MAIN TYPES OF DIGESTION AND THEIR DISTRIBUTION AMONG GROUPS OF LIVING ORGANISMS

Abstract

This type of digestion is characterized by the fact that enzymes synthesized by secretory cells are released into the extracellular environment, where their hydrolytic effect is realized. The secretion of hydrolytic enzymes from cells into the digestive cavities first appeared in coelenterates and ctenophores. In annelids, crustaceans, insects, cephalopods, tunicates, and chordates (with the exception of the lancelet), extracellular digestion predominates. It is especially developed in highly organized animals and humans, in which it provides the initial digestion of nutrients. In these organisms, secretory cells are located far enough from the digestive cavities, where the action of hydrolases is realized, so extracellular digestion is defined as distant. Distant digestion occurring in special cavities is referred to as cavitary. Extracellular digestion is characteristic of all heterotrophic organisms whose cells have a cell wall - bacteria, archaea, fungi, carnivorous plants, etc. With this method of digestion, enzymes are secreted into the external environment or are fixed on the outer membrane (in Gram-negative bacteria) or on the cell membrane. wall. Digestion of food occurs outside the cell, the resulting monomers are absorbed with the help of cell membrane transporter proteins.