MadSci Network: Biochemistry

Re: Why is blood afraid of sour substances such as lemons or vinegars?

Date: Fri Jan 5 11:19:56 2001
Posted By: Greta Hardin, Secondary School Teacher, Science
Area of science: Biochemistry
ID: 978240795.Bc

Fearful Blood...

Rhea - 
	I wish you had told me what the blood actually did, that made you label 
it "afraid."  After all, while blood is rather a complex substance, it is 
not complex enough to have emotions.  Instead it was participating in a 
chemical reaction.  Sour substances such as lemon juice and vinegar are 
acids.  What you saw was a chemical reaction of an acid and a base (blood 
is somewhat basic).  If you mix lemon juice and vinegar... no reaction, 
since they are both acids (sour substances).  If you mix them with water, 
again, no reaction.  Since water is neutral with a pH of 7, it is neither an 
acid or a base (actually it can also be both... but that is another story).  
If you are seeing a reaction between blood and these substances it must be a 
base.  If blood were an acid or neutral, there would be no reaction.  
However, since something did happen, it must be a base.  You may be  
wondering how I can be sure that it is an acid/base reaction at work, since 
I just told you blood is a complex substance.  I am basing my assumption on 
the fact that both lemon juice and vinegar are fairly simple substances.  
Vinegar is mainly acetic acid, and lemon juice is mainly citric acid.  
	To address the issue of blood types quickly - all blood reacted to the 
acids in the same way, regradless of type.  What determines blood type has 
nothing to do with the the pH of the blood.  Instead, it is a small string 
of molecules on the surface of the blood cells.  A type cells have one 
string, B type cells have another, and AB type have both stings.  O type 
cells have no string, which is why they are the "universal" donor.  The + or 
- is another molecule string that is independant of the A B or O type.

Hope this helps!

Greta Hardin

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