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MINDS ON: Partial List of Key Terms

This is a list for mind mapping Cellular Respiration.

Realize, though, that this list is not exhaustive so you should look for opportunities to include other relevant terminology related to aerobic and anaerobic respiration.

Substrate-level phosphorylation oxidative phosphorylation electron transport chain
 proton gradient glycolysis lactate fermentation
alcoholic fermentation pyruvate oxidation citric acid cycle
crista (plural is cristae) matrix ATP synthase
potential energy deamination beta-oxidation
feedback inhibition


Biochemical Reactions

Cellular respiration is used by all organisms. Autotrophs store carbohydrates and lipids using G3P from the light-independent reactions. Later, perhaps in response to an improvement in growing conditions, they tap into those stored energy sources. Heterotrophs similarly convert macronutrients they consume or have stored into ATP.

Just like in the light-dependent reactions, many organisms create a proton gradient that ATP synthase can use to phosphorylate ADP. Watch this process in the following animation from St. Olaf College.

Long Description


Look back at your graphic organizer from Unit 1, Nucleic Acids, we learned about coenzymes like NAD+, FAD, and Coenzyme A.

 These coenzymes play important roles in the steps of cellular respiration. You can see how these coenzymes function in this animation from McGraw-Hill.

Specifically, see how the connection between NAD+ and ATP is a main part of our understanding of energy production in this animation from Wiley Publishing.


Many biochemical reactions are used by cells in the steps of cellular respiration. Dozens of enzymes catalyze these reactions. For example, a cysteine amino acid in the active site of the enzyme glyceraldehyde-3-dehydrogenase is involved in both a reduction and phosphorylation reaction. Watch this animation from St. Olaf College.

Long Description


Interestingly, the substrate for glyceraldehyde-3-dehydrogenase is a molecule produced in photosynthesis. Likewise, using a proton gradient to produce ATP happens in both photosynthesis and cellular respiration. Even the overall chemical equation for aerobic cellular respiration reminds us of photosynthesis:

C6H12O6  +  6 O2  →  6 H2O  +  6 CO2

As we explore the steps in cellular respiration look for ways in which they are similar to the steps in photosynthesis.

How do small steps lead to changes?

Changes 8. Think of your work from Unit 2, Activity 4 on Photosynthesis or your past learning about plants and photosynthesis. Using these details as well as those you have just read, compare cellular respiration with photosynthesis. Your comparison should include at least 3 similarities and/or differences.

Energy for Movement

The primary purpose of cellular respiration is to produce ATP as needed for cells. If we think of food as fuel then how energy is stored and released from fuel is similar in many ways to energy transfer in food. When burning wood, heat is used to start the fire and it is also produced. In this video from the Genetic Science Learning Centre, we can see how ATP is also used to start cellular respiration and it is a product.

This is a screen capture of the video.

by Learn Genetics

For example, a lynx burns a lot of energy when it is chasing prey. Its muscle cells demand ATP so mitochondria convert potential energy into kinetic energy. Predators like the lynx only run for short periods of time before they slow down and their energy stores are depleted: either they have caught their prey, or the prey escaped.

A picture of a large cat with black spots on orange fur. It’s running over grass with a large rock in the background.

The lynx is a predatory feline native to North America and Eurasia. It stalks prey before attacking in a burst of speed.

Similarly, we become aware of the limitation to using our muscles as they tire during strenuous or repetitive work. Perhaps our muscles shake as we try to do one more push-up. Or maybe we find we just can’t run any further so we stop to catch our breath. These are changes that we seem to do involuntarily. Our muscle cells continue to produce ATP to move, only we change the way it is made. Try this simple investigation to explore this further.

Investigation: Muscle Fatigue

Materials Needed:

  • a clothespin (or binder clip)
  • a timer


  1. Hold a clothes pin in the thumb and index finger of your dominant hand. Open it all the way and close it as fast as possible in 30 seconds while the other fingers of the hand are held in a neutral position. Attempt to squeeze quickly and completely, to get the maximum number of squeezes for each trial.
  2. If possible, have a partner record the number so you can continue without resting.
  3. Repeat this process for nine more 30 second trials recording the result for each trial. Do not rest your fingers between trials.
  4. Repeat steps 1 and 2 for the non-dominant hand. Record all data in a table. You may find it useful to also graph the results for both hands on one graph in order to better interpret your results.

If you prefer you can download a copy of this investigation.

How do small steps lead to changes?

Use quantitative and qualitative results to answer one of the following questions.

  • What happened to your energy & ability to pinch the clothespin as you progressed through each trial? Explain why.
  • What might cause one to be able to get more squeezes, in other words, to have less fatigue? Explain in terms of biological concepts.
  • Suggest how the amount of ATP produced makes your muscle cells less efficient. When did this change in the amount of ATP produced occur in this investigation? How could you tell?
  • Your muscles would probably recover enough after 10 minutes to operate at the original efficiency. Explain why.

Support your answer with your data by sharing your graph or table using a picture, video or descriptions. Explain how the results provide details to answer your question.  Put this work into a document and submit in Teams.



Steps in a Process

Early experiments of cellular respiration focused on the consumption of oxygen gas and the production of carbon dioxide. Many biologists believed respiration to be a variation of combustion. Heat is evidence of energy production in cells. In one experiment, the amount of oxygen used and carbon dioxide made by guinea pigs was found to be equal to the gases used and made from the burning of carbon. Yet other experiments showed that the amount of oxygen used by living organisms to burn different types of food did not follow any logical patterns. Indeed, experiments with yeast showed that they could produce carbon dioxide even in the absence of oxygen. The process of producing energy in yeast and other microbes is called fermentation. Fermenting microorganisms have the ability to change food and drinks and so are used to make a range of foods including pickles, yogurt, alcohol, bread and cheese.

The rate of fermentation is shown in the following five experiments. Interpret and analyse the following graphs to make appropriate conclusions.

Long Description


As we saw for photosynthesis, cellular respiration must include different reactions: some that involve oxygen, and some that do not. Enzymes play an important role.

Later research has identified that cellular respiration of glucose involves reactions that occur in the cytoplasm and some that occur in mitochondria in eukaryotic cells. This first process is called glycolysis. It occurs in the cytoplasm and produces a molecule called pyruvate.

Pyruvate is a 3-carbon molecule. At the top is an anion form of a carboxyl group. Below it is a second carbon that is part of a carbonyl group. Below this is the last carbon which is attached to 3 hydrogens.

by Storyjumper

2 ATP molecules are produced per glucose molecule by substrate-level phosphorylation.  From there, pyruvate can undergo different reactions depending on which species it’s in and also the amount of oxygen available to the cell. Glycolysis itself is composed of 10 individual reactions which you can see here:


For this course there is no expectation for you to remember the sequence of reactions in glycolysis. For this reason, we can think of glycolysis as happening in 3 parts:

Three vertical flowcharts side-by-side. All three flowcharts show a large arrow starting at the top. Halfway down the arrow stops and two shorter arrows branch left and right. At the end of these shorter arrows, two large arrows point down. In the left flowchart showing the priming reactions, the first large arrow is coloured black. Above the arrow is shown 6 grey circles in a row representing 6-carbon glucose. Along the arrow 2 ATP are shown entering the reaction. At the bottom of the arrow is shown 6 grey circles with the first and last circles connected to a yellow P in a circle representing 6-carbon sugar diphosphate. In the middle flowchart showing the cleavage reactions, the branching arrows are coloured black. Above these arrows is shown the same 6-carbon sugar diphosphate. Below each arrow are shown 3 grey circles with the last circles connected to a yellow P in a circle representing 3-carbon sugar phosphates. The right flowchart showing the energy-harvesting reactions, the two large arrows coloured black. The same 3-carbon sugar phosphates are above these large arrows. Beside each large arrow are shown an NADH leaving the reaction and 2 ATP leaving the reaction later on. At the end of the arrows are 3 grey circles in a row representing 3-carbon pyruvate.

The three parts of glycolysis show how ATP is both used and produced.
by Edgar Gibson

Some steps in cellular respiration are aerobic, while others are anaerobic. For most eukaryotes, oxygen is one of the requirements of life. Much more ATP is produced using aerobic processes helping to provide energy for more complex forms of life. Glycolysis doesn’t require oxygen but is the first step in glucose metabolism for both aerobic and anaerobic respiration. The fermentation done by microorganisms involves anaerobic respiration.

Smaller eukaryotic and prokaryotic organisms can survive longer in low oxygen conditions, and many have adapted to produce energy without any oxygen. Under these anaerobic conditions all the energy produced from glucose is only made in glycolysis. The 2 NADH molecules are recycled back to NAD+. In this way the NAD+ can be used again for a new round of glycolysis with a new molecule of glucose.

Cells have evolved two different methods of recycling NADH. In general, most eukaryotes and certain bacteria perform lactate fermentation whereas certain fungi, like yeast, and other bacteria perform alcoholic fermentation. These two processes are summarized in the animation below by Thomas E. Schultz of the College of Science and Engineering at Central Michigan University.


 How do small steps lead to changes?

Changes 9. Compare lactate fermentation with alcoholic fermentation. Your comparison should include at least 3 similarities and/or differences.