Growth and Cell Reproduction The copier reproduces the pages, - PDF document

7/22/2009 Growth is a characteristic of all living things. • Your cells are like a photocopier: Growth and Cell Reproduction • The copier reproduces the pages, making p g , g exact copies; and your Cells divide to increase their numbers cells undergo a through a process of mitosis, which process that makes results in two daughter cells with exact copies of themselves too. identical sets of chromosomes. This enables you to grow because your You started out as a single cell, which cells multiply. quickly divided into two cells. • So, how did you end up with billions of • Two cells became cells when you four and four four and four started out with the became eight. union of just two cells? Eventually, you grew into an The process of one cell dividing into organism made of billions of cells. two daughter cells is called cell division. • As you continue to grow, your cells will divide to make more and more Each new cell cells. contains an exact copy of the DNA • Also, your cells divide to that’s found in all replace cells that have of your body cells. died or to repair damaged tissues. 1

7/22/2009 So how do cells divide to make As you learned earlier, prokaryotic cells, exact copies of themselves? like bacteria, do not have a nucleus. Well, there are two types of cells: prokaryotic • Their DNA is found bunched up in the and eukaryotic, and each of these types of cytoplasm. cells has a unique way of dividing. • Because of this, their cell division is simpler Because of this, their cell division is simpler than the division of eukaryotic cells. • First the chromosomes are duplicated. Then, the bacteria reproduce by merely Binary Fission Video Clip splitting in two. • This process is called binary fission. fission. • Each daughter cell contains one copy of the DNA from the original cell. Eukaryotic cells are usually larger and Chromosomes are made from protein more complex than prokaryotic cells, so and DNA in cells with a nucleus. their cell division is also more complex. • The proteins in a chromosome help • The DNA of a support its structure eukaryotic cell is and function, and the d f cti d the found in the nucleus, f d i h l genetic information of which is organized into structures called the cell is stored in the chromosomes. DNA. • Chromosomes organize DNA into distinct units. 2

7/22/2009 Different organisms have different Cell Division Video Clip numbers of chromosomes. • Humans, for example, have 46 chromosomes, but chickens have 78. However, you need to wait until just before A house fly has 12 chromosomes and a the cell divides to see these individual tomato plant has 24. chromosomes under a microscope. visible Do more chromosomes mean the organism is more complex? 3