NEET (UG) · Zoology, Class 11
Biomolecules: NEET PYQ, 2018–2026
Biomolecules (Zoology, Class 11) has been asked 25 times in the 7 NEET papers from 2018, 2020, 2021, 2023, 2024, 2025 and 2026: about 3.6 questions a paper, 9% of all Zoology questions. It is the 4th most-asked of 15 Zoology chapters. NEET 2026 had 2 from it. Last checked 28 October 2026.
Questions per paper
Year by year.
| Year | Questions |
|---|---|
| 2018 | 1 |
| 2020 | 4 |
| 2021 | 4 |
| 2023 | 4 |
| 2024 | 6 |
| 2025 | 4 |
| 2026 | 2 |
From 2021 to 2024 each paper had 200 questions (a Section B with a choice); the others had 180.
Inside the chapter
Topics asked most.
- Enzymes10
- Carbohydrates, lipids and nucleic acids8
- Proteins and amino acids5
- Metabolic pathways2
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10 Biomolecules questions to practise.
Our own questions, written in the NEET pattern and checked, each with an explanation. Pick an option to see the answer.
Q1 · Zoology · Biomolecules
In a DNA double helix, which pair of nitrogenous bases is held together by three hydrogen bonds?
Answer: (A)
Principle: in DNA, a purine always pairs with a pyrimidine. Adenine pairs with thymine through two hydrogen bonds, and guanine pairs with cytosine through three hydrogen bonds. Pairing of two purines or two pyrimidines would not fit the uniform width of the helix.
Q2 · Zoology · Biomolecules
In a double-stranded DNA molecule, adenine makes up 30% of the total bases. What percentage of the bases is guanine?
Answer: (A)
Principle: in double-stranded DNA, base pairing follows A with T and G with C (Chargaff's relation: A = T and G = C). Step 1: A = 30%, so T = 30% as well. Step 2: A + T = 60%, so G + C = 100% - 60% = 40%. Step 3: G = C, so G = 40% / 2 = 20%. The tempting errors are to pair A with G (giving 30%), to split the wrong remainder (35%), or to stop at 100% - A (70%) without accounting for both the T and the G/C split.
Q3 · Zoology · Biomolecules
Quinine, used to treat malaria, is extracted from the bark of a tree. Which class of secondary metabolite does it belong to, and which feature of its structure defines that class?
Answer: (A)
Quinine is a nitrogen-containing alkaloid derived from Cinchona bark. Classify a secondary metabolite by its chemical features: a nitrogen-containing ring indicates an alkaloid, isoprene units indicate a terpenoid, and a large repeating unit indicates a polymer. Quinine's structure matches the alkaloid definition, so the correct answer is alkaloid.
Q4 · Zoology · Biomolecules
The primary structure of a protein is:
Answer: (A)
The sequence of amino acids — which is the first, the second and so on — is the primary structure of a protein. The first amino acid is the N-terminal and the last the C-terminal amino acid.
Q5 · Zoology · Biomolecules
In a beta-pleated sheet, which pair of groups forms the hydrogen bonds that stabilise the structure?
Answer: (C)
Principle: secondary structure is stabilised by hydrogen bonds between backbone C=O and N-H groups. In an alpha helix these bonds run along one chain, between residues about four positions apart. In a beta-pleated sheet, the strands lie side by side and the bonds form between neighbouring segments, so the sheet is held together by inter-strand backbone hydrogen bonds. Side chains do not provide the main bonding pattern.
Q6 · Zoology · Biomolecules
Which statement correctly describes the forces that hold a substrate in the active site during enzyme catalysis, and what happens to the enzyme at the end of the catalytic cycle?
Answer: (B)
Principle: the enzyme–substrate complex is formed by weak, reversible, non-covalent interactions (hydrogen bonds, ionic attractions, van der Waals and hydrophobic contacts) between the substrate and specific amino acid residues of the active site. Substrate specificity comes from the complementarity of this site. Once the reaction proceeds, the product has a lower affinity for the site, so it is released, and the enzyme returns to its original form. Hence it is not consumed and can catalyse many cycles. Distinguish the stable, permanent bonds in a protein (peptide bonds in the backbone, disulphide bridges) from the transient bonds that hold substrate during catalysis.
Q7 · Zoology · Biomolecules
One molecule of pyruvate is converted into acetyl CoA by the pyruvate dehydrogenase complex before entering the Krebs cycle. How many molecules of CO2 and NADH are produced per molecule of pyruvate in this step?
Answer: (A)
Pyruvate has three carbons. In the link reaction, the carboxyl carbon is removed as CO2, NAD+ is reduced to NADH, and the remaining two-carbon acetyl group is attached to coenzyme A. So one pyruvate gives one CO2 and one NADH. Remember to scale by two for a full glucose molecule.
Q8 · Zoology · Biomolecules
Compared with a saturated fatty acid of the same chain length, why does a cis double bond in a fatty acid lower the melting point?
Answer: (A)
Saturated hydrocarbon tails are straight and pack tightly, so their melting point is higher. A cis double bond forces a bend of about 30 degrees, which disrupts the packing. Since the only forces between tails are weak van der Waals forces, less energy is needed to melt, giving a lower melting point. This is why unsaturated fats such as vegetable oils are liquid at room temperature.
Q9 · Zoology · Biomolecules
Chitin, the polymer that forms the exoskeleton of arthropods, is structurally closest to cellulose. Which statement correctly describes how chitin differs from cellulose?
Answer: (A)
Principle: cellulose is a beta-1,4 linked homopolymer of glucose, and chitin follows the same backbone pattern. Apply it: in chitin, each monomer is N-acetylglucosamine, meaning the C-2 hydroxyl of glucose is replaced by an acetamido group (-NHCOCH3). Students who recall the backbone pattern but not the substituent make the mistake of choosing a option with a different linkage or an extra component. Identify the substituent change at C-2 as the key difference.
Q10 · Zoology · Biomolecules
In which compartment of the mitochondrion do the reactions of the Krebs (citric acid) cycle take place?
Answer: (A)
Principle: the Krebs cycle takes acetyl CoA and oxidises it to CO2, producing NADH, FADH2 and GTP/ATP. Its enzymes are in the mitochondrial matrix. The matrix is separate from the membranes where the electron transport chain sits.
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All 25 real NEET questions from Biomolecules.
The questions from the actual papers, with the official answer and an explanation for each — chapter by chapter, or as full timed papers.
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About Biomolecules in NEET.
How many questions come from Biomolecules in NEET?
Biomolecules (Zoology, Class 11) has been asked 25 times in the 7 NEET papers from 2018, 2020, 2021, 2023, 2024, 2025 and 2026: about 3.6 questions a paper, 9% of all Zoology questions. It is the 4th most-asked of 15 Zoology chapters. NEET 2026 had 2 from it.
Which topics of Biomolecules are asked most in NEET?
Enzymes (10), Carbohydrates, lipids and nucleic acids (8), Proteins and amino acids (5), Metabolic pathways (2), counted over the papers from 2018–2026.
Is Biomolecules important for NEET 2027?
It is in the syllabus in force, so it can be asked. By past papers it ranks 4 of 15 in Zoology; use that to decide how much time it gets, not whether to study it.
Where can I solve Biomolecules NEET previous year questions?
On Nikaalle, free: sign up and practise every past NEET question from Biomolecules with an explanation for each, or sit the full papers timed. The ten questions on this page are our own, written in the same pattern.
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