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.
The basic structure of carbohydrates is a sugar molecule, and they are classified by how many sugar molecules they contain. Simple carbs: Simple carbohydrates, usually referred to as sugars, are naturally present in fruit, milk and other unprocessed foods.