Multiple Choice Questions (MCQs) for Class 12 Chemistry: Unit 10 Biomolecules
Access targeted multiple-choice questions for Unit 10 Biomolecules designed to align with the latest CBSE academic syllabus for Class 12 Chemistry. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.
Practice Unit 10 Biomolecules MCQs for Class 12 Chemistry
Navigate directly to the 50 objective questions for Unit 10 Biomolecules using the digital viewer below. Each practice set includes verified answer keys, allowing students to instantly cross-check their work and identify areas requiring further revision.
Multiple Choice Questions
(a) lipid
(b) cellulose
(c) protein
(d) vitamin
Show Answer & Explanation
Answer: (b) cellulose
Explanation:
1. Cellulose is the main structural constituent of the cell wall of plant cells.
Teacher's Note:
1. Cellulose is a linear polymer of β-D-glucose; humans cannot digest it as we lack the enzyme to break β-links.
(a) acidic amino acids
(b) essential amino acids
(c) basic amino acids
(d) non-essential amino acids
Show Answer & Explanation
Answer: (b) essential amino acids
Explanation:
1. Amino acids that the body cannot synthesise and must be supplied in the diet are called essential amino acids.
Teacher's Note:
1. Do not mix up the terms: non-essential amino acids can be made in the body.
(a) Alanine, tyrosine, cysteine
(b) Leucine, lysine, tryptophan
(c) Alanine, glutamine, lysine
(d) Leucine, proline, glycine
Show Answer & Explanation
Answer: (b) Leucine, lysine, tryptophan
Explanation:
1. Leucine, lysine, tryptophan are all essential amino acids.
Teacher's Note:
1. A set fails if even one member (alanine, glycine, proline, glutamine) is non-essential.
(a) Eutectic point
(b) Isoelectric point
(c) Effusion point
(d) Neutralization point
Show Answer & Explanation
Answer: (b) Isoelectric point
Explanation:
1. At the isoelectric point the amino acid exists as a zwitterion with no net charge, so it does not move in an electric field.
Teacher's Note:
1. Below pI an amino acid is a cation (moves to cathode); above pI it is an anion (moves to anode).
(a) H3N+–CH2COO−
(b) H3N+–CH2COOH
(c) H2NCH2COOH
(d) H2NCH2COO−
Show Answer & Explanation
Answer: (b) H3N+–CH2COOH
Explanation:
1. At pH 4, the medium is acidic and hence glycine exists as a cation:
2. H3N+–CH2–COO− (Zwitterion) + H+ → H3N+–CH2–COOH
Teacher's Note:
1. Glycine's pI is about 6; at a pH below pI the –COO− group picks up H+, leaving a cation.
(a) primary structure of proteins
(b) secondary structure of proteins
(c) tertiary structure of proteins
(d) quaternary structure of proteins
Show Answer & Explanation
Answer: (b) secondary structure of proteins
Explanation:
1. α-Helix and β-pleated sheet are the two types of secondary structure of proteins.
Teacher's Note:
1. Primary = sequence; secondary = local folding by H-bonds (α-helix, β-sheet); tertiary = overall 3-D folding.
Curdling of milk : A :: α-Helix : B (CBSE 2022)
(a) A = Primary structure, B = Secondary structure
(b) A = Denatured protein, B = Primary structure
(c) A = Secondary structure, B = Denatured protein
(d) A = Denatured protein, B = Secondary structure
Show Answer & Explanation
Answer: (d) A = Denatured protein, B = Secondary structure
Explanation:
1. Curdling of milk is a denatured protein while α-Helix denotes secondary structure.
Teacher's Note:
1. In curdling, lactic acid denatures milk protein; the primary structure stays, the higher structures are lost.
(a) peptide bonds
(b) van der Waals forces
(c) hydrogen bonds
(d) dipole-dipole interactions
Show Answer & Explanation
Answer: (c) hydrogen bonds
Explanation:
1. Both α-helix and β-pleated sheet are held by hydrogen bonds between >C=O and >N–H groups of peptide units.
Teacher's Note:
1. Peptide bonds make the primary chain; H-bonds give the secondary structure.
(a) peptides
(b) peptones
(c) proteones
(d) α-amino acids
Show Answer & Explanation
Answer: (d) α-amino acids
Explanation:
1. Proteins are finally hydrolysed in digestion to α-amino acids, which are absorbed into the blood.
Teacher's Note:
1. Digestion order: protein → proteoses → peptones → polypeptides → α-amino acids.
(a) Polysaccharides
(b) Vitamins
(c) Nucleotides
(d) Proteins
Show Answer & Explanation
Answer: (d) Proteins
Explanation:
1. Proteins are polymers of α-amino acids linked by peptide (–CO–NH–) bonds.
Teacher's Note:
1. Link the bond to the biomolecule: glycosidic – carbohydrates, peptide – proteins, phosphodiester – nucleic acids.
(a) 3
(b) 4
(c) 1
(d) 2
Show Answer & Explanation
Answer: (a) 3
Explanation:
1. Insulin has two polypeptide chains joined by two inter-chain disulphide bridges, and one more intra-chain disulphide bridge in chain A: total 3.
Teacher's Note:
1. Count both kinds: 2 linking chain A to chain B, plus 1 within chain A.
(a) Carbohydrates
(b) Proteins
(c) Lipids
(d) Enzymes
Show Answer & Explanation
Answer: (b) Proteins
Explanation:
1. Antibodies (immunoglobulins) are proteins produced by the body to fight foreign substances (antigens).
Teacher's Note:
1. Antibodies are globular proteins; they are not enzymes because they bind antigens rather than catalyse reactions.
(a) enzymes
(b) DNA
(c) vitamins
(d) hormones
Show Answer & Explanation
Answer: (c) vitamins
Explanation:
1. Vitamins cannot be synthesised by the body (with few exceptions such as vitamin D) and must be supplied in food.
Teacher's Note:
1. Hormones and enzymes are made by the body; vitamins are mainly taken from diet.
(a) Scurvy
(b) Pellagra
(c) Beri-Beri
(d) Cheilosis
Show Answer & Explanation
Answer: (d) Cheilosis
Explanation:
1. Riboflavin is vitamin B2; its deficiency causes cheilosis (fissuring at corners of mouth and lips).
Teacher's Note:
1. Pair them: B1 – beri-beri, B2 – cheilosis, niacin – pellagra, C – scurvy.
(a) Vitamin-A
(b) Vitamin-E
(c) Vitamin-B2
(d) Vitamin-K
Show Answer & Explanation
Answer: (d) Vitamin-K
Explanation:
1. Vitamin K is needed for clotting of blood; its deficiency increases blood clotting time.
Teacher's Note:
1. K for ‘koagulation’ is a handy memory aid.
(a) Vitamin B1
(b) Vitamin B2
(c) Vitamin B6
(d) Vitamin B12
Show Answer & Explanation
Answer: (d) Vitamin B12
Explanation:
1. Cyanocobalamine (contains cobalt) is vitamin B12.
Teacher's Note:
1. ‘Cobal’ in the name points to cobalt, found only in vitamin B12.
(a) ascorbic acid
(b) retinol
(c) calciferol
(d) thiamine
Show Answer & Explanation
Answer: (b) retinol
Explanation:
1. Vitamin A is retinol.
Teacher's Note:
1. Ascorbic acid = C, calciferol = D, thiamine = B1, retinol = A.
(a) vitamin D
(b) vitamin B group
(c) vitamin E
(d) vitamin A
Show Answer & Explanation
Answer: (c) vitamin E
Explanation:
1. Vitamin E (tocopherol) is called the antisterility vitamin; its deficiency causes loss of fertility.
Teacher's Note:
1. Vitamin E is fat soluble and also acts as an antioxidant.
(a) A, D
(b) A, B
(c) A, C
(d) D, B
Show Answer & Explanation
Answer: (a) A, D
Explanation:
1. Vitamins A, D, E and K are fat soluble and are absorbed along with fats; B and C are water soluble.
Teacher's Note:
1. Any option containing B or C can be rejected straight away, since these are water soluble.
(a) nucleosides
(b) nucleotides
(c) amino acids
(d) glucose
Show Answer & Explanation
Answer: (b) nucleotides
Explanation:
1. Nucleic acids are polynucleotides, i.e., polymers of nucleotides.
Teacher's Note:
1. Nucleoside = base + sugar; nucleotide = base + sugar + phosphate. Only nucleotides can join by phosphodiester links.
(a) a pentose sugar and phosphoric acid
(b) a nitrogenous base and phosphoric acid
(c) a nitrogenous base and pentose sugar
(d) a nitrogenous base, a pentose sugar and phosphoric acid
Show Answer & Explanation
Answer: (c) a nitrogenous base and pentose sugar
Explanation:
1. Nucleosides contain a nitrogenous base and a pentose sugar.
Teacher's Note:
1. Adding the phosphate group to a nucleoside gives a nucleotide.
(a) base + sugar
(b) base + phosphate
(c) sugar + phosphate
(d) base + sugar + phosphate
Show Answer & Explanation
Answer: (d) base + sugar + phosphate
Explanation:
1. A nucleotide is made of three units: a nitrogenous base, a pentose sugar and a phosphate group.
Teacher's Note:
1. Nucleotide = nucleoside + phosphate.
(a) are polymers of nucleotides
(b) are always double stranded
(c) have similar kind of sugar
(d) have similar type of pyrimidine bases
Show Answer & Explanation
Answer: (a) are polymers of nucleotides
Explanation:
1. Both DNA and RNA are polynucleotides. DNA is double stranded with deoxyribose and thymine; RNA is single stranded with ribose and uracil.
Teacher's Note:
1. List the differences (strands, sugar, pyrimidine base) and the one common feature stands out.
(a) cytosine
(b) guanine
(c) adenine
(d) thymine
Show Answer & Explanation
Answer: (d) thymine
Explanation:
1. Thymine is present in DNA but not in RNA.
Teacher's Note:
1. Thymine is 5-methyluracil – the methyl group is the only difference from uracil.
(a) adenine with thymine
(b) thymine with guanine
(c) cytosine with adenine
(d) uracil and adenine
Show Answer & Explanation
Answer: (a) adenine with thymine
Explanation:
1. In DNA, adenine pairs with thymine (two H-bonds) and guanine pairs with cytosine (three H-bonds).
Teacher's Note:
1. A–U pairing occurs in RNA, not DNA.
(a) cytosine
(b) thymine
(c) adenine
(d) uracil
Show Answer & Explanation
Answer: (a) cytosine
Explanation:
1. In DNA, guanine pairs with cytosine through three hydrogen bonds, while adenine pairs with thymine through two.
Teacher's Note:
1. A purine always pairs with a pyrimidine: A=T and G≡C.
(a) nucleotide
(b) nucleoside
(c) purine base
(d) pyrimidine base
Show Answer & Explanation
Answer: (b) nucleoside
Explanation:
1. Adenosine = adenine (base) + ribose (sugar); it has no phosphate, so it is a nucleoside.
Teacher's Note:
1. Names ending in -osine/-idine (adenosine, cytidine) are nucleosides; adding phosphate gives AMP, CMP (nucleotides).
Assertion–Reason Questions
Assertion (A): An aqueous solution of glycine at pH = 7 is not electrically neutral.
Reason (R): Glycine exists in electrically neutral form at isoelectric point (pI).
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation
Answer: (a) Both A and R are true, and R is the correct explanation of A.
Explanation:
1. Glycine is electrically neutral only at its isoelectric point (pI ≈ 6). pH 7 is above its pI, so some glycine molecules lose H+ to form anions and the solution is not electrically neutral.
Teacher's Note:
1. Neutral pH (7) and the isoelectric point are different things; each amino acid has its own pI.
Assertion (A): Insulin is a globular protein.
Reason (R): Globular proteins are water soluble.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation
Answer: (a) Both A and R are true, and R is the correct explanation of A.
Explanation:
1. Insulin has a spherical, folded polypeptide structure and is soluble in water; hence it is a globular protein.
Teacher's Note:
1. Globular proteins (insulin, albumins, haemoglobin, enzymes) are water soluble; fibrous proteins (keratin, myosin) are insoluble.
Assertion (A): Haemoglobin is a globular protein.
Reason (R): It contains four subunits.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation
Answer: (b) Both A and R are true, but R is not the correct explanation of A.
Explanation:
1. Haemoglobin is soluble in water (its chains are folded into a spherical shape), therefore it is a globular protein. Having four subunits relates to its quaternary structure.
Teacher's Note:
1. Number of subunits describes quaternary structure; it does not decide whether a protein is globular or fibrous.
Assertion (A): During curdling of milk protein present in milk is denatured.
Reason (R): Denaturation is caused by lactic acid formed from lactose (present in milk) by the bacteria present in milk.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation
Answer: (a) Both A and R are true, and R is the correct explanation of A.
Explanation:
1. Bacteria convert lactose into lactic acid; the change in pH denatures (coagulates) the milk protein, causing curdling.
Teacher's Note:
1. Change in pH, heat and chemicals all denature proteins by breaking H-bonds; primary structure stays intact.
Assertion (A): Keratin is a fibrous protein.
Reason (R): It is soluble in water.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation
Answer: (c) A is true, but R is false.
Explanation:
1. Keratin is insoluble in water.
Teacher's Note:
1. Fibrous proteins are insoluble in water; globular proteins are soluble.
Assertion (A): All enzymes are proteins but all proteins are not enzymes.
Reason (R): Enzymes are biocatalysts and possess a stable configuration having an active site pocket.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation
Answer: (a) Both A and R are true, and R is the correct explanation of A.
Explanation:
1. Only those proteins which have a stable configuration with an active site, at which the substrate binds, can act as biocatalysts (enzymes).
Teacher's Note:
1. Many proteins are structural (keratin) or transport proteins (haemoglobin), not catalysts.
Assertion (A): Vitamin C is also called ascorbic acid.
Reason (R): It contains a –COOH group.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation
Answer: (c) A is true, but R is false.
Explanation:
1. It does not contain a –COOH group but behaves like an acid.
Teacher's Note:
1. Vitamin C is acidic due to its enolic –OH groups, not a carboxyl group.
Assertion (A): Thymine occurs in RNA.
Reason (R): Thymine is a pyrimidine.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation
Answer: (d) A is false, but R is true.
Explanation:
1. Thymine does not occur in RNA but occurs in DNA.
Teacher's Note:
1. The pyrimidines are C, T and U; T is in DNA only and U is in RNA only.
Assertion (A): Adenosine is a nucleotide.
Reason (R): It contains adenine and ribose sugar.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation
Answer: (d) A is false, but R is true.
Explanation:
1. Adenosine is a nucleoside.
Teacher's Note:
1. Base + sugar = nucleoside; base + sugar + phosphate = nucleotide.
Assertion (A): The two strands in double strand helix structure of DNA are complementary to each other.
Reason (R): Disulphide bonds are formed between specific pairs of bases.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation
Answer: (c) A is true, but R is false.
Explanation:
1. Hydrogen bonds are formed between specific pair of bases.
Teacher's Note:
1. Disulphide bridges belong to proteins (between cysteine units), never to nucleic acids.
Assertion (A): DNA and RNA are chiral molecules.
Reason (R): Their chirality is due to chiral phosphate ester units.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation
Answer: (c) A is true, but R is false.
Explanation:
1. Chirality of DNA and RNA is due to chirality of D-sugars.
Teacher's Note:
1. The chiral centres are the carbons of D-ribose or D-2-deoxyribose; the phosphate units are not chiral.
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