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.
What makes one carbohydrate different from another is the number of sugar units it contains and how the units are linked together. 1  Simple carbohydrates: These carbohydrates have only one or two units of sugar. A carbohydrate with one unit of sugar is called a simple sugar or a monosaccharide (mono = one; saccharide = sugar). Fructose (fruit sugar) is a monosaccharide, and so are glucose (blood sugar), the sugar produced when you digest carbohydrates, and galactose, the sugar derived from digesting lactose (milk sugar). A carbohydrate with two units of sugar is called a double sugar or a disaccharide (di = two). Sucrose (table sugar), which is made of one unit of fructose and one unit of glucose, is a disaccharide. Complex carbohydrates: Also known as polysaccharides (poly = many), these carbs have more than two units of sugar linked together.