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 vs Complex Carbs. The difference between a simple and complex carb is in how quickly it is digested and absorbed - as well as it's chemical structure. Carbohydrates are sugars that come in 2 main forms - simple and complex. This is also referred to as simple sugars and starches. The difference between a simple and complex carb is in how quickly it is digested and absorbed - as well as it's chemical structure.