activation 1 the action or process of rendering an atom, molecule, or other substance reactive or more reactive, whether physicochemically, chemically, or biochemically. 2 the process of rendering material artificially radioactive: radioactivation. See radioactivation analysis. 3 the initial changes in an ovum during fertilization, covering the periodfrom first contact with a sperm to dissolution of the nuclear membranes. 4 the initial changes in the conversion of a spore to a vegetative cell. This can be effected by various agents or processes and may involve alteration of one of the spore’s outer layers.
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