Carbohydrates Practice Questions
20 free Carbohydrates practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following is considered a 'reducing sugar' because it has a free aldehyde or ketone group?
- A Sucrose
- B Starch
- C Glucose
- D Glycogen
Correct answer: Glucose
Glucose is a monosaccharide with a free aldehyde group, making it a reducing sugar. Sucrose is a non-reducing disaccharide because the reducing groups of glucose and fructose are involved in the glycosidic bond.
The bond formed between two monosaccharides by the loss of a water molecule is called a:
- A Peptide bond
- B Glycosidic bond
- C Phosphodiester bond
- D Ester bond
Correct answer: Glycosidic bond
A glycosidic bond is a type of covalent bond that joins a carbohydrate molecule to another group or saccharide. It is formed through a dehydration reaction between two carbon atoms.
In a polysaccharide chain, the right end is called the ______ end and the left end is called the ______ end.
- A Non-reducing, Reducing
- B Reducing, Non-reducing
- C Acidic, Basic
- D Hydrophilic, Hydrophobic
Correct answer: Reducing, Non-reducing
According to NCERT, in a polysaccharide like starch, the right end is the reducing end while the left end is the non-reducing end. This refers to the availability of the anomeric carbon for oxidation.
Starch forms helical secondary structures that can hold which molecule, resulting in a characteristic blue color?
- A Bromine
- B Chlorine
- C Iodine (I₂)
- D Fluorine
Correct answer: Iodine (I₂)
Starch consists of amylose and amylopectin; the helical portion of amylose can trap iodine (I₂) molecules. This interaction produces a dark blue-black color, which is a standard test for starch.
Which of the following is a structural polysaccharide found in the cell walls of algae and higher plants?
- A Glycogen (α-1,6)
- B Inulin (fructan)
- C Cellulose (β-1,4)
- D Starch (amylose)
Correct answer: Cellulose (β-1,4)
Cellulose is a linear homopolymer of glucose units linked by beta-1,4-glycosidic bonds. It provides mechanical strength and rigidity to plant cell walls.
Inulin is a polymer of which monosaccharide unit?
- A Glucose
- B Galactose
- C Fructose
- D Ribose
Correct answer: Fructose
Inulin is a storage polysaccharide found in plants like Dahlia tubers. It is a fructan, meaning it is composed of repeating units of fructose.
The complex polysaccharide 'Chitin' is found in the exoskeletons of arthropods. It is a homopolymer of:
- A N-acetyl galactosamine
- B N-acetyl glucosamine
- C N-acetyl mannosamine
- D Glucuronic acid units
Correct answer: N-acetyl glucosamine
Chitin is a modified polysaccharide containing nitrogen. It is made of repeating units of N-acetyl glucosamine (NAG) linked by beta-1,4-glycosidic bonds, providing structural support in fungi and arthropods.
Which of the following carbohydrates is NOT a polymer of glucose?
- A Cellulose (glucose)
- B Glycogen (glucose)
- C Amylopectin (glucose)
- D Inulin (fructose)
Correct answer: Inulin (fructose)
Cellulose, glycogen, and amylopectin (a component of starch) are all glucose polymers. Inulin is a polymer of fructose, making it the only non-glucose polymer in this list.
Glycogen is the major reserve food material in animals. It is structurally most similar to:
- A Linear amylose
- B Amylopectin
- C Linear cellulose
- D Inulin (fructan)
Correct answer: Amylopectin
Both glycogen and amylopectin are branched polymers of alpha-glucose. However, glycogen is more highly branched than amylopectin, with branches every 8–12 glucose units versus every 24–30 in amylopectin.
Which of the following is a disaccharide composed of glucose and galactose?
- A Maltose
- B Lactose
- C Sucrose
- D Trehalose
Correct answer: Lactose
Lactose, also known as milk sugar, is a disaccharide. It is formed by a glycosidic linkage between a glucose molecule and a galactose molecule.
Cotton fibers are predominantly composed of:
- A Starch granules
- B Glycogen chains
- C Cellulose fibers
- D Chitin polymer
Correct answer: Cellulose fibers
Cotton is almost pure cellulose. Because cellulose is a fibrous, structural polysaccharide with strong beta-1,4 linkages, it is ideal for the formation of plant fibers.
Why does cellulose not give a blue color with iodine test?
- A It is composed of only fructose units.
- B It contains nitrogen in its backbone.
- C Its linear structure lacks iodine-trapping helices.
- D Its molecular weight is too low to react.
Correct answer: Its linear structure lacks iodine-trapping helices.
Starch has a helical secondary structure (in amylose) that can hold iodine molecules, producing a blue-black color. Cellulose has a linear, non-helical structure and therefore cannot trap iodine to produce a color change.
Identify the 'animal starch' from the following options:
- A Cellulose
- B Glycogen
- C Chitin
- D Inulin
Correct answer: Glycogen
Glycogen is often called animal starch because it serves as the primary energy storage polysaccharide in animals and fungi, similar to how starch functions in plants.
A five-carbon monosaccharide found in RNA is:
- A Glucose (hexose)
- B Ribose (pentose)
- C Deoxyribose (pentose)
- D Erythrose (tetrose)
Correct answer: Ribose (pentose)
Ribose is a pentose (5-carbon) sugar. It is a fundamental component of ribonucleotides, which make up RNA. DNA contains the related but distinct sugar deoxyribose.
Maltose, also known as malt sugar, is composed of which two units?
- A One Glucose + One Fructose
- B One Glucose + One Galactose
- C Two Glucose units (α-1,4)
- D Two Fructose units (β-2,1)
Correct answer: Two Glucose units (α-1,4)
Maltose is a disaccharide produced during the digestion of starch. It consists of two alpha-glucose units linked by an alpha-1,4-glycosidic bond.
Which of the following is a heteropolysaccharide?
- A Cellulose (plant walls)
- B Starch (plant storage)
- C Peptidoglycan (bacterial)
- D Glycogen (animal storage)
Correct answer: Peptidoglycan (bacterial)
Homopolysaccharides such as cellulose, starch, and glycogen contain only one type of monosaccharide. Peptidoglycan contains different types of sugars and amino acids, making it a heteropolysaccharide found in bacterial cell walls.
Paper made from plant pulp is primarily which biomolecule?
- A Structural protein
- B Storage lipid
- C Cellulose fiber
- D Starch granule
Correct answer: Cellulose fiber
Plant pulp used in papermaking is largely derived from xylem and other tissues rich in cellulose. Therefore, paper is essentially processed cellulose.
Which of the following is the most abundant organic compound on Earth?
- A Glucose (monomer)
- B Cellulose (polymer)
- C Protein (polymer)
- D DNA (polymer)
Correct answer: Cellulose (polymer)
Cellulose is the most abundant organic polymer on Earth because it is the primary structural component of all plant cell walls, making up roughly one-third of all plant matter.
Table sugar (sucrose) is formed by the combination of:
- A Glucose and Glucose
- B Glucose and Galactose
- C Glucose and Fructose
- D Fructose and Galactose
Correct answer: Glucose and Fructose
Sucrose is a disaccharide commonly harvested from sugarcane or sugar beets. It consists of one glucose unit and one fructose unit.
Monosaccharides with a carbonyl group at the end of the carbon chain are called:
- A Ketoses
- B Aldoses
- C Hexoses
- D Pentoses
Correct answer: Aldoses
Aldoses are monosaccharides where the carbonyl group is an aldehyde (at the end of the chain), such as glucose. Ketoses have the carbonyl group as a ketone (within the chain), such as fructose.