Cell differentiation: As an organism develops, cells differentiate to form different types of cells.

The idea

Differentiation is the process by which a cell becomes specialised for a particular job. It begins as an organism develops from a fertilised egg, which divides by mitosis to produce many genetically identical cells. As development continues, different genes are switched on or off in different cells, so each cell makes only the proteins it needs. This changes the cell's shape and the organelles it contains, allowing it to carry out one function efficiently. For example, a muscle cell develops many mitochondria and protein filaments so it can contract, while a nerve cell grows a long axon so it can carry electrical impulses. In animals, most differentiation happens early and many specialised cells cannot divide again; in plants, some cells remain able to differentiate throughout life.

What earns the marks

• Differentiation is the process by which a cell becomes specialised for a particular function.
• Cells produced by mitosis are genetically identical, so differentiation involves switching genes on or off rather than changing the DNA sequence.
• Specialised cells have structures and organelles suited to their job, for example many mitochondria in muscle cells or a long axon in nerve cells.
• Differentiation allows a multicellular organism to carry out many different functions efficiently because each cell type is adapted to one role.
• In animals most differentiation occurs at an early stage, whereas many plant cells retain the ability to differentiate throughout life.

Common mistakes and how to put them right

• Thinking differentiation changes the genes or DNA in a cell.

  Put it right: The DNA is the same, but different genes are expressed, so different proteins are made.

• Confusing differentiation with cell division.

  Put it right: Mitosis produces more cells, whereas differentiation makes those cells specialised.

• Assuming all cells in an organism are identical.

  Put it right: They share the same genes but become different in structure and function.

• Writing that differentiation only happens in animals.

  Put it right: It happens in plants too, and plant cells often retain this ability.

Exam tips

• Define differentiation in one clear sentence before giving an example, so the key idea is explicit.
• Link each example of a specialised cell to a named feature and explain how that feature helps its function.
• Use the phrase 'genes switched on or off' rather than saying genes are lost or changed.
• When comparing plants and animals, state where differentiation mainly occurs and whether the cells can differentiate later.