- Cells divide by the process of mitosis for growth, and to replace worn or injured cells.
- Mitosis produces two daughter cells genetically identical to their parent cell, so the same cell functions continue.
- Mitosis takes place rapidly when new cells are forming, eg infants, plants germinating or tips of roots and stem, A high rate is needed for repair of tissue damage or replacement of cells eg bone marrow, skin.
- Rate of mitosis is further affected by temperature (affect enzymes), nutrient availability (phosphorus for DNA replication), and presence of mutagens and carcinogens.
Stages of mitosis
1) Interphase - DNA replication takes place, chromosomes are long threads.
2) Prophase - Chromosomes shorten/thicken. Nuclear membrane disappears. The chromatids are held by centromeres. Spindle fibres develop from the centrioles.
3) Metaphase - Spindle fibres twist and turn the chromatids, lining them up along the cell equator.
4) Anaphase - The centromere split, individual chromatids move toward cell poles pulled by forces acting on spindle fibres.
5) Telophase - The chromatids arrive at the cell poles. Nuclear membrane begin to form around each group of chromatids.
- The cytoplasm divides (cytokinesis) so two new daughter cells are formed. After telophase, the two new cells have the same number of chromosomes as each other and the parent cell.
- The daughter cells grow (interphase) then repeat the mitotic process.