**Core Concept**
Glutamine plays a crucial role in the detoxification of ammonia in the human body by facilitating its conversion to urea through the urea cycle. This process occurs primarily in the liver and is essential for maintaining nitrogen balance and preventing ammonia toxicity.

**Why the Correct Answer is Right**
Glutamine acts as a nitrogen acceptor, combining with ammonia to form glutamine. This reaction is catalyzed by the enzyme glutamine synthetase. The glutamine molecule then undergoes a series of reactions in the urea cycle, ultimately resulting in the production of urea, which is excreted by the kidneys. This process is vital for eliminating excess nitrogen from the body and preventing ammonia toxicity, which can cause neurological damage and other complications.

**Why Each Wrong Option is Incorrect**
**Option B:** Alanine is an amino acid involved in glucose metabolism and the glucose-alanine cycle, but it does not play a direct role in ammonia detoxification.
**Option C:** Methionine is an essential amino acid with various functions, including serving as a precursor for other sulfur-containing compounds. However, it is not directly involved in ammonia detoxification.
**Option D:** Glycine is a non-essential amino acid that plays a role in the synthesis of proteins, creatine, and other compounds. While it is involved in some nitrogen-containing compounds, it is not the primary amino acid responsible for ammonia detoxification.

**Clinical Pearl / High-Yield Fact**
The urea cycle, also known as the ornithine cycle, is a critical process for eliminating excess nitrogen from the body. Glutamine synthetase is the enzyme responsible for the first step of ammonia detoxification, converting ammonia into glutamine. This process is essential for maintaining nitrogen balance and preventing ammonia toxicity.

✓ Correct Answer: A. Glutamine