Altering Carrying Capacity by Changing Environmental Factors

A Carolina Essentials™ Activity

Total Time: 45-60 mins

Prep: 15 mins | Activity: 30-45 mins

Life Science


High School


This is a scenario-based activity in which students must use bacterial growth data to determine the carrying capacity of an “ideal” growing medium and then determine how two different treatments affect the growth and carrying capacity of the medium. Students must graph data, identify the carrying capacity of the system, and then explain how the treatments affected bacterial growth. Graphing may be completed by hand or digitally depending on the skill level of the students.


Look carefully at the colonies of Escherichia coli in the photo above. What questions could you ask about bacterial growth, colony size, and the carrying capacity of the plate and medium in which it’s growing?


prepared plate with escheria coli

Essential Question

How can mathematical representations be used to identify carrying capacity of an ecosystem?

Activity Objectives

  1. Graph E. coli data and determine the carrying capacity for the petri dish ecosystem in which it is growing.
  2. Use data to support how two different treatments affected the growth of E. coli in petri dishes.

Next Generation Science Standards* (NGSS)

PE HS-LS2-1. Use mathematical and/or computational representations to support explanations of factors that affect carrying capacity of ecosystems at different scales.

Science & Engineering Practices

Using Mathematics and Computational Thinking

Disciplinary Core Ideas

LS2.A: Interdependent Relationships in Ecosystems

Crosscutting Concepts

Scale, Proportion, and Quantity


Safety Procedures and Precautions

No PPE is required for the activity.

Teacher Preparation and Disposal

Copy or upload student activity page. There is no disposal of waste materials.

Student Procedures

These procedures were followed to generate
the data below:


  1. Inoculate 100 plates of optimal growth medium with 10 E. coli bacteria.
  2. Record the bacterial growth every 20 minutes for 6 hours.
  3. Repeat the procedures for optimal growth medium treated with chemical A.
  4. Repeat the procedures for optimal growth medium treated with chemical B.

Teacher Preparation and Tips

  1. You may wish to review graphing techniques, with the computer or by hand, with students.
  1. A good pre-activity assignment is to ask students to research E. coli food contamination news articles that have impacted their area.

Data and Observations

Average Data for 100 Plates


data table showing average data for 100 plates

data graph showing bacterial counts over time

Analysis & Discussion

Why was it necessary to test 100 untreated plates?

The untreated plates are a control for the research project. Optimal growth media or growing environment of the control plates allow for the establishment of the carrying capacity of the medium under the best bacterial growing conditions. The treated growth medium can then be compared to the control to determine if the treatments of the growth medium changed the time to reach carrying capacity and the amount of E. coli at the carrying capacity.

Use the data to explain how treatment A detergent and treatment B detergent affected the E. coli /petri dish ecosystem.

Treatment A decreased the amount of time the E. coli was maintaining carrying capacity individuals and carrying capacity was achieved at about 175 min. The number of cells at carrying capacity also decreased to about 5000 cells. Detergent A decreased maximum growth and the time it took to reach maximum growth. Treatment B had even a shorter time at carrying capacity (about 15 min.), and the number of cells at carrying capacity dropped to about 2600 cells. Carrying capacity was achieved at about 160 minutes which is another decrease. Detergent B showed additional impedance in E. coli growth.

Assuming that both detergents are safe for human consumption and animals, make an argument for which treatment detergent would you recommend for the next stage of testing?

Both detergents showed a decrease in the amount of cell growth and a lower number of cells at carrying capacity. Detergent B had larger decreases than Detergent A and cell growth peaked earlier with Detergent B. Since this product is designed to be used in the field as leafy vegetables are picked, I would recommend further research on Detergent B. The next research step could be to test the detergent on the vegetables with E. coli bacteria present. Researchers will also need to determine how the detergent affects the vegetable itself- color, freshness, odor, how long it stays fresh.


*Next Generation Science Standards® is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of, and do not endorse, these products.

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