Year 1 · Organs and cells · Section 2.6

Cell division

Cell division

Cells in your body continually die, for example in the outer layer of your skin. You lose millions of dead skin cells each day, but cell division produces replacements.

When new cells replace those lost, tissues can maintain their size. If more cells are produced than lost, an organism can grow.

Making a copy

Before a body cell divides, its DNA is copied. Each chromosome is duplicated. The copies are then separated into two nuclei, each with a complete set of chromosomes.

The original parent cell divides into two daughter cells. The daughter cells usually contain the same genetic information as the parent cell.

After division, cells can grow by making more cytoplasm. This is called cell growth.

The cell cycle

The cell cycle is the sequence of cell growth, DNA copying and division. Some daughter cells become specialised cells, such as skin cells or muscle cells. Others remain able to divide again.

Cell division and specialisation are important for growth and development. The exact fate of daughter cells depends on the tissue; division does not always produce one specialised and one unspecialised cell.

Stem cells

Some cells divide only a limited number of times, while others do not normally divide. Stem cells can renew themselves by dividing and can produce cells that develop into specialised types.

• Tissue stem cells: Usually produce a limited range of cell types associated with their tissue, such as muscle stem cells contributing to muscle repair.
• Bone marrow stem cells: Include blood-forming stem cells that produce blood cells, and other stem cell populations that can produce bone or fat cells.
• Embryonic stem cells: Come from an early embryo and can develop into almost any cell type in the body.

Stem cells have a high capacity for repeated division, but this does not mean every stem cell divides without limit in all conditions.