_________ in the blood carries oxygen from the respiratory organs to the rest of the body, where it releases the oxygen to burn nutrients to provide energy for metabolism:

_________ in the blood carries oxygen from the respiratory organs to the rest of the body, where it releases the oxygen to burn nutrients to provide energy for metabolism:

• A. Erythrocytes
• B. Leukocytes
• C. Platelets
• D. Hemoglobin

Answer: (D)

Oxygen transport in the blood is carried by hemoglobin, a protein inside red blood cells. In the lungs, hemoglobin binds oxygen to form oxyhemoglobin; as blood travels to tissues, it releases that oxygen where it’s needed for mitochondrial oxidative phosphorylation to produce ATP. Erythrocytes are the cells that house hemoglobin and move it through the bloodstream, but the actual oxygen-binding and delivery function belongs to the hemoglobin molecule itself, thanks to its iron-containing heme groups. Leukocytes and platelets have other roles (immunity and clotting), so they don’t carry oxygen. This binding and release cycle enables oxygen to be picked up where it’s abundant and delivered to cells that require it for metabolism.

Oxygen transport in the blood is carried by hemoglobin, a protein inside red blood cells. In the lungs, hemoglobin binds oxygen to form oxyhemoglobin; as blood travels to tissues, it releases that oxygen where it’s needed for mitochondrial oxidative phosphorylation to produce ATP. Erythrocytes are the cells that house hemoglobin and move it through the bloodstream, but the actual oxygen-binding and delivery function belongs to the hemoglobin molecule itself, thanks to its iron-containing heme groups. Leukocytes and platelets have other roles (immunity and clotting), so they don’t carry oxygen. This binding and release cycle enables oxygen to be picked up where it’s abundant and delivered to cells that require it for metabolism.