The Digestive System.
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Digestion is the breakdown of food into smaller particles that can be absorbed by into the blood stream and supply energy to an organism. There are many varying digestive systems for different animals. There is also external and internal digestion. External digestion is more primitive and is still used by fungi. This process uses enzymes secreted into the environment to break down food and diffuse back into the organism. Internal digestion occurs inside an organism and is more efficient, since food is captured and controlled.