Final answer:
Essential amino acids are amino acids that cannot be synthesized by the body and must be consumed through diet. There are nine essential amino acids.
Step-by-step explanation:
The body is able to synthesize most of the amino acids from components of other molecules; however, nine cannot be synthesized and have to be consumed in the diet. These are known as the essential amino acids. The 9 essential amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.