BiomoleculesNEET MCQs with solutions

Not quite — the answer is C.

NCERT defines carbohydrates as polyhydroxy aldehydes or ketones, or compounds yielding them on hydrolysis. Option D fails because deoxyribose (C5H10O4) does not fit CnH2nOn, so formula alone cannot define the class.

Not quite — the answer is A.

Monosaccharides cannot be hydrolysed into simpler carbohydrates. Glucose is a monosaccharide; sucrose is a disaccharide, starch and cellulose are polysaccharides.

Not quite — the answer is D.

Fructose is a ketohexose, meaning its carbonyl group is a ketone at C-2. Glucose, galactose and mannose are all aldohexoses, with the carbonyl at C-1. Fructose is the predominant sugar in honey alongside glucose.

Not quite — the answer is C.

Enzymes are biological catalysts, almost all of which are proteins, and exhibit high specificity for their substrates and the reactions they catalyse. Ribozymes are the exception as catalytic RNA. Polysaccharides and lipids do not function as catalysts under normal cellular conditions.

Not quite — the answer is C.

Carbohydrates are defined as polyhydroxy aldehydes or ketones, or substances that yield them on hydrolysis. Option A is a trap — carbohydrates contain -OH groups but are not acids; they lack the -COOH group.

Not quite — the answer is B.

Amylopectin is the branched component of starch with alpha 1,6 branch points; it gives a purple-brown colour with iodine, while amylose (unbranched) gives the characteristic blue-black colour. Option A is the reversal trap.

Not quite — the answer is A.

Amino acids contain both an amino group and a carboxyl group attached to the same alpha carbon, along with a hydrogen atom and a variable R group. This alpha carbon arrangement is the defining structural feature of all standard amino acids.

Not quite — the answer is B.

Amino acids undergo internal acid-base reaction where the carboxyl group donates a proton to the amino group of the same molecule, forming a dipolar ion (zwitterion) bearing both a positive charge on nitrogen and a negative charge on oxygen. Option A is wrong because the transfer is internal, not to solvent.

Not quite — the answer is A.

Nucleic acids are long-chain polymers of repeating nucleotide units responsible for storage and transfer of genetic information. Amino acids form proteins; monosaccharides form polysaccharides; fatty acids form lipids.

Not quite — the answer is A.

A nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group — these three together form the basic structural unit of nucleic acids. Option B describes components unrelated to nucleotides.

Not quite — the answer is A.

Glucose has an aldehydic carbonyl group at C-1 making it an aldohexose. Fructose has a ketonic carbonyl group at C-2 making it a ketohexose. Options B and C misstate both structures. Option D reverses the classifications.

Not quite — the answer is B.

Maltose is formed from two glucose units connected by an α-1,4 glycosidic linkage. One anomeric carbon remains free, so maltose is a reducing sugar. Option C describes the linkage in sucrose. Option D describes the branch points in glycogen and amylopectin.

Not quite — the answer is A.

Enzymes are mostly proteinaceous biological catalysts that speed up biochemical reactions without being consumed. Some enzymes called ribozymes are RNA-based, but the vast majority are proteins as stated in NCERT. Option B confuses cofactors with enzymes; options C and D are categorically incorrect.

Not quite — the answer is B.

Enzyme specificity arises from the precise 3D arrangement of amino acid residues at the active site, which is complementary only to a particular substrate — analogous to the lock-and-key mechanism. Option A incorrectly describes induced fit as causing non-specificity; induced fit still maintains specificity.

Not quite — the answer is A.

Vitamins are organic compounds required in minute quantities for normal metabolism, growth, and maintenance. They do not provide energy directly but regulate biochemical processes. Option D confuses vitamins with minerals — a frequent NEET-level mix-up.

Not quite — the answer is B.

Vitamins are classified as fat-soluble (A, D, E, K) — stored in liver and adipose tissue — and water-soluble (B complex, C) — not stored significantly and requiring regular dietary intake. Option A describes acids/bases, not vitamins.

Not quite — the answer is D.

Cellulose contains beta 1,4-glycosidic bonds and humans do not possess cellulase to hydrolyse them. Option B is a trap — cellulose is actually unbranched, not branched. Option C is partially true but not the biochemical reason.

Not quite — the answer is C.

Glycine has two identical hydrogen substituents on its alpha carbon, so it lacks a chiral centre and shows no optical activity. All other standard amino acids have four different substituents on the alpha carbon and are optically active.

Not quite — the answer is D.

Cellulose is a polysaccharide with thousands of β-glucose units linked by β-1,4 glycosidic bonds — far beyond the 2–10 unit range of oligosaccharides. Sucrose, maltose, and lactose are all disaccharides (oligosaccharides).

Not quite — the answer is D.

Starch contains a large number of glucose units joined by glycosidic linkages, making it a polysaccharide. Maltose, lactose, and sucrose are disaccharides yielding only two monosaccharide units on hydrolysis.

Not quite — the answer is C.

Fructose has a ketone functional group at C-2, making it a ketohexose. Glucose, galactose, and mannose all carry an aldehyde group at C-1 and are classified as aldoses.

Not quite — the answer is A.

Sucrose is a disaccharide that hydrolyses to give one glucose and one fructose molecule. Cellulose and starch are polysaccharides yielding hundreds to thousands of monosaccharide units.

Not quite — the answer is C.

Glycosidic linkages connect monosaccharide units in di- and polysaccharides. Maltose has an α-1,4 glycosidic linkage between two glucose units. Glucose, fructose, and ribose are monosaccharides with no glycosidic bonds.

Not quite — the answer is B.

α- and β-D-glucose are anomers differing only in the orientation of –OH at C-1 (anomeric carbon): axial in α, equatorial in β. This difference directly determines whether starch (α) or cellulose (β) linkages form.