* Hemoglobin is a protein found in red blood cells. It contains iron, which binds to oxygen molecules in the lungs. This oxygen-rich blood is then transported throughout the body, delivering oxygen to the cells.

Let's look at the other options:

* Plasma is the liquid portion of blood, which carries nutrients, hormones, and waste products. While important, it doesn't directly carry oxygen.

* White blood cells are part of the immune system, fighting infections. They don't play a role in oxygen transport.

* Platelets are cell fragments that help with blood clotting. They are not involved in oxygen transport.

Therefore, hemoglobin is the crucial component for carrying oxygen in the human body.