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In the answers to this question, we've learnt that carbon dioxide is necessary for mammalian life, but is it necessary in the atmosphere/to breathe it in?

Or does the act of respiration give a human (or other animal) enough carbon dioxide to fulfill all of the functions that carbon dioxide is needed for?

Or, phrased another way, if you put an animal in a carbon-dioxide-free atmosphere, and continually removed the carbon-dioxide that they generate upon respiration/exhalation, would they get enough carbon dioxide to fulfill these requirements:

  • fatty acid biosynthesis (FAS)
  • mammalian/bacterial biotin-dependent carboxylation reactions.
  • blood pH regulation
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  • $\begingroup$ possible duplicate of Is there any use of CO₂ in human body? $\endgroup$
    – Berne
    Commented Mar 8, 2015 at 7:45
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    $\begingroup$ I think the core of the question is very different from the suggested duplicate. The duplicate is on what CO2 is used for, this question is on how much CO2 is sufficient to fulfill it's roles. $\endgroup$
    – AliceD
    Commented Mar 8, 2015 at 8:58

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No it isn't necessary to breathe in CO2 from the atmosphere. For the buffer system your brain detects the amount of CO2 (H+ which is an indicator of excess or too little CO2) and adjusts your breathing automatically to compensate so that your blood's pH stays normal. No outside CO2 is needed. Your kidneys also play a similar role but the lungs are what provide a rapid response.

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    $\begingroup$ I know this seems intuitive, but can you add sources that support this answer? There are plenty of examples of short term non-CO2 breathing (nitrox, heliox, pure oxygen, etc.) but what about long-term? $\endgroup$ Commented Feb 21, 2015 at 0:02
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    $\begingroup$ The body is producing an excess of CO2 at all times. In fact, we need to keep venting it out just to keep alive. Furthermore, there is always expelled CO2 in our lungs, and since they never get fully empty, we always breathe air with some of our CO2. Therefore, although an answer with an experiment would be slightly better, this answer is well funded enough in basic biology. $\endgroup$
    – Pere
    Commented Nov 11, 2018 at 12:43
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No, mammals need not take in CO2 from atmosphere. The body's homeostatic function will maintain its composition by checking the amount of CO2 released out by lungs. So certainly animals would survive if put in a CO2 free atmosphere.

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  • $\begingroup$ So, fatty acid synthesis (for example) occurs using carbon dioxide created within the body? Also, got a cite? $\endgroup$
    – user3082
    Commented Feb 25, 2015 at 17:29
  • $\begingroup$ @Hari:It would be nice if you add some references to substantiate your claim.:) $\endgroup$ Commented Feb 27, 2015 at 3:54
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It is unneccessary for a mammal to breath in CO2, though our bodies are able to expel unneeded gasses easily. However, if there were no CO2 in the atmosphere, animals would all die, as no oxygen could be produced by plants. In other words, we don't need to breath in CO2, but we need it to be plentiful.

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