Pathogen - A biological agent that causes disease.⏎
Organism - A living being that can reproduce, grow, react to external stimuli, and maintain its internal equilibrium.⏎
Protozoa - A taxonomic group of single-celled microorganisms that live in almost every kind of habitat and include some pathogenic parasites of humans and other animals. ⏎
Peptic Ulcer - An open sore that develops on the inner lining of the stomach or upper small intestine.⏎