Using Protists as a Model of Succession (Part 3/3)

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Objective

Students will explain how succession occurs in an ecosystem by noting the changes in a hay infusion over a period of time.

Big Idea

By using protists as model organisms, we can shorten period of time succession occurs so we can observe changes in an ecosystem.

What Students Will Learn in this Lesson

1 minutes

This is the end of a two week observational study which started at the beginning of the unit.  Students will make one final observation and cell count of their hay infusions. They will discuss their findings and write a formal report. Here is an overview of what students will learn today. 

Hook

13 minutes

Students should make wet mount slides of their hay infusions (as described here).  They should make sketches of what they see at 6 different places on the slide. After ten minutes, have the students clean up their lab areas and return to their desks. Microscope slides should be disposed in the glassware bucket. Since this is the final day of the experiment, students should place the cultures in the autoclave for sterilization. 

(Note: Hay infusion culture should be sterilized at 15 lbs pressure for 15 minutes.  After the cultures cool, the liquid contents should be poured down the sink with copious amounts of water.  The solid contents should be disposed in the chemical disposal bucket.)

 

Looking at Student Logs

30 minutes

Have the students discuss their student logs that they have kept over the past two weeks. Ask them the following questions to keep the discussion moving:

  • When looking at your data, are there any patterns that you see at first glance?

 

  • What types of changes did you see in your hay infusion over the two week period?

 

  • Is there a way that you could quantify your observations so that you could better see if any patterns emerged?

 

Guide them in determining a way that they could present their findings in quantitatively. (Note: Most student groups in decide to compare the change in number of types of protists over time to the different treatment.)

Student groups will combine all of their group data on a class spreadsheet. (Note:  we use Google docs for this step.) Data is disaggregated by treatment (control, salt, and fertilizer) and type of protist group (animal-like, plant-like, or fungus-like).  All students should place their data in the same spreadsheet for analysis. Once all the students have completed the input of their data, then ask students how they could compare the distribution of data to get a clearer picture of what occurred to the amounts of different protists in each treatment over a two week time period. To help in this comparison, ask students to calculate the daily average (mean), standard deviation, and range (maximum and minimum) of the class data. (Note: If your students already have some experience using statistics, then they can also determine the median and variance.

Next, students can download the Google doc as a .csv file and import it into LoggerPro to determine the line of best fit. To determine the line of best fit, students should select Analyze, then Curve Fit. Next, they should select which data set (animal-like, plant-like,or fungi-like). Then, they should select the general equation and Try Fit. Once they have determined the function that best matches the distribution of their data, they should select Ok. Students should repeat this procedure for all data sets (animal-like, plant-like, or fungi-like) in each treatment (control, salt, or fertilizer).

Move about the room consulting with individual students and answering questions that may arise.

(Note: Here are some of the student graphs from my class' two work study: Salt treatment (Group 1)Salt treatment (Group 2)Fertilizer treatment, and Control).

Reporting Student Findings

10 minutes

Using the results of their descriptive statistical analysis and their graph with line of best fit, students will describe what occurred in their hay infusions over the two week period.  When writing their descriptions, students should consider the following questions: 

  • When you first started your hay infusions (day one), how many protists were in the hay infusions?
  • What was the first type of protists that occurred in the hay infusion? 
  • What protist showed up in the hay infusion next? 
  • What was the final protist group to arrive?
  • Explain these observations in light of what you know about protist life cycles. 
  • What occurred to the hay infusions when salt or fertilizer were added to them? 

 

Students should type their description and include their graphs that were generated in the previous student activity.

 

 

Putting it All Together: How Does This Model Succession

15 minutes

Explain the difference between primary and secondary succession. Then ask students to think of ways that their hay infusion might show evidence of succession in an ecosystem.  

  • Where would one see an ecosystem like the one in the hay succession?
  • Where was succession first studied?
  • What did scientists discover when studying those ecosystems?
  • What is the pioneer plant and animal species?  
  • Like what does the climax community look?  
  • Why study a community of protists instead of a mountainside or forest?

 

Guide students through writing a brief introduction of their paper by projecting a word document and asking for student input.  Modeling writing the introduction as the student answer the questions listed above.  

Allow the students class time to begin writing the procedure of the experiment. At the end of the writing period, bring students back together as a class. Have several volunteers individually read their procedures. Have students critique the procedure and offer suggestions where these procedures should be more detailed.  

Then have students insert the description they wrote in the previous section. Inform students that they have essentially written their formal lab report. They will need to edit it for spelling and convention errors. Their final draft is due in two days.