Why are some amino acids described as essential amino acids?
a) they are the ones most used in the body.
b) they can be stored in the body.
c) they are the only ones needed by the body.
d) they cannot be made by the body.

Option (D) is the correct answer.

Explanation:

Organic compounds which are simple and contains carboxylic acid group (COOH) and amino group are known as amino acids.

Amino acids which are synthesized by the human body are known as non-essential amino acids.

For example, alanine, aspartic acid etc are non-essential amono acids.

Whereas amino acids which are not synthesized by human body are known as essential amino acids.

For example, arginine, histidine, isoleucine etc are all essential amino acids.

Therefore, we can conclude that some amino acids described as essential amino acids because they cannot be made by the body.