cells...

With one look, you can usually tell whether someone is old or young. Wrinkled skin or smooth. Thinning hair or thick locks. Bifocals or Ray-Bans. These are just a few of the overt clues. Far less obvious are the age-related signs that show up on the molecular level. Ask a geneticist where to look and he may point you to a person's mitochondria. These rod-shaped residents of an animal cell provide the cell with energy, and each mitochondrion has its own DNA strand, which is distinct from the DNA in the chromosomes that dwell in the cell's nucleus. With age, this mitochondrial DNA (mtDNA) becomes riddled with mutations, both subtle and severe.

people don't think that aging is caused by aging by gray hair. But the most crazy thing about it is that it is caused by gray hair. what caused gray hair is the cells aging and as the cells start to die of and as they start to die the body agies.

VOCABULARY-
mitochondrial-an organelle found in large numbers in most cells, in which the biochemical processes of repiration and energy production occur. it has a double membrane, the inner layer being folded inword to form layers.
mutations-the action or process of mutating
engineered-a person who designs, builds, or maintains, engines, machines, or public works.