Final answer:
Hemoglobin constitutes approximately 90% of the dry weight of the cytoplasm of red blood cells, highlighting its importance in oxygen transport.
Step-by-step explanation:
Hemoglobin is a vital protein found in red blood cells (erythrocytes) that carries oxygen throughout the body and carbon dioxide back to the lungs for exhalation. In the cytoplasm of red blood cells, hemoglobin is the dominant component, making up about 90% of the dry weight of the cell. This high percentage is due to the critical role it plays in oxygen transport, binding oxygen to iron atoms in its structure. It is important to note that in the blood, erythrocytes constitute roughly 45% of the total volume, a measurement known as the hematocrit.