Which amino acid required in infants and not in adults?
**Core Concept**
The question tests the knowledge of essential amino acids, which are necessary for human growth and development. In infants, the body requires a specific amino acid that serves as a precursor for neurotransmitter synthesis, muscle growth, and other critical functions.
**Why the Correct Answer is Right**
The correct answer is **Histidine**. Histidine is an essential amino acid, meaning it cannot be synthesized by the human body and must be obtained through the diet. Infants require histidine for the synthesis of histamine, a neurotransmitter involved in various physiological processes, including gut motility and immune response. Histidine is also crucial for the growth and development of muscles, making it an essential component of infant nutrition.
**Why Each Wrong Option is Incorrect**
* **Option A:** Glutamine is a semi-essential amino acid, meaning it is conditionally essential, and its requirements can be met through dietary means. While it is essential for adults under certain conditions, it is not unique to infant nutrition.
* **Option B:** Leucine is a branched-chain amino acid (BCAA) that plays a crucial role in muscle growth and recovery. While it is essential for overall health, it is not unique to infant nutrition.
* **Option C:** Lysine is an essential amino acid involved in various bodily functions, including protein synthesis and immune response. However, it is not specifically required in infants to the extent that histidine is.
**Clinical Pearl / High-Yield Fact**
Remember that histidine is a critical amino acid for infant growth and development, particularly for neurotransmitter synthesis and muscle growth. This knowledge can help guide nutritional recommendations for infants and young children.
**Correct Answer:** C. Histidine.