17.2 Mitosis
- Syllabus
- 0610–2026–2027
- Topic
- 17.2
- Level
- —
Learning objectives
17.2.1Mitosis as nuclear division giving• Describe mitosis as nuclear division giving rise to genetically identical cells (details of the stages of mitosis are not required)17.2.2Role of mitosis in growth, repair• State the role of mitosis in growth, repair of damaged tissues, replacement of cells and asexual reproduction17.2.3Exact replication of chromosomes• State that the exact replication of chromosomes occurs before mitosis17.2.4During mitosis, the copies• State that during mitosis, the copies of chromosomes separate, maintaining the chromosome number in each daughter cell17.2.5Stem cells as unspecialised cells that• Describe stem cells as unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions
Define mitosis by its nuclear outcome
Mitosis is nuclear division that gives rise to genetically identical cells.
The copied genetic information is shared equally, so each daughter nucleus receives the same chromosome set and genetic information as the parent nucleus.
Mitosis describes nuclear division. Cell division usually follows, but detailed names and appearances of mitotic stages are not required here.
Connect mitosis to its four roles
Mitosis produces genetically identical cells, so it can increase cell number without changing the genetic instructions passed to the new cells.
| Role | Why identical new cells are useful |
|---|---|
| growth | increases the number of cells in an organism |
| repair of damaged tissues | supplies cells to rebuild the damaged region |
| replacement | replaces worn-out or dead cells with the same cell type |
| asexual reproduction | produces offspring from one parent without gamete fusion |
Production of gametes is a role of meiosis, not mitosis. Growth by mitosis increases cell number; it does not simply make every existing cell larger.
Place exact chromosome replication before mitosis
Before mitosis begins, every chromosome is replicated exactly. This makes a copy of the DNA in each chromosome, so the DNA mass in the cell doubles before nuclear division.
The two copies are needed because they will later be separated into different daughter nuclei. Exact replication preserves the same genetic information in both products.
Replication happens before mitosis, not during the separation itself. Doubling DNA does not double the chromosome number: each replicated chromosome consists of two copies awaiting separation.
Explain how mitosis maintains chromosome number
During mitosis, the copies of each chromosome separate and move into different daughter nuclei. Each daughter nucleus therefore receives one complete copy of every chromosome.
The chromosome number is maintained: if the parent nucleus has 16 chromosomes, each daughter nucleus also has 16—not 8 or 32.
The DNA was copied beforehand so it can be divided between two nuclei. Mitosis separates copies; it does not halve the chromosome number as meiosis does.
Explain what stem cells can become
Stem cells are unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for particular functions.
stem cell → mitosis → genetically identical daughter cells → some cells specialise by expressing the genes needed for a particular cell type
In an embryo, stem cells supply cells for growth and the formation of different tissues. In tissues such as skin or stomach lining, they can produce replacements for cells that are lost or damaged.
A stem cell is defined by being unspecialised and able to produce cells that can specialise. It is not already a specialised cell, and it divides by mitosis rather than meiosis.