Biomass is an energy source, consisting of the biological material from a living organism. The biological material is used by the Prototypes to cure and regenerate themselves.
Fresh bio-matter is required to perform regeneration of the body, which is acquired by consuming living organisms. Along with regeneration, biomass is also used to transform a Prototypes' body into a deadly weapon or create a protective armor to defend themselves.
Elizabeth Greene used a vast amount of biomass to construct an extremely large infected form around her. This behemoth form of hers was called as Mother by Blackwatch soldiers and was capable of destructive attacks.
Alex Mercer was able to regenerate his entire body after he was blasted to the city's shore by the nuclear weapon he had dropped into the sea. His remains were splattered into red puddles, seemingly inert. But once disturbed by a crow, he regenerates his body by consuming the fresh biomass of the crow.