However, in the form of N2, nitrogen is unusable by all organisms except for a few primitive bacteria that are capable of converting N2 gas to ammonia (NH3). This process of conversion is called nitrogen fixation, and makes the nitrogen available for use by organisms.
1 Simple carbohydrates have very simple chemical structures and are made of small molecules. 2  Complex carbohydrates have very complex structures while the molecules are large, unlike simple carbohydrates.
Simple carbohydrates include monosaccharides (one-unit sugars) and disaccharides (two-unit sugars). Monosaccharides include glucose, fructose and galactose. These can be absorbed directly and don't require further breakdown from enzymes, unlike disaccharides and polysaccharides.