CBSE · Class 12 · Chemistry · Chapter 14

Chapter 14
Biomolecules

Complete chapter resources for CBSE Class 12 Chemistry — carbohydrates, proteins, nucleic acids, and vitamins. Covers topic breakdown, key concepts, sample questions, previous year board questions, and instant AI question paper generation.

4Topics
4–6Board marks
8Sample questions
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Key Concepts — Chapter 14
  • Glucose formula: C₆H₁₂O₆ (aldohexose, open chain: CHO-(CHOH)₄-CH₂OH)
  • Peptide bond: −CO−NH− (formed by condensation of amino acids)
  • Reducing sugar: free anomeric −OH → reduces Fehling's / Tollen's reagent
  • DNA vs RNA: deoxyribose + thymine vs ribose + uracil
  • Nucleotide: phosphate + pentose sugar + nitrogenous base
  • Denaturation: disruption of secondary/tertiary structure (not primary)
Chapter Overview

What this chapter covers

Biomolecules are the large organic molecules essential to life — primarily carbohydrates, proteins, nucleic acids, and vitamins (along with lipids, which are briefly discussed). Chapter 14 in NCERT Class 12 Chemistry examines the chemical structure, classification, and biological functions of each class, with an emphasis on how molecular structure determines biological activity.

Carbohydrates are classified as monosaccharides, disaccharides, or polysaccharides based on the number of sugar units they contain. Proteins are polymers of amino acids linked by peptide bonds, and their function depends on four levels of structural organisation — primary, secondary, tertiary, and quaternary. Enzymes (biological catalysts) are a special class of proteins whose activity is highly specific, following a lock-and-key or induced-fit model.

Nucleic acids — DNA and RNA — store and transmit genetic information through sequences of nucleotides. Each nucleotide is built from a phosphate group, a pentose sugar (deoxyribose or ribose), and a nitrogenous base (adenine, guanine, cytosine, thymine in DNA; uracil replaces thymine in RNA). Board questions regularly ask students to compare DNA and RNA, explain protein structure levels, distinguish reducing from non-reducing sugars, and describe the role of vitamins in human health.

Topics

What's inside Chapter 14

As per NCERT Class 12 Chemistry (CBSE syllabus)

Topic 1
Carbohydrates
Classification into mono-, di-, and polysaccharides. Open-chain and cyclic (Haworth) structures of glucose and fructose. Reducing vs non-reducing sugars. Glycosidic bonds and examples (sucrose, starch, cellulose, glycogen).
Topic 2
Proteins & Enzymes
Amino acid structure, zwitterions, and peptide bond formation. Four levels of protein structure (primary to quaternary). Denaturation. Enzymes as biological catalysts — lock-and-key model, cofactors, and inhibition.
Topic 3
Nucleic Acids
Structure of a nucleotide (phosphate, sugar, nitrogenous base). Purine and pyrimidine bases. Watson–Crick double helix of DNA. RNA types (mRNA, tRNA, rRNA) and their roles. Key differences between DNA and RNA.
Topic 4
Vitamins & Hormones
Classification of vitamins as fat-soluble (A, D, E, K) and water-soluble (B-complex, C). Deficiency diseases associated with each vitamin. Brief introduction to hormones as chemical messengers and their role in physiological regulation.
Connections

How this chapter fits in

Useful for setting question difficulty and cross-chapter papers.

Builds on
Ch 12 · Aldehydes, Ketones & Carboxylic Acids
Carbonyl group chemistry underpins sugar open-chain structures and reducing reactions
Ch 13 · Amines
Amino group chemistry directly connects to amino acid structure and peptide bond formation
Chapter 14 Biomolecules
Leads to
Ch 15 · Polymers
Natural polymers (starch, cellulose, proteins) form the bridge to synthetic polymer concepts
Class 12 Biology · Molecular Basis of Inheritance
DNA replication, transcription, and translation build directly on nucleic acid structure from this chapter
Board Blueprint

Marks & question-type breakdown

Typical pattern based on CBSE Class 12 Chemistry board papers from the last five years.

Question type Marks Typical count What's usually tested
MCQ / Assertion–Reason 1 1 Identifying reducing sugars, DNA vs RNA, fat-soluble vitamins
Very Short Answer 2 1 Name the monomer / give the structural feature / define denaturation
Short Answer 3 0–1 Explain levels of protein structure or draw a nucleotide unit
Long Answer / Case-Based 4–5 0–1 Compare DNA and RNA, explain enzyme action, or classify carbohydrates with examples
Total (approximate) 4–6 2–3 Weightage varies across paper sets and years
Sample Questions

8 sample questions — generated by MarksZen AI

Aligned to CBSE Class 12 Chemistry Chapter 14. Covers all question types across Easy, Medium, and Hard difficulty.

Q1 Easy 1 mark MCQ
Which of the following is a non-reducing sugar? (a) Glucose (b) Fructose (c) Sucrose (d) Maltose
Q2 Easy 2 marks Short Answer
Define denaturation of proteins. Name one physical and one chemical agent that causes denaturation.
Q3 Medium 2 marks Short Answer
Draw the open-chain (Fischer projection) structure of D-glucose and label the aldehyde group and the chiral centres.
Q4 Medium 3 marks Short Answer
Distinguish between the primary and secondary structure of proteins. Name the type of bond responsible for each level of organisation.
Q5 Medium 3 marks Short Answer
Classify vitamins on the basis of their solubility. Give two examples in each category and name the deficiency disease associated with Vitamin C.
Q6 Hard 4 marks Long Answer
Compare the structure and function of DNA and RNA under the following heads: (i) Sugar present (ii) Nitrogenous bases (iii) Strand nature (iv) Biological function
Q7 Hard 5 marks Long Answer
With the help of a diagram, describe the Watson–Crick double helix model of DNA. Highlight the base-pairing rules and the forces holding the two strands together.
Q8 Hard 5 marks Case-Based
A student observes that starch gives a blue-black colour with iodine but does not reduce Fehling's solution, whereas glucose reduces Fehling's solution readily. (i) Explain why starch is a non-reducing carbohydrate. (ii) What type of glycosidic linkage is present in starch? Distinguish between amylose and amylopectin. (iii) Name one other polysaccharide that is a non-reducing carbohydrate and state its biological role.
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Previous Year Questions

From CBSE board examinations

Actual questions from past Class 12 Chemistry board papers — Biomolecules chapter.

Board 20222 marks
What are reducing sugars? Identify the reducing and non-reducing sugars from the following: glucose, sucrose, fructose, trehalose. (All India 2022)
Board 20233 marks
Describe the four levels of protein structure. What type of interactions or bonds are responsible for maintaining each level? (Delhi 2023)
Board 20202 marks
Write two points of differences between DNA and RNA on the basis of (i) the type of sugar present and (ii) the pyrimidine bases present. (CBSE 2020)
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FAQ

Questions teachers ask

How many marks does Biomolecules carry in the CBSE Class 12 Chemistry board exam? +
Biomolecules (Chapter 14) typically carries 4–6 marks in the CBSE Class 12 Chemistry board exam. Questions usually appear as one 2-mark short-answer and one 4-mark long-answer, often covering the classification of carbohydrates, primary/secondary structure of proteins, or the difference between DNA and RNA. The exact distribution varies by year and paper set.
What is the difference between reducing and non-reducing sugars, and why is it important for board exams? +
Reducing sugars (e.g., glucose, fructose, maltose, lactose) have a free aldehyde or ketone group that can reduce Fehling's or Tollen's reagent. Non-reducing sugars (e.g., sucrose, trehalose) have no free anomeric -OH and do not give a positive Fehling's test. Board questions regularly ask students to identify or distinguish between the two, and to explain why sucrose is non-reducing even though it is a disaccharide.
What are the four levels of protein structure, and how are they typically asked in board exams? +
Primary structure: the sequence of amino acids linked by peptide bonds. Secondary structure: local folding into alpha-helix or beta-pleated sheet stabilised by hydrogen bonds. Tertiary structure: overall 3D folding held by disulfide bridges, hydrophobic interactions, and hydrogen bonds. Quaternary structure: assembly of two or more polypeptide chains. Board questions most often ask students to distinguish primary from secondary structure, or to explain which bonds are responsible for each level.
How do DNA and RNA differ structurally? Is this asked in boards? +
DNA contains deoxyribose sugar and thymine; RNA contains ribose sugar and uracil. DNA is usually double-stranded and carries genetic information; RNA is usually single-stranded and is involved in protein synthesis. This comparison is a high-frequency 2-mark board question — students should memorise all four differences (sugar, base, strand count, function) and be able to draw or label a nucleotide unit.
How do I generate a custom question paper for Biomolecules using MarksZen? +
Sign up for a free MarksZen account, choose CBSE Class 12 Chemistry, select Chapter 14 (Biomolecules), set your preferred question-type mix and total marks — the AI generates a complete board-aligned paper with answer key in under 2 minutes, ready for PDF export.