Here's a breakdown:

* Hemoglobin: This is the protein found in red blood cells that carries oxygen throughout the body.

* Heme: A complex molecule within hemoglobin that contains iron. It's responsible for the red color of blood and is essential for oxygen binding.

When hemoglobin breaks down, heme is released. The heme molecule is further broken down into bilirubin, which is excreted in bile.