**Question:** Limiting amino acid in soyabean is -

A. Lysine
B. Leucine
C. Methionine
D. Threonine

**Core Concept:** Amino acids are the building blocks of proteins and are essential for human nutrition. Ingested proteins are broken down into their constituent amino acids, which can be absorbed into the bloodstream and used by the body for various functions. Amino acids can be classified as essential and non-essential based on whether they can be synthesized by the human body or not.

**Why the Correct Answer is Right:** Soyabean is a rich source of protein and contains all essential amino acids, including Lysine. Lysine is considered the limiting amino acid in soyabean because its concentration is the lowest compared to the other essential amino acids in the protein profile of soyabean. This means that the intake of soyabean alone may not be sufficient to meet the daily requirement for Lysine in the diet, necessitating the consumption of other protein sources to ensure adequate Lysine intake.

**Why Each Wrong Option is Incorrect:**

**Option A (Leucine):** Leucine is an essential amino acid, but it is not the limiting amino acid in soyabean. Leucine is more abundant than lysine in soyabean, making lysine the limiting amino acid.

**Option B (Methionine):** Methionine is an essential amino acid, but it is not the limiting amino acid in soyabean. Methionine concentration in soyabean is higher than lysine.

**Option C (Threonine):** Threonine is an essential amino acid, but it is not the limiting amino acid in soyabean. Threonine concentration in soyabean is higher than lysine.

**Option D (Lysine):** As explained earlier, lysine is the limiting amino acid in soyabean due to its lower concentration compared to other essential amino acids in the protein profile of soyabean.

**Core Concept:** Amino acid profiles vary among different proteins, and the concept of limiting amino acids is crucial for understanding protein quality and the need for a balanced diet.

**Why Each Wrong Option is Incorrect:**

1. **Option A (Leucine):** Leucine is an essential amino acid, but it is not the limiting amino acid in soyabean. Leucine concentration in soyabean is higher than lysine.
2. **Option B (Methionine):** Methionine is an essential amino acid, but it is not the limiting amino acid in soyabean. Methionine concentration in soyabean is higher than lysine.
3. **Option C (Threonine):** Threonine is an essential amino acid, but it is not the limiting amino acid in soyabean. Threonine concentration in soyabean is higher than lysine.
4. **Option D (Lysine):** As explained earlier, lysine is the limiting amino acid in soyabean due to its lower concentration compared to other essential amino acids in the protein profile of soyabe