NCERT Solutions for Class 11 Biology Chapter 9 – Biomolecules

NCERT Solutions for Class 11 Biology Chapter 9 – Biomolecules include a very essential topic of biology called ‘Biomolecules’. This particular chapter of NCERT Biology textbook discusses Biomolecules in an in-depth manner and provides an insight into the types of Biomolecules like Carbohydrates, Proteins, Amino acids etc. So in order to make your fundamentals stronger, you will need to refer to the NCERT Solutions as and when required. 

This chapter has 15 questions whose solutions we have provided for your reference. Biology, no doubt, can become a difficult subject to tackle in Class 11 if you are not sure about your basic concepts of Biomolecules. Keeping this in mind, subject experts at Instasolv have drafted this NCERT Solutions for Class 11 Chapter 9- Biomolecules in the simplest yet comprehensive manner. It is highly advised that you add these solutions to your everyday study collection. 

Important Topics for NCERT Solutions for Class 11 Biology Chapter 9- Biomolecules

In chapter 9 of class 11 biology, you will learn about the molecules which are involved in the maintenance and metabolic processes of living organisms. They include Carbohydrates, Lipid, Proteins, Nucleic acid and water molecules and are collectively known as Biomolecules. They can be classified into two types:

  1. Micromolecules: A molecule which is relatively of low molecular weight (1000 Daltons) that can regulate a biological process. All molecules like Amino acids, Carbohydrates, Sugars, Lipids fall under Micromolecules
  2. Macromolecules: A very large molecule. All molecules like Proteins and Nucleic acid falls under Macromolecules

Amino acids:

Alpha-Amino acids are simple molecules that are made of a central C-atom, bound to a primary NH2 group and COOH group. There are 20 amino acids known till date. Amino acids can be classified into acidic, basic and neutral amino acids on the basis of the number of amino and carboxyl groups. 

The amino acids which can be synthesized in our body are known as non-essential amino acids.

Example: Alanine, Cysteine and Glutamate. The amino acids which cannot be synthesized in the

body and have to be consumed manually are known essential amino acids. Example: Histidine,

Valine and Lysine.


Group of organic compounds based on the general formula Cx(H2O)y. The simplest carbohydrates are the sugars (saccharides), including glucose and sucrose. Polysaccharides are carbohydrates of much greater molecular weight and complexity (Starch, Glycogen and Cellulose).


    • Group of organic compounds, which are insoluble in water but are soluble in organic solvents such as benzene etc.
    • Lipids are broadly classified into two categories: complex and simple lipids.


  • Complex lipids: long-chain fatty acids including glycerides (fats and oils of animals and plants), glycolipids, phospholipids and waxes.
  • Simple lipids: doesn’t contain fatty acids and include steroids and terpenes.
  • Functions:


  1. A convenient means for storage of food energy in plants and animals.
  2. Waxes provide vital waterproofing for body surfaces.
  3. Terpenes include vitamins A, E and K and phytol (a component of chlorophyll) and occur in essential oils, such as menthol and camphor
  • Lipids can combine with protein to form Lipoproteins and polysaccharides to form Lipopolysaccharides.


They are polypeptides, linear chains of amino acids linked by polypeptide bonds.

Structure of proteins:


  • Primary structure: amino acids linked together by peptide bonds to form polypeptide chains. 
  • Secondary structure: polypeptide chains fold into regular structures. Types: 


  • Alpha helix: helical structure secured by hydrogen bonding. 
  • Beta pleated sheet: folded or pleated with hydrogen bonding.


  • Tertiary structure: forms when long chains fold into a hollow, woollen ball-like structure. Forces securing the structure are Hydrophobic interactions, Hydrogen bonding, Ionic Bonding and Van der Waals forces. 
  • Quaternary structure: it’s the assembly of more than one-unit polypeptides or subunit. 


Nucleic acids:

These are polynucleotides (nucleotides are the building blocks)

Components of a nucleotide- 

  1. Heterocyclic compound: nitrogenous bases. Ex: purines (adenine, guanine) and pyrimidines (uracil, thymidine, cytosine).
  2. A monosaccharide
  3. A phosphate unit


These are the catalysts of various biochemical reactions. 

They are globular proteins with an ‘active site’ to which a Substrate ‘S’ binds to form a product ‘P’. 

Enzyme cycle:

  1. Substrate(S) binds and fits into the active site of the enzyme(E).
  2. The enzyme alters its shape and binds more tightly to the Substrate forming the enzyme-substrate(ES) complex which is short-lived. 
  3. The active site breaks chemical bonds of the substrate and the ES dissociates to products(P) and the unchanged enzyme which forms an intermediate enzyme-product(EP) complex.
  4. The free enzyme is ready to bind to another substrate and continue the reaction. 

Discussion of Exercises for NCERT Biology Class 11 Solutions for Chapter 9

  • The first five exercises of the chapter are about the structure of proteins. 
  • Questions six and seven are about the composition of triglycerides and applications of proteins.
  • In some questions, you need to draw diagrams of amino acids. 
  • The exercise also includes questions about enzymes. 

To give you the ultimate opportunity to learn the varied and difficult concepts associated with “Biomolecules” in an elaborate and easy-to-understand manner, the NCERT solutions for Class 11 Biology Chapter 9 have been prepared by Instasolv. So take the guidance of these solutions to complete your homework or solve examination questions with flare and perfection.