Lesson 1: Defining the Tank as a System

What makes something a system rather than a collection of parts?
Where does this system begin and end?
What counts as an input or output?

System
Boundary
Component
Interaction
Input
Output
Variable
Observable
Inference
Feedback

HS-LS2-5: Develop a model to illustrate cycling of matter among ecosystem components.
Science and Engineering Practice: Developing and Using Models.
Crosscutting Concept: Systems and System Models.

Day 1: Observation Before Explanation

Students observe the tank without manipulating it. They are not told what is wrong or right. They are not given a lecture on aquaponics.

Students complete a structured observation protocol:

What do you see?
What is moving?
What is not moving?
What seems stable?
What seems variable?

Students sketch the tank and label visible components such as fish, plants, substrate, pump, tubing, bubbles, and water level.

They then identify which elements are directly observable and which must be inferred.

The purpose of this day is to slow thinking down. Students learn that careful observation precedes explanation.

Day 2: Defining System Boundaries

Students revisit their sketches and are asked to draw a boundary around what they believe counts as the system.

Class discussion follows:

Does the wall count?
Does the air above the tank count?
Does the food container count?
Does the classroom temperature count?

Students revise their diagrams to include:

Inputs such as fish food, water additions, electricity.
Outputs such as plant growth, fish waste, evaporation, harvested plants.

They begin identifying possible interactions between components without being taught the nitrogen cycle yet.

The purpose of this day is to shift from object thinking to interaction thinking.

Day 3: Initial System Model

Students construct a labeled system model that includes:

Components
Inputs
Outputs
Arrows showing interactions
At least one predicted invisible variable

Students write a brief explanation responding to the prompt:

Explain why our tank qualifies as a system. Include at least three interacting components and one example of cause and effect.

This model will later be revised in Phase 2 after deeper biological understanding is introduced.

The purpose of this segment is foundational. Students cannot meaningfully troubleshoot or design if they do not first understand that every change in the tank affects multiple interconnected parts.

DOK Level
DOK 1 for identifying components.
DOK 2 for classifying inputs and outputs.
DOK 3 for constructing a system model and explaining interactions.

Engineers and environmental scientists begin by defining system boundaries before conducting analysis. Whether designing water treatment facilities or agricultural systems, professionals must determine what counts as part of the system and what exists outside of it. Students are engaging in the same foundational practice.

A tank is just fish and water.
If you can see it, it is the only thing that matters.
Systems are static once set up.
If something looks clear, it is healthy.
Boundaries are obvious and fixed.

https://docs.google.com/document/d/1siFIsOAs45CxuUlyJt9dNRdT70eTva14fJMeE1qXHPk/edit?usp=sharing%20

System Diagram Submission
Students submit a labeled system model including components, arrows of interaction, and at least one inferred variable.

Written Explanation
Students submit a paragraph explaining why the tank is a system, using the terms input, output, and interaction correctly.