The Cell – JSS1 Intermediate Science Lesson Note (Second Term)

What is a cell?

If you look at a large building, you will see it is made of thousands of single bricks. If you look at a piece of cloth, it is made of many tiny threads.

In the same way, every living thing—whether it is a giant elephant, a tall palm tree, or you—is made of millions of tiny units called Cells.

Definition

The Cell is the smallest unit of life. It is the basic “building block” of all living things. Because cells are so tiny, we cannot see them with our naked eyes. We must use a Microscope to see them.

Types of Organisms

1. Unicellular: These are living things made of only one cell (like Amoeba).
2. Multicellular: These are living things made of many cells (like Humans and Trees).

Plant cells vs. animal cells

Although both plants and animals are made of cells, their cells look a bit different because they have different jobs to do.

The Animal Cell

Animal cells are usually round or irregular in shape. They are flexible because animals need to move around.

The Plant Cell

Plant cells are usually rectangular or “box-like.” They are very stiff and strong because they have to support the weight of the tree since plants don’t have bones.

Key Differences

• Cell Wall: Plants have a tough outer wall; animals do not.
• Chloroplast: Plants have these to make food; animals do not.
• Vacuole: Plants have one giant space in the middle; animals have very tiny ones.

THE PARTS OF A CELL (ORGANELLES)

Inside a cell, there are even smaller parts that do specific jobs. These are called Organelles (which means “little organs”).

1. The Nucleus (The Brain)

The nucleus is the control center of the cell. It tells the cell what to do and holds the information that makes you look like your parents.

2. The Cell Membrane (The Security Guard)

This is the thin “skin” around the cell. It decides what comes in (like food and water) and what goes out (like waste).

3. The Cytoplasm (The Jelly)

This is a clear, jelly-like liquid that fills the cell. All the other organelles float inside the cytoplasm.

4. Mitochondria (The Power House)

This is where the cell gets its energy. It “burns” food to give the cell the power to work.

5. Vacuole (The Store Room)

This is a space used to store food, water, or waste. In plants, it is very large and filled with liquid to keep the plant firm.

SPECIAL PARTS FOUND ONLY IN PLANTS

Plants have two special parts that animals do not have:

1. The Cell Wall

This is a thick, stiff layer outside the cell membrane. It acts like a “suit of armor” to give the plant its shape and protect it.

2. The Chloroplast

These are tiny green “kitchens.” They contain a green pigment called Chlorophyll. This is where the plant uses sunlight to make its own food.

Class Activity

Let’s see if you can remember the “nicknames” of the cell parts! Match the part to its job:

1. Nucleus → (Power House / Brain)
2. Mitochondria → (Security Guard / Power House)
3. Cell Membrane → (Security Guard / Store Room)
4. Vacuole → (Store Room / Jelly)

Summary Questions

1. Why do plants need a Cell Wall but animals do not?
2. Which part of the cell makes a leaf look green?
3. What instrument do we use to see a cell?

Homework

Using household items (like an empty box, jelly, strings, or beads), try to build a 3D model of either a plant cell or an animal cell. Label at least four parts!