An organism is any contiguous living system, such as an animalplant orbacterium. All known types of organisms are capable of some degree of response tostimulireproductiongrowth and development and homeostasis. An organism consists of one or more cells; when it has one cell it is known as a unicellular organism; and when it has more than one it is known as a multicellular organism. Most unicellular organisms are of microscopic size and are thus classified asmicroorganisms. Humans are multicellular organisms composed of many trillions of cells grouped into specialized tissues and organs.

ORGANISM ---> is a living thing (an individual, animal, plant, or single-celled life form) that is capable of reacting to stimuli, reproduction, growth, and homeostasis.