Final answer:
The nonessential amino acid in human nutrition among the provided options is Glutamine (C). Nonessential amino acids can be synthesized by the body, and Glutamine is not required to be obtained through diet under normal physiological conditions.
Step-by-step explanation:
In human nutrition, nonessential amino acids are those that our body has the ability to synthesize by itself, meaning that they do not necessarily need to be consumed through the diet. Among the options provided, Glutamine (C) is the correct answer, as it is one of the nonessential amino acids. This is in contrast to essential amino acids, which must be obtained from food because the body cannot produce them sufficiently.
Glutamine is involved in a variety of biochemical processes, including protein synthesis and regulation of acid-base balance in the kidneys. Its synthesis is part of a shared pathway involving glutamate and proline. Although conditionally essential in certain situations of stress or illness, under normal conditions, glutamine is considered nonessential because the body can produce it.
Other options such as Oxygen (A), Water (B), and Vitamin C (D) are not amino acids. Oxygen is a gas essential for cellular respiration, water is vital for all forms of life, and vitamin C is a water-soluble vitamin necessary for various bodily functions such as the synthesis of collagen.