Mitosis and the cell cycle: Cell division by mitosis is important in the growth and development of multicellular organisms.

The idea

Mitosis is a type of cell division that produces two genetically identical diploid cells from one parent cell. In multicellular organisms it underpins growth: an increase in cell number, not just cell enlargement, allows an organism to become larger. It also supports development, the process by which cells become organised into tissues and organs with specialised roles. For example, a root tip or shoot tip in a plant contains meristem cells that divide by mitosis, adding new cells behind the tip so the plant grows taller or longer. Similarly, in animals, mitosis replaces worn-out cells and repairs damaged tissue. Because the DNA is copied before division and each new cell receives a full set of chromosomes, the daughter cells can carry out the same functions as the parent cell.

What earns the marks

• Mitosis produces two daughter cells from one parent cell.
• The daughter cells are genetically identical to each other and to the parent cell.
• Each daughter cell receives a complete set of chromosomes, so the cells are diploid.
• Growth in multicellular organisms involves an increase in cell number by mitosis as well as an increase in cell size.
• Development involves mitosis providing new cells that become organised into tissues and organs.
• In plants, mitosis occurs in meristems such as root tips and shoot tips, allowing growth in length.
• In animals, mitosis is involved in growth, repair of damaged tissues and replacement of cells.

Common mistakes and how to put them right

• Thinking that mitosis produces gametes.

  Put it right: Gametes are produced by meiosis, whereas mitosis produces body cells for growth and repair.

• Believing that daughter cells are genetically different.

  Put it right: Mitosis produces genetically identical cells because the chromosomes are copied before division.

• Confusing growth with cell enlargement only.

  Put it right: Growth in multicellular organisms also requires an increase in cell number by mitosis.

• Assuming mitosis halves the chromosome number.

  Put it right: The chromosome number stays the same, so diploid parent cells produce diploid daughter cells.

Exam tips

• Link mitosis explicitly to growth and development in the context given, rather than describing the stages of mitosis in isolation.
• Use the phrase genetically identical when explaining the outcome of mitosis, and state that the chromosome number is maintained.
• Give a named example, such as a plant root tip or shoot tip, to show where mitosis occurs for growth.
• If asked to explain importance, refer to both growth and development, and mention repair or replacement where relevant.