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Author Topic: Why do we breath Oxygen and not Nitrogen?  (Read 20243 times)

dentstudent

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Why do we breath Oxygen and not Nitrogen?
« on: 08/08/2007 07:15:21 »
The atmosphere is 78% Nitrogen and only 21% oxygen. So why is it that animals have evolved to breath oxygen, when there is more nitrogen to be had? There are some tree's that fix nitrogen through their roots, but are there any animals that are nitrogen dependent?

eric l

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Why do we breath Oxygen and not Nitrogen?
« Reply #1 on: 08/08/2007 11:33:35 »
We are all of us (humans, animals and plants) nitrogen-dependent because every protein has nitrogen as one of the constituting elements.
Humans get their nitrogen for making proteins from vegetable and/or animal sources.  Even plants (and bacteria) that can fix nitrogen do not use nitrogen from the air in a direct way for building proteins, but in the form of ammonia or in the form of nitrates.
For more detail :  see the Wikipedia article on the "Nitrogen cycle" http://en.wikipedia.org/wiki/Nitrogen_cycle

Why oxygen :  oxygen can react with carbohydrates by an exothermic reaction, thus delivering energy.  I do not know of similar reaction of nitrogen with possible food components.
« Last Edit: 08/08/2007 11:36:03 by eric l »

another_someone

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Why do we breath Oxygen and not Nitrogen?
« Reply #2 on: 08/08/2007 19:27:03 »
Nitrogen is a fairly inert chemical (it does react, but not nearly as much as oxygen - this is why it is fairly stable in the atmosphere, whereas oxygen has to constantly be regenerated by photosynthesis).

More interesting is whether life could have formed using chlorine as an oxidising agent?  It would need a very different kind of photosynthesis to generate chlorine from sodium chloride, or some other chloride; but if such a photosynthesis were to exist, it would not seem implausible that some life form could develop to extract energy by using the free free chlorine to reverse that photosynthetic process just as animals today reverse the oxygen based photosynthetic processes of plants today.

cheryl j

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Why do we breath Oxygen and not Nitrogen?
« Reply #3 on: 10/11/2011 19:50:11 »
There are microorganisms that can utilize nitrogen gas (they are responsible for the nitrogen fixation ability of plants like beans.) But as stated above, N2 gas is less reactive. It takes more energy to break the N-N bond.

Living things get energy from a chemical reaction that involves the transfer of an electron, called a redox reaction. A variety of substances can be used as the electron donor and a variety of substances can be used as the electron acceptor.

In animals, O2 is the electron acceptor. Some organisms can use Nitrate (NO3) Nitrite (NO2) Sulfate (SO4), carbondioxide and Ferric iron as the electron acceptor.

Why we evolved to use oxygen, I'm not sure but I would guess it would have something to do with the relative abundance of things like O2, glucose, and water, and the energetic payout at the end, since not all redox reactions produce the same amount of energy.

Here's an interesting little factoid. Per weight, a chocolate chip cookie contains more energy than TNT. Which doesnt seem right since I can't blow up a car with a chocolate chip cookie, even if I set it on fire with my lighter. The difference between the two has to do with the rate at which the energy is released. And I suspect some chemical reactions might release energy too quickly or too slowly for certain kinds of living things.
« Last Edit: 11/11/2011 00:15:21 by cheryl j »

damocles

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Why do we breath Oxygen and not Nitrogen?
« Reply #4 on: 10/11/2011 22:47:09 »
The responses above are all correct in part. The real secret is that oxygen gas is the main source of the chemical energy that air-breathing creatures are wanting to exploit.

A physical chemist's perspective (I have little knowledge and no expertise at all in physiology or medicine):

Oxygen gas is a very high energy chemical. Nitrogen gas is a very low energy chemical.

The oxygen gas currently present in the Earth's atmosphere is a biological gas. It is the surplus from 2 billion years of photosynthesis:

sunlight energy + water + carbon dioxide (or oceanic bicarbonate ion) --> carbohydrate + oxygen gas + chemical energy.

The chemical energy is distributed between the carbohydrate and the oxygen gas. Most of it must be associated with oxygen gas because the most energy you can get from anaerobic (no oxygen) degradation of carbohydrate

carbohydrate --> graphite + water

is only about 15 % of the energy available when oxygen gas is available

carbohydrate + oxygen --> carbon dioxide + water.

Not only is nitrogen gas unreactive, it is also totally lacking in chemical energy. So the only energy available from any reaction involving nitrogen gas is the chemical energy from the other reactant.

Living things all need nitrogen in other forms as the basis of protein that is central to their function. But the "low chemical energy" thing is the reason that nitrogen-fixing organisms usually (if not always) exist in symbiotic arrangements with other organisms: "I will supply your nitrogen requirements from atmospheric nitrogen gas if you will provide for my energy needs for that chemistry, and for my own continued existence and reproduction".

CliffordK

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Why do we breath Oxygen and not Nitrogen?
« Reply #5 on: 10/11/2011 23:09:13 »
Of course, there is the natural cycle.

Plants use carbon dioxide to make hydrocarbons and release oxygen.
Animals (and decomposers) consume hydrocarbons and oxygen and release carbon dioxide.

Both halves of the equation  must exist for life as we know it to flourish on the planet.

Certainly other chemicals could perform the role, but carbon/hydrogen/oxygen make for a very elegant cycle.

Supercryptid

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Why do we breath Oxygen and not Nitrogen?
« Reply #6 on: 11/11/2011 02:40:27 »
Plants use carbon dioxide to make hydrocarbons and release oxygen.
Animals (and decomposers) consume hydrocarbons and oxygen and release carbon dioxide.
A bit of a nit-pick, but they make carbohydrates, not hydrocarbons; those two chemical classes have important differences in properties.

CliffordK

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Why do we breath Oxygen and not Nitrogen?
« Reply #7 on: 11/11/2011 07:45:09 »
Plants use carbon dioxide to make hydrocarbons and release oxygen.
Animals (and decomposers) consume hydrocarbons and oxygen and release carbon dioxide.
A bit of a nit-pick, but they make carbohydrates, not hydrocarbons; those two chemical classes have important differences in properties.

By most definitions, Carbohydrates are sugars, and chains of sugars.  There are two hydrogens for every oxygen, and a molecular formula of (Cm(H2O)n).

So, fatty acids, proteins, and all of our vitamins ARE NOT CONSIDERED CARBOHYDRATES.

Strictly speaking, most of the organic molecules in plants and the body do not contain 100% hydrogen and carbon (hydrocarbons).  However, they also are not all carbohydrates.

damocles

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Why do we breath Oxygen and not Nitrogen?
« Reply #8 on: 11/11/2011 08:18:34 »
on the other hand it is my understanding, (and I am not a biologist nor biochemist), that the initial product of a photosynthesis reaction is a carbohydrate (or close derivative of one) and that proteins and fatty acids etc are formed in subsequent biochemical processes. Is this not the case?

CliffordK

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Why do we breath Oxygen and not Nitrogen?
« Reply #9 on: 11/11/2011 09:32:00 »
While 5-yr-olds wish we could consume just candy...
We consume all the products in the plants... at least those parts that we eat, and derive energy from many of the plant constituents.
As well as consuming the products produced by animals that feed on plants.

Chlorophyll and the light dependent reactions catalyzes the production of ATP.
The Calvin Cycle. or the Light independent reactions produces Glyceraldehyde 3-phosphate (G3P) and 3-phosphoglycerate (3PG)

Some G3P is used to make fructose & other sugars.

However, it is also an intermediary in making a whole bunch of other stuff.
See the red compound in the middle of this chart

CZARCAR

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Why do we breath Oxygen and not Nitrogen?
« Reply #10 on: 11/11/2011 17:56:52 »
whoa!, can i get proteinized from eating carbohydrates & swallwoing N air?

CliffordK

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Why do we breath Oxygen and not Nitrogen?
« Reply #11 on: 11/11/2011 18:45:18 »
whoa!, can i get proteinized from eating carbohydrates & swallwoing N air?

Not exactly,

Your body can only produce about half of its amino acids.  The essential amino acids must be consumed from protein sources.

Your body can not build compounds using N2 from the air.  The nitrogen that the body uses is derived from protein and other sources of "reduced nitrogen".  It is usually excess nitrogen, which is then excreted as urea, a component of urine.

venkyreddy97

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Why do we breath Oxygen and not Nitrogen?
« Reply #12 on: 18/11/2011 13:49:33 »
The atmosphere is 78% Nitrogen and only 21% oxygen. So why is it that animals have evolved to breath oxygen, when there is more nitrogen to be had? There are some tree's that fix nitrogen through their roots, but are there any animals that are nitrogen dependent?
our body chemical composition setup done during evolution made persons hemoglobin to bind with oxygen with chance n it fitted for d survival n it continued in the evolution ..even nitrogen enters through lungs but there is no chemical structures n utility mechanisms which can bind, process r utilizing it....it purly by chance through evolution mechanisms....... 

venkyreddy97

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Why do we breath Oxygen and not Nitrogen?
« Reply #13 on: 18/11/2011 14:29:58 »
While 5-yr-olds wish we could consume just candy...
We consume all the products in the plants... at least those parts that we eat, and derive energy from many of the plant constituents.
As well as consuming the products produced by animals that feed on plants.

Chlorophyll and the light dependent reactions catalyzes the production of ATP.
The Calvin Cycle. or the Light independent reactions produces Glyceraldehyde 3-phosphate (G3P) and 3-phosphoglycerate (3PG)

Some G3P is used to make fructose & other sugars.

However, it is also an intermediary in making a whole bunch of other stuff.
See the red compound in the middle of this chart

All lining organisms r made up of some basic simpler compounds .when animals eat plants r anything they are digested n broken down into basic simpler compound which are common to almost all living organisms .....these simple compounds are then ABSORBED n matabolised into energy or big structural proteins n other macro molecules which make up our body... so what ever u may eat it is first digested n broken down into simple compounds
only these basic compound only can enter our mucosal barrier by specific carrier proteins.......

 

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