2. Why Do Cells Divide?

3. Why Do Cells Divide 1. Healing and Tissue Repair An average human looses 105 pounds of dead skin cells in their life Every second, millions of your body cells are injured or die and must be replaced Replacement of dead cells also occurs in plants

4. Why Do Cells Divide 2.Growth All plants and animals begin life as a single cell Only two ways for an organism to grow: 1) single cell gets bigger; or 2) the single cell divides into more cells

5. Why Do Cells Divide One of the most important jobs of a cell is to exchange materials with its environment (the body or outside world) The cell needs to get food and nutrients in and waste out

6. Why Do Cells Divide Why Don’t Cells Just Keep Getting Bigger? Eventually a cell will reach a size where it will not be able to get enough exchange of materials to sustain cell function

7. Why Do Cells Divide 3. Perpetuate Life Important for unicellular (prokaryotes) organisms like bacteria – creates 2 new organisms

8. Why Do Cells Divide 3. Perpetuate Life Also essential for reproduction of multicellular organisms

9. The Cell Cycle The repeating cycle in the life of a cell Interphase: when a cell is preparing for cell division; this is the majority of the time Mitosis: the process of 1 cell dividing into 2 cells

10. Interphase First Growth Phase (G 1 ) Period of growth for a cell Produces new proteins and organelles Synthesis Phase (S) Cell synthesizes entire copy of DNA Second Growth Phase (G 2 ) – shortest phase Cell produces organelles and structures for cell division

11. Mitosis Remember IPMAT Interphase, Prophase, Metaphase, Anaphase, Telophase Get a textbook and describe each phase of mitosis along with a picture (pg. 30-32) Also define cytokinesis and apoptosis

12. Homework 1. Describe the events in the cell cycle. 2. Explain how mitosis ensures genetic continuity. 3. How does mitosis make the growth and repair of cells possible in an organism? 4. Mitosis Webquest (available on class website)