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Cellular respiration review

Key Terms

Cellular respirationThe process by which organisms break down glucose into a form that the cell can use as energy
ATPAdenosine triphosphate, the primary energy carrier in living things
MitochondriaThe eukaryotic cell structure where cellular respiration occurs
CytoplasmThe contents of a cell between the plasma membrane and the nuclear envelope; includes cytosol which is the jelly-like substance that fills the space between organelles
AerobicProcess that requires oxygen
AnaerobicProcess that does not require oxygen
FermentationAn anaerobic pathway for breaking down glucose

Cellular respiration

Cellular respiration can occur both aerobically (using oxygen), or anaerobically (without oxygen).
During aerobic cellular respiration, glucose reacts with oxygen, forming ATP that can be used by the cell. Carbon dioxide and water are created as byproducts.
The overall equation for aerobic cellular respiration is:
In cellular respiration, glucose and oxygen react to form ATP. Water and carbon dioxide are released as byproducts.
The three stages of aerobic cellular respiration are glycolysis (an anaerobic process), the Krebs cycle, and oxidative phosphorylation.


Some organisms are able to continually convert energy without the presence of oxygen. They undergo glycolysis, followed by the anaerobic process of fermentation to make ATP.
  • Muscle cells can continue to produce ATP when oxygen runs low using lactic acid fermentation. However, this often results in muscle fatigue and pain.
  • Many yeast use alcoholic fermentation to produce ethanol. For this reason, humans have domesticated yeast to use for many commercial purposes including baking as well as beer and wine production.

Aerobic vs anaerobic respiration

ReactantsGlucose and oxygenGlucose
ProductsATP, water, COstart subscript, 2, end subscriptATP and lactic acid (animals); or ATP, ethanol, and COstart subscript, 2, end subscript (yeast)
LocationCytoplasm (glycolysis) and mitochondriaCytoplasm
StagesGlycolysis (anaerobic), Krebs cycle, oxidative phosphorylationGlycolysis, fermentation
ATP producedLarge amount (36 ATP)Small amount (2 ATP)

Common mistakes and misconceptions

  • Anaerobic respiration is a normal part of cellular respiration. Glycolysis, which is the first step in all types of cellular respiration is anaerobic and does not require oxygen. If oxygen is present, the pathway will continue on to the Krebs cycle and oxidative phosphorylation. However, if oxygen is not present, some organisms can undergo fermentation to continually produce ATP.
  • Plants undergo cellular respiration. Many people believe that plants undergo photosynthesis and animals undergo respiration. Really, plants do both! Plants simply undergo photosynthesis first as a way to make glucose. Animals don't need to photosynthesize since they get their glucose from the food they eat.
  • Cellular respiration is not simply the same as "breathing." This can be confusing! People often use the word "respiration" to refer to the process of inhaling and exhaling. However, this is physiological respiration, not cellular respiration. The two are related processes, but they are not the same.

Want to join the conversation?

  • spunky sam blue style avatar for user Arjun
    Here u say that at the end of the Aerobic ( Cellular) respiration 38/36 ATP will be released. At the same time, in some books say 32/30 ATP will release in the Cellular respiration. Moreover, they gave the steps as well.

    Total number of ATP molecules produced from one molecule of glucose, during aerobic respiration.
    In glycolysis :
    As ATP 2ATP
    From 2NADH 5ATP (oxidation phosphorylation)
    In pyruvate oxidation;
    From 2NADH 5ATP (oxidative phosphorylation)
    In Citric acid cycle;
    As ATP ATP (substrate level phosphorylation)
    From 6NADH 15ATP (oxidative phosphyrlation)
    From 2 FADH2 3ATP
    Total Number ATP = 32 ATP

    I think here is a wrong. Pls help me to solve this doubt.
    (14 votes)
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  • blobby green style avatar for user Elias Young
    I've read in a test prep text book that water is an input in the process of cellular respiration but I have not seen the same in this article or the accompanying video; is it true or false?
    (11 votes)
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  • blobby green style avatar for user nicol
    why is cellular respiration not the same as "breathing"
    (7 votes)
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  • orange juice squid orange style avatar for user Natalie
    Where does the water go after being produced as a byproduct? Is it sweat or urine or does it stay in the body? Thanks.
    (7 votes)
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    • leafers tree style avatar for user Õ_Õ
      it can become part of sweat or urine and leave the body, but it can also just join the multitude of water already in your body and go wherever the other water goes. it can even become water vapor and exit through your breath, just like the carbon dioxide.
      (10 votes)
  • duskpin tree style avatar for user Bob Bobbity
    I get that they also perform photosynthesis but how do carnivorous plants break down the animals they feed on into glucose?
    (7 votes)
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  • blobby green style avatar for user ABBY
    What happens when Cellular respiration is increased in cells?
    (4 votes)
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  • leaf red style avatar for user Moarz
    does both anaerobic and aerobic respiration occur simultaneously during exercise
    (4 votes)
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    • aqualine ultimate style avatar for user Zap
      when we are exercising, initially there will be aerobic respiration.
      but as the amount of oxygen requirement increases, the respiration will become anaerobic and thereby producing lactic acid in our muscle cells and causing muscle cells.
      hope it would be helpful to you :)
      (1 vote)
  • blobby green style avatar for user jam7
    What is the difference between cellular respiration and aerobic respiration?
    (3 votes)
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  • starky seed style avatar for user petrenmadeline
    how is cellular respiration affected by bronchitis
    (3 votes)
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  • blobby green style avatar for user Bruh12212
    I have yet another doubt good humans! I need solutions, answers that could potentially solve all future crises. Please respond with useful information:
    How would you use this relationship to investigate the amount of oxygen being produced if we can only measure changes in the amount of carbon dioxide moving in and out of the plants in the forest?
    Once more, I would like to thank all humanoids of this spectacular platform. My personal gratitude is expressed in this message to you all- god bless America and thank you for creating such an amazing website Sal Khan. You are a god and I worship you every morning. Thank you from the bottom of my heart. And thank you to each and everyone of you that decided to scroll down and ignore the want and need that you want to respond to my question with a fantastic answer. Shout out to Katy Perry for making me an intelligent person who was unfortunately incapable of being able to answer this one. Peace out and live good lives humanoids.

    Signing off,
    Anonymous (but not really)
    (3 votes)
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