Compost Bins Investigation

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SWBAT explain the role of decomposers and scavengers in ecosystems.

Big Idea

In this lesson, students will be creating three compost bins to investigate which scavenger (earthworm, darkling beetle, or a roly-poly) will decompose organic materials the fastest.

Lesson Overview

Inquiry Based Instructional Model

To intertwine scientific knowledge and practices and to empower students to learn through exploration, it is essential for scientific inquiry to be embedded in science education. While there are many types of inquiry-based models, one model that I've grown to appreciate and use is called the FERA Learning Cycle, developed by the National Science Resources Center (NSRC):

1. Focus

2. Explore

3. Reflect

4. Apply

A framework for implementation can be found here

I absolutely love how the Center for Inquiry Science at the Institute for Systems Biology explains that this is "not a locked-step method" but "rather a cyclical process," meaning that some lessons may start off at the focus phase while others may begin at the explore phase. 

Finally, an amazing article found at, How Inquiry-Based Learning Works with STEMvery clearly outlines how inquiry based learning "paves the way for effective learning in science" and supports College and Career Readiness, particularly in the area of STEM career choices. 

Unit Explanation

In this unit, students will first develop an understanding of the biotic and abiotic factors within ecosystems, the characteristics and classification of living organisms, and how plants and animals obtain and use energy to fulfill their needs. 

Then, students will delve deeper into the NGSS standards by examining the interdependent relationships within an ecosystem by studying movement of matter between producers, consumers, and decomposers by creating models of food chains and food webs.  

At the end of this unit, students will study ways that individual communities can use science ideas to protect the Earth's resources and environment.  

Summary of Lesson

Today, I will open the lesson by providing students with the opportunity to observe scavengers. Students will then set up an investigation to examine how the type of scavenger impacts the decomposition process within three different compost bins. 

Next Generation Science Standards  

This lesson will support the following NGSS Standard(s):

5-LS2-1.    Develop a model to describe the movement of matter among plants, animals, decomposers, and the environment.  

Scientific & Engineering Practices

For this lesson, students are engaged in the following Science & Engineering Practice:

Science & Engineering Practice 3: Planning and Carrying out Investigations

Students will be planning and conducting an investigation on composts bins. They will examine the controlled variables in order to conduct a fair test. 

Crosscutting Concepts

To relate ideas across disciplinary content, during this lesson I focus on the following Crosscutting Concept

Crosscutting Concept 6: Structure and Function

Studnets will analyze the substructures of scavengers and determine how these parts help the scavenger survive. 

Disciplinary Core Ideas

In addition, this lesson also aligns with the following Disciplinary Core Ideas

LS2.A:  Interdependent Relationships in Ecosystems

The food of almost any kind of animal can be §traced back to plants. Organisms are related in food webs in which some animals eat plants for food and other animals eat the animals that eat plants. Some organisms, such as fungi and bacteria, break down dead organisms (both plants or plants parts and animals) and therefore operate as “decomposers.” Decomposition eventually restores (recycles) some materials back to the soil. Organisms can survive only in environments in which their particular needs are met. A healthy ecosystem is one in which multiple species of different types are each able to meet their needs in a relatively stable web of life. Newly introduced species can damage the balance of an ecosystem. (5-LS2-1)

LS2.B:  Cycles of Matter and Energy Transfer in Ecosystems

Matter cycles between the air and soil and among plants, animals, and microbes as these organisms live and die. Organisms obtain gases, and water, from the environment, and release waste matter (gas, liquid, or solid) back into the environment. (5-LS2-1)

Choosing Science Teams

With science, it is often difficult to find a balance between providing students with as many hands-on experiences as possible, having plenty of science materials, and offering students a collaborative setting to solve problems. Any time groups have four or more students, the opportunities for individual students to speak and take part in the exploration process decreases. With groups of two, I often struggle to find enough science materials to go around. So this year, I chose to place students in teams of three! Picking science teams is always easy as I already have students placed in desk groups based upon behavior, abilities, and communication skills. Each desk group has about six kids, so I simply divide this larger group in half. 

Gathering Supplies & Assigning Roles

To encourage a smooth running classroom, I ask students to decide who is a 1, 2, or 3 in their groups of three students (without talking). In no time, each student has a number in the air. I'll then ask the "threes" to get certain supplies, "ones" to grab their computers, and "twos" to hand out papers (or whatever is needed for the lesson). This management strategy has proven to be effective when cleaning up and returning supplies as well!  


30 minutes

To begin today's lesson, a student shares her mushroom farm that she brought in from home: Student's Mushroom Farm. She walks around the classroom and students are eager to see this decomposer! In a later lesson, a student will bring in a large mushroom for students to touch and examine. This is what makes science come alive - when students become so involved and interested! 

Lesson Introduction & Goal 

I introduce today's learning goal: I can explain the role of decomposers and scavengers in ecosystems. I explain: Yesterday, you all did a great job researching the composting process! Today, you will get the opportunity to use your research to create three compost bins... one for darkling beetles, one for roly-poly isopods, and one for earthworms. 

Examining the Scavengers!

To provide students with a little background information and to inspire student engagement, I ask teams to gather the following materials: Darkling Beetles, Earthworms, & Roly Poly Isopods, magnifying glasses, and Paper Plates. I want students to take the time to examine each scavenger and their substructures that help them survive so I create a 3 Column Chart on the board and ask students to do the same in their science journals. 

I then invite students to empty out the contents of each cup onto three separate paper plates and to begin examining each of the scavengers closer: Students Examining the Scavengers. I give students about 10 minutes to discuss their observations with their teams. During this time, I conference with groups. 


I love how this group, Earthworm Observations, discover how the earthworms react when touched or when they feel they are in danger. 

Another group, Roly Poly Observations discovers that the roly poly bugs like to hide out in dark, moist environments. 


After teams have time to observe on their own, I ask students to raise their hands to share what they notice. I document student observations on the board and I also add in a few facts as we go along: Observations of Scavengers. Students take notes in their journals during this class discussion: Student Journal Example.

We begin by examining the earthworms first. Students love watching them move around on the paper plates and, in some cases, squirm off the side of the plate. One student points out that the earthworm has lines on it's body. I explain that these are segments and that the earthworm has a segmented body with around 100-150 segments or rings. 

After recording several more observations on the earthworms (such as the bristles used for moving and how it will withdraw to its burrow when in danger), we then move on to discussing the pill bugs (also called roly-poly bugs or isopods) and the darkling beetles. 

Once we finish, students return the scavengers to the plastic cups with lids until they are ready to add them to the compost bins later on.


40 minutes


For today's lesson, I will ask two teams of three to work together in order to build three compost bins. 

Prior to today's lesson, I set out the following materials for each group of six: 


As a side note, I had intended on giving students some non-biodegradable materials as well, such as a piece of aluminum foil or plastic wrap. This would have provided students with the opportunity to investigate how some materials decompose while others do not. The only reason why I did not give non-biodegradable materials to the students is because I forgot! 

Getting Ready

Before gathering supplies, I ask students to consider the Investigative Question. I then ask students to make a prediction by voting. Twenty-three students thought that the compost bin with earthworms would decompose fastest while one student voted for the pill bug's compost bin and four students voted for the darkling beetle's compost bin. Making predictions is an important part of not only the scientific method, but also activating student interest. If we had more time, I would have asked students to explain why they voted the way they did. I believe that many students thought that the bigger the organism, the faster the decomposing process would happen. 


This is a great lesson to review the types of variables in an investigation. To avoid confusion, I choose to focus on the controlled variables and changed variables in this investigation. Prior to today's lesson, I wrote the following on the board: Discussing Variables (Before)

At this point, I explain the difference between controlled variables and changed variables and then I ask students to turn and talk about the difference. Turning and talking allows for students to hear the concepts a second time and it encourages students to be attentive listeners. 

Per student suggestions, I then label the controlled variables and changed variables by drawing arrows to each of the three bins: Discussing Variables (Before). Students are quick to point out the importance of placing the same amount of grass, water, soil, and other materials in each bin. Then students decide that the only change that happens between all three bins is the type of scavenger. 


To gather materials, I ask the #1 students to get paper plates, the #2 students to get lettuce, and so on. Once students have all the necessary materials at their desks, I review some of the students' findings from yesterday, such as the fact that small pieces of organic matter decompose faster (enter the paper plate and knife) and the fact that water is needed in compost bins (which is why I provide groups with water bottles). I purposefully try to not provide too many directions as I want students to problem solve and make decisions about their compost bins as they go! 

Monitoring Student Understanding

Once students begin working, I conference with every group. My goal is to support students by asking guiding questions (listed below). I also want to encourage students to engage in Science & Engineering Practice 7: Engaging in Argument from Evidence

  1. What patterns have you noticed? 
  2. Why do you suppose ____? 
  3. What have you found so far? 
  4. Has your thinking changed? 
  5. What evidence do you have? 
  6. How did you decide _____?
  7. What conclusion can you draw about ____?
  8. Why do you think ____ is important?
  9. What is something that you are doing that you learned from your research? 

Student Conferences

During this conference, Conference 1, the student explains how her group is using their research to create their compost bins. 

Here, Conference 2, I ask the students to explain the controlled variables in their investigation. Even though most group members are making a conscious effort to keep variables the same, all students in the class need further exposure to the term "controlled variable."

Student Work

As students finish, they add scavengers to each of the compost bins. It's fun for students to watch these little creatures interact with their new environments! Next, students wrap each of their compost bins with aluminum foil and they place sticky notes on the top of each bin, indicating their team color, the date, and the type of scavenger in the bin: Team Compost Bins.