Modeling Cellular Respiration for Relevance and Reasoning Using BioInteractive Resources

Students often struggle with the unit covering cellular respiration. It’s too abstract, too detailed — or at least it’s sometimes taught that way. What does this have to do with our lives? they might ask. Why should we memorize a series of steps … and all these details?

They’re not wrong: the unit is often taught with a focus on details and not an emphasis on those details’ relationship to the whole. Students might learn the parts but not see a unifying process.

Relevance and reasoning is key to helping students engage and understand respiration as a process. The Next Generation Science Standards (NGSS) Performance Expectation HS-LS2-5 highlights the importance of respiration in high school education. It asks students to “develop a model to illustrate the role of photosynthesis and cellular respiration in the cycling of carbon among the biosphere, atmosphere, hydrosphere, and geosphere.”

Similarly, Vision and Change Core Competency 4, Pathways and Transformations of Energy and Matter, specifies that students should understand that “biological systems grow and change by processes based upon chemical transformation pathways and are governed by the laws of thermodynamics.”

But those frameworks often do not translate to relevance for high school or undergraduate students, so I use BioInteractive videos to help bring in that relevance, and modeling to help with reasoning.

Research-based educational practices highlight how to help students learn cellular respiration. A key practice is to first establish cellular respiration’s relevance to students by providing both a context and a foundation on which to learn the process. Students must want to engage in the learning and understand how cellular respiration is relevant to their learning before they explore the process in depth (Ausubel 1968, da Silva 2020). Secondly, the use of modeling, a metacognitive exercise, provides a way for students to develop a structure of understanding that ties both the details and the big picture to the relevant context.

Both NGSS and Vision and Change support modeling as a practice. In NGSS, HS-LS1 highlights the need to use modeling to understand cellular respiration as a chemical process in which bonds are broken and formed, resulting in a net transfer of energy. Vision and Change Core Competencies highlight the need for students to use modeling and simulation to understand the interactions between systems.

Developing Relevance

My theme for my cellular respiration unit is “Staying Alive.” Yes, I do use the Bee Gees song as a way to engage the students. I use many BioInteractive materials to teach the cell and the process of cellular respiration to help make it relevant and provide a framework for developing a model. At this point in the course, we’ve already addressed cell structure and membrane transport and how they help us “stay alive.” We’ve seen that active transport in a cell needs the addition of a phosphate from ATP to transport Ca⁺⁺ outward across a cell membrane and H⁺ into the cell, as shown by part of the ATP in Use animation. This animation provides context for what has been learned but is relatively abstract to students, so it doesn’t necessarily provide relevance. Therefore, we ask students about their foundational knowledge by having them reflect on:

• What do you already know about respiration, cellular respiration, and active transport?
• Is this information part of the big picture or a finer detail?
• What ideas would you like clarified?
• Can you relate it to what you already know?

Often, students still have difficulty seeing how respiration is relevant to their lives. This must happen for learning to be meaningful, so I also use a short video of a women’s triathlon where competitors run out of energy at the end of the race. This highlights the importance of energy to life’s function. During the video, we ask students to try to explain what happened to the runners at this part of the race. Students frequently understand that the runners have lost energy and that they need more energy to function properly. So how do we get that energy to stay alive? Students’ answers are often about food and how food “has energy,” but we need to focus on how we use food to make ATP.

The unit begins with a reminder about needing energy to stay alive. We watch the whole process of cellular respiration in a highly condensed version. The video Powering the Cell: Mitochondria by BioVisions incorporates detail in a compressed review. I use this with my freshman biology for majors class just to inspire awe in the whole process. Students often get amazed at all the chemistry in action — but also find the video hard to follow.

We ask:

• Is this information part of the big picture or a finer detail?
• What should we approach next?

To help students understand the process of respiration, especially its details, we must contextualize this within the overall purpose of staying alive. To do this, we teach overarching principles and give broad overviews of the process. This is where modeling can help, since models include both the big picture and details, by drawing relationships between parts of a whole and providing connections between concepts, similar to concept mapping. Unlike concept mapping, modeling usually contains more visualization of process details in the context of the physical structures. Additionally, with modeling, students can use metaphors or analogies to help elucidate difficult abstract concepts.

Incorporating Relevance in Modeling

In order to maintain relevance as we delve deeper into the process, I teach respiration “backward,” beginning with ATP synthesis by chemiosmotic phosphorylation and ending with glycolysis. Starting with the product we need, and asking where the energy to make it comes from, provides a big-picture context on which to hang details. I use specific questions as bridges between each process so that students can connect them with the need for energy. For example, where did the energy come from to drive the chemiosmotic process. The students respond “From the reservoir full of protons.” This normally takes two to three days, but it is well worth the effort.

Backward Overview Sequence

Staying Alive

We begin by asking what students need to stay alive; they respond with energy in the form of ATP. Therefore, for this learning sequence, we do not begin with glycolysis, which is typically the entry point to learning about respiration. Instead, we begin with chemiosmotic phosphorylation, which is the endpoint of aerobic respiration. We then trace our way backward from the generation of ATP through the electron transport chain, citric acid cycle, and finally end with glycolysis.

Making ATP: Chemiosmotic Phosphorylation

In chemiosmotic phosphorylation, a reservoir of protons provides a gradient needed to drive the generation of ATP by ATP synthase. We explore this and other cellular processes through a series of videos.

One of the difficulties that students have with the detailed versions of BioInteractive’s cellular respiration animations is they have so much going on in them that students don’t know where to focus. I use cartoon versions I made first to describe what students should be seeing, then show the corresponding BioInteractive videos to provide a highly dynamic model.

We start with my simplified cartoon of chemiosmotic phosphorylation. While watching the simplified version, I identify the movement of protons across the membrane and through the F₀ portion of the ATP synthase. This movement drives the rotation of the F₁ enzyme portion of the ATP synthase, which then adds a phosphate to an ADP molecule. I use another cartoon to show how the ADP and P are joined to make ATP in more detail.

We then watch the BioInteractive video ATP in Use, and students attempt to identify the same processes. I strongly suggest you pause at different points to draw comparisons to the simplified version. At minute 1:41, we ask students to identify the three parts of the ATP synthase and where the reservoir of protons is found. This can be done in groups or as individuals. I find that in groups the students are able to help assist in the reflective questions. We also ask them to reflect on what additional aspects they see in the process and to consider the similarities and the differences between the videos.

Example questions we ask include:

• What process actually makes most of the ATP in aerobic respiration?
• What part of what molecule actually puts the ADP and P together?
• What causes the F₁ portionto open and close?
• What causes the F₀ portion to rotate?

At the end of our chemiosmotic phosphorylation review, each student diagrams a model of the activity taking place, including the names of the cell structures and chemical components used in the making of ATP. I also do this on the white board to help students visualize what we are doing. We use analogies to aid in students’ understanding — like comparing this process to a hydroelectric dam and turbine, with the dam as the intermembrane space, the F₀ portion as the turbine, and the F₁ portion as the generator. (Since students also sometimes need a visual for dams, we use this video on hydroelectric power.)

We transition to the next section using the following linking question: What source of energy does chemiosmotic phosphorylation use to make ATP?

Electron Transport Chain

Chemiosmotic phosphorylation is driven by a reservoir of protons in the intermembrane space of the mitochondrial cristae. For chemiosmotic phosphorylation to keep producing ATP, this gradient must be generated and maintained by the electron transport chain (ETC), which continuously pumps protons across the inner membrane.

We watch a cartoon about the ETC that shows how the cell uses electrons to energize proteins to pump the protons into the reservoir. During the video, I highlight how the electrons arrive on the coenzymes and are passed to the proteins on the membrane.

The next cartoon we watch highlights how electrons are brought to the inner membrane and used by the ETC to pump protons. Electrons’ movement from one protein to the next powers the movement of protons into the reservoir. One key understanding that students obtain is how oxygen is used as the final acceptor of the electrons. Without it, the process shuts down.

Once students understand how the ETC maintains the proton gradient, I use the BioInteractive animation Electron Transport Chain and this BioVisions video to show the details of the process. I have students identify where each of the proteins is and how they work together to move the protons into the intermembrane space and eventually pass the electrons on to an oxygen molecule. I ask students how different parts of the membrane carry out the functions. They then add the ETC process to their previous model of chemiosmotic phosphorylation and note how these processes work together to make ATP.

At the end of the ETC section, we diagram a model of the activity taking place, including the names of the cell structures and chemical components used to pump protons.

We transition to the next section using the following linking question: Where do we get the electrons that are given to the coenzymes to power the pumping of the protons?

Citric Acid Cycle

Students need to connect several steps at this point: that the citric acid cycle provides the electrons for the ETC, which provides the proton gradient for ATP synthase, which makes ATP. In other words, always link each step to the big picture.

Electrons passed from the citric acid cycle (and other sources) activate the ETC. Therefore, students’ goal is to locate where in the process we obtain the electrons. Students watch the BioInteractive animation Citric Acid Cycle and the more simplified VCell video Glycolysis: The Reactions to identify those steps.

We then use the diagram/model of the citric acid cycle to show how those electrons are passed and used by the ETC. By identifying the reactions taking place, including the names of the cell structures and chemical components powering the ETC, students are constantly linking structural knowledge, process knowledge, and purpose knowledge to how we stay alive.

Students consider images that are models of the citric acid cycle and the electron transport system. How are these two models linked? How could they affect each other?

We transition to the next section using the following linking question: From where do we get the pyruvate to extract the electrons and pass them to the ETC with the coenzymes NADH and FADH₂?

Glycolysis

Pyruvate comes from glycolysis. We use the BioInteractive animation Glycolysis to trace the conversion of glucose to pyruvate.

So what does glycolysis need to produce the pyruvate? The answer is glucose (and, yes, other substances) from the foods we eat, either directly or through the breakdown of more complex foods.

Putting It All Together

Finally, we ask students to reorder the separate models they have developed from glycolysis to chemiosmotic phosphorylation and explain what each model does, how the models are linked, and what product is produced at each stage. Model development connects information into an integrated understanding. This is essential for being able to work with each part. This is an important reasoning mechanism for working in understanding complex concepts and issues.

Students connect their diagrams to summarize the whole process:

• Glycolysis uses glucose to produce pyruvate.
• The citric acid cycle takes electrons from pyruvate and passes them to the ETC using coenzymes.
• The ETC fills the proton reservoir of the mitochondrial intermembrane space by using the energy from electrons to pump in the protons.
• Chemiosmotic phosphorylation uses the energy of the proton gradient to power ATP synthase, which adds a P to ADP to form ATP.
• The images below show one of my students’ modeling exercise on cellular respiration.

As I look back on more than 20 years of teaching, students who’ve moved on in biology (to graduate schools, medical schools, or teaching) often contact me or respond to some of my posts on NABT’s Facebook page saying that they still remember “Staying Alive.” They remember chemiosmotic phosphorylation — not necessarily the details, but the purpose — and how each part of cellular respiration works together to produce ATP. Others want the links to the videos so they can refresh themselves on the topics. Because respiration became relevant to them, it remains in their memory to be called upon when needed, updated, or polished.

References

Ausubel, David P. (1968). Educational Psychology: A Cognitive View. New York: Holt, Rinehart & Winston. ISBN: 0030899516

da Silva, João Batista. “David Ausubel’s Theory of Meaningful Learning: an analysis of the necessary conditions.” Research, Society and Development 9, 4 (2020): e09932803. https://doi.org/10.33448/rsd-v9i4.2803.