OCR A Level Biology:复习笔记2.6.4 The Significance of Mitosis

• Mitosis is the process of nuclear division by which two genetically identical daughter nuclei are produced that are also genetically identical to the parent nucleus
• The process of mitosis is of great biological significance and is fundamental to many biological processes:

Growth of multicellular organisms

• The two daughter cells produced are genetically identical to one another (clones) and have the same number of chromosomes as the parent cell
• This enables unicellular zygotes (as the zygote divides by mitosis) to grow into multicellular organisms
• Growth may occur across the whole body of the organism or be confined to certain regions, such as in the meristems (growing points) of plants

Replacement of cells & repair of tissues

• Damaged tissues can be repaired by mitosis followed by cell division
• As cells are constantly dying they need to be continually replaced by genetically identical cells
• In humans, for example, cell replacement occurs particularly rapidly in the skin and the lining of the gut
• Some animals can regenerate body parts, for example, zebrafish can regenerate fins and axolotls regenerate legs and their tail amongst other parts

Asexual reproduction

• Asexual reproduction is the production of new individuals of a species by a single parent organism – the offspring are genetically identical to the parent
• For unicellular organisms such as Amoeba, cell division results in the reproduction of a genetically identical offspring
• For multicellular organisms, new individuals grow from the parent organism (by cell division) and then detach (‘bud off’) from the parent in different ways
• This type of reproduction can be observed in different plant, fungi and animal species
• Some examples of these are budding in Hydra and yeast and runners from strawberries