osmotrophy

Osmotrophy is a form of heterotrophic nutrition and a cellular feeding mechanism involving the direct absorption of dissolved organic compounds by osmosis. Organisms that use osmotrophy are called osmotrophs. Osmotrophy is used by diverse groups of organisms. Organisms that use osmotrophy include microorganisms like bacteria, many species of protists and most fungi. Invertebrate animal groups like molluscs, sponges, corals, brachiopods and echinoderms may use osmotrophic feeding as a supplemental food source. A common subset of osmotrophy is lysotrophy, in which organisms secrete enzymes into the extracellular environment to break down macromolecules into smaller, soluble molecules for absorption.

== Process == Osmotrophy, as a means of gathering nutrients in microscopic organisms, relies on the cellular surface area to ensure that proper diffusion of nutrients occurs in the cell. Some osmotrophs may have an internal digestive system, while still using osmosis as a way to gain supplemental nutrients. With bigger organisms, the surface-area-per-volume ratio drops and osmotrophy becomes insufficient to meet nutrient demands. Larger, macroscopic organisms that rely on osmotrophy, compensate with a very flat, thin body. A tapeworm is an example of such an adaptation.