/Concentration average has been generated

  1. Use tab 1 (data-class) of the HalodataTemplate.xls (Excel) to review the individual data points to begin a discussion on range of data, outliers, and any difficulties or variances they may have encountered while collecting the data from the spectrophotometer.
    1. Students will have had some exposure to the concept of an outlier in middle school-but will still benefit from a more detailed discussion on this concept and how to recognize data that are out of an acceptable range.
    2. This period of discussion is also a time to refer back to “why” a particular procedural step was carried out in a specific manner—i.e-saving the sample even after the spectrophotometer data has been collected. If a particular sample gave an unusually high or low absorbance reading-the student/group could return to the station and measure again. This is how professionals in the field proceed and this connection to “real” science can improve students lab procedures/habits.
  2. Use tab 2 (graph-class) to show the molarity/concentration averages plotted graphically.
    1. Based on the previous conversation about data reliability, variation, and outliers-examine the class data
  3. Use tab 3 (graph-class with SD bars) to introduce the standard deviation/range of the data points.
    1. Students may have heard the term standard deviation (depending on their math level), however, a definition of the term is not necessary at this point-rather a simplified description that these bars are like the range and represent the amount of variation in the data points (Formally, standard deviation is an average of the difference between each data point and the average of the sample)
    2. Elicit student responses on their confidence in the data and what could be done to increase their confidence in the data (repeat/multiple trials)
  4. Use tab 4 (data-district) and tab 6 (graph-district) to show the “district” data set.
    1. Use this larger data set to compare with the class data—are the curves relatively the same? Are the data points within the same range?
  5. Enter the class averages into tab 5 (data-district + class) and view tab 7 (graph-district + class)
    1. Elicit student responses on what the graph tells us in regard to the investigative question.
    2. Elicit student responses on what the graph tells us in regard to physical elements of the lake-especially the north arm that allowed for the increase in halobacteria.
  6. Graph the data and write a conclusion to the lab
    1. Students should graph the class data in their logbook/lab book or on their own paper-paying attention to correct graphing procedures (T.A.I.L.S.)
    2. Students write a conclusion to the original investigative question—citing high and low data points and using appropriate explanatory language to make sense of the data. The student instructions (Graph and Conclusion Student Instructions.doc (Google Doc | Word Doc) give the full prompt.

***Here is a good breakpoint for a standard (50 minute) class period***

Assessment—Grading the Graph and Conclusion
  1. The PowerPoint HaloDataAnalysis-Grader.ppt (Google Slides | PowerPoint)which contains the rubric for grading the graph and conclusion should be projected.
    1. It may be beneficial to reinforce the idea that this grading exercise is on an assessment-which will count for a grade and that the class should stay together-so that the teacher can answer any questions or make any necessary clarifications about each point/criterion.
    2. The PowerPoint is formatted to reveal the criteria for each value point line by line
    3. The final slide has a suggested method for calculating the graph and conclusion grade-if a teacher chooses to follow a WASL-style- standards-based grading scheme.
  2. The grading of the graph and conclusion will generally take no more than approximately 20 minutes-which should allow a teacher to proceed to the next step of the assessment—students plan an investigation.

    Assessment–Planning an investigation This lesson is an assessment of students’ investigation planning skills. Return to the potential hypothesis list (generated at outset of Halo activities) and have students plan an investigation from one of these potential hypotheses. Students would plan up to “procedure”. Use Halobacterium Investigation Plan for student instructions.

    ***This plan can be graded/assessed in class by using the document “Halo Investigation Plan Grader” ***

  3. Begin reposting/reprojecting the list of potential hypotheses that were generated during the class discussion on Halo growth and Observations of the north arm of the Great Salt Lake.
    1. Students will have suggested topics such as pollution, temperature, light intensity, etc—they are free to choose any one of these topics-and plan an appropriate investigation (Question/Hypothesis-Procedure)
    2. It may be beneficial to allow students to briefly review/look at the materials list/procedure for the salinity to help them get started with their plan.
  4. Give the investigation plan prompt (Halobacterium Investigation Plan.doc) (Google Doc | Word Doc) and have students plan an appropriate investigation
    1. It may be beneficial to inform students that this exercise is an assessment and should be taken seriously
    2. This assessment should also be completed be EACH student-some other investigation plans may be done in groups/pairs-but being that this experience happens early in the year, it is important to assess each student’s ability in planning an investigation.

***Number 4 is designed to be a breakpoint for a standard (50 minute) class period***

Assessment—Grading the Investigation Plan
  1. Begin by having students staple or attach a copy of the HaloDataAnalysis-Grader.ppt (Google Slides | PowerPoint) to their investigation plan and turn it in. (a copy of the rubric for each student will need to be printed ahead of time)
    1. To ensure objectivity by the student grader-it may be helpful to use an assigned number rather than a name on the student writer’s paper.
  2. Pass out the papers/plans according to your in-class grading procedure (ensuring that students don’t have their own paper)
    1. So that students will be more familiar with what is written in the plan they are grading-they should be given 3-4 minutes to read the plan-without using the rubric or assessing points—just to get an idea of what they’ll be assessing
    2. It will be important to stress to students that the grading proceed together as a class and that any one student no rush ahead on the rubric as the class will assess each criterion-and clarify any questions they may have.
    3. Grade the plans according to the provided rubric
      1. The rubric follows a WASL-style value points system for grading
      2. A suggested method for calculating a student grade based on a WASL-style value points to standard is:
        10, 9 value points= Exceeds Standard
        8, 7 value points= Meets Standard
        6, 5 value points= Approaches Standard
        4 and below= Below Standard

    ***Tips for clarifying Investigation Plan Rubric Attributes are listed below***

    Tips for in-class grading of the investigation plan:

    Scoring Rubric for Awarding Value Points for Investigation Attributes


    1. If the response does not plan an appropriate procedure for this investigative question, the response cannot earn any of the eight possible procedure value points (e.g. the response repeats the procedure from the salinity lab).
    2. If there is no manipulated variable present, no points shall be awarded for either manipulated or controlled variables.
    3. If the response simply names the bulleted attributes listed after “Procedure that includes:” without writing a procedure, no procedure points may be awarded.
    4. The ‘right’ amount of ingredients (i.e. ‘x’ mL or ‘y’ grams) needed to carry out the procedure does not need to be given in the material list.
    5. Vague materials used in the procedure (i.e. 1mL) may be credited if the vagueness is clarified in the materials list (i.e. 1mL of insecticide)
    6. If pre-measured amounts of materials are listed in the materials list, a measuring device may not be needed in the materials list.
    7. Measuring a vague parameter (e.g. amount of halo instead of O.D/population size) may be credited as a responding variable but is too vague to repeat, so no point can be awarded for ‘logical steps.’
    8. The word “repeat” at the end of a step, refers to that step only. If “repeat” is listed as a separate step or in a new paragraph, it refers to go back to the beginning.
    9. If the response correctly implies the controlled, manipulated, or responding variables but identifies them incorrectly, the appropriate value points may not be awarded.

    You completed Instructional Activities. Please move to Assessment via the above tab.


How will I know they know

  • Grading of graph and conclusion using WASL-style rubric (HaloDataAnalysis-Grader.ppt (Google Slides | PowerPoint)
  • Grading of investigation plan using WASL-style rubric (HaloInvestPlanGrader.doc (Google Doc | Word Doc)



This lesson can easily be adapted for various levels of students. Leaving out or adding data can be easily achieved with the Excel template. For more data, see the Baliga Lab website or contact Claudia at cludwig@systemsbiology.org. Remind students that viewing the data as a graph helps to visualize this seemingly complex data set. Use the printouts as ways to keep students on task and organized with their analysis.