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.
Carbohydrates are present in food in the form of starch, sugar and fiber. A carbohydrate is a molecule containing carbon, oxygen and hydrogen, and can be either simple or complex. Both simple and complex carbohydrates can be healthy food options. Simple carbohydrates are monosaccharides and disaccharides.