where does the carbon come from that we exhale?

[rogerxd45]

ok so we breath in oxygen (well air) and exhale carbon dioxide.

 

so where does the carbon come from needed to form CO2?

 

and while we are on the subject do plants use the carbon from CO2 to build the plant material or is it used for something else?

[Mr Skeptic]

We get our carbon from glucose, which the plants create during photosynthesis.

[insane_alien]

yep, your body is reacting the oxygen from inhalation with various carbohydrates and proteins(to a lesser extent) to create energy. this results in CO2 and water, both of which are released upon exhalation(although some of the water goes to sweat and urine). esentially its a combustion reaction without the fire.

 

plants will store the carbon in the form of carbohydrates when they capture it from air.

[nec209]

Plants need carbon dioxide to live and give out oxygen . And well people need oxygen to live and give out carbon dioxide.

 

Not sure where the carbon dioxide comes from I would say the food.It is your job of blood to pick up carbon dioxide in your body and take it to lungs to braath out.Some say carbon dioxide like free redicals over time does damage to the body.

 

In a perfect world there should be no carbon dioxide .Anyways there is way more people here that know lots about this subject.

[insane_alien]

In a perfect world there should be no carbon dioxide .Anyways there is way more people here that know lots about this subject.

 

hypocapnia(lower than normal CO2 levels in the blood) can be fatal. for one it can actually cause you to stop breathing unless you do it conciously.

 

this is because the part of the brain that controls your breathing(although you aren't concious of it) controls the rate by monitoringthe CO2 level in your blood. if its low your breathing will slow down, if it's high then your breahting will speed up. if its zero you'll forget to breathe.

 

not to mention it will cause cramps, pins and needles, tetany, low calcium in the blood, alkalosis, nerve and muscle excitability.

 

so no, in a perfect world carbon dioxide would still exist.

[nec209]

hypocapnia(lower than normal CO2 levels in the blood) can be fatal. for one it can actually cause you to stop breathing unless you do it conciously.

 

this is because the part of the brain that controls your breathing(although you aren't concious of it) controls the rate by monitoringthe CO2 level in your blood. if its low your breathing will slow down, if it's high then your breahting will speed up. if its zero you'll forget to breathe.

 

not to mention it will cause cramps, pins and needles, tetany, low calcium in the blood, alkalosis, nerve and muscle excitability.

 

so no, in a perfect world carbon dioxide would still exist.

 

 

So a liitle bit is okay but too much is bad?What part of the brain controls the carbon dioxide and oxygen level?

 

You say if there was no carbon dioxide it can be fatal ,stop breathing ,brain that controls breathing controls the rate by monitoring the CO2 . Why does the brain not control the oxygen level?

 

 

not to mention it will cause cramps, pins and needles, tetany, low calcium in the blood, alkalosis, nerve and muscle excitability.

 

Why does lack of carbon dioxide do that? Why too low or too high carbon dioxide is bad?

 

Too high oxygen can this be bad too?

[insane_alien]

The brainstem measures CO2 because its easy. It just has to monitor blood pH levels. Monitoring O2 would be more difficult and hence more expensive from an energy point of view and not likely to evolve since there are few areas on earth where we are likely to be in places lacking CO2 and being low in oxygen.

 

so the brain measures CO2 and controls the level by varying the speed you breathe at.

 

too much oxygen can also be fatal. counterintuitively, oxygen is actually toxic anything above 60kPa partial pressure of oxygen will eventually kill you. unlikely to be encountered unless you are a diver.

[nec209]

Monitoring O2 would be more difficult and hence more expensive from an energy point of view and not likely to evolve since there are few areas on earth where we are likely to be in places lacking CO2 and being low in oxygen.

 

This is the part I do not understand.

[insane_alien]

simply put, the body cannot measure O2 content in the blood. and CO2 is a better indicator of how much oxygen the body currently requires, high CO2 usually means your are being more active and should breathe more.

 

as to the evolutionary conditions, how many places on earth have low oxygen in the atmosphere appart from high altitude where it is impossible to live without dieing of cold?

 

we've never developed the need to develop the ability to sense oxygen levels in our blood. the ability to do so would come at a cost of energy(meaning we would need to eat more) so since those without it would do just as well as those with it, the evolutionary pressures are against developing a biological oxygen sensor.

[Mr Skeptic]

Dissolved CO2 is carbonic acid, which changes the pH. pH is very easy to measure, as it affects pretty much all proteins. Also, that makes pH a dangerous variable, so that the pH level has to be monitored regardless. If CO2 were to build up in your blood it would rapidly become toxic, an breathing is how we get rid of it, so it would naturally be linked to breathing.

 

Oxygen levels would be harder to measure; perhaps they would need a specialized protein. Since the CO2 level is so much easier to measure and has to be linked to breathing, and for the most part we get CO2 in our blood by using oxygen, it's only natural that it is the variable we would measure.

[D H]

Plants need carbon dioxide to live and give out oxygen . And well people need oxygen to live and give out carbon dioxide.

 

In a perfect world there should be no carbon dioxide .Anyways there is way more people here that know lots about this subject.

Those two sentences are contradictory. Without CO₂ there would be no plants, and without plants there would be no animals (including us).

[Mr Skeptic]

Oh and obviously, plants inhale oxygen and exhale CO2 ... at night. Otherwise they'd starve.

 

We steal the food they made and inhale the O2 they released, doing the reaction intended to provide them with energy, in our own bodies to instead provide us with the energy.

[CharonY]

From a biological viewpoint O2 levels are not terribly hard to measure. Bacteria use oxidation states all the time. To my knowledge an equivalent has not been detected in humans yet (well last time I looked was around 5 years ago), but there is oxygen-dependent regulation going on. On the cellular level, that is.

As a side-note, the CO2 comes from the oxidation of C-sources which of course is not limited to carbohydrates.

Edited February 3, 2010 by CharonY