Final answer:
Bicarbonate ions are the main molecule that buffers the lower pH in blood caused by hydrogen ions released from muscle cells, working to stabilize pH and prevent excessive acid buildup.
Step-by-step explanation:
The molecule that buffers the lower blood pH caused by the hydrogen ions released from muscle cells is bicarbonate ions. In the blood, bicarbonate ions act in conjunction with carbonic acid to form a buffering system. This system maintains blood pH within a narrow range, which is crucial for survival. When bicarbonate ions combine with free hydrogen ions, they become carbonic acid, thus removing hydrogen ions and moderating changes in pH. This prevents an excessive buildup of hydrogen ions that would otherwise reduce the blood's pH to dangerous levels. Additionally, hemoglobin within red blood cells can bind to hydrogen ions to help buffer pH changes, but the main buffering agent in this scenario is the bicarbonate ion.