Biomolecules
11 solved NEET Biology previous year questions on Biomolecules, each with the correct answer and a full explanation.
Q1
Glucose on prolonged heating with HI gives
✓ Correct answer: a) -hexane
ExplanationGlucose on prolonged heating with HI (hydroiodic acid) undergoes a complete reduction reaction.HI is a strong reducing agent that removes all the oxygen atoms (from the aldehyde and hydroxyl groups) and replaces them with hydrogen atoms.This results in the formation of a straight-chain alkane with six carbon atoms, which is n- hexane (C₆H₁₄).
Q2
Which of the following statement is not true for glucose? [JEE Main 2020, 8 Jan (Shift 1)]
✓ Correct answer: b) Glucose gives Schiff's test for aldehyde
ExplanationThe statement that is not true for glucose is that glucose gives Schiff's test for aldehyde.Here is an analysis of each statement: A. Glucose exists in two crystalline forms α and β: This statement is true.Glucose forms cyclic hemiacetal structures and can exist in two anomeric forms, α-D-glucopyranose and β-D- glucopyranose.B. Glucose gives Schiff's test for aldehyde: This statement is not true (false).Although glucose has an aldehyde group in its open-chain structure, in an aqueous solution, it predominantly exists in a stable cyclic (pyranose) form where the aldehyde group is involved in a hemiacetal linkage and is not free to react with Schiff's reagent.Thus, it gives a negative Schiff's test.C. Glucose reacts with hydroxylamine to form oxime: This statement is true.Because the cyclic form of glucose can exist in equilibrium with a small amount of the open-chain form, it can still undergo some reactions characteristic of aldehydes, such as reacting with hydroxylamine (NH2O ) to form an oxime.D. The pentaacetate of glucose does not react with hydroxylamine to give oxime: This statement is also true.In glucose pentaacetate, the aldehyde group is protected by acetylation, and all hydroxyl groups are also acetylated.This prevents the formation of the open-chain structure required to react with hydroxylamine to form an oxime.
Q3
Which of the following statements is not true about RNA? [JEE Main 2019, 12 Apr (Shift 1)]
✓ Correct answer: a) It has always double stranded α-helix structure
ExplanationRNA is usually single-stranded and does not form a double-stranded α-helix structure.Double-stranded RNA is rare and occurs only in some viruses.
Q4
Which of the following are not secondary metabolites in plants? [NEET 2021]
✓ Correct answer: a) Amino acids, glucose
ExplanationAmino acids, glucose are not secondary metabolites rather they are the examples of primary metabolites.Rest all other belongs to secondary metabolites.
Q5
Water present in human body is
✓ Correct answer: d) 65-70 %
ExplanationCorrect answer: Option D Water is the most abundant component of living cells, making up 60–95% of a cell’s total mass, depending on the cell type.In the human body, water is a major constituent of both intracellular fluid (inside cells) and extracellular fluid (blood plasma, lymph, and interstitial fluid).On average, about 65– 70% of the human body weight is water.This high water content is essential for maintaining cell turgor, biochemical reactions, nutrient transport, and temperature regulation.Organs like the brain, kidneys, and muscles contain a higher percentage of water, whereas bones and fat have lower water content.Water also provides a medium for enzymes to function and facilitates the movement of solutes, gases, and waste products.Thus, considering the average water content in the human body, the correct option is D – 65– 70%.
Q6
Which protein found in maximum amount?
✓ Correct answer: d) RuBisCO
ExplanationRuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is widely considered the most abundant protein on Earth (in the biosphere).It is a critical enzyme involved in the first major step of carbon fixation during photosynthesis in plants, algae, and cyanobacteria, converting atmospheric carbon dioxide into organic molecules.Its essential role in sustaining life and the vast amount of plant biomass on the planet means it is produced in large quantities, making up a significant percentage (up to 50%) of total soluble protein in plant leaves.A. Catalase: Catalase is a highly efficient enzyme that breaks down hydrogen peroxide, protecting cells from damage, and is found in most living organisms.B. Zinc carbonic anhydrase: Carbonic anhydrase is a very fast-acting enzyme vital for maintaining acid-base balance and transporting carbon dioxide in biological systems.C. Transferase: Transferases are a class of enzymes that catalyze the transfer of functional groups between molecules and are involved in many biochemical pathways.This is a general class of enzymes.
Q7
Which one of the following is not a constituent of cell membrane?
✓ Correct answer: b) Proline
ExplanationProline is an amino acid and is not a structural component of the cell membrane.Cell membranes mainly contain phospholipids, glycolipids, proteins, and cholesterol.Answer: B — Proline
Q8
The essential chemical components of many coenzymes are
✓ Correct answer: b) vitamins
ExplanationThe essential chemical components of many coenzymes are vitamins.Coenzymes are non-protein organic molecules that bind to enzymes to assist in their catalytic activity.Many coenzymes, particularly those derived from the water-soluble B-complex vitamins, cannot be synthesized by the body and must be obtained from the diet.Examples include:Niacin (Vitamin B3) is a precursor for the coenzymes NAD and NADP (nicotinamide adenine dinucleotide and its phosphate).Riboflavin (Vitamin B2) is a precursor for FAD and FMN (flavin adenine dinucleotide and flavin mononucleotide).
Q9
The correct statement regarding RNA and DNA, respectively is
✓ Correct answer: d) the sugar component in RNA is ribose and the sugar component in DNA is - deoxyribose.
ExplanationThe correct answer is: 4 — the sugar component in RNA is ribose and the sugar component in DNA is 2′-deoxyribose Explanation: RNA contains the sugar ribose, which has a hydroxyl group (-OH) at the 2′ carbon.DNA contains 2′-deoxyribose, which lacks the hydroxyl group at the 2′ carbon, making it more stable.Arabinose is a sugar found in some plants but is not a component of nucleic acids.
Q10
Prosthetic groups differ from co-enzymes in that
✓ Correct answer: b) they (prosthetic groups) are tightly bound to apoenzymes
ExplanationBoth prosthetic groups and coenzymes are types of cofactors, which are non-protein components required for an enzyme's activity.The key difference lies in how they bind to the protein part of the enzyme, known as the apoenzyme.Prosthetic groups are permanently and tightly bound to the apoenzyme, often through strong covalent bonds.An example is the heme group in hemoglobin, which is essential for its function.Coenzymes are loosely and temporarily bound to the apoenzyme.They typically bind during the reaction and are released afterward.
Q11
The protein portion of an enzyme is called : [NEET 2025]
✓ Correct answer: a) Apoenzyme
ExplanationThe correct answer is Apoenzyme.An enzyme may consist of two parts: a protein portion and a non-protein component.The protein part alone of an enzyme is called the apoenzyme.By itself, the apoenzyme is usually inactive and cannot catalyse a reaction efficiently.For the enzyme to become fully functional, it often needs a cofactor, which may be a metal ion or an organic molecule.When the apoenzyme combines with its required cofactor, the complete and active enzyme formed is called a holoenzyme.A prosthetic group is a tightly bound cofactor, while a coenzyme is an organic cofactor that is loosely attached.Thus, among the given options, apoenzyme specifically refers to the protein portion of an enzyme and is the correct answer.
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