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What is a cell?

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Quick answer

A cell is the smallest unit of life — the basic building block that makes up every living thing, from bacteria to blue whales. Some organisms are a single cell; humans are made of tens of trillions of them, each running the chemistry that keeps us alive.

Key things to understand

  1. All living things are made of one or more cells — a core idea of biology.
  2. Cells contain a watery interior (cytoplasm), genetic instructions (DNA), and tiny structures called organelles that do specific jobs.
  3. There are two broad types: simple prokaryotic cells (like bacteria) and complex eukaryotic cells (like plant and animal cells) that have a nucleus.
  4. Cells copy themselves by dividing, which is how bodies grow and repair.
  5. Specialized cells do different jobs — nerve cells carry signals, muscle cells contract, red blood cells carry oxygen.

People also ask

What are the main parts of a cell?
Most cells have a membrane (outer boundary), cytoplasm (the interior), DNA (instructions), and organelles such as mitochondria that power the cell.
What's the difference between plant and animal cells?
Plant cells have a rigid cell wall and chloroplasts for photosynthesis; animal cells have neither — but both share a nucleus, a membrane, and mitochondria.
How many cells are in the human body?
Estimates put it around 30–40 trillion cells, not counting the trillions of bacteria that live in and on us.