Chapter 7 Enzymes Notes - Class 9 Biology Punjab Board

This page provides Class 9 Biology Chapter 7, Enzymes, notes for Punjab Board students following the PCTB syllabus for the 2026-2027 session. It includes solved exercises, important MCQs, and short and long questions covering metabolism, the mechanism of enzyme action, factors that affect enzyme activity, and enzyme inhibition, and can be read online by SSC Part 1 and Matric Part 1 students.

Chapter 7 of Class 9 Biology, Enzymes, builds directly on the biomolecules chapter by examining a specific and critically important class of proteins. The chapter begins with metabolism — the sum of all chemical reactions occurring in a living organism — and distinguishes between anabolic and catabolic reactions, setting the context for why enzymes are essential. Students are then introduced to enzymes as biological catalysts, learning about their protein nature, their specificity for particular substrates, and the concept of the active site where the enzyme-substrate complex forms.

The mechanism of enzyme action is covered in detail, including the lock-and-key model and the induced fit model, helping students understand how enzymes lower the activation energy of a reaction without being consumed in the process. The chapter then examines the key factors that affect enzyme activity — temperature, pH, substrate concentration, and enzyme concentration — and explains why each factor influences the rate of an enzyme-catalysed reaction. The final topic is enzyme inhibition, covering competitive and non-competitive inhibition and how inhibitors affect an enzyme's ability to bind its substrate.

This chapter is important for Punjab Board exams because enzymes are a recurring topic in Biology at this level. Punjab Board papers regularly include short questions on factors affecting enzyme activity, the mechanism of enzyme action, and the difference between competitive and non-competitive inhibition. These solved notes are structured to help SSC Part 1 students understand each concept clearly and revise all key definitions, models, and comparison points efficiently before their annual exams.