RBCs contain hemoglobin (say: HEE-muh-glow-bin), a protein that carries oxygen. Blood gets its bright red color when hemoglobin picks up oxygen in the lungs. As the blood travels through the body, the hemoglobin releases oxygen to the different body parts. Each RBC lives for about 4 months.

The body makes three types of blood cells. White blood cells fight infection, platelets help blood clot and red blood cells carry oxygen throughout the body. Red blood cells have an iron-rich protein that gives blood its red color, called hemoglobin. Hemoglobin lets red blood cells carry oxygen from the lungs to all parts of the body.

The cytoplasm of a red blood cell is rich in hemoglobin, an iron -containing biomolecule that can bind oxygen and is responsible for the red color of the cells and the blood. Each human red blood cell contains approximately 270 million hemoglobin molecules.

The most abundant cells in vertebrate blood are red blood cells. These contain hemoglobin, an iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas thereby increasing its solubility in blood.

There’s no need to build up the suspense: Blood is red. It might vary from a bright cherry red to a dark brick red, but it’s always red. “If you get a cut,” says Dr. Lichtin, “red is the only color you’re going to see come out.” The reason? It has to do with the hemoglobin molecules within your red blood cells.