Hair turns color when we age because the follicles at the base of the hair shaft cease to produce melanin. Melanin is a chemical that gives the hair shaft its color (black, brown, blond, red, and all shades in between). The darkness or lightness of your hair depends on how much melanin each strand contains. With age, the cells in the follicle that produce melanin die off. As they do so, that hair strand will become silver, grey, or white, as it grows.

You decide that the introduction should also discuss the extremophiles that are referred to as the archaea. these single-cell organisms are considered "extremophiles" due to their ability to survive and reproduce in environmental conditions that would be hostile for most living organisms. archaea species have been isolated from highly acidic sulfur springs, ocean floor thermal vents with temperatures that exceed boiling, and subarctic ice well below freezing. while still considered to be prokaryotic, the archaea have numerous differences that place them apart from the bacteria. choose the characteristics that separate the archaea from other prokaryotic cells. select all that apply. view available hint(s) select all that apply. archaea lack true peptidoglycan in their cell walls. the morphology of the cell is rigid and is geometric in shape, similar to a sphere or cylinder. the cytoplasmic membrane lipids of archaea have branched or ringform hydrocarbon chains. all currently identified and characterized archaea have been linked as the causative agent to an animal or human disease.