Science
What is a cell in science?
Quick answer
A cell is the smallest living unit. Every living thing is made of one or more cells, each with a membrane, cytoplasm and, in plants and animals, a nucleus that controls it.
In one sentence
A cell is the smallest unit of life: every living thing is built from cells, just as a wall is built from bricks.
Explained
All living things are made of cells. Some, like bacteria, are just a single cell. A human body has around 30 trillion. Most cells are far too small to see without a microscope.
In 1665, the scientist Robert Hooke looked at a thin slice of cork through an early microscope. He saw tiny box-shaped spaces and called them "cells", after small rooms.
Think of a cell as a tiny factory:
- The cell membrane is the security fence. It controls what goes in and out.
- The cytoplasm is the jelly-like factory floor where chemical reactions happen.
- The nucleus is the control office. It holds DNA, the instructions for building and running the cell.
- Mitochondria are the power stations. They release energy from food through respiration.
Plant cells have all of these, plus three extras:
- a stiff cell wall that gives support, like a box around the fence
- chloroplasts, where photosynthesis happens
- a large vacuole full of watery sap that keeps the cell firm
Cells also specialise. In your body, red blood cells carry oxygen, nerve cells carry messages, and muscle cells contract to move you. They share the same basic plan but their shapes suit their jobs.
Examples
| Cell | Where | Special feature |
|---|---|---|
| Red blood cell | blood | no nucleus, dimple shape to carry more oxygen |
| Nerve cell | brain and nerves | long fibres to carry messages |
| Root hair cell | plant roots | long thin "hair" to absorb water |
| Leaf cell | leaves | lots of chloroplasts |
| Bacterium | almost everywhere | a whole living thing in one cell |
Common mistakes
- "Cells and atoms are the same." Atoms are much smaller and not alive. A single cell contains trillions of atoms.
- "Plant cells don't have mitochondria." They do. Plants respire as well as photosynthesise.
- "All cells have a nucleus." Bacteria have no nucleus, and human red blood cells lose theirs as they mature.
Quick quiz
Cells
Check what you know with 4 quick questions.
Question 1 of 4
Which part of a cell controls what it does?
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Related topics
Living things
Living things are organisms that grow, feed, get rid of waste, sense the world and reproduce. Plants, animals, fungi and bacteria are all alive.
Photosynthesis
Photosynthesis is how green plants make their own food. They use energy from sunlight to turn carbon dioxide from the air and water from the soil into sugar, giving out oxygen.
The human body
The human body is made of trillions of cells that form organs, such as the heart, lungs and brain. Organs work together in systems that keep you moving, breathing, eating and thinking.
Atoms
An atom is the tiny building block of all matter. It has a nucleus of protons and neutrons in the middle with electrons around it. The number of protons decides which element it is.
Evolution
Evolution is the way living things change over many generations. Individuals with features that help them survive tend to have more young, so those features become more common over time.
The heart
The heart is a muscle about the size of your fist that pumps blood around your body, carrying oxygen and food to every cell and taking waste away.