In biology, an organism(s) is any contiguous living system, such as an animal, plant, fungus, or bacterium. All known types are capable of some degree of response to stimuli, reproduction, growth and development and homeostasis. When it has one cell it is known as a unicellular organism when it has more than one it is known as a multicellular organism. Most unicellular are of microscopic size and are thus classified as microorganisms. Humans are multicellular organisms composed of many trillions of cells grouped into specialized tissues and organs.
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Pharmacology is the branch of medicine and biology concerned with the study of drug action, where a drug can be broadly defined as any man-made, natural, or endogenous (from within body) molecule which exerts a biochemical and/or physiological effect on the cell, tissue, organ, or organism (sometimes the word pharmacon is used as a term to encompass these endogenous and exogenous bioactive species). More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function. If substances have medicinal properties, they are considered pharmaceuticals.
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