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NCERT Notes for Class 11 Biology Chapter 9 Biomolecules- Download PDF Notes
Edited By Irshad Anwar | Updated on Apr 05, 2025 12:28 PM IST
NCERT Notes for Class 11 Biology Chapter 9 Biomolecules: Biology is the study of life, and at the core of it, biomolecules play a significant part in maintaining life processes. This chapter of NCERT explores the structure, function, and importance of these vital organic molecules that serve as the building units of life.
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This Story also Contains
- What Are Biomolecules?
- Types of Biomolecules
- Chapter-Wise NCERT Class 11 Notes Biology
From the food we consume to the DNA with our genetic information, biomolecules play a role in all aspects of life. Biomolecules are engaged in crucial processes such as energy generation, growth, repair, and metabolism. Students who wish to perform well in biology and competitive examinations like NEET can have a clear understanding from these NCERT Notes for Class 11.
These NCERT Class 11 Biology Notes discuss carbohydrates, proteins, lipids, nucleic acids, and enzymes, their structure, types, and biological significance. Let us learn the major concepts of this chapter step by step.
Also, students can refer to:
- NCERT Solutions for Class 11 Biology Chapter 9 Biomolecules
- NCERT Exemplar for Class 11 Biology Chapter 9 Biomolecules
What Are Biomolecules?
Biomolecules are organic molecules essential for the structure and function of living organisms. These molecules are primarily composed of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Biomolecules are involved in various biological processes, such as energy production, growth, metabolism, and genetic information transfer.
Definition and Importance of Biomolecules
Biomolecules are chemical compounds present in living organisms that contribute to cellular functions and life-sustaining processes. Their importance includes:
Providing Energy: Carbohydrates and lipids serve as energy sources.
Structural Components: Proteins and lipids contribute to cell membranes and tissues.
Genetic Information: Nucleic acids (DNA & RNA) store and transmit genetic instructions.
Catalysis of Reactions: Enzymes (proteins) speed up biochemical reactions.
Cell Communication: Hormones and neurotransmitters regulate body functions.
Classification of Biomolecules
Biomolecules are categorized into two major types:
Organic Biomolecules: Contain carbon and hydrogen and form the backbone of life. Examples include carbohydrates, proteins, lipids, and nucleic acids.
Inorganic Biomolecules: Do not contain carbon-hydrogen bonds and are essential for biological functions. Examples include water, minerals, and gases like oxygen and carbon dioxide.
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Types of Biomolecules
The different types of biomolecules are described as follows:
1. Carbohydrates
Carbohydrates are organic compounds composed of carbon (C), hydrogen (H), and oxygen (O) in a ratio of 1:2:1. Their general formula is (CH₂O)ₙ.
Classification of Carbohydrates
Carbohydrates are categorized based on their complexity:
Monosaccharides (Simple Sugars): The smallest carbohydrate units, e.g., glucose, fructose, galactose.
Disaccharides: Formed by the condensation of two monosaccharides, e.g., sucrose (glucose + fructose), lactose (glucose + galactose).
Polysaccharides: Long chains of monosaccharides, e.g., starch (plant storage), glycogen (animal storage), and cellulose (plant cell walls).
Functions of Carbohydrates
Provide immediate energy through glucose metabolism.
Act as structural components (e.g., cellulose in plants, chitin in fungi).
Play a role in cell recognition and signaling (glycoproteins).
2. Proteins
Proteins are macromolecules composed of amino acids linked by peptide bonds. Each amino acid contains an amino group (-NH₂), a carboxyl group (-COOH), and a variable side chain (R-group).
Classification of Proteins
Proteins are classified based on their structure and function:
Structural Proteins: Provide support, e.g., collagen in connective tissues.
Functional Proteins: Enzymes, hormones, and antibodies perform specific biological functions.
Fibrous Proteins: Insoluble, providing structural support, e.g., keratin in hair.
Globular Proteins: Soluble, involved in metabolism, e.g., hemoglobin.
Functions of Proteins
Catalyzes biochemical reactions (enzymes).
Provide structural support (collagen, keratin).
Transport molecules (hemoglobin carries oxygen).
Regulate body functions (hormones like insulin).
Defend against infections (antibodies in immunity).
3. Lipids
Lipids are hydrophobic molecules composed mainly of carbon, hydrogen, and oxygen. They are insoluble in water but soluble in organic solvents like ethanol.
Classification of Lipids
Simple Lipids: Fats and oils (triglycerides) composed of glycerol and fatty acids.
Compound Lipids: Contain additional groups, e.g., phospholipids in cell membranes.
Derived Lipids: Steroids (cholesterol), terpenes, and fat-soluble vitamins.
Functions of Lipids
Store energy for long-term use.
Act as structural components of cell membranes (phospholipids).
Serve as insulation and protection (fat in the body).
Function as signaling molecules (steroids like hormones).
4. Nucleic Acids
Nucleic acids are polymers of nucleotides, where each nucleotide consists of:
A pentose sugar (ribose in RNA, deoxyribose in DNA).
A phosphate group.
A nitrogenous base (adenine, guanine, cytosine, thymine in DNA, uracil in RNA).
Types of Nucleic Acids
Nucleic acids are classified as:
- DNA (Deoxyribonucleic Acid):
Double-stranded helix.
Stores genetic information.
Composed of adenine (A), thymine (T), cytosine (C), and guanine (G).
2. RNA (Ribonucleic Acid):
Single-stranded.
Involved in protein synthesis.
Contains uracil (U) instead of thymine.
Functions of Nucleic Acids
DNA stores and transmits genetic information.
RNA helps in protein synthesis by translating genetic codes into proteins.
Regulates gene expression and cellular activities.
Also Read:
Chapter-Wise NCERT Class 11 Notes Biology
Biomolecules are the building blocks of life, and they are the foundation of all biological functions. Carbohydrates supply energy, proteins construct and repair tissues, lipids store energy and create membranes, and nucleic acids contain genetic information. Knowledge of biomolecules is essential for understanding biological functions at the cellular and molecular levels.
Subject Wise NCERT Solutions
Frequently Asked Questions (FAQs)
1. What are biomolecules?
Biomolecules are organic molecules essential for life, including carbohydrates, proteins, lipids, and nucleic acids. They are involved in cellular structure, metabolism, and genetic information transfer, playing key roles in energy production, growth, and biochemical reactions.
2. What are the four major types of biomolecules?
The four major biomolecules are carbohydrates (energy sources), proteins (structural and functional roles), lipids (energy storage and membrane components), and nucleic acids (DNA and RNA, responsible for genetic information storage and transfer).
3. What are the primary and secondary metabolites?
Primary metabolites are essential for growth and development (e.g., amino acids, nucleotides). Secondary metabolites are non-essential but aid in defense and signaling (e.g., alkaloids, flavonoids). They play significant roles in medicine and plant protection.
4. What are enzymes? How do they work?
Enzymes are biological catalysts that speed up biochemical reactions by lowering activation energy. They work through the lock and key or induced fit model, binding specific substrates at their active site to form products.
5. What are proteins and their functions?
Proteins are polymers of amino acids linked by peptide bonds. They function in structural support (collagen), enzymatic activity (enzymes), transport (hemoglobin), immunity (antibodies), and hormonal regulation (insulin).
6. What is the structure and function of carbohydrates?
Carbohydrates consist of carbon, hydrogen, and oxygen in a 1:2:1 ratio. They function as energy sources (glucose), storage molecules (starch, glycogen), and structural components (cellulose in plants, chitin in fungi).
7. What are lipids? How are they different from carbohydrates?
Lipids are hydrophobic molecules that include fats, oils, and steroids. Unlike carbohydrates, they do not follow a fixed ratio of elements and serve as long-term energy stores, cell membrane components, and hormonal precursors.
8. What are lipids? How are they different from carbohydrates?
Lipids are hydrophobic molecules that include fats, oils, and steroids. Unlike carbohydrates, they do not follow a fixed ratio of elements and serve as long-term energy stores, cell membrane components, and hormonal precursors.
9. What are nucleic acids? What are their types?
Nucleic acids are macromolecules that store genetic information. The two types are DNA (deoxyribonucleic acid), which carries genetic instructions, and RNA (ribonucleic acid), which helps in protein synthesis and gene expression.
10. What are nucleic acids? What are their types?
Nucleic acids are macromolecules that store genetic information. The two types are DNA (deoxyribonucleic acid), which carries genetic instructions, and RNA (ribonucleic acid), which helps in protein synthesis and gene expression.
11. What is the difference between DNA and RNA?
DNA is double-stranded, contains deoxyribose sugar, and uses thymine (T) as a base. RNA is single-stranded, contains ribose sugar, and uses uracil (U) instead of thymine. DNA stores genetic information, while RNA aids in protein synthesis.
12. What is the difference between DNA and RNA?
DNA is double-stranded, contains deoxyribose sugar, and uses thymine (T) as a base. RNA is single-stranded, contains ribose sugar, and uses uracil (U) instead of thymine. DNA stores genetic information, while RNA aids in protein synthesis.
13. What are the properties of enzymes?
Enzymes are highly specific, work at optimal temperature and pH, speed up reactions without being consumed, and can be inhibited or activated. They function through an active site where substrates bind and react.
14. What are the properties of enzymes?
Enzymes are highly specific, work at optimal temperature and pH, speed up reactions without being consumed, and can be inhibited or activated. They function through an active site where substrates bind and react.
15. What is the role of biomolecules in metabolism?
Biomolecules regulate anabolic (building) and catabolic (breaking) processes in metabolism. Carbohydrates provide energy, proteins function as enzymes, lipids store energy, and nucleic acids control genetic processes essential for cellular function.
16. What is the role of biomolecules in metabolism?
Biomolecules regulate anabolic (building) and catabolic (breaking) processes in metabolism. Carbohydrates provide energy, proteins function as enzymes, lipids store energy, and nucleic acids control genetic processes essential for cellular function.
17. What are the different types of carbohydrates?
Monosaccharides: Single sugar units (glucose, fructose).
Disaccharides: Two sugar units (sucrose, lactose).
Polysaccharides: Long sugar chains (starch, glycogen, cellulose).
These serve as energy sources, storage molecules, and structural components.
18. What are the different types of carbohydrates?
Monosaccharides: Single sugar units (glucose, fructose).
Disaccharides: Two sugar units (sucrose, lactose).
Polysaccharides: Long sugar chains (starch, glycogen, cellulose).
These serve as energy sources, storage molecules, and structural components.
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