Home / IB DP Biology- B1.2 Proteins – IB Style Questions For SL Paper 1A

IB DP Biology- B1.2 Proteins - IB Style Questions For SL Paper 1A -New Syllabus

IBDP Biology SL Paper 1 - All Chapters

Question

The table shows some essential and non-essential amino acids. 

Essential amino acidsNon-essential amino acids
ValineAlanine
LysineGlycine
What is a valid conclusion for an amino acid in the table?
(A) Lysine is synthesized by the human body.
(B) Alanine can only be obtained from food.
(C) Glycine is not used in the human body.
(D) Valine must be supplied in the diet.
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{D}} \)

Essential amino acids cannot be synthesized by the human body in sufficient amounts and therefore must be obtained from the diet. Since valine is an essential amino acid, it must be supplied in food. In contrast, alanine and glycine are non-essential amino acids and can be synthesized by the body.

Question

How are amino acids joined together to form a dipeptide?
(A) Single bond between a carbon and a hydrogen
(B) Hydrolysis reaction forming a hydrogen bond
(C) Anabolism forming a double bond
(D) Condensation reaction forming a peptide bond
▶️ Answer/Explanation
Detailed solution

Amino acids are joined by a condensation reaction between the amino group of one amino acid and the carboxyl group of another. This reaction releases a water molecule and forms a covalent peptide bond.
✅ Answer: (D)

Question

What describes the structure of proteins?

I. Proteins are made from amino acids linked together by peptide bonds.
II. The sequence of amino acids in all proteins is the same.
III. A protein may consist of more than one polypeptide.

A. I and II only
B. I and III only
C. II and III only
D. I, II and III

▶️ Answer/Explanation

Answer: B. I and III only

Explanation:
Proteins are made of smaller units called amino acids, which are connected by peptide bonds to form a polypeptide chain. The sequence of amino acids in each protein is unique and determines how the protein folds and what function it performs. Some proteins are made of only one polypeptide, while others consist of two or more polypeptides working together.

Option Evaluation:

A. Incorrect – Statement I is correct, but Statement II is wrong. Not all proteins have the same amino acid sequence; each protein has a unique sequence.

B. Correct – Statement I is correct (proteins are made from amino acids linked by peptide bonds), and Statement III is also correct (some proteins consist of more than one polypeptide). This is the correct answer.

C. Incorrect – Statement II is false, so this option is wrong even though Statement III is correct.

D. Incorrect – Statement II is incorrect, so all three statements cannot be true.

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