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Term describing behaviour that is freely emitted by an animal and can be reinforced by the experimenter.
A variety of instrumental conditioning in which an animal emits a behaviour at a time it decides and that behaviour is then reinforced by its consequences. For example, an animal might press a lever in a Skinner box to earn a pellet of food. Not all instrumental conditioning can be described as operant. For instance, where an experimenter puts a rat in a maze and then removes it after its choice, is not described as operant since the timing of behaviour is not under the control of the rat.
A class of drug that includes opium, morphine and heroin.
A distinct structure in the body serving a particular function, e.g. brain or kidney.
A group of organs that all work together, e.g. the cardiovascular system, the urinary system, the digestive system. Also sometimes called body system.
The movement of water across a membrane that is freely permeable to water but not to solutes (dissolved substances), from a region of low solute concentration to one where the solute concentration is higher.
A disease of bones. It is brought about when old bone is lost faster than new bone is gained in the remodelling process.