Cells come in all shapes, sizes, and functions with life spans that vary correspondingly. Such cells specialize to perform different functions. Each specialized cell pays close attention to its neighbors as it gets food from its surroundings and expels waste into it. These cells adhere to, tightly cooperate with, and depend on each other for life. Large co-ops of similar cells form tissues.
Tissues cooperate and form organs.
Organs carry out the basic functions of an organism. This tremendous array of cells has an equally vast spread of life spans. Neutrophils are white blood cells that find, engulf, and destroy foreign microbes. They cannot, however, reproduce themselves. That's the price these cells pay for specialization.