Tagyiroti fasli, soli va shabonaruzii muhit ba tabiati zinda va nizomi organizmho tasiri khele nazarras merasonand.
Dar biologiya mafhumi muntazami manoi tagyiroti davrii vazifahoi fiziologiro dorad. Dar inson nizomi khob va bedori, dar jonvaron nizomi khobi mavsimi ba mushohida merasad, masa- lan, dar baze hayvonoti shirmak (yurmon, khorpusht, khirs) va gay- ra (rasmi 6).
Muntazami ba hamohangsozii faoliyati organizm bo muhiti beruna muvofiqi maqsad ast.