Final answer:
Cells are replaced through apoptosis or by stem cells that differentiate into the required cell types. Osteoblasts and osteoclasts are involved in bone tissue maintenance. Cell division is essential for repairing damaged tissue like skin.
Step-by-step explanation:
Cells are responsible for replacing dead or dying cells through several mechanisms. In the human body, most cells that are no longer needed, damaged, or potentially dangerous are cleared away via a process called apoptosis, or programmed cell death. However, the body also needs to replace these cells. This is where stem cells come into play. These cells serve as a pool of progenitors that can differentiate into various cell types needed for replacement. For example, red blood cells, which have a finite lifespan of about 60 days, are regularly replaced by reticulocytes that are produced in the bone marrow.
Another example is the regeneration of bone tissue. The osteoblasts are cells that form new bone, while osteoclasts are responsible for bone resorption. Together, these cells maintain the dynamic balance of bone formation and breakdown, ensuring the body's skeleton remains robust and capable of repair after injuries.
Furthermore, cell division plays an essential role in the repair of damaged tissue, such as when skin cells divide to repair a wound. Whether through stem cell differentiation or the division of existing cells, the body has mechanisms in place to ensure that worn-out or damaged cells are replaced and that overall tissue function is maintained.