Students investigate possible water source contamination by coliform bacteria. In the first investigation, students use sterile technique to collect water samples and plate them on selective media. The media allow students to differentiate between general coliform, Escherichia coli, and noncoliform bacteria colonies. After 24 to 48 hours, they analyze the results and compare their findings to local water quality standards for coliform bacteria.

In the second investigation, students analyze samples from a fictional location. Based on the results of their analysis, students infer potential sources of contamination and propose design solutions to reduce the environmental impacts of human activities linked to bacterial contamination of water. Students describe the importance of clean water to public health with the goal of answering the driving question, "How can we monitor a community’s water for coliform contamination?"

Time Requirement
Teacher prep, approximately 2 class periods. Pre-lab, investigation, and assessment, 3 to 4 class periods.

Digital Resources
Includes 1-year access to digital resources that support 3-dimensional instruction for NGSS. Digital resources may include a teacher manual and student guide, pre-lab activities and setup videos, phenomenon videos, simulations, and post-lab analysis and assessments.

Performance Expectation(s)
HS-LS2-7

Crosscutting Concepts
Cause and Effect

Disciplinary Core Ideas
LS2.C: Ecosystem Dynamics, Functioning, and Resilience
ETS1.B: Developing Possible Solutions

Science and Engineering Practices
Constructing Explanations and Designing Solutions

Learning Objectives

• Describe the impact of coliform contamination of water supplies on public health and how it may disrupt the functioning of an ecosystem.
• Collect empirical evidence of E. coli and total coliform bacteria counts using a common test of the safety of water for human use.
• Gain practice in plating and culturing bacteria with sterile technique.
• Use evidence to evaluate whether freshwater samples meet water quality standards of numbers of allowable coliforms.
• Design and evaluate a solution for reducing the impacts of human activities on the environment.

Prerequisite Knowledge and Skills
Students should feel comfortable with mathematical manipulation, including multiplication and division. They should have basic knowledge of the water cycle and the awareness that human activity and other factors affect the health of aquatic ecosystems.

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