In this form of heterotrophic nutrition, organisms take food in bulk into their bodies. The food moves within a digestive tract, or alimentary canal, and is systematically digested. The final products(nutrients) which are soluble are absorbed and assimilated. The undigested food residues are expelled through the anus (or mouth for a few animals) in the process of egestion or defecation. Most animals and insectivorous plants are holozoic.
Stages in holozoic nutrition
- Ingestion: The process of taking complex organic food into the body through the mouth
- Digestion: The breaking down of complex, insoluble organic food molecules into simpler, soluble, diffusible ones. This occurs in two ways: mechanical or physical digestion, and chemical or enzymatic digestion, sometimes also called hydrolysis(because water is needed). Digestion may be extracellular(occurring outside cells) or intracellular(occurring inside cells)
- Absorption: The uptake of soluble nutrients from the region of digestion across a membrane, into the body tissue proper.
- Assimilation: The utilization of absorbed food molecules by the body; e.g for energy provision or synthesis of new tissues.
- Egestion: The elimination of indigestible food residues. It is different from excretion.