3. All the following are true of RBC's except? a. contain nuclei b. contain hemoglobin c. biconcave disc shape d. life span of approximately 120 days

Red blood cells (RBCs), also known as erythrocytes, are unique little guys! They actually lose their nuclei during maturation in the bone marrow, allowing for more space to pack in hemoglobin, the protein that carries oxygen. This biconcave disc shape not only helps them carry oxygen more efficiently but also aids in their flexibility, allowing them to squeeze through the tiniest capillaries. In the journey of life, RBCs typically last about 120 days in circulation before they are broken down and recycled by the body. This process is crucial for maintaining healthy blood composition and ensuring a fresh supply of red blood cells is always on hand for oxygen transport. Talk about a well-oiled delivery system!