From Wikitroid, the Metroid wiki
Bio-Doors are
Bio-Barriers that live on
Zebes and
SR388. They are easily recognizable by their single eye and often block entrances to boss rooms.
Samus can destroy them by firing three
Missiles or one
Super Missile at the eye. They will sometimes defend themselves by covering their eye with a strong shield or will shoot plasma from their eye. On the
Biologic Space Laboratories research station, destroying a Bio-Door will always cause a
Red X to float away, replenishing a large amount of Samus's ammunition and energy.
Samus facing a Bio-Door aboard the Biologic Space Laboratories research station.
