AIIMS 2019 Zoology Amino Acids MCQ Question

Option D is correct because glycine and serine are indeed classified as non-essential amino acids, but tyrosine is considered a conditionally essential amino acid, as it can be synthesized from phenylalanine in the body under normal circumstances. This means that while glycine and serine do not need to be obtained from the diet, tyrosine may require dietary intake if phenylalanine is not adequately supplied. Options A and B are incorrect because they misrepresent the classification of tyrosine; option A incorrectly states that all three are non-essential, while option B fails to acknowledge the conditional status of tyrosine. Understanding the distinction between essential and non-essential amino acids is crucial for nutritional science and metabolic health.