Cell Differentiation

From one cell to many cell types

A multicellular organism begins with cells that have not yet taken on all the different roles needed in the finished organism. As the organism develops, some cells change into particular types of cell. This process is called differentiation.

Differentiation does not simply make a cell larger or create another copy of it. It changes the cell so that it becomes specialised for a particular function. For example, cells needed for contraction require a different set of features from cells needed to transport substances.

This is different from mitosis. Mitosis increases cell number by producing genetically identical cells; differentiation gives cells different structures and roles. Growth and development therefore work together: mitosis supplies new cells, while differentiation produces the variety of specialised cells that the organism needs.

How a cell becomes specialised

Cells in the same organism generally contain the same genetic information, but they do not need to use every gene in the same way. During differentiation, particular genes are switched on or off. The active genes direct the production of particular proteins, and these proteins contribute to the cell's structures and activities.

As a result, the differentiating cell acquires different sub-cellular structures in suitable numbers or forms. These enable it to carry out a certain function. A cell with many mitochondria, for instance, can release more energy by aerobic respiration for an energy-demanding activity. Once its structures suit a particular role, it has become a specialised cell.

The important causal sequence is:

different genes active → different proteins produced → different sub-cellular structures and features → a specialised function.

Why differentiation matters

A large organism cannot function efficiently if every cell has the same role. Differentiation creates the range of cell types needed for division of labour. Similar specialised cells can work together in tissues; different tissues can form organs, and organs can cooperate in organ systems.

Differentiation is therefore essential to development: it allows an organism to build functioning tissues and organs rather than remaining merely a collection of similar cells. Structural differences between cell types allow different jobs to be performed within the same organism.

Differentiation in animals

In animals, most types of cell differentiate at an early stage of development. Once many animal cells have become highly specialised, they lose the ability to change into other cell types.

A mature animal undergoes much less growth than an embryo or young animal. Consequently, cell division in mature animals is mainly restricted to repair and replacement. New cells may be produced to replace worn-out or damaged cells and to repair injured tissues. This does not mean that all cell division stops, nor that every mature animal cell can divide; it describes the main reason cell division continues in the adult body.

Differentiation in plants

The pattern is different in plants. Many types of plant cell retain the ability to differentiate throughout the plant's life. This continuing capacity supports growth at regions such as root and shoot tips and allows new specialised tissues to be produced as the plant grows.

The distinction must be stated carefully: it is most types of animal cell that differentiate early, while many types of plant cell can continue to differentiate throughout life. It is not an absolute rule applying to every cell in either group.