Cells as little factories — overview of cell function: WASSCE Biology

In the Cell Structure topic, you learned what cells look like and where each part is located. Now we look at what each part actually DOES. Cells are not random bags of organelles — they are highly organised factories, with every part doing a specific job. WAEC tests this constantly: "State the function of the [organelle]."

Definition

Function — the job or role of a part. The function of the heart is to pump blood. The function of the nucleus is to control the cell.

Organelle — a small structure inside a cell that does a specific job. Like an organ inside an organism, but inside a single cell.

Metabolism — all the chemical reactions happening inside the cell. Building and breaking down molecules.

Coordination — when many parts work together to accomplish a goal. Inside a cell, every organelle is coordinated with the others.

The factory analogy

Think of a cell as a factory making products. Different rooms in the factory do different jobs:

The office has the manager and the plans (instructions) for what to make. This is the nucleus.
The power plant generates the energy for all the work. This is the mitochondrion.
The assembly line puts together products following the plans. These are the ribosomes.
The conveyor belt moves products from one place to another. This is the endoplasmic reticulum.
The packaging department prepares finished products for shipping. This is the Golgi apparatus.
The storage area holds raw materials and waste. These are the vacuoles.
The walls and gates control what comes in and out. These are the cell membrane (and cell wall in plants).
The cleaning crew removes waste. These are the lysosomes (in animal cells).

This analogy is not perfect but helps you remember the functions. Each organelle has its role, and they all work together.

Why every cell needs all these functions

Every cell needs to:

Get instructions for what to do. That's the nucleus — it contains DNA, the instructions.
Generate energy. That's the mitochondrion — energy from respiration.
Make proteins. That's the ribosomes — proteins do almost everything in cells.
Move things around inside. That's the ER, the Golgi, and the cytoskeleton.
Get raw materials in, waste out. That's the membrane controlling exchange.
Store things temporarily. That's the vacuoles.
Clean up. That's the lysosomes.

Without any one of these functions, the cell cannot live. Like a factory missing its power plant, or its assembly line, or its loading dock — it would stop working.

A quick reference table

Here is a high-yield summary of organelles and their functions. Memorise it.

Organelle	Main function	Where found
Nucleus	Controls cell activities; contains DNA	All eukaryotic cells
Mitochondrion	Releases energy through respiration	All eukaryotic cells
Chloroplast	Photosynthesis — makes food	Plant cells (green parts)
Ribosome	Makes proteins	All cells (free or on rough ER)
Endoplasmic reticulum (rough)	Synthesises proteins; transports them	Eukaryotic cells
Endoplasmic reticulum (smooth)	Makes lipids; detoxifies	Eukaryotic cells
Golgi apparatus	Packages and modifies proteins	Eukaryotic cells
Vacuole	Storage; in plants, also maintains turgor	All cells; large in plants
Cell membrane	Controls what enters and leaves	All cells
Cell wall	Gives shape and support	Plants, fungi, bacteria
Lysosome	Breaks down waste and damaged parts	Animal cells
Centriole	Helps in cell division	Animal cells (not in plants)

This table is the core of the topic. You'll see these functions explained in detail in the next lessons.

What organelles do together

The organelles aren't just sitting around — they cooperate constantly. A typical cell activity, like making a protein:

Nucleus: A gene's instructions are copied (from DNA to mRNA).
The mRNA leaves the nucleus through a pore.
Ribosome (often on rough ER): Reads the mRNA and assembles the protein from amino acids.
Rough ER: Packages the new protein for transport.
Golgi apparatus: Modifies the protein (e.g. adds sugars) and prepares it for delivery.
Vesicles: Carry the protein to where it's needed — inside the cell or out of it.

All of this happens within minutes. Multiple proteins are made in this way constantly. The factory runs 24/7.

Plant vs animal cell function — key differences

WAEC sometimes tests differences in function between plant and animal cells.

Feature	Animal cell	Plant cell
Photosynthesis	No (no chloroplasts)	Yes (in green parts)
Cell wall	No (just membrane)	Yes (cellulose)
Vacuole	Small or absent	Large central vacuole
Chloroplasts	No	Yes (in photosynthesising cells)
Centriole	Yes	No
Shape	Variable (no fixed shape)	Fixed (because of cell wall)
Cytokinesis	Pinching of membrane	New cell wall forms in middle

These differences are not just structural — they reflect functional differences. Plants make their own food (so they need chloroplasts). Animals do not (so they don't). Plants are rooted in place (so they need a rigid wall). Animals move (so a flexible membrane is enough).

Why understanding function matters

For WAEC, you need to do more than just label parts. You need to know what each part DOES. A common type of question:

"State the function of the mitochondrion." → Answer: It releases energy through respiration.
"Explain how the nucleus controls the cell." → Answer: It contains DNA with the genetic instructions; it sends out mRNA copies that direct protein synthesis.
"Why are red blood cells red?" → Answer: They contain haemoglobin, a red pigment that carries oxygen.

Knowing functions earns marks. Just knowing names doesn't.

The link to specialisation

Not every cell uses all organelles equally. Cells specialise — some are mostly about energy production; others about transport; others about communication. The structure of each cell reflects its specialised function.

For example:

A muscle cell has LOTS of mitochondria because it needs energy.
A nerve cell is long and thin to carry signals across long distances.
A red blood cell has NO nucleus to carry more oxygen.
A root hair cell has a very thin wall and a long extension to maximise water absorption.

We'll cover specialisation in detail in lessons 6-8. For now, just notice the pattern: structure follows function. A cell's shape and organelle content are matched to its job.

Common mistake

Students sometimes know all the organelles by name but cannot say what they do. Don't memorise just the names — memorise the functions. WAEC asks about functions far more than about labelling. Practice: take any organelle and state its function in one sentence.

Worked example

Question: State the functions of THREE organelles found in animal cells. For each, describe how that function affects the cell as a whole.

Solution:

1. Nucleus. Function: Controls all cell activities. It contains DNA — the genetic instructions for everything the cell does. The nucleus sends out mRNA copies of these instructions to ribosomes, which then make the proteins the cell needs. Without the nucleus, the cell would have no instructions and could not function.

2. Mitochondrion. Function: Releases energy through respiration. It breaks down glucose in the presence of oxygen, releasing energy that the cell uses for movement, building molecules, and all life processes. Cells with many mitochondria (like muscle cells) can do lots of work; cells with few mitochondria (like fat cells) are mostly for storage.

3. Ribosome. Function: Makes proteins. It reads instructions from mRNA and assembles amino acids into proteins. Proteins are needed for almost everything — they form structural materials, enzymes for chemical reactions, and signal molecules. Without ribosomes, no proteins could be made and the cell could not grow or function.

WAEC tests this

State the function of [organelle] — repeated in nearly every WAEC paper. Memorise each.
What is the function of the cell membrane? — controls what enters and leaves.
Why do muscle cells have many mitochondria? — they need lots of energy for contraction.
Difference between functions of nucleus and ribosome — comparison question.
State the role of the Golgi apparatus — packages and modifies proteins.
Why do plant cells have a cell wall but animal cells do not? — plants are stationary and need structural support; animals move and need flexibility.

Summary

Every cell is a tiny factory with organelles doing specific jobs.
Key functions: control (nucleus), energy (mitochondria), protein-making (ribosomes), transport (ER), packaging (Golgi), storage (vacuoles), boundaries (membrane and cell wall), cleanup (lysosomes).
Plant cells have chloroplasts for photosynthesis; animal cells do not.
Plant cells have large central vacuoles and cellulose cell walls; animal cells have small vacuoles and just a membrane.
All organelles cooperate to carry out the cell's activities — making proteins, generating energy, growing, reproducing, etc.
Structure follows function — different cells specialise by adjusting their organelle content.
WAEC tests functions, not just labels. Always know what each organelle DOES.
The next lessons cover each major organelle and its function in detail.

Cells as little factories — overview of cell function