Final answer:
Hemoglobin loaded with oxygen is called oxyhemoglobin, which refers to hemoglobin molecules that have bound oxygen molecules to their heme groups, resulting in a bright red color.
Step-by-step explanation:
Hemoglobin is a metalloprotein found in red blood cells (erythrocytes), which is responsible for the transport of oxygen from the lungs to the body's tissues. Each hemoglobin molecule is made up of four subunits, each containing a heme group. This heme group binds to oxygen, and when all four hemes in a hemoglobin molecule are each bound to an oxygen molecule, it is referred to as oxyhemoglobin. Oxyhemoglobin is characterized by its bright red color and is a crucial part of the body's oxygen transport system.
The correct answer to the question 'What is hemoglobin loaded with oxygen called?' is option 2) Oxyhemoglobin. This is because oxyhemoglobin refers to hemoglobin that has oxygen bound to its iron-containing heme groups.