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.
Carbs are converted to energy (glucose) more quickly and easily than protein and fat. Simple carbs convert the fastest (sugar is a simple carb), while complex carbs require more digestion because they are larger molecules. Fiber is one type of carb that we tend not to get enough of.