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Petronela, Petrana
Nedeľa, 31. mája 2020
Cell division
Dátum pridania: 27.12.2001 Oznámkuj: 12345
Autor referátu: kris_d
 
Jazyk: Angličtina Počet slov: 790
Referát vhodný pre: Stredná odborná škola Počet A4: 2.5
Priemerná známka: 3.00 Rýchle čítanie: 4m 10s
Pomalé čítanie: 6m 15s
 
Cell division

One of the most important natural needs of every being is its reproduction - a part of the life (or cell) cycle. Mitosis - specified as a cell division (division of nucleus) - is the major stage in the reproduction of quite a lot of organisms and their parts, as well.
Firstly, I would like to explain the phases occurring in the mitosis. Those are the prophase, metaphase, anaphase and telophase. In the prophase (“before form”), chromosomes condense (become shorter and thicker); both the nucleolus and the nuclear envelope disappear. Centrioles replicate and separate, and form a bundle of microtubule fibers (each of them "catches" one chromosome). In the later metaphase (“middle form“) chromosome align together on a central (metaphase) plate and start doing dancelike movements. Anaphase (“again form”) begins, when centromeres that link the sister chromatids, together creating the whole chromosome, split. Each spindle fiber pulls one chromatid (one half of the particular chromosome) apart and toward opposite poles; it moves with floppy arms lagging behind the centromeres. Then chromatids start behaving like separate chromosomes. The final telophase (“end form”) starts as the spindle fibers disperse and chromatids arrive at the opposite poles. Then the nucleolus and nuclear envelope reappear, chromosomes decondense and the cytoplasm starts dividing. Mitosis is the shortest phase of the cell cycle (which is a part of the life cycle), though, it is not less important than the other phases (interphase and later cytokinesis-division of cytoplasm). There are three main importance of mitosis: growth of multicellular organisms, repairing or replacing of old and damaged tissues and cells and finally asexual reproduction. Every cell has a maximum size that it cannot grow bigger than. Usually it is very small and that is why every tissue or organ in multicellular organisms is built by a great amount of specialized cells. Because of the upper border of cells’ size, the only chance for the organ how to grow up is multiplying cells by their dividing. It would be very complex if every cell needed to combine specialized male and female cells (gametes) for replicating itself. In this case, no meiosis (sexual reproduction) is needed and therefore mitosis is the easiest and fastest way of dividing cells and then growth of certain organs. An example of this kind of growth is almost every being – plants, animals and fungi, as well.
 
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