Color is the least reliable
<span>Food molecules like lipids, proteins and polysaccharides are broken down enzymatically via digestion process, which occurs in our intestine cells (digestive system). Those large polymeric molecules are broken down into their monomer subunits—proteins into amino acids, polysaccharides into sugars, and fats into fatty acids and glycerol. Formed small organic molecules are now ready for the oxidation (a process that produces ATP and consumes O2) which occurs partly in the cytosol and in the mitochondrion. Oxidation processes include glycolysis and citric acid cycle which are differently required in different tissues. Nervous system (nerve cells) rely almost entirely on a constant supply of <span>glucose<span> from the bloodstream. In contrast, liver cells supply glucose to actively contracting muscle system which needs a lot of ATP energy.</span></span></span>
The term pharynx may also be used to describe a differentialed portion of the invertebrate.
