Here's why:

* Hemoglobin is a protein found within red blood cells. Its main function is to carry oxygen from the lungs to the body's tissues and return carbon dioxide from the tissues to the lungs.

* Red blood cells are the most numerous type of blood cell. They are responsible for transporting oxygen throughout the body.

Think of them as a team:

* Red blood cell: The delivery truck.

* Hemoglobin: The cargo (oxygen) inside the truck.

They work together to deliver oxygen, not to create anything new.