Expert: Florence M Rollwagen - 9/5/2008

Question
Hello Sir..
         I've a question that during respiration we take in oxygen and give out carbondioxide i.e, only oxygen is important for our body..Right? So why do we give out carbondioxide but not only carbon extracting oxygen from it as it is useful for our body? Why don't we utilize oxygen from carbondioxide also?

Answer
Ah, Pooja, you must be doing respiration in your biology class.  But you have been given only part of the story.

The oxygen that we take in gets turned into water by the cellular respiration process.  The carbon dioxide comes from breakdown products in the Krebs Cycle.  They are two different processes in respiration.

The first process, glycolysis, breaks sugar (glucose, a six carbon sugar) into two three carbon molecules of pyruvate.  

The second process, the Krebs Cycle, breaks the pyruvate up into three molecules of carbon dioxide (a simplification).

The third process, the electron transport chain (ETC) takes all the high energy electrons generated in the Krebs Cycle (breaking chemical bonds yields energy) and collects their energy using the ETC.  At the end of the ETC, the last electron is accepted by oxygen, grabs two protons (hydrogen nuclei) and becomes water.

You can look at the entire process here:

http://vcell.ndsu.nodak.edu/animations/

Click on "Atp Synthesis" and "Electron Transport Chain"

For the Krebs cycle go to:

http://www.youtube.com/watch?v=JNd4QQXluJ0&feature=related

Hope this helps!

FM Rollwagen, PhD