**Core Concept**
Essential amino acids are those that cannot be synthesized by the human body and must be obtained through the diet. There are nine essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

**Why the Correct Answer is Right**
Essential amino acids play a crucial role in protein synthesis, enzyme function, and hormone production. They cannot be synthesized by the human body and must be obtained through the diet. The correct answer will be an amino acid that can be synthesized by the human body.

**Why Each Wrong Option is Incorrect**
* **Option A:** Histidine is an essential amino acid, it cannot be synthesized by the human body and is required for the synthesis of histamine and other biologically important compounds.
* **Option B:** Lysine is an essential amino acid, it plays a crucial role in protein synthesis and is required for the growth and development of cells.
* **Option C:** Arginine is a semi-essential amino acid, but it is not a correct answer as it can be synthesized by the human body under normal conditions. However, in certain situations such as liver disease or severe burns, arginine becomes essential. The correct answer should be a non-essential amino acid.
* **Option D:** Glutamate is a non-essential amino acid, it can be synthesized by the human body through the transamination of alpha-ketoglutarate.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the essential amino acid requirements can vary depending on age, sex, and overall health status. Additionally, certain medical conditions such as liver disease or severe burns can make previously non-essential amino acids essential.

**Correct Answer:** D. Glutamate