Student Experience 2: What are decomposers?

Purposes

To help students understand what decomposers need to survive.
To help students understand that decomposers are consumers.

Description

Ask students to look at their drawings from Part One and name the various organisms found in Sunrise Farm Pond. Ask them to name which of the organisms are producers (algae and underwater plants). Once the producers have been determined, ask them what the other organisms in the pond are (perch, minnows, mayfly larvae). If they are not familiar with the term “consumer,” ask students to describe what these organisms need to survive. They should realize that the things the organisms need to survive are the same things humans need (i.e., food, water, and air; particularly oxygen). Let the students know that these organisms are all in a group called consumers, and that, unlike producers, consumers are organisms that cannot make food within their own bodies.

Crosscutting Concepts

Patterns Applying what they learned about producers’ needs in Part One of the pathway, students are able to classify organisms based on patterns of what they need to survive. Emphasizing these patterns (i.e., the commonalities and differences in needs of various organisms) can support students’ ability to differentiate between producers and consumers.

Recall with students that in the first student experience, they saw videos with rotting fruit. Another way to describe what happened to the fruit is “decomposition.” Ask students what they think caused the fruit and vegetables to decompose. They may mention the bugs or the mold that appeared on the fruit and vegetables in the time-lapse videos. Let students know that these are decomposers, and that decomposers are necessary for decomposition. Take a class poll about whether students think decomposers are producers or consumers, and call on volunteers to defend their answers. If they are unsure, ask students to think about what producers and consumers need to survive. Record these lists for all students to see.

Next, let students know they will be conducting an experiment to explore whether decomposers are producers or consumers. Take five paper plates (one for each condition) and place a strawberry, piece of melon (watermelon, cantaloupe, etc.), and piece of bread on each. Tell students that they are going to place the plates of food in different conditions to test what helps or hinders decomposers. Ask students to make suggestions based on the lists that they created for the needs of producers and consumers. In the end, you will want to make sure that you have the following conditions: one plate in sunlight, one in dark, one where each item has been dunked in water. Students may make other suggestions, such as placing a plate in cold or heat or adding dirt. Once the five conditions have been decided upon, add the necessary items to the plates and place each in a gallon zip bag. Then place the bags in the agreed-upon locations. Have students record observations for each plate at regular intervals for one week. It is not necessary to pause instruction during this week; you can continue with the next student experiences as the experiment runs its course.

Science Practices

Planning and Carrying Out Investigations Students work collaboratively to design a class investigation focused on decomposition. In setting up the investigation, students make suggestions for conditions to test and make predictions about what will happen under the various conditions. Over the course of a week, students make observations to gather evidence related to decomposers’ needs.

Analyzing and Interpreting Data Although students’ data is most likely to be qualitative (e.g., descriptions and pictures of what they observe), encourage students to also consider ways for incorporating quantitative measurements (e.g., how many different types of mold/fungi, how many visible spots of each, estimated size or proportion of food that is covered).

Before (Top row: plate kept in dark, plate kept in sunlight; Bottom row: plate kept in refrigerator, plate with water added on top of the foods, plate with dirt added on top of the foods)

After One Week (Top row: plate kept in sunlight, plate with dirt added on top of the foods, plate kept in dark, plate with water added on top of the foods; Bottom row: plate kept in refrigerator)

Questions to Ask Students

On the first day:

If decomposers are producers, what are their needs? What about if they are consumers?
How do you think the decomposers will react to the different conditions?
- Which conditions do you predict will be most helpful for decomposer growth? Why?
- Which conditions do you predict will be least helpful? Why?

At the end of the week:

What do you see in the bags with the food?
In which condition did the mold/fungi first appear?
Which condition was most helpful for decomposer growth? Which was the least?
Do you think decomposers are producers or consumers? Why?
- What do decomposers need to grow and survive?
An important point to make during this student experience is that decomposers are consumers and thus have the same needs as consumers (e.g., food, water, oxygen). Have students think about how these needs factor into the experiment.
- What is the food?
- Where is the water in the bag? How did the plate with the extra water do?
- What do you think might have happened if we removed the air from the bag? Why do you think that?

Student Thinking

Some students believe that decomposition is a process that occurs in the absence of decomposers (i.e., that material decomposes on its own).
Some students think mushrooms are plants (Barman, 2006), leading them to believe that decomposers are producers.
Some students think decomposers, such as mold, are abiotic entities (i.e., not alive/not a consumer) (Leach, 1992; Leach, 1996).

Implementation Tips

Seal the bags using tape (such as duct tape or packing tape) to avoid unpleasant odors.
Use fresh bread (i.e., bread without a lot of processed ingredients or preservatives) to see the decomposition within the time frame. (Bread with preservatives will take longer to mold.) Fresh bread is available in the bakery section of most grocery stores.
Students may think there is no oxygen in the bag because it is sealed, but there is because there was air in the bag initially.
Students should see that the mold grows in the dark and in the light, which indicates light is not necessary for its growth. This demonstrates that the mold is not photosynthesizing, and thus is not a producer.
You should have several kinds of mold/fungi by the end of the experiment. Make sure to point this out to students. There are many kinds of decomposers, including many kinds of fungi.
Condensation will likely form inside the bag, which may make it difficult to see inside. It is okay to lift the plastic away from the food to get a better view, but do not open the bags or press down on the foods in the bags.
Do not open the bags at the end of the week because of the possibility of breathing in the spores. Throw the bags away in a trash can that students do not have access to. Click here for photos of the foods at the end of the week if you would like to show your students.