Extracellular Digestion

All about Intercellular and Extracellular Digestion

If you don’t know much about biology and the digestive system you may never have thought about the difference between intercellular and extracellular digestion—the two ways that the body can absorb nutrients.  The importance of the two, however, has everything to do with the reason why we evolved and the fungi didn’t.

What is intercellular digestion?

Intercellular digestion is when an individual cell must swallow up its prey completely during digestion.  Fungi are one of the main practitioners of this skill.  It is common among the oldest kind of life on the planet.

What is extracellular digestion?

Extracellular, means “outside the cell.”  So, as you have no doubt figured out, extracellular digestion is when an individual cell does not have to fully surround its nutrient in order to absorb it.

In fact, human beings mostly employ extracellular digestion.  Why?  The reason has everything to do with our level of evolutionary development.  The reason why fungi have intercellular digestion is because they are very simple ancient creatures who play very simple roles.

In other words, in order for us to develop into the complicated creatures that we currently are, we needed to have a different, more complicated system of cellular absorption.  The reason why digestion outside of the cell is important is that it frees up a number of cells to do things other than digest.  When food enters our bodies, what happens first is the enzymes in your mouth start to break the food down and ready if for digestion.  In many ways this is exactly the reason why we became complex and fungus didn’t.  Because we can use division of labor on the cellular level in order do things more efficiently, this means that other cells can remain untouched by the digestive process except to have energy delivered right to them.

Enzymes are the key to extracellular digestion.  The enzymes are the chemicals that go out and break down the nutrient so the body’s cells can then absorb them when they are brought back in, say, the blood stream.  The body may also then be able to absorb the fat that remains and store it for later use.

Different enzymes will be in charge of different parts of digestive processes.  You might think of it as a carcass out in the savannahs.  Each enzyme is like a different kind of a creature that comes along to take its cut of the carcass.  First, come the lines and tigers, then the hyenas and vultures, then the smaller creatures and bugs until there is nothing left of the carcass but bones.  Well, from the moment that a piece of meat hits your palette, a similar process starts to take place as a variety of enzymes come along and start the digestive process. In the end, only the waste product remains.


Though we usually consider our intelligence as the thing that characterizes us as a species—we might say that our ability to have extracellular digestion may be a strong part of what characterizes the Animal Kingdom.  In other words, we might say that what separates the Animal Kingdom from the protozoa is this kind of complicated digestion.

Many critics of Evolution for example, make the argument that the leap from very simple celled organism to the multiple celled, heterogeneous cells actually seems fairly dubious. The cells would somehow have to have known that they were going to work together.  Critics then argue that the only way that this could have occurred was if there was some sort of an intelligent plan guiding the organisms.

So, as it turns out, the distinction between intercellular and extracellular digestion actually touches on lots of important issues having to do with our place in the world.