Identify the essential amino acids from the following.
(A) Threonine
(B) Serine
(C) Histidine
(D) Lysine
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A), (C) and (D) only
Amino acids that the body can make are non-essential amino acids; those that the body cannot make and that must be taken in the diet are essential amino acids. Ten amino acids are essential: valine, leucine, isoleucine, arginine, lysine, threonine, methionine, phenylalanine, tryptophan and histidine.
(A) Threonine — Correct. It cannot be synthesised in the body and must come from food.
(B) Serine — Incorrect. Serine is non-essential: the body makes it from intermediates of glucose metabolism (and from glycine).
(C) Histidine — Correct. It is one of the ten essential amino acids.
(D) Lysine — Correct. Lysine, the basic amino acid with a \( \ce{H2N-(CH2)4-} \) side chain, is essential.
NCERT (2026-27 edition):
Classification of Amino Acids – “… The amino acids, which can be synthesised in the body, are known as non- essential amino acids. On the other hand, those which cannot be synthesised in the body and must be obtained through diet, are known as essential amino acids (marked with asterisk in Table 10.2).”
