Final answer:
Approximately 98.5% of the oxygen in systemic arterial blood is bound to hemoglobin, a protein in red blood cells. Hemoglobin greatly enhances the blood's capacity to transport oxygen, carrying up to four oxygen molecules per molecule of hemoglobin.
Step-by-step explanation:
About 98.5% of the oxygen carried by systemic arterial blood is attached to a protein known as hemoglobin. Hemoglobin is found within erythrocytes (red blood cells) and is pivotal in the transport of oxygen from the lungs to the tissues of the body. While a small fraction of oxygen (1.5%) dissolves directly into the blood plasma, the vast majority is bound to the iron-containing heme groups within hemoglobin molecules.
Each hemoglobin molecule can carry up to four oxygen molecules, with iron ions in the heme groups acting as the binding sites for oxygen. This binding of oxygen to hemoglobin forms a compound known as oxyhemoglobin. The bright red color of oxygenated blood in the systemic arteries is a result of oxyhemoglobin, whereas deoxygenated blood has a darker red appearance due to reduced hemoglobin, also called deoxyhemoglobin.
The efficient transport of oxygen by hemoglobin enables the blood to carry significantly higher amounts of oxygen than would be possible if it solely relied on the oxygen dissolved in plasma. This system is essential to meet the energy demands of the human body.