Nutrition is the biological process by which an organism, such as a plant or animal, takes in and utilizes food. This food is converted to energy which is used to keep the organism alive. While plants and animals have distinctly different nutritional requirements, there are some commonalities.

Theories about nutrition have been posed throughout history. During the time of the ancient Greeks, Anaxagoras (c.500-c.428 B.C.) suggested that nutrition was a result of the fact that everything contained a small amount of everything else. For example, he believed that when food was eaten, the part of the food that was hair would become part of the hair while the part of it that was muscle would become muscle. Theories about plant nutrition were also advanced. For example, Aristotle believed that plants got all their nutritional needs from the soil. This theory was widely accepted until the seventeenth...