Biological Buffers

For your information (not required material): 

A buffer solution resists marked changes in pH that would otherwise result from addition of an acid or base. A buffer works by removing hydrogen ions from the solution when they are in excess and donating hydrogen ions to the solution when they are low. Most buffers are weak acids and their salts which dissociate in solution as shown in the following example:

	This weak acid dissociates so slightly that the concentration of the product is negligible. (click on image for a larger version)
	This salt dissociates almost completely. (click on image for a larger version)

Together in a buffer solution, these compounds act to nullify the effect of adding H+ or OH- ions as follows:

(click on image for a larger version)

An example of an important biological buffer system is the maintenance of human blood at pH 7.4 several buffer systems act to maintain the pH of blood. These include a carbonate-bicarbonate buffer system, a phosphate buffer system, and a protein buffer system. Proteins can act as buffers because each protein molecule is both a weak acid and a weak base. The weakly acidic carboxylic acids counteract rising pHs while the weakly basic amino groups can counteract falling pHs. Plasma proteins and hemoglobin (blood's oxygen-carrying pigment,a protein) enhance the blood's buffering capacity. (Proteins also help with buffering within cells.)

Carbonate-bicarbonate buffering is vital to oceans, rivers, and lakes. This buffer system has been pressed to (and beyond) its limits in waters seriously affected by acid rain. The change in pH of such waters has caused many organisms in these lakes to die. Massive fish kills are not uncommon in such areas, including the Adirondacks of upstate New York.

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