Final answer:
Glycine is the non-essential amino acid among the options given, while Valine, Lysine, and Threonine are essential amino acids and must be obtained through diet.
Step-by-step explanation:
Among the amino acids listed, Glycine is classified as a non-essential amino acid. Non-essential amino acids are those that can be synthesized by the human body and do not necessarily need to be obtained from dietary sources. In contrast, Valine, Lysine, and Threonine are all considered essential amino acids, meaning they must be obtained through the diet as the body cannot produce them on its own.