AQA A Level Biology复习笔记2.3.2 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 (as seen with many plant species) new individuals grow from the parent organism (by cell division) and then detach (‘bud off’) from the parent in different ways. Some examples of these are budding in Hydra and yeast and runners from strawberries