The big idea
A brick wall is built from lots of small bricks. Living things are built in a similar way, from tiny units called cells. A cell is the smallest part of a living thing that is itself alive. Some living things, like bacteria, are just one cell. You are made of roughly 30 trillion of them!
Let's explore
Most cells are far too small to see with your eyes alone. A typical animal cell is about a fiftieth of a millimetre across. But inside each one there are smaller parts, and each part has a job.
Parts found in both animal and plant cells:
- Nucleus – the control centre. It holds the instructions (DNA) that tell the cell what to do and how to grow.
- Cytoplasm – a jelly-like liquid where most of the cell's chemical reactions happen.
- Cell membrane – a thin, flexible outer layer. It controls what goes in and out, a bit like a security guard at a gate.
- Mitochondria – tiny parts where respiration happens, which means releasing energy from food.
Extra parts found in plant cells:
- Cell wall – a strong layer outside the membrane, made of a material called cellulose. It gives the cell a firm, boxy shape and supports the plant.
- Vacuole – a large space filled with a watery liquid called cell sap. When it is full, it pushes outwards and keeps the plant firm.
- Chloroplasts – green parts that trap light energy to make food by photosynthesis.
| Part | Animal cell | Plant cell |
|---|---|---|
| Nucleus, cytoplasm, membrane, mitochondria | Yes | Yes |
| Cell wall | No | Yes |
| Large permanent vacuole | No | Yes |
| Chloroplasts | No | Yes (in green parts) |