Grade 9 Biology Unit 3 : Cells

Unit 3 of your Grade 9 Biology course is called “Cells.” In this unit, you will learn what cells are, why they are important, and how they form the basic building blocks of all living things.

First, Chapter 3.1 explains the definition of a cell and shows how every living thing—from the smallest bacterium to large plants and animals—is made of cells. You’ll learn the difference between unicellular organisms (made of just one cell) and multicellular organisms (made of many cells).

In Chapter 3.2, you will discover cell theory. You will meet the scientists who helped develop this key idea and learn three basic facts: all living things are made of cells, the cell is the smallest unit of life, and new cells come from pre-existing cells.

Chapter 3.3 focuses on cell structure and function. You will explore the different parts of a cell—like the nucleus, cell membrane, and cytoplasm—and see what each part does to keep the cell alive.

In Chapter 3.4, you’ll study the two main types of cells: prokaryotic cells (like bacteria, which have no nucleus) and eukaryotic cells (like plant and animal cells, which have a nucleus and other organelles).

Chapter 3.5 compares animal and plant cells. You’ll see how they are similar (both have a nucleus, cytoplasm, and cell membrane) and how they are different (only plant cells have a cell wall, chloroplasts, and large vacuoles).

In Chapter 3.6, you’ll learn how to observe cells under a microscope. You’ll practice making slides of onion cells and cheek cells, and how to draw and label what you see.

Chapter 3.7 explores how the cell interacts with its environment. In 3.7.1, you will learn about passive transport—how substances like water, oxygen, and carbon dioxide move in and out of the cell without using energy. In 3.7.2, you’ll study active transport—how cells use energy to move substances against a concentration gradient.

Finally, Chapter 3.8 introduces you to the levels of biological organization. You will learn how cells form tissues, tissues form organs, organs form systems, and systems work together to make up an organism.

By the end of Unit 3, you will be able to define a cell, explain cell theory, describe the structure and function of major cell parts, compare plant and animal cells, use a microscope to observe cells, and understand how substances move in and out of cells.

To help you reach these goals, this unit provides clear quick notes, step-by-step examples, microscope activities, solved questions, and diagrams, all matched to the national exam.