Class 12 Chemistry Chapter 10 Biomolecules NCERT Solutions

See below the key highlights of the Biomolecules chapter:

• Carbohydrates are classified into three groups - monosaccharides, disaccharides and polysaccharides.
• Glucose is obtained from starch and it is the most important source of energy in mammals.
• Proteins are the polymers of the 20 different amino acids, which are linked by peptide bonds.
• The chapter covers the 10 essential amino acids. These should be provided by the diet as they cannot be synthesized by our body.
• It covers the secondary or tertiary structure of proteins and the denaturation of proteins.
• The chapter covers the vitamins, which are classified as the fat-soluble A, D, E, and K and the water-soluble B and C groups.
• There are two types of nucleic acids - DNA and RNA.

For comprehensive notes of Class 12 Physics, Chemistry & Maths, the students need to click on NCERT Class 12 Notes.

Biomolecules Class 12 is an important chapter of Chemistry. The main topics on which the students should focus for the entrance exam include carbohydrates, nucleic acids, proteins, and enzymes. Also, on the properties, structures, and functions of carbohydrates, proteins, amino acids, lipids, and nucleic acids. See the table below for the topics covered in the Biomolecules chapter:

Exercise	Topics Covered
10.1	Carbohydrates
10.2	Proteins
10.3	Enzymes
10.4	Vitamins
10.5	Nucleic Acids
10.6	Hormones

Class 12 Biomolecules Weightage in NEET, JEE Main Exams

Exam	Number of Questions	Weightage
NEET	few questions, often around 6	10-15%
JEE Main	3-4 questions	8-9%

Important Reactions of Class 12 Chemistry Biomolecules 

1. Reactions of Carbohydrates

Reduction of Aldoses and Ketoses

• • Glucose + H₂ → Sorbitol (CH₂OH-(CHOH)₄-CH₂OH)

  • (Using reducing agents like NaBH₄ or H₂/Ni)

Oxidation Reactions

• • Mild oxidation (Br₂):

    • Glucose → Gluconic acid

  • Strong oxidation (HNO₃):

    • Glucose → Saccharic acid

Osazone Formation

• • Glucose + Phenylhydrazine → Glucosazone
    (Used to distinguish sugars)

Glycosidic Bond Formation

• • Monosaccharide + Alcohol → Glycoside

    • e.g., Glucose + Methanol → Methyl glucoside

Mutarotation

• • α-Glucose ⇌ β-Glucose (in aqueous solution)
    (Change in optical rotation due to ring–open–ring conversion)

2. Reactions of Proteins (Amino Acids)

Zwitter Ion Formation

• • H₂N–CH(R)–COOH ⇌ ⁺H₃N–CH(R)–COO⁻

Peptide Bond Formation

• • Amino Acid₁ + Amino Acid₂ → Dipeptide + H₂O
    -COOH + -NH₂ → -CO-NH- (Peptide bond)

Reaction with Ninhydrin (For detection of α-amino acids)

• • Amino acid + Ninhydrin → Purple/blue complex

Reaction with Formaldehyde (Used in titration)

• • NH₂ group reacts with HCHO to form methylene derivative

3. Reactions of Nucleic Acids

Hydrolysis of DNA/RNA

• • DNA/RNA + H₂O (acid or enzyme) → Sugar + Phosphoric acid + Nitrogenous base

Formation of Nucleoside

• • Sugar + Base → Nucleoside

Formation of Nucleotide

• • Nucleoside + Phosphate → Nucleotide

Phosphodiester Bond Formation

• • Nucleotide₁ + Nucleotide₂ → Dinucleotide + H₂O

4. Reactions of Enzymes

Catalysis Reaction

• • Substrate + Enzyme → Enzyme-substrate complex → Product + Enzyme

Temperature and pH Sensitivity

• • Enzymes are deactivated at high temperatures or extreme pH

5. Tests for Biomolecules

Fehling’s and Benedict’s Test (for Reducing Sugars)

• • Glucose + Fehling’s → Red ppt of Cu₂O

Biuret Test (for Proteins)

• • Protein + Biuret reagent → Violet color

Xanthoproteic Test (for Aromatic Amino Acids)

• • Protein + HNO₃ → Yellow color

The link is given below for students to download the free Biomolecules NCERT PDF. These solutions are aligned with the NCERT syllabus. The NCERT solutions are prepared by the subject matter experts to help students get a high score in the CBSE Board exam and other entrance exams like NEET and JEE Main.
Download Here: NCERT Solution for Class XII Chemistry Biomolecules PDF

Read Here

NCERT Notes for Class 11 & 12

Class 12 Chemistry NCERT Solutions

NCERT Solutions Class 11 and 12 for Maths, Physics, Chemistry

 

NCERT Chemistry Biomolecules intext solutions are provided here. Students can verify their answers using the biomolecules chemistry class 12 ncert solutions. Intext questions are based on the topics taught in class 12 Chemistry Ch 10 Biomolecules.

Q 14.1 Glucose or sucrose is soluble in water but cyclohexane or benzene (simple six membered ring compounds) is insoluble in water. Explain.

Ans Glucose and sucrose are carbohydrates (optically active polyhydroxy aldehydes or ketones).  Structure of glucose: Structure of sucrose: As you can see both the compounds have five –OH and eight –OH groups respectively. These –OH groups are responsible for the extensive hydrogen bonding with water. This –H bonding is responsible for the solubility of glucose and sucrose in water. In case of cyclohexane or benzene (simple six-membered ring compounds) , they do not contain any – OH groups. Hence, they cannot undergo –H bonding with water and are insoluble.

Q 14.2 What are the expected products of hydrolysis of lactose?

Ans Lactose is a disaccharide carbohydrate (made up of two monosaccharide units) composed of β-D-galactose and β-D-glucose units. Hydrolysis breaks the glycosidic bond converting sucrose into β-D- galactose and β-D-glucose. NOTE: But however, this reaction is so slow that it takes years for the solution of sucrose to undergo negligible change. Hence an enzyme called sucrase is added to proceed rapidly.

Q 14.3 How do you explain the absence of aldehyde group in the pentaacetate of D-glucose?

Ans D-glucose reacts with hydroxylamine (NH2OH) to form oxime due to the presence of the aldehyde functional group (-CHO). This is due to the cyclic structure of glucose which forms an open chain structure in an aqueous medium, which then reacts to give an oxime. But in case of pentaacetate of D-glucose, it does not form open chain structure in an aqueous medium so it does not react with NH2OH.

Q 14.4 The melting points and solubility in water of amino acids are generally higher than that of the corresponding halo acids. Explain.

Ans Amino acids are organic compounds containing amine (basic) and carboxyl (acidic) functional group with a specific side chain. Both acidic and basic group are present in the same molecule. In, aqueous solution carboxyl group can lose a proton (H+) and amino group can accept a proton (H+) giving rise to the dipolar ion called as zwitter ion. Zwitter ion is shown below: In this zwitter ion there is the presence of both positive as well as negative charge, so there is the development of strong electrostatic force of attraction between the molecules and the water. For this reason solubility of amino acids is higher. Due to strong electrostatic interaction there is formation of strong bond between them, hence the melting point of amino acid is higher than the halo acids (as they do not exhibit such dipolar behaviour).

• Familiarise yourself with various questions on a single topic 

• Enhance Conceptual knowledge 

• Improve problem-solving skills 

• Help to improve time management skills 

• Best for practice and revision 

• Best resource to prepare for the board exam and other entrance tests