Frequently Asked Questions

Q1. Define carbohydrates.

Answer:
Carbohydrates are polyhydroxy aldehydes, polyhydroxy ketones, or compounds that yield such substances on hydrolysis.

Q2. Name the three classes of carbohydrates.

Answer:

Monosaccharides
Oligosaccharides
Polysaccharides

Q3. Give two examples of monosaccharides.

Answer:

Glucose
Fructose

Q4. Which carbohydrate is called animal starch?

Answer:
Glycogen

Q5. Which carbohydrate forms the plant cell wall?

Answer:
Cellulose

Frequently Asked Questions

Q1. Why is glucose called aldohexose?

Answer:
Because glucose contains an aldehyde group and has six carbon atoms.

Q2. What are anomers?

Answer:
Anomers are stereoisomers that differ in configuration at the anomeric carbon atom.

Q3. Why does glucose not show aldehyde reactions?

Answer:
Because glucose mainly exists in cyclic hemiacetal form, where the free aldehyde group is absent.

Q4. What is the difference between D and L notation?

Answer:
D and L indicate configuration based on comparison with glyceraldehyde, not optical rotation.

Q1. What is a glycosidic linkage?

Answer:
A glycosidic linkage is an oxygen bridge joining two monosaccharide molecules formed by elimination of water.

Q2. Why is sucrose a non-reducing sugar?

Answer:
Because the aldehyde group of glucose and ketone group of fructose are involved in glycosidic bond formation, leaving no free reducing group.

Q3. Name the storage carbohydrates of plants and animals.

Answer:

Plant → Starch

Animal → Glycogen

Q4. Give the hydrolysis products of:

Sucrose:
Glucose + Fructose

Lactose:
Galactose + Glucose

Q5. Differentiate between starch and cellulose.

Starch	Cellulose
Made of α-glucose	Made of β-glucose
Storage polysaccharide	Structural polysaccharide
Digestible by humans	Not digested by humans

Q1. What are essential amino acids?

Answer:
Amino acids that cannot be synthesized by the body and must be obtained through diet are called essential amino acids.

Q2. What is peptide linkage?

Answer:
The amide bond formed between the –COOH group of one amino acid and –NH₂ group of another amino acid is called peptide linkage.

Q3. What happens during denaturation of proteins?

Answer:
Secondary and tertiary structures are destroyed, but the primary structure remains unchanged.

Q4. Name the two types of secondary protein structures.

Answer:

α-Helix
β-Pleated sheet

Q1. What are enzymes?

Answer:

Enzymes are biological catalysts that increase the rate of biochemical reactions. Most enzymes are globular proteins.

Q2. Why are enzymes called biocatalysts?

Answer:

Because they catalyse chemical reactions occurring in living organisms.

Q3. Why are vitamins required in small amounts?

Answer:

Vitamins regulate important biological functions and are needed only in small quantities for normal growth and health.

Q4. Classify vitamins.

Answer:

Vitamins are classified into:

Fat-soluble vitamins: A, D, E, K
Water-soluble vitamins: B group and C

Q5. Why can vitamin C not be stored in the body?

Answer:

Vitamin C is water soluble and is easily excreted through urine, so it cannot be stored.

Quick Revision Chart

ENZYMES
   |
Biological catalysts
   |
Mostly proteins
   |
Lower activation energy
   |
Highly specific


VITAMINS
   |
Small quantity required
   |
      ┌─────────────┐
      |             |
Fat soluble     Water soluble
A,D,E,K          B,C

Q1. What are nucleotides?

Answer:

Nucleotides are the basic structural units of nucleic acids. Each nucleotide contains a nitrogenous base, pentose sugar, and phosphate group.

Q2. Give the difference between nucleoside and nucleotide.

Answer:

A nucleoside contains sugar and nitrogenous base, whereas a nucleotide contains sugar, nitrogenous base, and phosphate group.

Q3. Name the bases present in DNA.

Answer:

DNA contains:

Adenine
Guanine
Cytosine
Thymine

Q4. Which base is present in RNA instead of thymine?

Answer:

Uracil.

Q5. Write the base pairing rule in DNA.

Answer:

Adenine pairs with thymine and guanine pairs with cytosine.

1. Why is sucrose non-reducing?

Because both reducing groups of glucose and fructose participate in glycosidic bond formation.

2. What is a peptide bond?

The amide bond formed between two amino acids is called a peptide bond.

3. What happens during protein denaturation?

Secondary and tertiary structures are destroyed while the primary structure remains unchanged.

4. Name the storage carbohydrates.

Plant → Starch
Animal → Glycogen

5. Write the components of a nucleotide.

Nitrogenous base
Pentose sugar
Phosphate group

I will prepare a high-quality copyright-free question bank from Class 12 Chemistry Chapter: Biomolecules based on the uploaded NCERT chapter.

The question bank will include:

✅ Multiple Choice Questions (MCQs)
✅ Multiple Correct Answer Questions
✅ Assertion–Reason Questions
✅ Fill in the Blanks
✅ True/False Questions
✅ Match the Following
✅ One-word Answer Questions
✅ Very Short Answer Questions
✅ Short Answer Questions
✅ Long Answer Questions
✅ Case-Based Questions

I will focus on quality over quantity — questions will test concepts, reactions, structures, differences, and NCERT-important points rather than simple repetition.

Because a complete quality question bank will be very long, I will provide it in parts.

Class 12 Chemistry

Chapter: Biomolecules

Part 1: Multiple Choice Questions (MCQs)

Section A: Carbohydrates

1. Carbohydrates are chemically defined as:

A. Polyhydroxy aldehydes or ketones
B. Hydrocarbons containing oxygen
C. Amino acids containing hydroxyl groups
D. Polymers of fatty acids

Answer: A

2. The simplest carbohydrates are:

A. Polysaccharides
B. Monosaccharides
C. Disaccharides
D. Oligosaccharides

Answer: B

3. Glucose is classified as:

A. Ketohexose
B. Aldopentose
C. Aldohexose
D. Ketopentose

Answer: C

4. Fructose is:

A. Aldohexose
B. Ketohexose
C. Aldopentose
D. Disaccharide

Answer: B

5. The molecular formula of glucose is:

A. C₆H₆O₆
B. C₆H₁₂O₆
C. C₁₂H₂₂O₁₁
D. C₅H₁₀O₅

Answer: B

6. Glucose is commonly known as:

A. Milk sugar
B. Cane sugar
C. Blood sugar
D. Malt sugar

Answer: C

7. Fructose is commonly called:

A. Fruit sugar
B. Milk sugar
C. Animal sugar
D. Malt sugar

Answer: A

8. Hydrolysis of sucrose gives:

A. Two glucose molecules
B. Glucose and fructose
C. Glucose and galactose
D. Fructose and galactose

Answer: B

9. Which of the following is a non-reducing sugar?

A. Glucose
B. Maltose
C. Lactose
D. Sucrose

Answer: D

10. The bond joining two monosaccharide units is called:

A. Peptide bond
B. Hydrogen bond
C. Glycosidic linkage
D. Ionic bond

Answer: C

11. Sucrose contains:

A. α-D-glucose and β-D-fructose
B. Two glucose molecules
C. Two fructose molecules
D. Glucose and galactose

Answer: A

12. Maltose is composed of:

A. Glucose + fructose
B. Glucose + glucose
C. Galactose + glucose
D. Fructose + fructose

Answer: B

13. Lactose is also known as:

A. Cane sugar
B. Fruit sugar
C. Milk sugar
D. Malt sugar

Answer: C

14. Which polysaccharide is stored in animals?

A. Cellulose
B. Starch
C. Glycogen
D. Amylose

Answer: C

15. The structural carbohydrate present in plant cell walls is:

A. Glycogen
B. Cellulose
C. Starch
D. Maltose

Answer: B

16. Starch is composed of:

A. α-D-glucose units
B. β-D-glucose units
C. Fructose units
D. Galactose units

Answer: A

17. Cellulose contains:

A. α-D-glucose units
B. β-D-glucose units
C. Fructose units
D. Ribose units

Answer: B

18. Amylose is:

A. Branched component of starch
B. Unbranched component of starch
C. Protein molecule
D. Disaccharide

Answer: B

19. Amylopectin contains:

A. Only linear chains
B. Branch points
C. Amino groups
D. Nitrogen atoms

Answer: B

20. Humans cannot digest cellulose because:

A. It is poisonous
B. It contains nitrogen
C. Humans lack enzyme to break β-linkage
D. It is a protein

Answer: C

Section B: Proteins and Amino Acids

21. Proteins are polymers of:

A. Fatty acids
B. Amino acids
C. Monosaccharides
D. Nucleotides

Answer: B

22. The general structure of an amino acid contains:

A. –NH₂ and –COOH groups
B. –OH and –CHO groups
C. Only –COOH group
D. Only –NH₂ group

Answer: A

23. The simplest amino acid is:

A. Alanine
B. Glycine
C. Valine
D. Lysine

Answer: B

24. Amino acids present naturally in proteins generally have:

A. D-configuration
B. L-configuration
C. No configuration
D. Racemic mixture

Answer: B

25. Amino acids that cannot be synthesised by the body are called:

A. Neutral amino acids
B. Essential amino acids
C. Acidic amino acids
D. Basic amino acids

Answer: B

26. The bond joining amino acids is:

A. Glycosidic bond
B. Peptide bond
C. Hydrogen bond
D. Ester bond

Answer: B

27. Peptide linkage is represented as:

A. –COO–
B. –NH₂
C. –CO–NH–
D. –OH

Answer: C

28. The primary structure of protein represents:

A. Folding of protein
B. Sequence of amino acids
C. Number of subunits
D. Helical structure

Answer: B

29. α-Helix and β-pleated sheet are examples of:

A. Primary structure
B. Secondary structure
C. Tertiary structure
D. Quaternary structure

Answer: B

30. Haemoglobin shows:

A. Primary structure only
B. Secondary structure only
C. Quaternary structure
D. No structure

Answer: C

31. Loss of biological activity of proteins due to heat or pH change is called:

A. Hydrolysis
B. Denaturation
C. Polymerisation
D. Reduction

Answer: B

32. During denaturation, which structure remains unchanged?

A. Secondary structure
B. Tertiary structure
C. Primary structure
D. Quaternary structure

Answer: C

Section C: Enzymes and Vitamins

33. Enzymes are mainly:

A. Carbohydrates
B. Proteins
C. Lipids
D. Minerals

Answer: B

34. Enzymes act as:

A. Reactants
B. Biological catalysts
C. Products
D. Inhibitors

Answer: B

35. Enzymes increase reaction rate by:

A. Increasing activation energy
B. Decreasing activation energy
C. Changing products
D. Increasing temperature

Answer: B

36. Vitamins soluble in fats are:

A. B and C
B. A, D, E and K
C. Only C
D. Only B

Answer: B

37. Vitamin C deficiency causes:

A. Rickets
B. Scurvy
C. Beriberi
D. Night blindness

Answer: B

38. Vitamin D deficiency causes:

A. Scurvy
B. Rickets
C. Beriberi
D. Anaemia

Answer: B

39. Vitamin B₁ deficiency causes:

A. Beriberi
B. Scurvy
C. Rickets
D. Blindness

Answer: A

40. Vitamin A deficiency causes:

A. Anaemia
B. Night blindness
C. Scurvy
D. Beriberi

Answer: B

Section D: Nucleic Acids

41. The basic unit of nucleic acids is:

A. Amino acid
B. Nucleotide
C. Monosaccharide
D. Fatty acid

Answer: B

42. A nucleotide consists of:

A. Sugar + base
B. Sugar + phosphate
C. Base + sugar + phosphate
D. Protein + phosphate

Answer: C

43. A nucleoside contains:

A. Nitrogenous base and sugar
B. Sugar and phosphate
C. Base and phosphate
D. Base, sugar and phosphate

Answer: A

44. The sugar present in DNA is:

A. Ribose
B. Glucose
C. Deoxyribose
D. Fructose

Answer: C

45. The sugar present in RNA is:

A. Ribose
B. Deoxyribose
C. Glucose
D. Galactose

Answer: A

46. Which nitrogenous base is present in DNA but absent in RNA?

A. Adenine
B. Guanine
C. Cytosine
D. Thymine

Answer: D

47. Which nitrogenous base replaces thymine in RNA?

A. Adenine
B. Uracil
C. Guanine
D. Cytosine

Answer: B

48. Purine bases are:

A. Cytosine and thymine
B. Adenine and guanine
C. Uracil and thymine
D. Cytosine and uracil

Answer: B

49. Pyrimidine bases include:

A. Adenine and guanine
B. Adenine and thymine
C. Cytosine, thymine and uracil
D. Guanine and cytosine

Answer: C

50. The double helix structure of DNA was proposed by:

A. Watson and Crick
B. Fischer and Haworth
C. Mendel and Darwin
D. Pasteur and Koch

Answer: A

51. In DNA, adenine pairs with:

A. Guanine
B. Cytosine
C. Thymine
D. Uracil

Answer: C

52. In DNA, guanine pairs with:

A. Adenine
B. Cytosine
C. Thymine
D. Uracil

Answer: B

53. The number of hydrogen bonds between A and T is:

A. One
B. Two
C. Three
D. Four

Answer: B

54. The number of hydrogen bonds between G and C is:

A. One
B. Two
C. Three
D. Four

Answer: C

55. The main function of DNA is:

A. Digestion of food
B. Storage of genetic information
C. Energy production
D. Hormone synthesis

Answer: B

56. mRNA stands for:

A. Messenger RNA
B. Molecular RNA
C. Modified RNA
D. Multiple RNA

Answer: A

57. tRNA helps in:

A. Carrying amino acids
B. Breaking proteins
C. Storing glucose
D. Forming lipids

Answer: A

58. rRNA is associated with:

A. Ribosomes
B. Mitochondria only
C. Cell membrane
D. Enzymes

Answer: A

Section E: Mixed Concept MCQs

59. Which one is a reducing sugar?

A. Sucrose
B. Maltose
C. Cellulose
D. Starch

Answer: B

60. Which carbohydrate is called animal starch?

A. Cellulose
B. Starch
C. Glycogen
D. Sucrose

Answer: C

61. The storage carbohydrate of plants is:

A. Glycogen
B. Starch
C. Cellulose
D. Lactose

Answer: B

62. Which molecule contains peptide bonds?

A. Protein
B. Starch
C. DNA
D. Vitamin C

Answer: A

63. Which biomolecule contains glycosidic linkage?

A. Carbohydrates
B. Proteins
C. Vitamins
D. Minerals

Answer: A

64. The bond between amino acids is formed by:

A. Elimination of ammonia
B. Elimination of water
C. Addition of oxygen
D. Removal of carbon dioxide

Answer: B

65. Which amino acid is optically inactive?

A. Alanine
B. Valine
C. Glycine
D. Lysine

Answer: C

66. A protein with multiple polypeptide chains has:

A. Primary structure
B. Secondary structure
C. Tertiary structure
D. Quaternary structure

Answer: D

67. The α-helix structure of proteins is stabilised mainly by:

A. Ionic bonds
B. Hydrogen bonds
C. Glycosidic bonds
D. Peptide bonds

Answer: B

68. The enzyme-substrate complex is formed at:

A. Active site of enzyme
B. Nucleus
C. Cell wall
D. Ribosome

Answer: A

69. Vitamin K deficiency affects:

A. Vision
B. Blood clotting
C. Bone formation
D. Digestion

Answer: B

70. Vitamin B₁₂ deficiency causes:

A. Scurvy
B. Pernicious anaemia
C. Rickets
D. Beriberi

Answer: B

Section F: Multiple Correct Answer Questions

(More than one option may be correct)

71. Which of the following are monosaccharides?

A. Glucose
B. Fructose
C. Sucrose
D. Ribose

Answers: A, B, D

72. Which of the following are polysaccharides?

A. Starch
B. Cellulose
C. Glycogen
D. Lactose

Answers: A, B, C

73. Which are reducing sugars?

A. Glucose
B. Maltose
C. Lactose
D. Sucrose

Answers: A, B, C

74. Which are fat-soluble vitamins?

A. Vitamin A
B. Vitamin D
C. Vitamin E
D. Vitamin C

Answers: A, B, C

75. Components of a nucleotide are:

A. Nitrogenous base
B. Pentose sugar
C. Phosphate group
D. Amino acid

Answers: A, B, C

76. Which are nitrogenous bases of DNA?

A. Adenine
B. Guanine
C. Thymine
D. Uracil

Answers: A, B, C

77. Functions of proteins include:

A. Growth and repair
B. Enzyme formation
C. Genetic information storage
D. Structural roles

Answers: A, B, D

78. Characteristics of enzymes include:

A. High specificity
B. Biological catalytic activity
C. Consumption during reaction
D. Lowering activation energy

Answers: A, B, D

79. Examples of globular proteins are:

A. Insulin
B. Albumin
C. Keratin
D. Haemoglobin

Answers: A, B, D

80. Examples of fibrous proteins are:

A. Keratin
B. Myosin
C. Insulin
D. Silk protein

Answers: A, B, D

Section A: Assertion–Reason Questions

Instructions:

Choose the correct option:

A. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
B. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
C. Assertion is true, but Reason is false.
D. Assertion is false, but Reason is true.

1.

Assertion: Glucose is called an aldohexose.
Reason: Glucose contains an aldehyde group and six carbon atoms.

Answer: A

2.

Assertion: Fructose is a ketohexose.
Reason: Fructose contains a ketone group and six carbon atoms.

Answer: A

3.

Assertion: Sucrose is a non-reducing sugar.
Reason: Both reducing groups of glucose and fructose participate in glycosidic bond formation.

Answer: A

4.

Assertion: Maltose is a reducing sugar.
Reason: It contains a free aldehyde group.

Answer: A

5.

Assertion: Cellulose cannot be digested by humans.
Reason: Humans do not have enzymes to break β-glycosidic bonds.

Answer: A

6.

Assertion: Glycogen is called animal starch.
Reason: It is the storage polysaccharide of animals.

Answer: A

7.

Assertion: Starch is a polymer of α-D-glucose.
Reason: Starch contains amino acid units joined by peptide bonds.

Answer: C

8.

Assertion: Proteins are polymers.
Reason: Proteins are made up of amino acid units.

Answer: A

9.

Assertion: Glycine is optically inactive.
Reason: Glycine has two hydrogen atoms attached to the α-carbon.

Answer: A

10.

Assertion: Peptide bonds are amide linkages.
Reason: They are formed between amino and carboxyl groups of amino acids.

Answer: A

11.

Assertion: Enzymes are biological catalysts.
Reason: Enzymes increase reaction rate by lowering activation energy.

Answer: A

12.

Assertion: Vitamins are required in small quantities.
Reason: They regulate many important biological functions.

Answer: A

13.

Assertion: Vitamin C is stored in the human body in large amounts.
Reason: Vitamin C is water soluble.

Answer: D

14.

Assertion: DNA contains thymine.
Reason: RNA contains uracil instead of thymine.

Answer: B

15.

Assertion: Adenine forms a pair with thymine in DNA.
Reason: They form two hydrogen bonds.

Answer: A

Section B: Fill in the Blanks

1. Carbohydrates are also called ______ compounds.

Answer: polyhydroxy aldehydes or ketones

2. Glucose is an example of ______.

Answer: aldohexose

3. Fructose contains a ______ group.

Answer: ketone

4. The bond joining two monosaccharides is called a ______ linkage.

Answer: glycosidic

5. Sucrose is commonly known as ______ sugar.

Answer: cane

6. Lactose is also called ______ sugar.

Answer: milk

7. Maltose contains two molecules of ______.

Answer: glucose

8. The storage carbohydrate in plants is ______.

Answer: starch

9. The storage carbohydrate in animals is ______.

Answer: glycogen

10. Cellulose is made up of ______ glucose units.

Answer: β-D

11. Proteins are polymers of ______.

Answer: amino acids

12. The bond between amino acids is called a ______ bond.

Answer: peptide

13. The simplest amino acid is ______.

Answer: glycine

14. The zwitterionic form of amino acids contains both and charges.

Answer: positive, negative

15. The sequence of amino acids in protein represents its ______ structure.

Answer: primary

16. α-Helix is a type of ______ protein structure.

Answer: secondary

17. Loss of biological activity of protein is called ______.

Answer: denaturation

18. Enzymes reduce the ______ energy of reactions.

Answer: activation

19. Vitamin A deficiency causes ______ blindness.

Answer: night

20. Vitamin C deficiency causes ______.

Answer: scurvy

21. DNA contains ______ sugar.

Answer: deoxyribose

22. RNA contains ______ sugar.

Answer: ribose

23. A nucleotide consists of sugar, phosphate and ______.

Answer: nitrogenous base

24. Adenine pairs with ______ in DNA.

Answer: thymine

25. Guanine pairs with ______ in DNA.

Answer: cytosine

Section C: True or False

1. Glucose is a ketohexose.

Answer: False

2. Fructose is a monosaccharide.

Answer: True

3. Sucrose is a reducing sugar.

Answer: False

4. Maltose contains two glucose units.

Answer: True

5. Cellulose is the storage carbohydrate of animals.

Answer: False

6. Glycogen is highly branched.

Answer: True

7. Proteins are made up of nucleotides.

Answer: False

8. Amino acids contain amino and carboxyl groups.

Answer: True

9. Glycine is optically active.

Answer: False

10. Peptide linkage is represented as –CO–NH–.

Answer: True

11. Enzymes are consumed during reactions.

Answer: False

12. Vitamins are required in large quantities.

Answer: False

13. Vitamin D deficiency causes rickets.

Answer: True

14. DNA contains uracil.

Answer: False

15. RNA helps in protein synthesis.

Answer: True

Section D: Match the Following

1.

Column I	Column II
Glucose	Aldohexose
Fructose	Ketohexose
Lactose	Milk sugar
Sucrose	Cane sugar

Answer:

Glucose → Aldohexose
Fructose → Ketohexose
Lactose → Milk sugar
Sucrose → Cane sugar

2.

Column I	Column II
Vitamin A	Night blindness
Vitamin C	Scurvy
Vitamin D	Rickets
Vitamin K	Blood clotting

Answer:

A → Night blindness
C → Scurvy
D → Rickets
K → Blood clotting

3.

Column I	Column II
DNA	Genetic information
mRNA	Carries message
tRNA	Transfers amino acids
rRNA	Ribosome component

Answer:

DNA → Genetic information
mRNA → Carries message
tRNA → Transfers amino acids
rRNA → Ribosome component

4.

Column I	Column II
Starch	Plants
Glycogen	Animals
Cellulose	Plant cell wall
Protein	Amino acids

Answer:

Starch → Plants
Glycogen → Animals
Cellulose → Plant cell wall
Protein → Amino acids

Part 4: One-Word, Very Short Answer, Short Answer, Long Answer & Case-Based Questions

Section A: One-Word Answer Questions

1. Name the simplest monosaccharide.

Answer: Glucose

2. Name the sugar present in DNA.

Answer: Deoxyribose

3. Name the sugar present in RNA.

Answer: Ribose

4. Name the storage polysaccharide of animals.

Answer: Glycogen

5. Name the structural polysaccharide of plants.

Answer: Cellulose

6. Name the bond joining monosaccharide units.

Answer: Glycosidic bond

7. Name the bond joining amino acids.

Answer: Peptide bond

8. Name the amino acid that is optically inactive.

Answer: Glycine

9. Name the biological catalysts.

Answer: Enzymes

10. Name the vitamin responsible for preventing scurvy.

Answer: Vitamin C

11. Name the vitamin deficiency causing rickets.

Answer: Vitamin D

12. Name the nucleic acid responsible for hereditary information.

Answer: DNA

13. Name the RNA that carries amino acids.

Answer: tRNA

14. Name the RNA present in ribosomes.

Answer: rRNA

15. Name the scientist(s) who proposed the DNA double helix model.

Answer: Watson and Crick

Section B: Very Short Answer Questions

1. What are carbohydrates?

Answer:

Carbohydrates are polyhydroxy aldehydes, polyhydroxy ketones, or compounds that produce them on hydrolysis.

2. What are monosaccharides?

Answer:

Monosaccharides are the simplest carbohydrates that cannot be hydrolysed into smaller carbohydrate units.

Examples:

Glucose
Fructose

3. Why is glucose called aldohexose?

Answer:

Glucose contains an aldehyde group and six carbon atoms, so it is called aldohexose.

4. Why is fructose called ketohexose?

Answer:

Fructose contains a ketone group and six carbon atoms, so it is called ketohexose.

5. What is a glycosidic linkage?

Answer:

The bond formed between two monosaccharide molecules by loss of water is called a glycosidic linkage.

6. Why is sucrose non-reducing?

Answer:

Sucrose is non-reducing because both reducing groups participate in glycosidic bond formation.

7. Define polysaccharides.

Answer:

Polysaccharides are carbohydrates made up of a large number of monosaccharide units joined together.

Examples:

Starch
Cellulose

8. What are essential amino acids?

Answer:

Amino acids that cannot be synthesised by the human body and must be obtained through diet are called essential amino acids.

9. What is a zwitter ion?

Answer:

A zwitter ion is a dipolar form of amino acid containing both positive and negative charges.

10. What is denaturation of proteins?

Answer:

The loss of biological activity of proteins due to changes in temperature or pH is called denaturation.

11. What are enzymes?

Answer:

Enzymes are biological catalysts that increase the rate of biochemical reactions.

12. Why are vitamins needed in small amounts?

Answer:

Vitamins regulate important biological functions and are required only in small quantities.

13. What is a nucleotide?

Answer:

A nucleotide is the basic unit of nucleic acids containing:

Nitrogenous base
Sugar
Phosphate group

14. What is a nucleoside?

Answer:

A nucleoside contains a nitrogenous base and sugar but no phosphate group.

15. Write the complementary base pairs in DNA.

Answer:

Adenine pairs with thymine.

Guanine pairs with cytosine.

Section C: Short Answer Questions

1. Differentiate between reducing and non-reducing sugars.

Answer:

Reducing Sugars	Non-Reducing Sugars
Have free reducing groups	Do not have free reducing groups
Give positive reducing tests	Do not give reducing tests
Example: glucose, maltose	Example: sucrose

2. Explain the classification of carbohydrates.

Answer:

Carbohydrates are classified into:

(a) Monosaccharides

Simplest carbohydrates.

Examples:

Glucose
Fructose

(b) Disaccharides

Contain two monosaccharide units.

Examples:

Sucrose
Maltose
Lactose

(c) Polysaccharides

Contain many monosaccharide units.

Examples:

Starch
Cellulose
Glycogen

3. Explain the formation of a peptide bond.

Answer:

A peptide bond is formed when the carboxyl group of one amino acid reacts with the amino group of another amino acid with elimination of water.

The linkage formed is:

–CO–NH–

4. Explain the levels of protein structure.

Answer:

Proteins have four levels:

Primary structure:

Sequence of amino acids.

Secondary structure:

Folding into α-helix or β-pleated sheet.

Tertiary structure:

Three-dimensional folding of a single chain.

Quaternary structure:

Arrangement of multiple polypeptide chains.

5. Explain the classification of vitamins.

Answer:

Vitamins are classified into:

Fat-soluble vitamins:

Water-soluble vitamins:

B-group
C

6. Write differences between DNA and RNA.

Answer:

DNA	RNA
Contains deoxyribose sugar	Contains ribose sugar
Double-stranded	Usually single-stranded
Contains thymine	Contains uracil
Stores genetic information	Helps in protein synthesis

Section D: Long Answer Questions

1. Explain the structure and functions of DNA.

Answer:

DNA is a nucleic acid responsible for storing genetic information.

It consists of nucleotides containing:

Nitrogenous base
Deoxyribose sugar
Phosphate group

According to Watson and Crick, DNA has a double helical structure.

Features:

Two complementary strands
Sugar-phosphate backbone
Base pairing through hydrogen bonds

Base pairing:

A = T

G ≡ C

Functions:

Stores hereditary information
Transfers genetic information
Controls protein synthesis

2. Explain enzymes and their mechanism of action.

Answer:

Enzymes are biological catalysts that increase the rate of biochemical reactions.

Characteristics:

Mostly proteins
Highly specific
Reduce activation energy

Mechanism:

Step 1:

Enzyme binds with substrate.

↓

Step 2:

Enzyme-substrate complex forms.

↓

Step 3:

Product is formed and enzyme is released.

3. Explain different types of proteins.

Answer:

Proteins are classified as:

Fibrous proteins:

Long fibre-like structures
Generally insoluble
Provide structural support

Example:
Keratin

Globular proteins:

Spherical structures
Usually soluble

Examples:
Insulin, haemoglobin

Section E: Case-Based Questions

Case Study 1: Carbohydrates

A student studied different carbohydrates and found that glucose is a monosaccharide, sucrose is a disaccharide, and starch is a polysaccharide.

Questions:

1. Glucose belongs to which category?

Answer: Monosaccharide

2. Sucrose contains which two sugars?

Answer: Glucose and fructose

3. Name the storage polysaccharide of plants.

Answer: Starch

4. Why is sucrose called non-reducing sugar?

Answer: Because its reducing groups are involved in glycosidic bond formation.

Case Study 2: Proteins

Proteins are formed by joining amino acids through peptide bonds. Their structure determines their function.

Questions:

1. What are the building blocks of proteins?

Answer: Amino acids

2. Name the bond joining amino acids.

Answer: Peptide bond

3. Which structure represents amino acid sequence?

Answer: Primary structure

4. What happens during denaturation?

Answer: Secondary and tertiary structures are destroyed while primary structure remains unchanged.

Case Study 3: Nucleic Acids

DNA and RNA are nucleic acids involved in genetic activities.

Questions:

1. What is the basic unit of nucleic acids?

Answer: Nucleotide

2. Which sugar is present in DNA?

Answer: Deoxyribose

3. Which base replaces thymine in RNA?

Answer: Uracil

4. Which RNA carries amino acids?

Answer: tRNA

Part 4 Completed (Questions 141–200)

Next part will contain:

✅ Part 5: Highest-level Board Practice Set

HOTS questions
Previous-year style questions
Assertion-based case studies
Complete chapter mock test (50 marks)
Answer key included.

Part 5: HOTS Questions + Board Pattern Questions + Full Chapter Mock Test

Section A: HOTS (Higher Order Thinking Skill) Questions

1. Why does glucose exist mainly in cyclic form rather than open-chain form?

Answer:

Glucose contains both aldehyde and hydroxyl groups. These groups react within the molecule to form a cyclic hemiacetal structure, which is more stable than the open-chain form.

2. Why is sucrose called an invert sugar after hydrolysis?

Answer:

Sucrose hydrolyses to form glucose and fructose. The optical rotation of the mixture changes because fructose has opposite optical rotation compared to glucose. Therefore, the product mixture is called invert sugar.

3. Why can humans digest starch but not cellulose?

Answer:

Starch contains α-glycosidic linkages that can be broken by human enzymes, whereas cellulose contains β-glycosidic linkages that humans cannot hydrolyse due to the absence of suitable enzymes.

4. Why are proteins called polymers?

Answer:

Proteins are formed by the repeated joining of many amino acid molecules through peptide bonds, making them polymers.

5. Why do amino acids have high melting points?

Answer:

Amino acids exist as zwitter ions containing positive and negative charges. Due to ionic interactions between these ions, they have high melting points.

6. Why does denaturation not affect the primary structure of proteins?

Answer:

Denaturation breaks weak interactions such as hydrogen bonds and affects higher-level structures, but peptide bonds of the primary structure remain intact.

7. Why are enzymes highly specific?

Answer:

Enzymes contain specific active sites with shapes complementary to particular substrates, allowing only specific reactions.

8. Why are vitamins required in very small amounts?

Answer:

Vitamins mainly regulate metabolic activities and act as essential helpers in biological processes, so only small quantities are needed.

9. Why is DNA suitable for storage of genetic information?

Answer:

DNA has a stable double helical structure with complementary base pairing, allowing accurate storage and copying of genetic information.

10. Why is RNA important even though DNA stores genetic information?

Answer:

RNA acts as an intermediate molecule that helps convert genetic information stored in DNA into proteins.

Section B: Board Pattern Short Questions

1. Write two differences between starch and cellulose.

Answer:

Starch	Cellulose
Polymer of α-D-glucose	Polymer of β-D-glucose
Storage carbohydrate	Structural carbohydrate

2. Give two examples of essential amino acids.

Answer:

Examples:

Valine
Lysine

3. Name the two types of secondary structures of proteins.

Answer:

α-Helix
β-Pleated sheet

4. What are fibrous proteins? Give one example.

Answer:

Fibrous proteins are proteins having long fibre-like structures and are generally insoluble in water.

Example:

Keratin

5. What are globular proteins? Give one example.

Answer:

Globular proteins have spherical folded structures and are generally soluble in water.

Example:

Insulin

6. Name the vitamins that are fat soluble.

Answer:

Vitamin:

7. Name the deficiency disease caused by lack of vitamin C.

Answer:

Scurvy

8. What is the role of tRNA?

Answer:

tRNA carries amino acids to ribosomes during protein synthesis.

9. What is the function of mRNA?

Answer:

mRNA carries genetic information from DNA to ribosomes.

10. What is the function of rRNA?

Answer:

rRNA forms an important component of ribosomes.

Section C: Long Answer Board Questions

1. Explain the classification of carbohydrates with examples.

Answer:

Carbohydrates are classified into three categories:

1. Monosaccharides

These are the simplest carbohydrates.

Examples:

Glucose
Fructose

2. Disaccharides

They contain two monosaccharide units.

Examples:

Sucrose
Maltose
Lactose

3. Polysaccharides

They contain many monosaccharide units.

Examples:

Starch
Cellulose
Glycogen

2. Explain the structure of proteins.

Answer:

Protein structure is divided into four levels:

Primary Structure:

The sequence of amino acids in a protein chain.

Secondary Structure:

Regular folding of the chain into:

α-helix
β-pleated sheet

Tertiary Structure:

Overall three-dimensional folding of a single chain.

Quaternary Structure:

Arrangement of multiple polypeptide chains.

3. Explain DNA structure according to Watson and Crick model.

Answer:

DNA has a double helical structure.

Important features:

Two polynucleotide chains are present.
Chains are complementary.
Sugar-phosphate backbone forms the outer part.
Nitrogen bases are present inside.
Adenine pairs with thymine.
Guanine pairs with cytosine.

This structure allows DNA to store and transmit genetic information.

Section D: Complete Chapter Mock Test

Class 12 Chemistry — Biomolecules

Maximum Marks: 50

Part A: MCQs (1 × 10 = 10 Marks)

1. The monomer unit of proteins is:

A. Glucose
B. Amino acid
C. Nucleotide
D. Fatty acid

Answer: B

2. Vitamin C deficiency causes:

A. Rickets
B. Scurvy
C. Beriberi
D. Anaemia

Answer: B

3. The sugar present in RNA is:

A. Ribose
B. Glucose
C. Deoxyribose
D. Fructose

Answer: A

4. Sucrose is:

A. Reducing sugar
B. Non-reducing sugar
C. Polysaccharide
D. Monosaccharide

Answer: B

5. The bond joining amino acids is:

A. Glycosidic bond
B. Peptide bond
C. Hydrogen bond
D. Ionic bond

Answer: B

6. Animal storage carbohydrate is:

A. Starch
B. Cellulose
C. Glycogen
D. Maltose

Answer: C

7. DNA contains:

A. Uracil
B. Thymine
C. Ribose
D. Fructose

Answer: B

8. Enzymes are:

A. Proteins
B. Sugars
C. Vitamins
D. Minerals

Answer: A

9. Vitamin D deficiency causes:

A. Scurvy
B. Rickets
C. Beriberi
D. Blindness

Answer: B

10. Genetic information is stored in:

A. RNA
B. Protein
C. DNA
D. Vitamins

Answer: C

Part B: Short Answer (2 × 5 = 10 Marks)

1. Define nucleoside.

Answer:

A nucleoside contains a nitrogenous base and sugar but no phosphate group.

2. Define denaturation.

Answer:

Loss of biological activity of proteins due to change in temperature or pH is called denaturation.

3. Write two examples of polysaccharides.

Answer:

Starch
Cellulose

4. Name two water-soluble vitamins.

Answer:

Vitamin B group
Vitamin C

5. Write the base pairing rule of DNA.

Answer:

Adenine pairs with thymine and guanine pairs with cytosine.

Part C: Long Answer (5 × 6 = 30 Marks)

1. Explain peptide bond formation.

Answer:

When the amino group of one amino acid reacts with the carboxyl group of another amino acid, water is eliminated and a peptide bond is formed.

The linkage formed is:

–CO–NH–

2. Explain different types of RNA.

Answer:

Three types of RNA are:

mRNA:
Carries genetic information.

tRNA:
Transfers amino acids.

rRNA:
Forms ribosomes.

3. Explain vitamins classification.

Answer:

Vitamins are:

Fat-soluble:
A, D, E, K

Water-soluble:
B group and C

4. Explain enzyme action.

Answer:

Enzyme combines with substrate at active site to form enzyme-substrate complex. The product is formed and enzyme is released unchanged.

5. Explain protein classification.

Answer:

Proteins are:

Fibrous proteins:
Long fibre-like structures, insoluble.

Example: Keratin

Globular proteins:
Spherical structures, soluble.

Example: Insulin