Draw it to Know it - Hemoglobin & Myoglobin: 1. Heme Group

Good structural representation with main features annotated.

Chemistry LibreTexts - Oxygen Binding

Great, concise treatment.

Biology LibreTexts - Heme Proteins

It's good to pay a visit to the role of heme as a prosthetic group with redox functions in cytochromes beyond its role in oxygen carriers.

Topic Resources

Interdisciplinary MCAT Course Videos
Conceptual Vocabulary
Images for Teachers
figures for classroom presentation