TECHNOLOGY FOCUS - BIOLOGY - Preparation (Claimed): Preparing (I) comprises forming a liquid dispersion of solubilized precursor for hydrophilic polymer and microorganisms for (I), subjecting the dispersion to solidification conditions to form a solid structure of the hydrophilic polymer, where the solid structure has an interior structure having many interconnected major cavities containing the microorganisms, and the solidification conditions do not unduly adversely affecting the population of the microorganisms and maintaining the solid structure containing microorganisms under conditions that do not adversely affect the population of the microorganisms in the interior of the solid structure for a time sufficient to enable the microorganisms to undergo a phenotypic alteration to maintain their population substantially stable and to become substantially irreversibly retained in the interior of the solid structure. Preferred Method: The solidification conditions include the presence of a crosslinking agent, and the precursor is a solubilized prepolymer. The metabolic process is a catabolic process comprising a reduction process. Preferred Components: The HEV is at least 5000. The solid structure defines an external skin. The skin has pores of an average diameter of 1-10 microns and comprises 1-30% of the surface area of the external skin. In (I), 40-70 vol.% of the biocatalyst comprises major cavities and the biocatalyst contains smaller cavities. The major cavities are quiescent. The HEV is at least 20000 and the concentration of microorganisms in the interior of the solid structure is at least 100 g/l based upon the volume defined by the exterior of the solid structure. (I) contains an exo-network of microorganisms. The microorganism population is a single strain-type. (I) further comprises polysaccharide. The microorganism population exhibits at least one phenotypic change. ACTIVITY - Antifouling; Virucide; Antibacterial; Tranquilizer; Plant Growth Stimulant; Animal Attractant; Animal Repellent.    MECHANISM OF ACTION - None given.    EXAMPLE - No suitable example given.