Decomposers is one of the six Carbon TIME units. If you are new to teaching Carbon TIME, read the Carbon TIME FAQ: Which Units Should I Teach.

The Decomposers Unit supports students in using core disciplinary ideas, science practices, and cross-cutting concepts to develop scientific explanations of how different decomposers transform matter and energy as they grow, move, and function.

Follow these steps to get ready to teach the Decomposers Unit

Lead Editor for 2019 Version

Kirsten D. Edwards, Department of Teacher Education, Michigan State University

Principal Authors

Kirsten D. Edwards, Department of Teacher Education, Michigan State University

Hannah K. Miller, Education Department, Johnson State College

Christa Haverly, Department of Teacher Education, Michigan State University

Christie Morrison Thomas, Department of Teacher Education, Michigan State University

Elizabeth Tompkins, Michigan State University

Charles W. “Andy” Anderson, Department of Teacher Education, Michigan State University

Contributing Authors

Beth Covitt, Jenny Dauer, Jennifer Doherty, Allison Freed, Ellen Holste, Wendy Johnson, Craig Kohn, Emily Scott, Carly Seeterlin, Nick Verbanic


Craig Douglas, Kendra Mojica

This research is supported in part by grants from the National Science Foundation: A Learning Progression-based System for Promoting Understanding of Carbon-transforming Processes (DRL 1020187) and Sustaining Responsive and Rigorous Teaching Based on Carbon TIME (NSF 1440988). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation or the United States Department of Energy.

Contact the MSU Environmental Literacy Program for more information:

The Driving Question

The Decomposers Unit starts by asking students to express their ideas about the driving question about an anchoring phenomenon, “What happens when bread molds?”

Carbon is the key! In the unit, students learn to tell the story of how matter and energy are transformed as they move through decomposer systems. A particularly powerful strategy for explaining how decomposer systems transform matter and energy involves tracing carbon atoms. For more information about the Next Generation Science Standards disciplinary core ideas included in this unit see the sections on the Matter Movement, Matter Change, and Energy Change Questions below and the Unit Goals.

Research base. This unit is based on learning progression research that describes the resources that students bring to learning about plants and the barriers to understanding that they must overcome. It is organized around an instructional model that engages students in three-dimensional practices.

Before beginning the Decomposers Unit, you need to decide what to teach and importantly, what not to teach! Use this page to choose the unit sequence that’s most appropriate for your students.

  • Some activities are REPEATING ACTIVITIES (). Omit these activities if students have already completed them in another unit (unless you’d like students to repeat them as review).
  • Other activities are TWO-TURTLE ACTIVITIES (), which place a higher demand on students. Decide whether the higher demand required by these activities will be useful or distracting for your students. The Carbon TIME Turtle Trails Document document provides further info about choices for making units more or less demanding, depending on your students’ needs.

Unless otherwise noted in the table below, all activities in the unit should be taught.

Decomposers Unit Sequence and Decisions Table

Here, we present two ways to think about how lessons are sequenced in the Decomposers Unit. The Instructional Model, immediately below, emphasizes how students take on roles of questioner, investigator, and explainer to learn and apply scientific models they can use to answer the driving question. Further below, the Unit Storyline Chart highlights the central question, activity, and answer that students engage with in each lesson of the Decomposers Unit.

Instructional Model

Like all Carbon TIME units, this unit follows an instructional model (IM) designed to support teaching that helps students achieve mastery at answering the driving question through use of disciplinary content, science practices, and crosscutting concepts. To learn more about this design, see the Carbon TIME Instructional Model.

Decomposers unit map

The core of the Carbon TIME IM is the Observation, Patterns, Models (OPM) triangle, which summarizes key aspects to be attended to as the class engages in unit inquiry and explanation. The OPM triangle for the Decomposers Unit, shown below, articulates the key observations students make during the unit investigation, the key patterns they identify through analyzing their investigation data, and the central scientific model that can be used to answer the unit’s driving question. During the inquiry portion of the unit (Lesson 3), the class moves from making observations to identifying patterns, eventually using these patterns to make evidence-based arguments. During the explanation portion of the unit (Lessons 4, 5, and 6), the class learns the atomic-molecular model, makes connections across scales, and uses the atomic-molecular model to explain how decomposers grow, move, and function. Across the unit, classroom discourse is a necessary part of 3-dimensional Carbon TIME learning. The Carbon TIME Discourse Routine document provides guidance for scaffolding this discourse in lessons.

Observations, Patterns, Models, and Explanations in the Decomposers Unit

Decomposers IM

The tables below show goals for this unit in two forms. A list of Next Generation Science Standards (NGSS) addressed by this unit is followed by a table showing specific target performances for each activity.

Next Generation Science Standards

The Next Generation Science Standards (NGSS) performance expectations that middle and high school students can achieve through completing the Plants Unit are listed below. To read a discussion of how the Carbon TIME project is designed to help students achieve the performances represented in the NGSS, please see Three-dimensional Learning in Carbon TIME.

High School

  • HS. Chemical Reactions. HS-PS1-4. Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.

  • HS. Chemical Reactions. HS-PS1-7. Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

  • HS. Matter and Energy in Organisms and Ecosystems. HS-LS1-6. Construct and revise an explanation based on evidence for how carbon, hydrogen, and oxygen from sugar molecules may combine with other elements to form amino acids and/or other large carbon-based molecules.

  • HS. Matter and Energy in Organisms and Ecosystems. HS-LS1-7. Use a model to illustrate that cellular respiration is a chemical process whereby the bonds of food molecules and oxygen molecules are broken and the bonds in new compounds are formed resulting in a net transfer of energy.

Middle School

  • MS. Structure and Properties of Matter. MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures.

  • MS. Chemical Reactions. MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.

  • MS. Chemical Reactions. MS-PS1-5. Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.

  • MS. Matter and Energy in Organisms and Ecosystems. MS-LS1-7. Develop a model to describe how food is rearranged through chemical reactions forming new molecules that support growth and/or release energy as this matter moves through an organism.

  • MS. Matter and Energy in Organisms and Ecosystems. MS-LS2-3. Develop a model to describe the cycling of matter and flow of energy among living and nonliving parts of an ecosystem.

Resources You Provide

Pre-Lesson Activity 0.1

  • Bread slices (4 per group of students)
  • Digital Balance
  • Labels for Petri dishes
  • Permanent marker (1 per group of 4 students)
  • Petri dishes with 4 lids (4 per group of students)
  • Roll of tape (1 per group or class)
  • Spray bottle with water for misting the bread (1 per class or group or class)

Activity 1.1

  • Pencils (1 per student, for paper version)

Activity 1.2

Activity 2.1

Activity 2.2

Activity 2.3

  • Pencils (1 per student)

Activity 2.4

Activity 3.1

Activity 3.2

Activity 3.3

Activity 4.1

Activity 4.2

Activity 5.1

Activity 5.2

  • scissors (1 per pair of students)
  • removable or re-stick tape (1 dispenser per pair of students)

Activity 5.3

Activity 5.4

Activity 6.1

Activity 6.2

Activity 6.3

Activity 6.4

  • computers (1 per pair of students, for option 2 in step 3)
  • blank posters (1 per pair of students or small group, for option 3 in step 3)

Activity 6.5

  • Pencils (1 per student)