Hemoglobin is a protein found in red blood cells that is responsible for transporting oxygen from the lungs to the rest of the body and carrying carbon dioxide back to the lungs for exhalation. It is made up of four subunits, each containing an iron atom that binds to oxygen. Hemoglobin enables efficient oxygen exchange in tissues and is crucial for cellular respiration. Its ability to bind and release oxygen is influenced by factors like pH and carbon dioxide levels. Hemoglobin levels are an important indicator of overall health, with abnormal levels often signaling conditions like anemia or respiratory disorders.