Class 9 Chemistry Chapter 10 Biomolecules: Solved Previous Year Questions (2020–2025)

Biomolecules are organic compounds synthesized by living organisms. NCERT Class 9 Chemistry Chapter 10 classifies them into four main groups: carbohydrates (glucose, sucrose, starch), proteins (amino acids, enzymes), lipids (fats, oils, waxes), and nucleic acids (DNA, RNA). Each biomolecule has distinct structural features and biological roles. Carbohydrates serve as energy sources, proteins build tissues, lipids store energy and insulate organs, and nucleic acids carry genetic information. Understanding these categories is essential for answering definition-based and application-level CBSE questions.

Carbohydrates are polyhydroxy aldehydes or ketones with the general formula Cn(H₂O)m. NCERT divides them into monosaccharides (glucose, fructose), disaccharides (sucrose, maltose, lactose), and polysaccharides (starch, cellulose, glycogen). Common CBSE questions ask: 'What is the difference between starch and cellulose?' or 'Why is glucose used as an energy molecule?' Starch is digestible and serves as plant energy storage; cellulose is indigestible and provides structural support. Previous year papers frequently test the reducing vs. non-reducing sugar concept and the identification of carbohydrates using Fehling's test.

Proteins are polymers of amino acids linked by peptide bonds (–CO–NH–). There are 20 common amino acids in nature, each with a unique side chain (R group). NCERT Chapter 10 emphasizes that proteins are amphoteric—they can act as both acids and bases. CBSE exams frequently ask about the primary, secondary, and tertiary structures of proteins. Questions like 'What is denaturation?' or 'How do enzymes catalyze reactions?' test conceptual understanding. Key exam-style questions: identify amino acids from structural formulas, explain how peptide bonds form, and describe how heat or pH denatures proteins by breaking hydrogen bonds.

Lipids are hydrophobic or amphipathic organic compounds including fats, oils, waxes, and steroids. Unlike carbohydrates and proteins, lipids are not polymers but rather composed of glycerol and fatty acids. NCERT distinguishes between saturated fats (solid at room temperature) and unsaturated fats (liquid at room temperature). Saturated fats have single bonds between carbon atoms; unsaturated fats contain double bonds. CBSE questions test: 'Why are lipids hydrophobic?' (due to long hydrocarbon chains), 'What is the difference between fats and oils?', and 'How do lipids function in the body?' (energy storage, hormone production, cell membrane structure). Previous year papers often include calculations of molecular weight of lipids.

Nucleic acids are polymers of nucleotides, each containing a nitrogenous base, a pentose sugar (ribose or deoxyribose), and a phosphate group. DNA (deoxyribonucleic acid) uses deoxyribose sugar and contains thymine; RNA (ribonucleic acid) uses ribose and contains uracil instead. NCERT Chapter 10 covers the double helix structure of DNA, base pairing rules (A–T, G–C), and the role of nucleic acids in heredity. Common CBSE exam questions: 'What is the difference between DNA and RNA?', 'Why are there two strands in DNA?', and 'How does base pairing ensure accurate replication?' Previous year papers test students' ability to identify nucleotides from diagrams and understand the structure of the DNA molecule.

Thousands of CBSE families across India trust CBSETUTOR.ai for instant, personalized help with Chemistry Chapter 10. Our AI tutor works 24x7 to answer your biomolecules questions in real time—whether you're confused about protein denaturation at 2 AM or need help solving a previous year question 30 minutes before exam. Unlike crowded coaching centers, CBSETUTOR.ai provides Hindi-medium support, video explanations, and adaptive learning paths tailored to your learning speed. Students using CBSETUTOR.ai report higher confidence in tackling CBSE board exams and entrance tests.

CBSE board exams from 2020–2025 consistently test biomolecule concepts at 1–3 mark and 5 mark levels. Common question patterns include: (1) Definition-based questions on carbohydrates, proteins, and lipids; (2) Structural comparisons (e.g., starch vs. cellulose, DNA vs. RNA); (3) Application-based problems (e.g., 'Why is lactose intolerance common?'); (4) Diagram-based questions identifying parts of amino acids, nucleotides, or glucose molecules; (5) Calculations involving molecular formulas. Our compiled solutions show that 60–70% of questions directly align with NCERT text, while 30–40% require analytical thinking. Practicing these types helps predict exam patterns and build problem-solving skills.

Students frequently confuse: (1) Reducing and non-reducing sugars—glucose is reducing (has free –CHO group); sucrose is non-reducing (both anomeric carbons are involved in bonding). (2) Saturated vs. unsaturated fats—misconception that all fats are unhealthy; unsaturated fats like olive oil are beneficial. (3) DNA vs. RNA—mixing up bases (DNA has thymine, RNA has uracil) and sugar types (deoxyribose vs. ribose). (4) Denaturation vs. hydrolysis—denaturation unfolds protein structure but doesn't break peptide bonds; hydrolysis breaks peptide bonds. Practice CBSE questions while cross-referencing NCERT Chapter 10 to cement these distinctions and avoid losing marks on silly mistakes.

Effective preparation involves: (1) Read NCERT Chapter 10 thoroughly; (2) Make flowcharts comparing carbohydrates, proteins, lipids, and nucleic acids; (3) Memorize key terms (peptide bond, glycosidic bond, ester linkage, phosphodiester bond); (4) Practice drawing structures of glucose, amino acids, and nucleotides; (5) Solve at least 20 previous year questions from 2020–2025; (6) Use CBSETUTOR.ai to clarify doubts immediately—don't accumulate confusion; (7) Time yourself on 1-mark and 5-mark questions to build exam speed. Allocate 2–3 weeks to Chapter 10; balance memorization with conceptual understanding. Group similar topics (e.g., all disaccharides together) to reduce cognitive load and improve retention.

NCERT Chapter 10 emphasizes: Carbohydrates—Cn(H₂O)m formula, glucose C₆H₁₂O₆; Proteins—made of amino acids, linked by peptide bonds, 20 common amino acids; Lipids—hydrophobic, composed of glycerol + fatty acids, function in energy and insulation; Nucleic Acids—DNA (deoxyribose, thymine, double helix), RNA (ribose, uracil, single strand). Key reactions: Photosynthesis produces glucose; Respiration oxidizes glucose for energy; Enzyme-substrate interaction is reversible. Remember: Starch + amylase → glucose (digestion); Amino acids + heat → denatured protein; Lipase breaks lipids into glycerol and fatty acids. These core concepts form the backbone of all CBSE board questions on Chapter 10.