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 are those that are more quickly digested. They are often added to processed and prepared foods in the form of refined sugars and processed sweeteners. Some sources of carbohydrates are healthier than others. Learn how many carbs you need and which carbs to stay away from.