Peptic Ulcer - An open sore that develops on the inner lining of the stomach or upper small intestine.⏎
Prion - A causative agent of infectious disease that is composed primarily of protein.⏎
Pathogen - A biological agent that causes disease.⏎
Natural Selection - The process by which certain heritable traits that contribute to the survival and reproductive success of an organism become more widespread within a population over successive generations.⏎
Nanometer - A unit of length equal to one one-billionth (1 x 10-9) of a meter.⏎