[MaeP]

Hi! I have been given an assignment to do which involves writing about the roles Oxygen and Carbon Dioxide play in sustaining life on earth. I have done most of it but one section has stumped me.
I have to include specific acid/base reactions and redox reactions relating to life and a specific stoichiometric calculation using one of the selected reactions involving the sustaining of life.

What could be a redox reaction relating to life? As in a redox reaction which occurs in nature that aids in the supporting of life on earth.
Also what could be an acid/base reaction also relating to supporting life?

I was thinking that I would use photosynthesis as the redox reaction, but this seems a bit obvious, are there any others?
i.e. Photosynthesis:
6CO₂ + 6H₂O ---> C₆H₁₂O₆ + 6O₂

This is necessary for life because it produces Oxygen which we all need to live.


Thanks in advance for any help =P

[Karakth]

This is necessary for life because it produces Oxygen which we all need to live.

And let's not forget that without it, no-one would have any food

As an acid base reaction, I would suggest the neutralisation reaction of when stomach contents (acidic) come into contact with pancreatic juices (basic).

[Yggdrasil]

Another important redox reaction is cellular respiration (glucose + oxygen + ADP + Pi --> carbon dioxide + water + ATP), which allows organisms to produce energy.

As for acid-base reactions (although this isn't exactly a standard acid-base reaction), here's a pretty useful one for humans:

CO₂ + 2H₂O <--> HCO₃^- + H₃O⁺

This reaction (the bicarbonate buffer reaction) is important because 1) it helps keep blood at the correct pH and 2) it allows blood to transport CO₂ from cells in the body to the lungs.

[MaeP]

Thanks for that, you actually made me realise that i could also include reactions that occur inside the human body, i was concentrating on the environment, but this might actually be better.   so thanks again.

Another quick question (not sure if I should post this in another thread or not).
C6H12O6 + 6O2 -> 6 CO2 + 6 H2O + energy

This is the reaction that occurs in our body that converts glucose and oxygen into energy for us to use. My question is: Is this also a redox reaction (I noticed its the opposite of what happens in  photosynthesis). Would this mean that the opposite is occuring? i.e. oxygen is being reduced to H2O? etc.

[Karakth]

Yes, glucose is oxidised whilst oxygen is reduced, you are correct.

[MaeP]

Thanks  

[MaeP]

As for acid-base reactions (although this isn't exactly a standard acid-base reaction), here's a pretty useful one for humans:

CO₂ + 2H₂O <--> HCO₃^- + H₃O⁺

This reaction (the bicarbonate buffer reaction) is important because 1) it helps keep blood at the correct pH and 2) it allows blood to transport CO₂ from cells in the body to the lungs.

Hi, again, I googled bicarbonate buffer reactions, and the stuff i found either wasnt helpful or was too advanced for my understanding.  
Could you please explain what happens during this reaction? In what part of the body it occurs? What would happen if it didn't/couldn't occur?
Also, are you sure that is the equation? A site i found gave the following equation:

H3O + HCO3 <-> H2CO3 + H2O <-> 2H2O + CO2

And stated that only the first part is an acid/base reaction. i.e. only
H3O + HCO3 <-> H2CO3 + H2O is an acid base reaction. Which gets me confused.
Any help would be greatly appreciated.

Thanks again.

EDIT:
I found out what would happen if it didnt occur, the body would go into a state of metabolical acidosis, which can result in coma and death.
So you weren't joking when you said that its pretty useful!  

[Yggdrasil]

If you want straight acid-base reactions, here probably the most relevant ones:

CO₃^2- + H₃O⁺ <--> HCO₃^- + H₂O

HCO₃^- + H₃O⁺ <--> H₂CO₃+ H₂O

Basically, the presence of carbonate and bicarbonate ions in the blood stream help regulate blood pH by acting as a buffer (look up buffers in wikipedia for more information about how buffers help maintain a constant pH).  Since most processes in biological systems are greatly affected by changes in pH, the bicarbonate buffer system helps to prevent the pH of the blood from changing greatly.

Also, carbon dioxide is transported in the blood stream primarily as bicarbonate and carbonate ions.  Since metabolic activity produces carbon dioxide, the transport of bicarbonate ions helps to remove carbon dioxide from the body, since the lungs remove carbon dioxide from the blood.

[MaeP]

Since metabolic activity produces carbon dioxide, the transport of bicarbonate ions helps to remove carbon dioxide from the body, since the lungs remove carbon dioxide from the blood.

So does it transport the carbon dioxide from cells in the body into the lungs which then remove it from the body (when you exhale) or does it remove the CO₂ in some other way?

Also, I need to write a stoichiometric equation involving one of the given reactions; i have included the following reactions:
Photosynthesis
6H₂O + 6CO₂ + light ? C₆H₁₂O₆ + 6O₂

Energy from glucose and oxygen (in the body)
C₆H₁₂O₆ + 6O₂ ? 6CO₂ + 6H₂O + energy

and
Carbonic-acid-Bicarbonate Buffer equation
H₃O⁺ + HCO₃^- <--> H₂CO₃ + H₂O <--> 2H₂O + CO₂

I would prefer to do a stoichiometric equation using the carbonic-acid-bicarbonate buffer equation but I cant get any measurements of (for example) the average amount of CO₂ produced. etc.
Which equation do you think will suite my needs the best? What should I solve using stoich.?

Thanks

[Yggdrasil]

In the body, the concentration of CO₂ is high, so it disolves in the blood to form carbonic acid.  When the blood passes through the alveoli in the lungs, the carbonic acid transforms back into carbon dioxide because the concentration of carbon dioxide in the air in the lungs is low.  The concentration of carbon dioxide in the lungs is kept low through breating.

What do you mean by stoichiometric equation?  Do you have to take a certain number of reactant and calculate how much product you'll create?  Do these number have to be real numbers (e.g. the real concentration of bicarbonate ion in human blood)?

[MaeP]

Im pretty sure that the numbers do have to be real, and yes I have to take a certain number of reactant and calculate how much product ill create. So using the carbonic-acid-bicarbonate buffer reaction, if i had (for example) how much carbon dioxide & water was produced i could figure out how much carbonic acid is used to create that much carbon dioxide etc.
Or if all else fails (i cant do a stoichiometry equation with the buffer) i could do a stoichiometry equation using photosynthesis. To show how much glucose is produced using a certain amount of water and carbon dioxide.

[Yggdrasil]

It would be hard to do a real stoichiometric equation with the bicarbonate buffer system, because the reaction isn't complete.  In the blood-stream, the reaction is at equilibrium, so you'll have bicarbonate being converted to carbonic acid and carbonic acid being converted to bicarbonate as well.  It would probably be best to use either photosynthesis or cellular respiration for the stoichiometry part.