Section 2: Resources

Picture of Practice

Realizing that Decomposing Matter Doesn't Disappear:
5th Grade Lesson

The following picture of practice looks in on two lessons as students explore the idea that matter is conserved during the decomposition process. By observing decomposing plants turning into part of the soil, students understand that matter does not disappear. In the first lesson, students set up an experiment and make predictions about what will happen. In the second lesson, students consider the outcome of their experiment.

Setting up the Experiment: Collecting Initial Thoughts and Predictions

• Mr Wahl: We've been talking about decomposition, but today we're going to think about what happens to all the stuff that decomposes. What do you think happens to leaves, twigs, Styrofoam cups, and everything that you might find on the ground or in the trash? Scientists call all this stuff "matter." Does anyone have any idea what happens to it?
• Judy: Well, I think things like logs and leaves turn to rot.
• Mr. Wahl: What do you mean by "turn to rot," Judy?
• Judy: Well, the stuff gets all dirty. Sometimes it kinda smells.
• Mr. Wahl: Is there anything you noticed about the size of the logs or leaves as they rot?
• Judy: Oh yeah, it breaks up into pieces.
• Billy: I think the stuff gets eaten by worms.
• Eli: And bugs, too! I see all sorts of bugs eating garbage and leaves. So I guess the leaves and stuff end up in the bugs' stomach.
• Mr. Wahl: Interesting. Does anyone else have any other ideas?
• Dan: Well after a while it just disappears.
• Jo-Jo: Yeah, I think the stuff turns into nothing.
• Mr. Wahl: Can you think of a way that we might be able to find out whether or not the stuff disappears over time?
• Billy: We could watch it to see what happens.

At this point, Mr. Wahl does not confirm or disprove students' ideas. The discussion is kept as open as possible, with ideas flowing freely.

• Mr. Wahl: You came up with lots of interesting ideas about what happens to matter, or stuff, during decomposition. Over the next few weeks, we'll make careful observations of the materials in our decomposition chambers. Right now, let's talk about what we should put in our decomposition chambers. What kinds of things would you put in it?
• Billy: leaves, pieces of wood, maybe some dirt
• Mr. Wahl: Those sound like good things to put in. Why did you choose those items, Billy?
• Billy: Well, that's the kind of stuff I see rotting in the forest.
• Mr. Wahl: OK. Are there any other ideas about what to put in our chambers?
• Suzi: Maybe some dead insects or a dead mouse or something like that (Some of her classmates respond with "ugh" sounds.)
• Mr. Wahl: Good thinking, Suzi, dead insects and animals also decompose. For this activity though, we'll just use dead plants.

The class continues to brainstorm a list of all sorts of organic materials.

• Mr. Wahl: Alright, we have lots of ideas of organic materials we can add. Does anyone have any ideas of some inorganic things they might put in their decomposition chamber?
• Janis: What's "organic matter" and "inorganic matter"?
• Mr. Wahl: Good question, Janis. Organic matter is stuff made from living things. It includes things such as grass clippings, coffee grounds, newspaper strips, pine needles, pieces of lettuce, leaves, or other forms of organic matter. Inorganic matter is stuff made from non-living things, like Styrofoam cups or plastic wrappers.
• Tyrone: Wait, did you say "newspaper" was "organic"?
• Mr. Wahl: Another good question. Does anyone know where newspapers come from?
• Class: Trees!
• Mr. Wahl: Great, and are trees living or non-living things?
• Class: Living!
• Mr. Wahl: Yes. Now, are there any other questions?
• Judy: Yeah, how do we know what stuff to put in there?
• Mr. Wahl: Well, that's really up to you and your partner to choose what you want in your decomposition chamber. Remember, we are looking to see what happens to all kinds of stuff over time.
• Eli: If we all put in different materials, won't different things happen?

A discussion ensues about what sorts of difference students might notice with the organic versus inorganic matter. The students decide it will be useful to have different groups use different materials to compare possible differences.

Reflecting on Observations

A month or two later, students discuss their predictions about what might happen to what they observed happening to the matter over time. Mr. Wahl stresses that everyone's contributions help the class to better understand what's going on.

• Mr. Wahl: Are there any volunteers to share what they have observed in their chamber? Tell the class what you put in your chamber and any changes you noticed over time.
• Noah: We put soil and leaves and twigs in. We also put in a plastic dinosaur that Joey found.
• Mr. Wahl: And what did you observe over time?
• Noah: We noticed that the leaves got broken up, but the dinosaur didn't.
• Mr. Wahl: OK. Did you notice any overall changes to the different layers in your chamber?
• Noah: Yeah, the layer with the leaves and grass clippings and stuff is a lot smaller than it used to be. And I think it looks like the layer with the soil got bigger. But the plastic dinosaur looks pretty much the same.
• Mr. Wahl: Very interesting. Did anyone else notice anything similar? Anything different?
• Julie: We also noticed that the leaves broke apart the most. It kinda looks like they're becoming big, chunky pieces of soil.
• Mr. Wahl: Did you notice anything about the amount of soil in your chamber?
• Julie: Yeah, I guess its kinda like Noah said, it looks like there's more soil now.
• Dan: But there isn't as much stuff as before, look how much lower it got. I think that the little pieces break down to invisible pieces. It just sort of disappears.
• Julie: Maybe some things break down and go into the ground, and some things just disappear.
• Mr. Wahl: That's one idea. Can anyone think of another possible explanation?
• Rebekah: Well, if the pieces got smaller they would fit together like puzzle pieces so it would look like it takes less space even if the amount of stuff is the same.

Mr. Wahl has the students create models to illustrate Rebekah's idea. They present a variety of examples by cutting up Styrofoam, weighing out small and large steel balls to show that the same mass can fit in different amounts of space, and so on.

• Mr. Wahl: So what do these comparison suggest?
• Olivia: That the amount of stuff could stay the same even if it looks like less.
• Mr. Wahl: But we noticed that the plant matter did break down. Where do you think it went?
• Tyrone: Well, it looks like it just became soil. That would explain why our layer of dirt looks a little bigger now.
• Eli: So the stuff doesn't disappear, it just turns to dirt.
• Mr. Wahl: Alright, so what about the plastic dinosaur? Why didn't it become part of the soil?
• Janis: Well, because it's made from stuff that is not alive.
• Mr. Wahl: So do you think that all inorganic things cannot break down into soil?
• Janis: No.
• Mr. Wahl: Why not?
• Janis: Because I saw a really old chunk of a Styrofoam cup once that looked like it was rotting. If you wait a long time it might turn into soil.
• Mr. Wahl: Good observation, Janis. Can anyone think of any other examples of inorganic matter breaking down into soil?
• Olivia: Rocks break down into smaller pieces.

The class discusses other examples of the decomposition of inorganic matter. Students seem to understand the idea that all matter, organic and inorganic, eventually does not disappear, but rather, breaks down into parts of the soil or whatever surrounding environment it is in.