Important Questions Class 12 Chemistry Chapter 10 Biomolecules With Answers

Biomolecules are carbon-based molecules that form the chemical foundation of living systems.
Carbohydrates, proteins, enzymes, vitamins, nucleic acids, and hormones control structure, energy, heredity, and body functions.

Food, heredity, enzymes, and hormones all meet inside one Chemistry unit. Important Questions Class 12 Chemistry Chapter 10 help students revise Biomolecules through definitions, reactions, structures, differences, and NCERT-style reasoning. CBSE 2026 questions can test carbohydrates, reducing sugars, glucose reactions, amino acids, protein structures, vitamins, enzymes, DNA, RNA, and hormones. This chapter is scoring because most answers depend on fixed definitions and clear chemical logic. Students should also revise Class 12 Chemistry NCERT Solutions, Class 12 Chemistry Revision Notes, and CBSE Class 12 Chemistry Sample Papers for stronger board preparation.

Key Takeaways

• Carbohydrates: Carbohydrates are optically active polyhydroxy aldehydes or ketones.
• Proteins: Proteins are polymers of alpha-amino acids joined by peptide bonds.
• Nucleic Acids: DNA and RNA are polynucleotides made from sugar, phosphate, and nitrogenous bases.
• Vitamins And Enzymes: Vitamins support body functions, while enzymes act as specific biocatalysts.

Important Questions Class 12 Chemistry Chapter 10 Structure 2026

Important Questions Class 12 Chemistry Chapter 10 Biomolecules Overview

Biomolecules connect organic chemistry with living systems. The chapter tests how structure decides function in carbohydrates, proteins, vitamins, nucleic acids, enzymes, and hormones.

Q1. What Are Biomolecules?

Biomolecules are complex molecules present in living systems and required for life processes. They include carbohydrates, proteins, nucleic acids, lipids, vitamins, enzymes, and hormones.

They form cells, store energy, transfer genetic information, and regulate chemical reactions inside organisms.

Q2. Why Are Biomolecules Important In Living Systems?

Biomolecules are important because they support growth, energy production, heredity, repair, and regulation. A living body works through coordinated chemical reactions.

Carbohydrates provide energy, proteins build tissues, enzymes speed up reactions, and nucleic acids transfer hereditary information.

Biomolecules Class 12 Chemistry Important Questions On Carbohydrates

Carbohydrates form a major part of food and plant storage material. These Biomolecules Class 12 Chemistry Important Questions focus on definitions, classification, glucose, and polysaccharides.

Q3. What Are Carbohydrates?

Carbohydrates are optically active polyhydroxy aldehydes or ketones. They also include compounds that give such units on hydrolysis.

Example: glucose is a polyhydroxy aldehyde, while fructose is a polyhydroxy ketone.

Q4. How Are Carbohydrates Classified On Hydrolysis?

Carbohydrates are classified into monosaccharides, oligosaccharides, and polysaccharides. This classification depends on the number of monosaccharide units formed after hydrolysis.

Monosaccharides:
They cannot be hydrolysed into simpler carbohydrate units.
Examples: glucose, fructose, ribose.

Oligosaccharides:
They give 2 to 10 monosaccharide units on hydrolysis.
Example: sucrose gives glucose and fructose.

Polysaccharides:
They give many monosaccharide units on hydrolysis.
Examples: starch, cellulose, glycogen.

Q5. What Are Reducing And Non-Reducing Sugars?

Reducing sugars reduce Fehling’s solution and Tollens’ reagent. They contain a free aldehydic or ketonic group in solution.

All monosaccharides are reducing sugars.

Maltose and lactose are reducing disaccharides because they can produce a free aldehyde group in solution.

Sucrose is a non-reducing sugar because the reducing groups of glucose and fructose form the glycosidic bond.

Q6. What Is Glycosidic Linkage?

Glycosidic linkage is the oxygen linkage between two monosaccharide units. It forms after the loss of one water molecule.

Example: sucrose has a glycosidic linkage between C1 of α-D-glucose and C2 of β-D-fructose.

This linkage joins monosaccharide units in disaccharides and polysaccharides.

Q7. What Are The Hydrolysis Products Of Sucrose And Lactose?

Sucrose gives glucose and fructose, while lactose gives galactose and glucose on hydrolysis. These products come from breaking glycosidic linkages.

Sucrose hydrolysis:
Sucrose + water → glucose + fructose

C₁₂H₂₂O₁₁ + H₂O → C₆H₁₂O₆ + C₆H₁₂O₆

Lactose hydrolysis:
Lactose + water → β-D-galactose + β-D-glucose

Sucrose is non-reducing, while lactose is reducing.

Q8. What Is The Difference Between Starch And Cellulose?

Starch is a storage polysaccharide, while cellulose is a structural polysaccharide. Both contain glucose units but differ in linkage and function.

Q9. What Is Glycogen?

Glycogen is the storage carbohydrate in animals. It is also called animal starch.

It has a structure similar to amylopectin but is more highly branched.

It occurs mainly in the liver, muscles, and brain.

When the body needs glucose, enzymes break glycogen into glucose.

Q10. What Happens When D-Glucose Reacts With HI, Bromine Water, And Nitric Acid?

D-glucose gives different products with different reagents because it contains aldehyde and alcohol groups. These reactions prove key structural features of glucose.

With HI on prolonged heating:
D-glucose → n-hexane

This shows that all six carbon atoms are in a straight chain.

With bromine water:
D-glucose + bromine water → gluconic acid

This shows the presence of an aldehyde group.

With nitric acid:
D-glucose + nitric acid → saccharic acid

This shows the presence of one aldehyde group and one primary alcohol group.

Q11. Why Does D-Glucose Not Give Schiff’s Test?

D-glucose does not give Schiff’s test because the free aldehyde group is not available in its cyclic form. Glucose mainly exists as cyclic hemiacetal structures.

The OH group at C5 adds to the CHO group and forms a six-membered ring.

This explains why glucose does not form a hydrogensulphite addition product with NaHSO₃.

It also explains why glucose pentaacetate does not react with hydroxylamine.

Class 12 Chemistry Biomolecules Important Questions On Proteins

Proteins are polymers of alpha-amino acids. These Class 12 Chemistry Biomolecules important questions cover amino acids, peptide bonds, structure, and denaturation.

Q12. What Are Amino Acids?

Amino acids are organic compounds containing amino group and carboxyl group. In proteins, only α-amino acids occur after hydrolysis.

General structure:
H₂N-CH(R)-COOH

R represents the side chain.

Examples: glycine, alanine, valine, leucine, lysine, and glutamic acid.

Q13. What Are Essential And Non-Essential Amino Acids?

Essential amino acids cannot be synthesised by the body and must come from diet. Non-essential amino acids can be synthesised in the body.

Essential amino acids:
Examples: valine, leucine, lysine, methionine.

Non-essential amino acids:
Examples: glycine, alanine, serine, glutamic acid.

Essential amino acids are important for growth and body maintenance.

Q14. What Is Peptide Linkage?

Peptide linkage is the amide bond formed between two amino acids. It forms when the COOH group of one amino acid reacts with the NH₂ group of another amino acid.

Reaction pattern:
Amino acid 1-COOH + H₂N-amino acid 2 → amino acid 1-CO-NH-amino acid 2 + H₂O

Peptide linkage:
-CO-NH-

A dipeptide contains two amino acids joined by one peptide linkage.

Q15. What Are The Four Levels Of Protein Structure?

Protein structure is studied at primary, secondary, tertiary, and quaternary levels. Each level explains a different degree of organisation.

Primary structure:
It is the sequence of amino acids in a polypeptide chain.

Secondary structure:
It includes α-helix and β-pleated sheet arrangements.

Tertiary structure:
It shows the overall folding of the polypeptide chain.

Quaternary structure:
It shows the arrangement of two or more polypeptide subunits.

Q16. What Is The Difference Between Fibrous And Globular Proteins?

Fibrous proteins are fibre-like and insoluble, while globular proteins are spherical and usually soluble. Their shapes decide their functions.

Q17. What Is Denaturation Of Proteins?

Denaturation is the loss of biological activity of a protein due to change in temperature or pH. It disturbs secondary and tertiary structures.

During denaturation, hydrogen bonds and other stabilising forces break.

The primary structure remains intact.

Examples: coagulation of egg white on boiling and curdling of milk.

Q18. Why Do Amino Acids Show Amphoteric Behaviour?

Amino acids show amphoteric behaviour because they contain both acidic and basic groups. The carboxyl group acts as acidic, and the amino group acts as basic.

In aqueous solution, amino acids form zwitter ions.

Zwitter ion form:
⁺H₃N-CH(R)-COO⁻

This form contains both positive and negative charges.

Biomolecules Class 12 Questions With Answers On Enzymes And Vitamins

Enzymes and vitamins regulate essential body functions. These Biomolecules Class 12 questions with answers help students revise direct theory and deficiency-based concepts.

Q19. What Are Enzymes?

Enzymes are biological catalysts that speed up chemical reactions in living systems. Most enzymes are globular proteins.

They work under mild body conditions and show high specificity.

Example: maltase catalyses the hydrolysis of maltose into glucose.

Reaction:
Maltose + water → 2 glucose

C₁₂H₂₂O₁₁ + H₂O → 2C₆H₁₂O₆

Q20. How Are Vitamins Classified?

Vitamins are classified into fat-soluble and water-soluble vitamins. This classification depends on their solubility.

Fat-soluble vitamins:
Vitamins A, D, E, and K.

They are stored in the liver and fat tissues.

Water-soluble vitamins:
B group vitamins and vitamin C.

They are excreted in urine and must be supplied regularly.

Vitamin B₁₂ is an exception because it can be stored in the body.

Q21. Which Vitamin Helps In Blood Clotting?

Vitamin K helps in blood clotting. Its deficiency increases blood clotting time.

Green leafy vegetables are a major source of vitamin K.

This is a common one-mark question from vitamins Class 12 Chemistry.

Q22. Why Cannot Vitamin C Be Stored In The Body?

Vitamin C cannot be stored because it is water-soluble. It is readily excreted through urine.

The body needs a regular supply of vitamin C through diet.

Citrus fruits, amla, and green leafy vegetables are good sources.

Its deficiency causes scurvy.

Class 12 Chemistry Chapter 10 Questions And Answers On Nucleic Acids

Nucleic acids carry hereditary information and guide protein synthesis. This section covers Class 12 Chemistry Chapter 10 questions and answers from DNA, RNA, nucleotides, and bases.

Q23. What Are Nucleic Acids?

Nucleic acids are long-chain polymers of nucleotides. They are also called polynucleotides.

There are two main types of nucleic acids: DNA and RNA.

DNA stores genetic information.

RNA helps in protein synthesis.

Q24. What Is The Difference Between A Nucleoside And A Nucleotide?

A nucleoside contains sugar and base, while a nucleotide contains sugar, base, and phosphate. This is the main structural difference.

Nucleoside:
Base + pentose sugar

Nucleotide:
Base + pentose sugar + phosphoric acid

Nucleotides join through phosphodiester linkage to form nucleic acids.

Q25. Why Are DNA Strands Complementary?

DNA strands are complementary because bases pair in a specific pattern. Adenine pairs with thymine, and cytosine pairs with guanine.

Base pairing:
Adenine pairs with thymine
A pairs with T

Cytosine pairs with guanine
C pairs with G

Hydrogen bonds hold these base pairs together.

Q26. What Are The Structural Differences Between DNA And RNA?

DNA is double-stranded and contains deoxyribose, while RNA is usually single-stranded and contains ribose. Their bases also differ.

Q27. What Are The Types Of RNA?

The three types of RNA are mRNA, rRNA, and tRNA. Each type performs a different role in protein synthesis.

mRNA:
It carries the message from DNA.

rRNA:
It forms part of ribosomes.

tRNA:
It carries amino acids during protein synthesis.

These RNAs help convert genetic information into proteins.

Biomolecules Class 12 Important Questions On Hormones

Hormones act as chemical messengers in the body. Biomolecules Class 12 important questions on hormones usually test functions and examples.

Q28. What Are Hormones?

Hormones are molecules that act as intercellular messengers. Endocrine glands produce them and release them directly into the blood.

They regulate growth, metabolism, stress response, reproduction, and biological balance.

Examples include insulin, glucagon, thyroxine, testosterone, and estradiol.

Q29. How Do Insulin And Glucagon Regulate Blood Glucose?

Insulin lowers blood glucose, while glucagon raises blood glucose. Together, they maintain blood glucose within a narrow range.

Insulin releases when blood glucose rises rapidly.

Glucagon acts when blood glucose needs to increase.

This opposite action helps maintain homeostasis.

Q30. What Is The Role Of Thyroxine?

Thyroxine regulates metabolism and supports normal body functions. It is an iodinated derivative of the amino acid tyrosine.

Low thyroxine levels cause hypothyroidism.

Hypothyroidism may cause lethargy, obesity, and enlargement of the thyroid gland.

Iodised salt helps reduce iodine deficiency.

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