From Big Medical Encyclopedia

ACTIVITY (Latin activus — active) in biology — fundamental property live, expressed in ability of biological system (see) to ignore, overcome or use external influences for implementation of the requirements, and also in ability of forecasting of external influences and the choice of the optimum program of behavior, i.e. in ability is reasonable to react to environmental factors. On the basis of the active and selective relation to external environment biological systems carry out functions of reproduction and development. In more detail — see. Organism .

D. I. Dubrovsky.