# Nucleus

The control centre of a cell. It holds the DNA, the instructions for building and running the cell.

Biology (school) · Part 01: Cells · Card 2 of 12 · Last updated 2026-10-19

## Analogy

The head office that keeps the master plans.

## In practice

A red blood cell has no nucleus, so it cannot divide or repair itself.

## Practice

### Flashcards

- **What does the nucleus do?** It controls the cell and holds the DNA.

### Interview questions

**Explain how a sperm cell is adapted to its function.**

- It has a tail to swim
- It has many mitochondria for energy
- It carries half the genetic information in its nucleus

## Questions people ask

### Do all cells have a nucleus?

No. Animal, plant and fungus cells have a nucleus. Bacteria do not. Their DNA floats loose in the cytoplasm. Some human cells also lose their nucleus as they develop, such as mature red blood cells, which makes more room to carry oxygen.

### What is inside the nucleus?

The nucleus contains the cell's DNA, which is packed into structures called chromosomes. Human body cells have 46 chromosomes. The DNA carries the instructions for making proteins. A double membrane with small holes surrounds the nucleus, and it controls what can pass in and out.

## Related concepts

- [Mitochondria](https://studyvisually.com/learn/science/biology-school/biology-school-part-1/biology-school-part-1-concept-5)
- [Specialised cell](https://studyvisually.com/learn/science/biology-school/biology-school-part-1/biology-school-part-1-concept-10)
- [Cell](https://studyvisually.com/learn/science/biology-school/biology-school-part-1/biology-school-part-1-concept-1)
- [Cytoplasm](https://studyvisually.com/learn/science/biology-school/biology-school-part-1/biology-school-part-1-concept-3)

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