Hemoglobin: The Oxygen-Carrying Pigment in Blood - Definition & Function

The pigment in blood that carries oxygen is haemoglobin. Haemoglobin is an iron-containing protein found in red blood cells that binds to oxygen in the lungs and transports it to tissues throughout the body. When oxygenated, haemoglobin is bright red, and when deoxygenated, it is dark red.