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Mitochondrial Mysteries

The Origin of Organelles and Cellular Respiration


Anna K.S. Jozwick
Biological Sciences
Goucher College
Megan M. Lee
Center for Natural Sciences
Goucher College


This interrupted case study follows two college freshmen as they learn about the origin and functioning of mitochondria within our cells. The case is divided into two modules that can be taught separately or together. The first considers the origin of mitochondria and chloroplasts by examining the endosymbiotic theory, according to which ancient bacteria were initially engulfed by a larger cell and subsequently developed an association that became more obligate throughout evolutionary history. Students critically examine evidence to support this theory by comparing characteristics of each organelle to those of prokaryotes. The second module summarizes the process of cellular respiration by describing where in the cell or within the mitochondria each step occurs, the inputs and outputs, and the importance of creating and utilizing a proton gradient for ATP production. This case study was developed for a first-semester introductory biology course, but could be modified for a high school AP biology course or 200-level undergraduate course focused on cell biology.


  • Provide evidence to support the endosymbiotic theory explaining the acquisition of mitochondria and chloroplasts by eukaryotic cells.
  • Write and revise testable hypotheses.
  • Summarize the structure and function of the mitochondria in the eukaryotic cell.
  • Describe the outputs and location of each step of cellular respiration within the eukaryotic cell or mitochondria.
  • Explain the role of electron carriers, oxygen, protons, and protein complexes in the process of cellular respiration.


Endosymbiosis; mitochondria; mitochondrial DNA; cellular respiration; evolution; energy; ATP; organelle; Kearns-Sayre syndrome; eukaryote; prokaryote; electron carrier; chloroplast

Topical Areas


Educational Level

High school, Undergraduate lower division


PDF, PowerPoint

Type / Methods

Clicker, Interrupted



Subject Headings

Anatomy  |   Biology (General)  |   Cell Biology  |   Microbiology  |   Molecular Biology  |   Physiology  |  

Date Posted


Teaching Notes

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Teaching notes are intended to help teachers select and adopt a case. They typically include a summary of the case, teaching objectives, information about the intended audience, details about how the case may be taught, and a list of references and resources.

Supplemental Materials

As explained in the teaching notes, the PowerPoint presentation below is used to guide the case in class. Additionally, an alternative version of the case consisting of the second module only is provided.  

  PPT Slide Deck (~3 MB)
  Alt. Version: Cellular Respiration Only

Answer Key

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The following video(s) are recommended for use in association with this case study.

  • How We Think Complex Cells Evolved
    This video provides a basic explanation of the theory of endosymbiosis. It details the origins of mitochondria and chloroplasts. Running time: 5:41 min. Produced by Adam Jacobson, animation by Camilla Gunborg Pedersen, TED-Ed, 2015.
  • Cellular Respiration
    This is a short video describing the four stages of cellular respiration. Running time: 2:47 min. Produced by RicochetScience, 2016.
  • Cellular Respiration and the Mighty Mitochondria
    This video is a detailed description of the process of aerobic cellular respiration that includes ATP structure, cellular organization and protein functions. Running time: 7:48 min. Produced by Amoeba Sisters, 2014.