Student Experience 5: How should we revise our pond model?

Purposes

For students to form and express connections among ideas from previous experiences about decomposers and their interactions with abiotic factors.
To assess the development of students’ understanding of how the fertilizer overload affects algae and the resulting impacts on the decomposers and oxygen in the pond.

Description

Revisit the driving question (Why are the fish dying in the Sunrise Farm Pond?) and cross-sectional pond models students made in Part 1. Ask students to again draw what they think might be happening in the pond based on what they have learned about decomposers. After they have completed their models, have students make comparisons to their original models.

Science Practices

Developing and Using Models In this experience, students make revisions to their model. In addition to prompting students’ thinking with the provided questions about their model, it is also important to have students reflect on how their model has changed over time, and what that suggests about how their ideas about the mystery have changed.

Constructing Explanations Like in Part 1, students’ revisions are driven by their new understandings and developing explanations of what is happening at Sunrise Farm Pond. Their models should reflect their thinking about the predicted causes, and these new predictions should be supported using evidence from their investigations of decomposition.

Crosscutting Concepts

Cause and Effect Students’ thinking about the possible causes may have changed after their experiences with decomposers in Part 2. Encourage students to revise based on what they now predict are the causes and to be explicit about the relationship between the cause and effect.

Questions to Ask Students

Describe your model. Why do you think the different things you included are important?
How is this model different from your earlier ones? What have you learned that affected your new model?
How does your model help to explain what happens when nutrients in fertilizer get into the pond water?
How are the decomposers’ needs being met by the pond?
What impacts are the decomposers having on the pond and its resources?

Student Thinking

Students will likely understand that decomposers in the pond are consuming the dead algae (their food), and their water source is the pond itself. Students also should understand that, because they are consumers, the decomposers are using oxygen from the pond (all decomposers use oxygen their process of decomposition). Because there is more organic material (dead stuff) for the decomposers to eat than there had been before the fertilizer was added, the decomposers are using more of the pond’s oxygen. This leads to less oxygen being available for the other living creatures in the pond.

Implementation Tips

In a pond environment, decomposers are mainly bacteria. Students will likely not know this. It is okay to tell them that the decomposers are bacteria.
A third sample pond model, which corresponds to this stage of the pathway, is available for your reference. Again, student models may not include all of the elements appearing in the sample. Continue using the rubric for student models to monitor student thinking.