Class 9 Biology Chapter 7 Enzymes explains how chemical reactions occur in living organisms. Enzymes are special biological catalysts that speed up metabolic reactions inside cells without being consumed.
In this chapter, students learn about the structure, characteristics, mechanism, and factors affecting enzyme activity. Understanding enzymes is important because they control almost every biochemical reaction in living organisms.
These notes are prepared according to the 2026 new syllabus of Punjab Board and include all important topics required for exam preparation.
Key Topics Covered
The following important topics are included in these notes:
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Introduction to Enzymes
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Characteristics of Enzymes
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Structure of Enzymes
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Enzyme-Substrate Complex
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Lock and Key Model
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Factors Affecting Enzyme Activity
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Importance of Enzymes in Biological Systems
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MCQs, Short Questions, and Long Questions
Class 9 Biology Chapter 7 MCQs – Enzymes
1. Primarily, all enzymes are
(a) Nucleic acids
(b) Proteins ✅
(c) Carbohydrates
(d) Lipids
2.What is metabolism?
(a) Digestion only
(b) Physical changes only
(c) Sum of all chemical reactions ✅
(d) Only energy release
3. Inthe food industry, enzymes are used to:
(a) Kill bacteria
(b) Convert starch into sugars ✅
(c) Make vitamins
(d) Act as preservatives
4. What is the optimum temperature for most human enzymes?
(a) 25°C
(b) 100°C
(c) 37°C ✅
(d) 0°C
5. Which of the following is a non-competitive inhibitor?
(a) Vitamin B
(b) Mercury ✅
(c) Glucose
(d) Amylase
Class 9 Biology Chapter 7 Short Questions – Enzymes
1. Define metabolism:
Metabolism is the sum of all chemical reactions that occur in a living organism to maintain life.
2. Differentiate between catabolism and anabolism:
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Catabolism: The breakdown of complex molecules into simpler ones, releasing energy.
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Anabolism: The synthesis of complex molecules from simpler ones, which requires energy.
3. Define an enzyme. What is its role in metabolism?
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An enzyme is a biological catalyst, usually a protein, that speeds up chemical reactions in the body without being consumed.
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In metabolism, enzymes control and accelerate both catabolic (breakdown) and anabolic (synthesis) reactions, ensuring that the organism’s chemical processes occur efficiently.
4. Differentiate between competitive and non-competitive inhibition:
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Competitive inhibition: The inhibitor resembles the substrate and binds to the active site, preventing the substrate from binding.
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Non-competitive inhibition: The inhibitor binds elsewhere on the enzyme, changing its shape and making the active site ineffective.
5. What is metabolism?
Metabolism is the sum of all chemical reactions that occur within an organism to sustain life. It includes both energy-releasing processes (catabolism) and energy-consuming processes (anabolism).
6. What is the Lock and Key Model of enzyme action?
The Lock and Key Model suggests that an enzyme’s active site has a fixed shape, and the substrate fits into it perfectly, just like a key fits into a lock, enabling the enzyme to catalyze the reaction efficiently.
📥 Download Chapter 7 Notes – Enzymes
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Detailed explanations of all topics
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Important MCQs
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Short Questions
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Long Questions for exam preparation
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Why These Notes Are Helpful
These notes help students:
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Understand enzyme functions easily
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Prepare for board exams and tests
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Revise the complete chapter quickly
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Practice important exam questions