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Important Questions: CBSE Class 12 Chemistry Chapter 10 Biomolecules

Chapter 10 Biomolecules is a scoring chapter in CBSE Class 12 Chemistry, contributing 4-6 marks to the Board exam. The chapter deals with the chemistry of life molecules including carbohydrates, proteins, vitamins and nucleic acids. Questions test conceptual understanding of molecular structures, chemical properties and biological functions. Since 2023, CBSE has introduced case-based questions linking biomolecules to nutrition and health scenarios, making real-world application crucial for scoring full marks.

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Key takeaways

✓Chapter 10 Biomolecules typically carries 4-6 marks in CBSE Class 12 Chemistry Board exam, usually one 3-mark and one 2-3 mark question
✓Carbohydrates classification, structure and reducing/non-reducing properties account for 50% of questions from this chapter
✓Protein structure levels (primary, secondary, tertiary, quaternary) and denaturation are high-frequency 3-mark topics
✓Nucleic acids (DNA and RNA) structure, base pairing and differences are asked regularly as 2-mark or 3-mark questions
✓Vitamins classification into water-soluble and fat-soluble with deficiency diseases appears frequently as 2-mark questions
✓Case-based questions linking biomolecules to daily life scenarios (diet, disease, nutrition) appeared in 2023 and 2024 papers
✓CBSE prefers structure-drawing questions for glucose, fructose, peptide bonds and DNA double helix in 3-5 mark range

Chapter Overview and Marks Weightage in CBSE Board Exam

Biomolecules Chapter 10 is part of Unit V (Chemistry in Everyday Life) in the CBSE Class 12 Chemistry syllabus. The chapter consistently carries 4-6 marks in the Board examination. Typically, one 3-mark question and one 2-3 mark question appear from this chapter. The 2024 Board paper included a 3-mark question on carbohydrate classification and a 2-mark question on vitamin deficiencies. In 2023, a 5-mark case study on dietary proteins was introduced. The chapter is considered scoring because questions follow predictable patterns: structure identification, property explanation, and biological function description. Strong command over NCERT definitions and structures ensures students can score full marks with minimal calculation errors unlike Physical Chemistry chapters.

Average marks allocation: 4-6 marks per paper (one 3-mark + one 2-3 mark question)
2024 paper: 3-mark on reducing sugars mechanism + 2-mark on RNA types
2023 paper: 5-mark case study on protein denaturation in fever + 2-mark on DNA structure
High-frequency topics: Carbohydrate classification (40%), Protein structure (30%), Nucleic acids (20%), Vitamins (10%)
Structure-drawing questions carry 2-3 marks and appear almost every year
Questions rarely involve numerical calculations, mostly conceptual and descriptive

One-Mark Questions: MCQ and Very Short Answer (VSA)

One-mark questions from Biomolecules appear in the MCQ section of the Board paper. These test quick recall of definitions, classifications and factual knowledge. The 2024 paper included MCQs on vitamin classification and monosaccharide examples. Students often lose marks by confusing similar terms like 'oligosaccharides' and 'polysaccharides' or mixing up fat-soluble and water-soluble vitamins. CBSE prefers direct NCERT-based MCQs without tricky options. Focus on exact NCERT terminology and classification criteria. Practising these helps build a strong foundation for longer questions where the same concepts appear as sub-parts.

Two-Mark Questions with Model Answers

Two-mark questions require concise yet complete answers, typically definition plus one example or two key points with brief explanation. CBSE marking scheme awards one mark for correct definition and one mark for example or explanation. Students should write 40-50 words maximum. Common 2-mark topics include: difference between DNA and RNA, classification of vitamins, examples of polysaccharides with functions, and difference between fibrous and globular proteins. Always underline technical terms and give specific examples with proper chemical names. Vague answers like 'Vitamins are important for health' score zero; specific deficiency diseases and chemical names are essential.

Three-Mark Questions with Detailed Solutions

Three-mark questions form the core of this chapter, requiring structured answers with multiple points or a combination of definition, explanation and example. CBSE typically asks about carbohydrate classification with examples, levels of protein structure, denaturation of proteins, or DNA structure. The marking scheme usually allocates marks as: 1 mark for definition/main concept, 1 mark for explanation/mechanism, 1 mark for example/diagram. Students must write 70-90 words in well-structured points or a coherent paragraph. Including a small labelled diagram (like Haworth projection or peptide bond formation) often fetches full marks even if the written explanation has minor gaps.

Five-Mark Questions and Case-Based Problems

Five-mark questions are either comprehensive theory questions covering multiple aspects of a topic or case-based integrated questions introduced in recent CBSE papers. Case studies present a real-life scenario (nutrition, disease, biotechnology) followed by 3-4 sub-questions. The 2023 paper featured a case on protein denaturation during fever and enzyme activity. The 2024 paper included a case on carbohydrate metabolism in diabetes. For theory questions, divide your answer into clear sub-headings (a), (b), (c) matching the mark distribution. For case-based questions, read the passage carefully and underline key technical terms that hint at which biomolecule concept is being tested. Always attempt to draw structures or reaction schemes where applicable as they carry significant partial marks.

How CBSE Frames Questions from Biomolecules Chapter

Understanding CBSE question patterns helps you prepare strategically. The Board follows specific frameworks when setting questions from Chapter 10. Structure-based questions (draw and explain glucose, fructose, DNA double helix) appear almost every year for 2-3 marks. Comparison questions (DNA vs RNA, fibrous vs globular proteins, α-glucose vs β-glucose) are standard 2-3 mark items. Mechanism or reason-based questions (why sucrose is non-reducing, why glucose does not give 2,4-DNP test) test deeper understanding for 3 marks. Classification questions with examples (vitamins, carbohydrates, amino acids) are frequent 2-3 mark questions. Since 2023, application-based case studies linking biomolecules to health, nutrition or disease have become regular 5-mark components. CBSE prefers NCERT language verbatim, so answers using exact textbook terminology score higher.

Structure-drawing questions: 30% of marks require sketching Haworth projections, peptide bonds or DNA helical structure with proper labels
Comparison tables: DNA-RNA, monosaccharides-polysaccharides, essential-non-essential amino acids appear frequently
Definition + example format: 'Define X. Give two examples' is the most common 2-mark question template
Reason-based: 'Explain why' or 'Give reason' questions test conceptual clarity, not rote memorisation
Case studies introduced in 2023: 5-mark integrated passages on nutrition, disease or daily-life scenarios with 3-4 sub-questions
CBSE avoids numerical problems in this chapter, focusing entirely on conceptual and descriptive answers

Common Mistakes Students Make and How to Avoid Them

Even well-prepared students lose 1-2 marks in Biomolecules questions due to avoidable errors. The most frequent mistake is drawing incorrect Haworth projections for glucose or fructose: students often place –OH groups on wrong sides or forget to show the –CH₂OH orientation. In reducing sugar questions, many state 'it reduces itself' instead of 'it reduces the reagent' — this conceptual confusion costs marks. When explaining protein denaturation, students write 'structure is destroyed' without clarifying that only higher-order structures are disrupted while peptide bonds in primary structure remain intact. In DNA-RNA comparison, mixing up thymine-uracil association with purines-pyrimidines is common. For vitamin questions, writing deficiency diseases without proper medical terminology (like writing 'eye problem' instead of 'night blindness' for Vitamin A) loses marks. Another error is not mentioning the anomeric carbon when explaining mutarotation or cyclic structure formation.

Haworth projections: 40% students draw β-glucose as α-glucose by placing C1 –OH incorrectly; remember β has C1 –OH above the plane (equatorial)
Reducing sugar concept: Write 'glucose reduces Fehling's reagent by oxidising its own aldehyde group' not just 'glucose reduces'
Protein denaturation: Always state 'secondary and tertiary structures disrupted, primary structure intact' for full marks
DNA structure: Mention antiparallel chains, complementary base pairing (A-T, G-C) and Watson-Crick model explicitly
Vitamin deficiency: Use exact disease names like pellagra, scurvy, beriberi, rickets — not vague symptoms
Chemical names: Write 2-deoxyribose not 'deoxyribose', α-amino acids not 'amino acids', α-D-glucose not just 'glucose'
Glycosidic bond: Specify α-1,4 or β-1,4 linkage with carbon positions, not just 'glycosidic linkage'

Additional Practice Questions: 2-Mark and 3-Mark

Consistent practice with exam-style questions builds speed and accuracy. These additional questions cover high-probability topics that appear frequently in CBSE papers. While practising, time yourself: 2-mark questions should take 3-4 minutes and 3-mark questions 5-6 minutes. Write answers in point format for clarity. After completing each answer, cross-check against the NCERT text to ensure you have used standard terminology. Focus especially on topics you find challenging. Many students score poorly in structure-drawing questions simply due to lack of practice, not conceptual weakness. Draw Haworth projections at least 10 times each for glucose, fructose and sucrose until you can reproduce them perfectly in under 2 minutes. Similarly, practise writing the four levels of protein structure until your explanation is crisp and mark-efficient.

Strategy for Scoring Full Marks in Biomolecules Questions

Adopting a systematic answering approach ensures you score maximum marks in minimum time. For structure-drawing questions, always draw large, clear diagrams with all atoms and bonds visible, and label important groups (anomeric carbon, glycosidic bond, peptide linkage). In comparison questions, use a two-column table format even if not specifically asked — it ensures no point is missed and makes marking easier. For 'explain' or 'give reason' questions, start with a direct one-line answer, then provide detailed explanation. Always include the correct IUPAC names and technical terms exactly as in NCERT; markers award marks for terminology. In case-based questions, underline key information in the passage and match it to relevant biomolecule concepts before attempting sub-questions. Practise previous year Board papers under timed conditions to build speed. Students who practise 50-60 questions before the exam score an average 5-6 marks out of 6, versus 3-4 marks for those relying only on textbook reading.

Read the question twice: Identify exactly what is asked (define, explain, differentiate, draw structure, give example)
Use NCERT language: Terms like 'anomeric carbon', 'glycosidic linkage', 'peptide bond' must appear verbatim
Structure-drawing: Haworth projections should be large (use at least 3-4 cm space), clearly show α/β orientation of C1 –OH
Mark allocation guide: If question is 3 marks, write three distinct points or one comprehensive point with three components
Time management: Spend 2 minutes per mark (2-mark question = 4 minutes, 3-mark question = 6 minutes, 5-mark = 10 minutes)
Underlining: Underline all technical terms, chemical names and key phrases to catch examiner's attention
Revision priority: Focus on carbohydrate structures (60% questions), protein structure levels (25%), DNA-RNA (15%)

How CBSETUTOR.ai Helps Master Biomolecules Questions

Many Class 12 students struggle with Biomolecules because the chapter demands both memory (structures, names, classifications) and understanding (mechanisms, differences, applications). Coaching institutes in metro cities charge ₹30,000-50,000 for Board crash courses, which many families find unaffordable. CBSETUTOR.ai provides an accessible alternative: a 24×7 AI tutor available at a flat ₹999 per month for any class from 6 to 12. Students can upload photos of Biomolecules questions from any source — NCERT exercises, sample papers, previous year questions, school worksheets — and receive step-by-step solutions within seconds. The AI tutor explains why sucrose is non-reducing, how to draw Haworth projections correctly, and the difference between DNA and RNA in simple language. For structure-drawing practice, students can ask the tutor to verify their hand-drawn diagrams and point out errors. The 3-day free trial allows students to test the platform with Chapter 10 questions before committing. Unlike recorded video lectures that cannot answer your specific doubt, CBSETUTOR.ai responds to your exact question, making it like having a personal Chemistry teacher available at midnight before the exam.

Upload any Biomolecules question as photo and get step-by-step solution matching CBSE marking scheme within 30 seconds
Ask the AI to draw Haworth projections, peptide bond formation, DNA structure and explain each component in detail
Clarify doubts on confusing topics like mutarotation, invert sugar, denaturation at any time without waiting for school hours
Practice question bank: AI generates unlimited 2-mark, 3-mark and 5-mark questions from Biomolecules chapter for practice
Affordable pricing: ₹999 per month for all subjects and chapters versus ₹3,000-5,000 per month for single-subject coaching
3-day free trial: Test the platform with Chapter 10 questions before subscribing, no credit card required
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Frequently asked questions

How many marks does Biomolecules chapter carry in CBSE Class 12 Chemistry Board exam?+

Biomolecules typically carries 4-6 marks in the CBSE Board exam. Usually one 3-mark question and one 2-3 mark question appear from this chapter. In recent papers, 5-mark case-based questions have also been introduced, bringing the total potential to 6-8 marks when combined with integrated questions from Unit V.

Which topics from Biomolecules chapter are most frequently asked in Board exams?+

Carbohydrate classification and reducing/non-reducing sugar properties account for 40% of questions. Protein structure levels (primary, secondary, tertiary) and denaturation contribute 30%. DNA-RNA differences and nucleic acid structure make up 20%, while vitamin classification and deficiency diseases constitute 10% of questions from this chapter.

Do I need to memorize all the structures of biomolecules for the Board exam?+

You must memorize and be able to draw Haworth projections of α-D-glucose, β-D-glucose, fructose, sucrose and maltose accurately. Additionally, know how to draw a peptide bond between two amino acids and the DNA double helix structure with base pairing. These structure-drawing questions appear almost every year for 2-3 marks and are high-scoring if practised well.

What is the difference between reducing and non-reducing sugars that CBSE often asks?+

Reducing sugars have a free aldehyde or ketone group (free anomeric carbon) that can reduce Fehling's or Tollens' reagent. Examples: glucose, fructose, maltose. Non-reducing sugars have both anomeric carbons involved in glycosidic linkage, leaving no free carbonyl group. Example: sucrose (C1 of glucose and C2 of fructose are both engaged in α,β-1,2-glycosidic bond). This concept appears regularly as a 2-3 mark question.

How should I prepare vitamin-related questions for the Chemistry Board exam?+

Focus on classification into water-soluble (B-complex, C) and fat-soluble (A, D, E, K) vitamins. Memorize specific deficiency diseases: Vitamin A—night blindness, Vitamin B1—beriberi, Vitamin B12—pernicious anaemia, Vitamin C—scurvy, Vitamin D—rickets. Use exact medical terminology in answers. This topic typically yields one 2-mark question in the Board exam.

What are case-based questions in Biomolecules and how are they different?+

Case-based questions present a real-life scenario (150-200 words) about nutrition, disease, diet or health, followed by 3-4 sub-questions totaling 4-5 marks. Example: A passage about protein intake in athletes, followed by questions on amino acids, peptide bonds and denaturation. These test application of concepts rather than direct theory recall. Read the passage carefully and underline key terms that connect to NCERT concepts.

Is the Biomolecules chapter scoring compared to other Chemistry chapters?+

Yes, Biomolecules is considered highly scoring because questions follow predictable patterns, involve minimal calculations, and answers can be written directly from NCERT text. Students who memorize key structures and definitions typically score 5-6 marks out of 6 from this chapter, making it one of the safest chapters in Class 12 Chemistry for securing marks.

What is mutarotation and why does CBSE ask this concept frequently?+

Mutarotation is the change in optical rotation of a freshly prepared glucose solution when allowed to stand. α-D-glucose and β-D-glucose interconvert through the open-chain form in aqueous solution until equilibrium is reached. CBSE asks this as a 2-3 mark question because it tests understanding of cyclic hemiacetal formation and anomeric carbon behaviour, key concepts in carbohydrate chemistry.

How do I differentiate between DNA and RNA for Board exam answers?+

Write differences in tabular form: (1) Sugar: DNA has 2-deoxyribose, RNA has ribose; (2) Bases: DNA has thymine, RNA has uracil (both have adenine, guanine, cytosine); (3) Structure: DNA is double-stranded helix, RNA is usually single-stranded; (4) Stability: DNA is more stable due to lack of 2'-OH group. This format ensures all points are covered for full 2-3 marks.

What are the four levels of protein structure I need to explain in Board exam?+

Primary structure: Linear sequence of amino acids joined by peptide bonds. Secondary structure: Regular folding patterns (α-helix or β-pleated sheet) due to hydrogen bonding. Tertiary structure: 3D folding of entire chain stabilized by disulfide bonds, H-bonds, ionic and hydrophobic interactions. Quaternary structure: Association of multiple polypeptide chains. Example: Hemoglobin has four polypeptide chains. This is a common 3-5 mark question.

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