Every single cell in your body desperately needs Oxygen to survive and must instantly get rid of toxic Carbon Dioxide. To move these invisible gases from your lungs to your toes, the human body uses an incredibly complex, high-speed fluid highway: The Blood.
However, Oxygen and Carbon Dioxide have completely different chemical properties, so they are transported by the blood in two completely different ways.
Oxygen Transport: 97% of Oxygen is transported by chemically binding to the 'Hemoglobin' pigment inside Red Blood Cells.
Carbon Dioxide Transport: Over 70% of CO₂ is transported simply dissolved in the liquid 'Blood Plasma' (in the form of bicarbonate ions).
Hemoglobin Iron: The Hemoglobin pigment is physically made of Iron (Fe), which is why human blood is bright red when carrying oxygen.
Respiratory Pigment: Hemoglobin is officially known as the human 'Respiratory Pigment'.
Oxygen gas does not dissolve very well in water, so it cannot simply float freely in the liquid blood. Instead, it needs a special 'vehicle' to carry it. Inside our Red Blood Cells (RBCs), there is a bright red, iron-rich protein pigment called Hemoglobin. Hemoglobin acts exactly like a powerful magnet for oxygen. When you breathe fresh air into your lungs, the Oxygen instantly chemically binds to the Hemoglobin inside the Red Blood Cells (forming Oxyhemoglobin). The beating heart then violently pumps these Red Blood Cells to every single tissue in the body, where the Hemoglobin releases the oxygen to the hungry cells.
Unlike oxygen, toxic Carbon Dioxide (CO₂) is highly soluble in water. Therefore, it does not strictly need to be carried by Hemoglobin. When a human cell produces toxic Carbon Dioxide waste, it throws the CO₂ out into the blood. Because it is highly soluble, the massive majority of this Carbon Dioxide simply dissolves directly into the liquid Blood Plasma (the watery part of the blood). The flowing liquid plasma carries the dissolved CO₂ back to the lungs, where it bubbles out into the alveoli and is exhaled through the nose.
Oxygen is transported by chemically binding to the red respiratory pigment called Hemoglobin, which is packed tightly inside the millions of Red Blood Cells flowing from the lungs to the body tissues.
Because Carbon Dioxide is highly soluble in water, it is mostly transported in a dissolved state directly within the liquid Blood Plasma, traveling from the body tissues back to the lungs to be exhaled.
Oxygen has a very low solubility in water. If we relied only on dissolved oxygen in the plasma, our blood could only carry 3% of the oxygen we need to survive, and we would instantly suffocate. Hemoglobin is mandatory.
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