tl;dr Higher activation energy required to activate slip-systems Ductile and brittle are relative terms, since the deformation of a material and the corresponding mode of failure depends on many conditions in addition to crystal structure such a...
Skin cells live about two or three weeks. Colon cells have it rough: They die off after about four days. Sperm cells have a life span of only about three days, while brain cells typically last an entire lifetime (neurons in the cerebral cortex, for example, are not replaced when they die).
A typical animal cell cycle lasts roughly 24 hours, but depending on the type of cell, it can vary in length from less than 8 hours to more than a year. Most of the variability occurs in G1. Click for larger image. Look here if you want to see a cell cycle.