Teacher Guide: Cell Respiration stem case and Handbook Grade Level: 9th 12th Subjects

Recommended STEM Case Order: The Cell Respiration STEM Case should not be used as the first case experience for your students as cell respiration is a difficult process for many students to learn. We highly recommend that students use one of the introductory case studies first such as diffusion, osmosis, or homeostasis to help familiarize students with the case study format. Using the Enzymes and/or Photosynthesis cases, or the Cell Respiration Handbook prior to using the case will also help your students.

Follow Up: Your students can learn more about cyanide poisoning at the following links:

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  Cyanide
  
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  Treatment of Cyanide Poisoning
  

Scientific Background: Cell respiration is extremely complex and involves many different processes and enzymes. As such, it can be a challenging topic for students to understand. One common misconception that students can have is that glucose and oxygen react directly with one another to produce ATP, carbon dioxide and water. This can be addressed by examining cell respiration in slightly more detail than just considering “inputs and outputs” (often miscalled “reactants and products”).

Cell respiration can be simplified into 4 main steps: 1. Glycolysis - the splitting of glucose into 2 molecules of pyruvate, 2. The Krebs Cycle - using pyruvate to make NADH (and FADH₂ for AP level), 3. The ETC - taking electrons from NADH (and FADH₂) and moving them down a chain of proteins to move H⁺ across the mitochondrial membrane, and 4. ATP Synthase - H⁺ move through the enzyme to make ATP. Each of these steps uses and makes different things, as shown below:

Process	Uses	Makes
Glycolysis	Glucose	Pyruvate
Krebs Cycle	Pyruvate	NADH, Carbon Dioxide
ETC	NADH, Oxygen	H^+ Gradient
ATP Synthase	H^+ Gradient	ATP

Since we know what is made and used at each step, we can predict what will happen to their concentrations if a step is inhibited. For example, if glycolysis is stopped, then no pyruvate will be made (concentration will decrease). Without pyruvate the krebs cycle will not make NADH (decrease), no NADH will be used by the ETC to make the H⁺ gradient (decrease) and no ATP will be made (decrease). As such, the case can be solved without detailed knowledge of biochemistry as just spotting patterns in the data is sufficient. This can be beneficial to students when they are asked to interpret data in their other studies and exams.