21. Lipids and Carbohydrates   Previous PageNext Page
       Polysaccharides: Cellulose and Starch

If we could digest the, b-1,4 glucose bond of cellulose, then almost limitless new food supplies would become available to us. (The dark side of this new food supply is that we probably would permit the population of Earth to grow unchecked until we had stripped the planet bare like locusts. H. sapiens has not yet been known for his self-control.) However, our digestive enzymes cannot break the cellulose bond. Aside from some bacteria and protozoa, the only organisms that can digest cellulose are termites, a few species of cockroaches, and ruminant mammals such as cows, sheep, goats, and camels.

These cellulose eating insects and mammals can function only because they have populations of bacteria and protozoa in their digestive tracts that chew up the b-1,4 bonds with the enzyme cellulase, thereby providing their hosts with digestible materials. In cattle the microorganisms are housed in the rumen, the first of four stomachs. Here bacteria convert plant fibers into acetic, propionic, and butyric acids. These acids are absorbed by the cow as nutrients through the walls of the rumen, and generate 60 to 80 liters Of CO2 and methane gas per day, which must be eliminated by continual belching.

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