Organism - A living being that can reproduce, grow, react to external stimuli, and maintain its internal equilibrium.⏎
Respiratory Tract - The part of the anatomy that has to do with the passage of air and includes the nose, larynx, trachea, and lungs.⏎
Nanometer - A unit of length equal to one one-billionth (1 x 10-9) of a meter.⏎
Prion - A causative agent of infectious disease that is composed primarily of protein.⏎
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.⏎