This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Which of the following is a Semi-essential aminoacid- 
Select and explain. 
A. Tyrosine, B. Histidine, C. Alanine, D. Isoleucine
B: Histidine
Answer: B: Histidine 
Explanation: Ans. is 'b' i.e., Histidine* Histidine is a semiessential aminoacid, as this aminoacid can be synthesized by metabolic pathways in human. But the synthetic rate is not sufficient enough to meet the increased demands during growth spurts.* Tyrosine and Alanine are non essential aminoacids* Isoleucine is an essential aminoacid