University:
Winston-Salem Forsyth County Schools
Course:
AP Biology
Academic year:

2015
Views:

395

Pages:

2
Author:

pleidegijz62

Mitosis & Meiosis One of the requirements for living things is that they must be made of cells. Another characteristic is that all living things must experience growth. So, how exactly do living things grow? How do babies grow up to be adults? The answer lies in the cellular process of mitosis. Mitosis is the process by which eukaryotic cells divide. You should remember from our study on cells that a eukaryotic cell contains a nucleus. Most of your cells are eukaryotic, so most of your cells –skin cells, lung cells, and stomach cells -- undergo mitosis. Mitosis does not occur in prokaryotic organisms like bacteria, nor does it occur in some of your cells (but more on that later.) The most important thing to know about mitosis is that it results in new cells that have the same number of chromosomes as the old cells. So, this is a form of asexual reproduction. For one-celled organisms like amoeba, paramecia, and euglena, this causes the offspring to be exact clones of the parents. In humans, this results in new cells that replace old ones. Without mitosis, your old cells would die and your body would wear out. But the new cells – with the same number of chromosomes – take over the job of their parents. A basic representation of mitosis: Mitosis is also what causes babies to grow. After a sperm fertilizes an egg, a zygote is formed. This zygote is only one-cell, and it undergoes mitosis repeatedly until it develops into a baby made of trillions of cells. The same process happens in humans to change their height and girth as they age. Meiosis You read earlier that some cells in humans do not undergo mitosis. Two particular cells that reproduce through another method are sperm cells and egg cells, also called gametes. Instead of mitosis, gametes reproduce through a process called meiosis. While mitosis results in new cells with the same number of chromosomes, meiosis causes new cells to have half the number of chromosomes. In humans, sperm cells and egg cells both have 23 chromosomes. When fertilization occurs the zygote will have 46 chromosomes. Once the zygote has formed, mitosis begins and the new cells will all have 46 chromosomes. Mitosis and meiosis are both crucial to life. Without meiosis, organisms would not be able to reproduce effectively. If organisms did not undergo mitosis, then they would not be able to grow and replace worn-out cells. They are two of the most important cellular process in existence.