The equation of cellular respiration is as follows:
6 O2 (g) + C6H12O6 (aq) $\rightarrow$ 6 CO2 (aq) + 6 H2O (aq) + ATP

How is the water produced expelled from the body (of course, after some of it is used)? Is it expelled in urine? Or is the water vapour we breath out actually the by-product of respiration? Or, is it expelled in both methods/ways?

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    $\begingroup$ Homework is an appropriate tag for this question. Take a look at this to learn what fall under homework. $\endgroup$
    – Tyto alba
    Feb 14, 2017 at 9:01
  • $\begingroup$ Sure. I misconstrued homework questions to be relating to questions that come in your assignments/projects/etc. Good that I read it. Thanks. $\endgroup$
    – Ramana
    Feb 14, 2017 at 9:04
  • $\begingroup$ there is complex interchange of substance between different metabolic pathways. $\endgroup$
    – JM97
    Feb 14, 2017 at 13:32
  • $\begingroup$ @SanjuktaGhosh. As one who taught this for 24 years, I doubt this is a homework question, I think it's curiosity. $\endgroup$
    – bpedit
    Feb 14, 2017 at 17:21
  • $\begingroup$ It appeared trivial to me because the water produced as byproduct in a reaction becomes part of the cytoplasm's water and it can be used up either in any other metabolisms where it is needed or by simple diffusion end up in blood from where it might get excreted out or recycled back to the cells. The water can even be excreted as sweat or end up in any other body secretions. As such though it is curiosity but is eligible for homework tag. @bpedit $\endgroup$
    – Tyto alba
    Feb 14, 2017 at 17:47

1 Answer 1


Edited: I was wrong, the balance varies quite a bit by species. Reptiles and birds are far more water efficient than large mammals becasue they do not lose water through sweat or urine. There are animals that are metabolically water neutral, but humans are not one of them. In humans the water produced metabolically does far exceed the water used metabolically. I should have realized that reptile also produce less water. source 1source 2

In humans there are three main ways water is take in, drinking, injection (food), and a net metabolic production. There are four major losses, urine, sweat, respiration, and feces. so it is through one of these four methods.

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  • $\begingroup$ This doesn't sound right. Metabolically, the human body is a net producer of water, as the respiration equation suggests. We require water because of respiration, sweat and urination, but this is a matter of using ingested water as a solvent to "flush out" other waste products. Water is not consumed by the body for metabolic purposes. $\endgroup$
    – Roland
    Feb 14, 2017 at 21:50
  • $\begingroup$ it can't be only urine and sweat , becasue organisms that use uric acid and don't sweat still need to drink. $\endgroup$
    – John
    Feb 14, 2017 at 22:10
  • $\begingroup$ I did a major edit, I am so used to dealing with birds and reptiles I hadn't considered how much it might vary. $\endgroup$
    – John
    Feb 14, 2017 at 22:31

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