Cell Growth and Division How do we grow? Is each cell getting larger? Or Are there more cells? Living things grow by producing more cells! Why can’t we just have larger cells? Why is it necessary for our cells to divide? Remember… How is the cell controlled? How does the cell know what to do? How does the cell get nutrients? How does the cell remove wastes? Quick Review With a partner, define the following terms: Nucleus Chromosomes DNA Cell membrane Diffusion Limits to Cell Growth The larger the cell becomes, the more demands the cell places on its DNA and the more trouble the cell has moving enough nutrients and wastes across the cell membrane. DNA “Overload” DNA = information found in the nucleus that controls a cell’s function When a cell is small, the information stored in the DNA is able to meet the cell’s needs When a cell gets larger, it does not make more DNA and the DNA is no longer able to meet the large cell’s needs resulting in an “information crisis” DNA Exchanging Materials Nutrients and waste diffuse through the cell membrane. The rate of this exchange depends on the surface area of the cell But the rate of using nutrients and producing wastes depend on the volume of the cell. Surface Area & Volume As a cell increases in size, the volume increases more rapidly than the surface area, so the ratio of volume to surface area decreases creating a problem. As the cell grows larger, it will be difficult for the cell to get enough nutrients and release wastes as quickly as they are needed or produced by the cell. Surface Area by Volume Ratio Divide Surface area by Volume to get a ratio. Volume increases much more rapidly than surface area. Cell Division Before a cell becomes too large, it divides to form two cells. The two new cells are called daughter cells. The process by which the cell divides into two new daughter cells is called cell division. Why divide? DNA: Before the cell divides, it replicates (copies) all of its DNA, so each new daughter cell gets one complete copy of genetic information and there is no shortage. Material Exchange: Each new daughter cell has an increased ratio of surface area to volume, so enough materials may be exchanged based on the demands of the cell. Why else must things reproduce? Cellular Reproduction Reproduction – the life process by which living things produce other living thing of the same species It is necessary for the survival for the species Two types of Reproduction through cell division: Sexually reproducing organisms go through mitosis and meiosis Asexually reproducing organisms only go through mitosis What about me? At this very moment, group of cells in your body are growing, dividing, and dying. Worn out skin is being replaced and bruises are healing. Red blood cells are being produced in your bones at a rate of 2 to 3 billion to replace those that wear out. http://video.google.com/videoplay?docid=-7204725871954420481 Review the cycle Organisms go through stages, or a life cycle, while they are alive. A simple cycle consists of birth, growth and development, and death. In cell division, the nucleus divides and then the cytoplasm divides to form two new daughter cells. The cell cycle is a series of events that takes place in a cell from one division to the next.