Pathogen - A biological agent that causes disease.⏎
Nanometer - A unit of length equal to one one-billionth (1 x 10-9) of a meter.⏎
Parasitism - A close relationship between two organisms in which one organism, the parasite, benefits at the expense of the host organism.⏎
Peptic Ulcer - An open sore that develops on the inner lining of the stomach or upper small intestine.⏎