Amanda has taught high school science for over 10 years. They have a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. They also are certified in secondary special education, biology, and physics in Massachusetts.
What Is Cell Division?
If you've ever had a cut or a scrape, you've seen that it doesn't last forever, right? After a few days or maybe a week, you have new skin and all traces of the cut are gone. How did this happen? Well, your body's ability to heal itself depends entirely on a process called cell division. Cell division is the process of one cell dividing into two. When you get a cut, cells in and below your skin divide to fix the wound and make new skin. Without cell division, we wouldn't make it very far!
The cells in our body, like skin cells, are a type of cell called eukaryotic. Eukaryotic cells have a special part called the nucleus that holds DNA. They also have other structures that are important for cell function that prokaryotes do not have. What's a prokaryote? Well, animal, plant and fungi cells are all eukaryotic. But bacteria are prokaryotic, meaning they have no nucleus. Their DNA floats freely around the cell.
Since making new cells involves doubling DNA, eukaryotes and prokaryotes go through cell division differently. Let's first take a look at the simpler process, called binary fission, that prokaryotes go through. Then later we'll discuss mitosis, which is how eukaryotes divide.
Binary fission is the process of one prokaryotic cell dividing into two new cells. Prokaryotes have a simpler cell structure than eukaryotes, so their process of cell division is also simpler. First, the cell must duplicate its DNA so each new cell gets the exact same amount as the original. The bacteria moves the DNA to either side of the cell. Next, the cell membrane and cell wall, the outer coverings of a bacterial cell, start to bud into the center. The two cells are covered with a new membrane and cell wall, and separate. The end product is two identical cells. Because this process is so simple, bacteria can reproduce as fast as every 20 minutes. Their growth is exponential, and with even a small contamination in food it's easy to have an army of bacteria on your hands in a short amount of time.
Mitosis in Animals
Mitosis is the process of cell division in eukaryotes. Plants, animals and fungi are all eukaryotes. Fungi and plants have a slightly different cell structure than animals, so their cell division is also slightly different. Let's start with mitosis in animal cells.
First, like bacteria, animal cells need to double their DNA. They do this inside the nucleus and then continue to grow and double other cell structures for each new cell. After this, the animal cell enters mitosis. The first stage of mitosis is prophase, where the nucleus starts to fragment and spindle fibers that will move the DNA around the cell start to form. The DNA condenses into chromosomes for easier sorting during cell division as well. In metaphase, the chromosomes line up along the midline of the cell with the help of the spindle fibers. In anaphase, the chromosomes start to pull apart towards opposite sides of the cell. Next, in telophase the two new nuclei reform and the large cell pulls apart into two. Then in the last phase, cytokinesis, the midsection of the cell pulls together like a drawstring and separates into two identical cells, called a cleavage furrow.
Mitosis in Plants
Mitosis in plant cells is a little different because they have a cell wall. A cell wall is a hard, rigid structure outside the cell membrane. Animal cells only have a cell membrane. Plant cells have a cell wall shaped like a square or rectangle, so they look like a grid under the microscope.
Plant cells go through the same steps as animal cells. The main difference between mitosis in plant and animal cells is cytokinesis. Plant cells do not split in two using a cleavage furrow like animal cells do. Instead, the cell wall grows from the center of the cell, forming a cell plate. The cell plate extends outward, ultimately separating the two cells.
Mitosis in Fungi
Finally, fungi have a unique way of going through mitosis called closed mitosis. All of the steps of mitosis actually occur within the nucleus. The nucleus does not dissolve in prophase like it does in plant and animal cells. At the end of telophase, the nucleus first splits into two. Then the entire cell divides, forming two new cells.
In summary, cell division is the process of making two cells from one original cell. In prokaryotes, a cell simply duplicates its DNA and moves it to opposite ends of the cell before rebuilding the cell membrane and cell wall. This process is called binary fission. Eukaryotic cells go through mitosis to divide. DNA is duplicated and condensed into chromosomes. In animal and plant cells, during prophase the nucleus breaks down and spindle fibers form. During metaphase the chromosomes line up at the middle, and they're pulled to opposite ends of the cell during anaphase. During telophase the nuclear envelope reforms and the cells pull apart in cytokinesis. In animal cells, a cleavage furrow separates the cells, whereas plant cells use a cell plate to reform the cell wall. Fungi are special in that they go through closed mitosis. In closed mitosis, all of the steps animal and plant cells go through take place in the nucleus. The nucleus divides into two and then the cell divides.
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