NCERT Notes for Class 11 Biology Chapter 9 Biomolecules- Download PDF Notes

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Students can get well-organized notes for the Biomolecules chapter in PDF format. These notes explain important terms, concepts, and reactions clearly. Students can access the NCERT notes for class 11 Biology chapter 9 PDF anytime, even without the internet. By using the NCERT Class 11 Biology Notes, they can perform well in the exam without any further help.

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NCERT Notes for Class 11 Chapter 9

Biomolecules are the essential compounds that make up every living organism and play an important role. These notes help students understand topics like carbohydrates, proteins, lipids, nucleic acids, and enzymes in a simple and clear manner. Each topic is explained step by step with easy definitions and examples. The Biomolecules Class 11 Notes also highlight key terms for quick revision and better exam preparation.

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 categorised into two major types:

1. Organic Biomolecules: Contain carbon and hydrogen and form the backbone of life. Examples include carbohydrates, proteins, lipids, and nucleic acids.

2. 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.

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 categorised 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 wall).

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 signalling (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., haemoglobin.

Functions of Proteins

• Catalyses biochemical reactions (enzymes).

• Provide structural support (collagen, keratin).

• Transport molecules (haemoglobin 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) are 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:

1. 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

• NCERT Notes for Class 11 Physics
• NCERT Notes for Class 11 Chemistry
• NCERT Notes for Class 11 Mathematics

Biomolecules Previous Year Questions and Answers

Here are some important previous year questions from this chapter to help students practice and test their knowledge and understanding. Students can easily solve these questions by using the NCERT Class 11 Biology Chapter 9 Notes Biomolecules.

Question 1. The primary structure of a protein molecule has

Option 1. Two ends

Option 2. One end

Option 3. Three ends

Option 4. No ends

Answer:

The primary structure of a protein molecule consists of a specific sequence of amino acids linked by peptide bonds. This sequence is determined by the gene encoding the protein and dictates its overall structure and function. Any change or mutation in the sequence can alter the protein's properties, potentially affecting its biological activity. The primary structure serves as the foundation for the protein's higher-order structures, including secondary, tertiary, and quaternary forms.

Hence, the correct answer is option (1), Two ends

Question 2. Glycogen is a homopolymer made of

Option 1. Glucose units

Option 2. Galactose units

Option 3. Ribose units

Option 4. Amino acids

Answer:

Glycogen is indeed a homopolymer made of glucose units. The term "glycogen" comes from the Greek words "glyco" (meaning sweet, referring to glucose) and "gen" (meaning to produce), so it essentially means "a substance that produces glucose."

Hence, the correct answer is option (1), Glucose Units

Question 3. Which of the following sugars has the same number of carbon atoms as present in glucose?

Option 1. Fructose

Option 2. Erythrose

Option 3. Ribulose

Option 4. Ribose

Answer:

Among the options, it is fructose that falls in the category of monosaccharides. Fructose is often referred to as fruit sugar because it is naturally found in fruits, honey, and some vegetables. Glucose and fructose both fall in this category, and they have 6 atoms of carbon.

Hence, the correct answer is option (1), Fructose

Also Read:

• NCERT Solution
• NCERT Solutions for Class 11
• NCERT Solutions for Class 11 Biology

Chapter-Wise NCERT Class 11 Notes Biology

The chapter-wise Notes for class 11 biology are given below: