Class 9 Chemistry Chapter 11 – Biochemistry Notes, Explanation, and MCQs

Biochemistry is one of the most interesting chapters in Class 9 Chemistry because it explains the chemistry of life itself. Every living organism — including humans, animals, and plants — depends on chemical substances and reactions to survive. In this chapter, students learn about biomolecules such as carbohydrates, proteins, fats, enzymes, and nucleic acids.

This topic is extremely important for FBISE, Matric, and O-Level students because questions from biochemistry frequently appear in board exams, MCQs, and conceptual short questions. Understanding this chapter also builds a strong foundation for Biology, Medical Sciences, Biotechnology, and higher-level Chemistry.

Class 9 Chemistry Biochemistry Carbohydrates Proteins and Fats showing molecular structures, food sources, and classification of biomolecules for basic chemical understanding

What is Biochemistry?

Biochemistry is the branch of science that studies the chemical composition of living organisms and the chemical reactions that occur inside them. It combines both Chemistry and Biology to explain how life functions at the molecular level.

Inside every cell, thousands of chemical reactions take place every second. These reactions help organisms grow, produce energy, repair tissues, and reproduce. Biochemistry helps scientists understand these processes in detail.

Important Definition:
Biochemistry is the study of chemical substances and processes occurring in living organisms.

Biomolecules – The Chemicals of Life

Biomolecules are large chemical compounds found in living organisms. These molecules are responsible for maintaining life processes. The major biomolecules discussed in Class 9 Chemistry are:

Carbohydrates
Proteins
Lipids (Fats and Oils)
Nucleic Acids

These compounds mainly contain carbon, hydrogen, oxygen, and nitrogen. Some also contain phosphorus and sulfur.

Carbohydrates

Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen. They are the body's main source of energy and are essential for daily activities.

General Formula of Carbohydrates:

(CH₂O)_n

Types of Carbohydrates

Monosaccharides: Simple sugars such as glucose and fructose.
Disaccharides: Formed by two monosaccharides, such as sucrose and lactose.
Polysaccharides: Complex carbohydrates such as starch, glycogen, and cellulose.

Functions of Carbohydrates

Provide energy to the body
Store energy in plants and animals
Help in structural support

Students often confuse glycogen and starch in exams. Remember that plants store energy as starch, while animals store energy as glycogen.

Proteins

Proteins are complex biomolecules made from amino acids. They are essential for growth, tissue repair, and body functions.

Amino acids join together through peptide bonds to form proteins. Hair, muscles, skin, enzymes, and antibodies are all protein-based structures.

Functions of Proteins

Build and repair body tissues
Help produce enzymes and hormones
Strengthen the immune system
Support muscle development

Students commonly lose marks by forgetting the name of the bond between amino acids. Always remember: amino acids are connected by peptide bonds.

Lipids – Fats and Oils

Lipids include fats and oils. They are made from fatty acids and glycerol. Lipids store a large amount of energy and help protect internal organs.

Compared to carbohydrates and proteins, lipids provide the highest amount of energy.

1 gram carbohydrate = 4 kcal energy
1 gram protein = 4 kcal energy
1 gram lipid = 9 kcal energy

Types of Lipids

Saturated fats: Butter, ghee, animal fats
Unsaturated fats: Olive oil, fish oil

Unsaturated fats are generally considered healthier because they support heart health when consumed in balanced amounts.

Enzymes – Biological Catalysts

Enzymes are special proteins that speed up chemical reactions inside living organisms without being consumed in the reaction.

Without enzymes, many reactions in the human body would occur too slowly to support life.

Important Properties of Enzymes

They are highly specific
They work in very small quantities
They are affected by temperature and pH
They speed up reactions

Examples of Enzymes

Amylase: Converts starch into maltose
Lipase: Breaks fats into fatty acids and glycerol
Protease: Breaks proteins into amino acids

In board exams, enzyme-related MCQs are extremely common. Students should memorize the function of each major enzyme carefully.

Nucleic Acids – DNA and RNA

Nucleic acids are biomolecules responsible for storing and transferring genetic information.

DNA

DNA stands for Deoxyribonucleic Acid. It contains genetic instructions and controls inherited characteristics.

RNA

RNA stands for Ribonucleic Acid. It helps in protein synthesis and exists in different forms:

mRNA – Messenger RNA
tRNA – Transfer RNA
rRNA – Ribosomal RNA

Balanced Diet and Nutrition

Nutrition is the process by which organisms obtain and use food for energy, growth, and repair.

A balanced diet contains carbohydrates, proteins, fats, vitamins, minerals, water, and fiber in correct proportions.

Malnutrition

Malnutrition occurs when the body receives too little or too much nutrition.

Under-nutrition: Marasmus, anemia, rickets
Over-nutrition: Obesity

Students should understand that deficiencies in proteins, vitamins, or minerals can weaken the immune system and affect body growth.

Important Exam Tips for Class 9 Biochemistry

Memorize definitions carefully
Learn examples of carbohydrates, proteins, and lipids
Understand enzyme functions instead of rote learning
Revise differences between DNA and RNA
Practice past paper MCQs regularly

A common mistake students make is mixing up monosaccharides, disaccharides, and polysaccharides. Practice classification tables regularly to avoid confusion in exams.