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Decomposers | Activity 3.2

Activity 3.2: Observing Bread Molding (60 min over 2 days)

Students work in groups to make and record observations of bread molding (mass change) and bromothymol blue (color change). Then they compare their observations with other groups and work to identify patterns and reach consensus about their results.

Materials You Provide

Resources Provided


Prepare the BTB, digital balances, Petri dishes, containers, and the materials from the Pre-Lesson. Use the instructions on the BTB Information and Instructions Handout for details about how to prepare the BTB. If you plan to use the poster to record student data, re-post the poster on the wall. Print one copy of 3.2 Observing Bread Molding Worksheet for each student. Prepare a computer with an overhead projector to display the PPT and video. You may want to print one copy of BTB Color Handout for each group, but this is optional.


1. (Day 1) Use the instructional model to show students where they are in the course of the unit

Show slide 2 of the 3.2 Observing Bread Molding PPT.


  • Use the class discussion when you compare their data to Mrs. Drayton’s class to interpret how successful your students are at identifying patterns in the class data. Use the 3.2 Grading the Observing Bread Molding Worksheet to determine if your students had any trouble with data collection.
  • During this activity, note students' success in measuring changes in mass and BTB. Also note students' ability to reach a consensus about patterns in data and how they interpret results.
  • The discussions in steps 10 and 12 can be helpful for informal assessment in two ways: 1) It can help you assess your students’ skills in identifying sources of error and finding patterns in data, and 2) it can help you assess how well students identify the limits of the evidence. Do they recognize that the investigation does not fully answer the Matter Change Question or the Energy Question?


  • Be sure to collect results from the different groups and compare their measurements.
  • Discuss threats to accuracy of measurement.
  • Check to see if students can identify unanswered questions from the investigation.


  • Have students design their own investigation. Students may wish to engineer their own investigation to answer the Three Questions and to evaluate their predictions. For example:
    • Students might choose to add controls to the experiment by including both a Petri dish of yellow BTB (made by blowing into blue BTB with a straw) and a Petri dish of blue BTB in the chamber.
    • Students might also choose to set up a chamber with a Petri dish of blue BTB alone without bread.

Extending the Learning

  • Follow the same procedures to investigate other types of decomposition, such as food scraps, grass clippings, leaves, or wood.