Here's why:

* Hemoglobin's Function: Hemoglobin is the protein found in red blood cells. Its primary function is to bind and carry oxygen throughout the body.

* White Blood Cell Function: White blood cells (also called leukocytes) are part of the immune system. They fight infections and protect the body from foreign invaders like bacteria, viruses, and parasites.

While red blood cells are primarily composed of hemoglobin, white blood cells have different structures and contain different proteins that enable them to perform their immune functions.