A diagram of the process of cell division by mitosis.
Click on image for full size
Courtesy of National Center for Biotechnology Information, NIH
How New Cells Are Made: Mitosis
An animal, plant, or other multicellular organism needs to make more cells in order to grow larger. One cell divides into two during growth. Unicellular organisms, like protists, which have only one cell, often reproduce by splitting their one cell into two or more. The process by which the genetic material within the cell nucleus (chromosomes) divides is called mitosis.
Human cells each have 46 chromosomes and when they divide each of the two new cells has 46 chromosomes. Where do the additional chromosomes come from? The genetic material is duplicated so that the same number of chromosomes is in the next generation of cells. After chromosomes are duplicated, dividing them up is a four-step process.
Step 1: Prophase
During this step the cell gets ready for mitosis. Duplicated chromosomes are held together. By the end of prophase they have changed from thin threads into thick rods. Fibers made of protein begin to form that will eventually help pull the pairs of chromosomes apart.
Step 2: Metaphase
The membrane around the nucleus brakes apart and the chromosomes line up at the middle of the cell. The fibers that started to develop during prophase have become stronger and attach at both ends of the cell as well as to each chromosome. If the cell were a globe, the fibers would be attached at the north and south poles while the chromosomes would be lined up along the equator.
Step 3: Anaphase
During this step, the action really happens! Those thick fibers attached to the two “poles” of the cell pull the duplicated chromosomes apart into two groups.
Step 4: Telophase
A nucleus membrane forms around both groups of chromosomes and the rest of the cell begins to divide. With the same genetic material, these two cells are just like the one they were made from!
Shop Windows to the Universe Science Store!
"Science, Evolution, and Creationism
", by the National Academies, provides fascinating background on these topics for all, and is particularly useful for the Earth and space science classroom. Check our other books
in our online store
You might also be interested in:
Though not the largest kingdom, with a mere 300,000 species catalogued, many might argue that the Kingdom Plantae just may be the most important group of living organisms. In the process known as "photosynthesis",...more
Members of the Kingdom Protista are the simplest of the eukaryotes. Protistans are an interesting assemblage of organisms classified for what they are not. Protistans lack characteristics shared by plants,...more
Do you look a bit like your siblings? Do you and your siblings look a bit like your parents? The similarities are because, unless you were adopted, you and the other members of your family have genetic...more
Jupiter's atmospheric environment is one of strong gravity, high pressure, strong winds, from 225 miles per hour to 1000 miles per hour, and cold temperatures of -270 degrees to +32 degrees (freezing temperature)....more
In July, 1996, it was announced that Dr. David McKay, along with a team of scientists at Johnson Space Center (a division of NASA), had discovered possible fossils of bacteria in an ancient rock from Mars....more
Saturn's atmospheric environment is one of strong gravity, high pressure, strong winds, from 225 miles per hour to 1000 miles per hour, and cold temperatures of -270 degrees to +80 degrees. With winds...more
Titan's atmosphere is a lot like the Earth's, except that it is very cold, from -330 degrees to -290 degrees! Like the Earth, there is a lot of Nitrogen and other complex molecules. There also may be an...more