True or False: Red blood cells are filled with hemoglobin.

Red blood cells, also known as erythrocytes, are indeed filled with hemoglobin, which is a crucial protein that allows these cells to transport oxygen from the lungs to the tissues and return carbon dioxide from the tissues back to the lungs. Hemoglobin comprises about a third of the total weight of red blood cells and gives them their characteristic red color.

The presence of hemoglobin within red blood cells is essential for the proper functioning of the circulatory system across different species, not just in humans or specific types of animals. Therefore, stating that red blood cells are filled with hemoglobin is a fundamental aspect of their structure and function, and this characteristic applies to all healthy mammals, including adult humans and many other vertebrates.

This understanding reinforces the importance of hemoglobin in maintaining oxygen levels in the body, facilitating cellular respiration, and ensuring efficient metabolic processes.