Mitosis is one way biological cells replicate. During mitosis, a single cell splits into two identical cells. In single-celled organisms, mitosis is the only viable form of reproduction. In complex organisms, mitosis is responsible for repairing damaged tissues and helping an organism grow.
In a single-celled organism, such as an amoeba, mitosis is how the cell reproduces. This asexual reproduction is also how many cells within a complex organism, such as a human, create new cells. Mitosis happens through five distinct phases: prophase, prometaphase, metaphase, anaphase and telophase. During prophase, the cell's DNA material -- the chromosomes -- becomes visible. In prometaphase, the cell's nuclear membrane dissolves, allowing the chromosomes to move. By metaphase, the chromosomes are perfectly lined up in the middle of the cell. During anaphase, the chromosomes split in two and are pulled to opposite ends of the cell. Finally, in telophase, each set of chromosomes is surrounded by a new nucleus, and the cell begins to cleave in half. Through a process known as cytokinesis, the single cell breaks apart into two identical cells, completing the reproduction.
As plants and animals age, most also grow in size. Mitosis creates the cells necessary to add more mass to the body, as well as more cells to cope with the growth, such as new blood cells. It should be noted that not all cells in the human body undergo mitosis or other forms of reproduction. Nerves and muscle cells do not. After the body has made enough nerve and muscle cells, it does not have a mechanism in place to make any more.
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When an organism is injured, mitosis occurs to replace the damaged cells. This repair is especially important for skin and blood vessels, which protect and oxygenate muscles and organs in the body. Mitosis also helps replace blood lost through a wound. In certain organisms, like lizards, mitosis can replace entire lost limbs such as tails or legs.
Errors in Mitosis
Because mitosis is so important to the repair and growth of cells in the body, when problems occur, they are serious in nature. One major complication of faulty mitosis is cancer. Mutations in DNA can occur during the mitosis process, and if they aren't caught, cancerous cells can arise. Mitosis errors can also occur during the development of a fetus, leading to chromosomal disorders such as Down syndrome and Turner syndrome.