Blood pigment is an important component of red blood cells, and is responsible for transporting oxygen throughout the body. Hematin, heme, hemoglobin, and haemoglobin are all terms used to describe the same blood pigment. Hematin is a 7-letter term, heme is a 4-letter term, hemoglobin is a 10-letter term, and haemoglobin is an 11-letter term. All of these terms refer to the same molecule, which is a protein that contains iron and is responsible for carrying oxygen in the blood.