Leon Vlieger at The Inquisitive Biologist:
In this second foray into the biology of death, I will examine programmed cell death or PCD. You might have heard of the process of apoptosis, but, as the previously reviewed The Biology of Death mentioned, this is just one of many ways in which cells can actively kill themselves. It is a vital part of life in multicellular organisms, for instance sculpting our hands so that we are not born with webs of skin between our fingers, or allowing leaves to fall from the trees in autumn by triggering cell death in so-called abscission zones. These are small sacrifices to serve the larger organism. Surprisingly, single-celled (unicellular) organisms also show PCD. But wait, is that not tantamount to suicide? How did that evolve?
More here.