1. Red blood cells: These cells lack a nucleus and other organelles when they mature. Their primary function is to transport oxygen throughout the body. Once they've reached the end of their lifespan (about 120 days), they are broken down in the spleen and liver.

2. Skin cells: The outer layer of our skin (the epidermis) is composed of dead cells. These cells, called keratinocytes, produce keratin, a protein that provides protection and structure. As new cells are produced from the lower layers, the older ones are pushed to the surface, die, and eventually slough off.