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Decomposers | Lesson 6 - Explaining Other Examples of Decomposers Growing, Moving, and Functioning

Lesson 6: Explaining Other Examples of Decomposers Growing, Moving, and Functioning

Students do optional readings about a different types of decomposers. Then they practice explaining other examples of decomposers growing, moving and functioning and take the unit posttest.

Guiding Question

How do other decomposers grow, move, and function?

Activities in this Lesson

  • (Optional) Activity 6.1: Exploring Different Kinds of Decomposers (varies)
  • Activity 6.2: Explaining Other Examples of Decomposers Growing, Moving, and Functioning (50 min)
  • (Optional) Activity 6.3: Explaining How All Decomposers Grow, Move, and Function (50 min)
  • Activity 6.4: Decomposers Unit Posttest (20 min)


  1. Describe systems and processes in decomposers in a hierarchy of scales, including atomic-molecular and macroscopic scales
  2. Explain the chemical changes that occur when decomposers digest food and create new biomass
  3. Explain the chemical changes that occur during cellular respiration, representing the changes with molecular models and chemical equations
  4. Identify forms of energy involved in decay: chemical energy, movement, and heat energy

NGSS Performance Expectations

Middle School

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

High School

  • Chemical Reactions. HS-PS1-4. Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends on the changes in total bond energy.
  • Chemical Reactions. HS-PS1-7. Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
  • 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.
  • 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.

Background Information

In this final lesson of the unit, students have completed the inquiry and application sequences for decomposers growth and movement. The activities in the previous lessons were designed to walk students through a cognitive apprenticeship model of Establishing the Problem, Modeling, Coaching, and Fading. The results of the unit posttest will help you determine if your students are ready to move on to the final stage: Fading. After the Fading stage, students will be expected to carry forward concepts from this unit into future units. If the results from your posttest imply that a majority of your students are still struggling with certain concepts, it might be valuable to return to some of the main concepts they are struggling with before moving on to the next Carbon TIME unit.

Activity 6.1 introduces students to a crucial type of decomposer that has not previously been discussed in the unit: bacteria. This prepares students to complete the fading phase of the Application Activity Sequence in the following activity.

Activity 6.2 is the Fading phase of the Application Activity Sequence, which provides students with important less-scaffolded practice with digestion, biosynthesis, and cellular respiration. Students should take more responsibility for their work than in Lessons 4 and 5, which included the Modeling and Coaching phases. Students answer the Three Questions for different decomposers growing and moving using the Explanations Tools, coordinating accounts at the macroscopic and atomic-molecular scales. Macroscopic scale accounts include these components:

  • the structure of the system (the decomposer in this case) and the movement of materials through the system;
  • the location where chemical changes takes place (outside and inside decomposers’ cells);
  • the materials involved in the chemical changes: the reactants going in and the products coming out.

Atomic-molecular scale accounts include three different ways of representing chemical change:

  1. molecular models, with twist ties to represent units of energy, that students use to physically rearrange the atoms of the reactants into the atoms of the products;
  2. a chemical equation that shows how atoms are rearranged into new molecules in a compact way (but does not account for energy);
  3. the Explanations Tools, which provide a way for students to account for changes in matter and energy in writing and answering the Three Questions.

Activity 6.3 is the second part of the Fading phase of the Application Activity Sequence. In this activity, students write generalized explanations, which focus on the cellular scale, of how all decomposers grow, move, and function.

Activity 6.4 includes summative assessment for the unit. You can track students’ progress by having them take the unit posttest (identical to the unit pretest) and comparing the results of the two assessments.

Key carbon-transforming processes: Digestion, Biosynthesis, and Cellular Respiration

Unit Map

Decomposers Lesson 4 Unit Map

Talk and Writing

This lesson of the unit represents the fading portion of the Explanations Phase. This means that students are expected to develop explanations for carbon-transforming processes they studied in this unit in new and novel contexts. The table below shows specific talk and writing goals for the Explanations phase of the unit.

Talk and Writing Goals for the Explanations Phase

Teacher Talk Strategies That Support This Goal

Curriculum Components That Support This Goal

Examine student ideas and correct them when there are problems. It’s ok to give the answers away during this phase! Help students practice using precise language to describe matter and energy.

Let’s think about what you just said: air molecules. What are air molecules?

Are you talking about matter or energy?

Remember: atoms can’t be created. So that matter must have come from somewhere. Where did it come from?

Let’s look at the molecule poster again… is carbon an atom or a molecule?

Molecule Poster

Three Questions Poster


Focus on making sure that explanations include multiple scales.

The investigation gave us evidence for what was happening to matter and energy at a macroscopic sale. But what is happening at an atomic-molecular scale?

What is happening to molecules and atoms?

How does energy interact with atoms and molecules during chemical change?

Why doesn’t the macroscopic investigation tell us the whole story?

Let’s revisit our scale poster… what is happening to matter at the molecular scale?

Molecular Models

Molecular Modeling Worksheets

Explanations Tool

PPT Animation of chemical change

Powers of Ten Poster

Encourage students to recall the investigation.

When did this chemical change happen during our investigation?

How do we know that? What is our evidence?

What were the macroscopic indicators that this chemical change took place?

Evidence-Based Arguments Tool

Investigation Video

Elicit a range of student explanations. Press for details. Encourage students to examine, compare, and contrast their explanations with others’.

Who can add to that explanation?

What do you mean by _____? Say more.

So I think you said _____. Is that right?

Who has a different explanation?

How are those explanations similar/different?

Who can rephrase ________’s explanation?

Explanations Tool