Here's why:

* Blood pH: Blood needs to maintain a very narrow pH range (slightly alkaline, around 7.35-7.45) to function properly.

* Buffer System: The body uses a complex buffer system to keep blood pH stable. The bicarbonate buffer system is a key part of this.

* Bicarbonate's Role: Bicarbonate ions act as a base, accepting hydrogen ions (H+) when blood becomes too acidic. This reaction helps to neutralize the excess acidity and maintain the proper pH balance.

It's important to note that there are other buffers in blood, but bicarbonate is the primary base that helps maintain the pH balance.