easy
Which protein inside red blood cells carries oxygen from the lungs to the rest of the body?
- Myoglobin
- Hemoglobin
- Collagen
- Keratin
Why B? And why not the others?
Correct answer: B. Hemoglobin
Hemoglobin is the oxygen courier, and it dominates the cell that carries it: about 95 percent of a red blood cell's dry weight is hemoglobin. Each molecule holds four iron atoms, and each iron atom grabs one oxygen molecule in the lungs and releases it in the tissues; that iron is also what makes blood red. Myoglobin is the most tempting wrong choice because it really does bind oxygen, but it stores it inside muscle cells rather than transporting it in the blood. Collagen is the structural protein of skin, tendon, and bone, and keratin builds hair and nails; neither ever touches oxygen transport.
Source: Encyclopaedia Britannica: hemoglobin