1. THE IMPORTANCE OF CELL DIVISION Science 9

2. Where do cells come from?  New cells come from pre-existing cells through the process of cell division  This is how dead and damaged cells are replaced in the human body

3. Functions of Cell Division – Healing and Tissue Repair  Every second of your life, millions of cells are becoming damaged or dying in the human body  They constantly need replacing  Some of the activities we undergo remove these cells such as washing, getting dressed, rubbing hands on your clothes, etc.

4. Functions of Cell Division - Growth  As the number of cells increase in a living thing, so does its size  Human growth begins with the division of a fertilized egg cell  All cells are approximately the same size  They need to divide because if they continued to grow, they would not be able to acquire all the materials they would need to survive  Also, the distance the nucleus is from all other parts of the cell must be kept at a minimum so that messages can be translated quickly and efficiently

5. Functions of Cell Division - Reproduction  Cell division promotes life  Cell division in unicellular organisms like bacteria produces two more organisms  Cell division is also critical for reproducing multicellular organisms

6. Cell Division  There are approximately 100 trillion cells in the human body  However, it began as a single fertilized egg  It divided into two cells and so on until you were produced

7. The Cell Cycle – step 1  There are two phases of cell division: when it is dividing and when it is not  The actual phase where it divides is small compared to the other events that take place within the cell  The stages between cell divisions is called interphase  During this time, cells take in nutrients, which are important for energy, growth, and repair of the cell

8. The Cell Cycle – step 2  A phase of rapid growth occurs  This is a period of interphase because cell division is not occurring

9. The Cell Cycle – step 3  The cell prepares for division by duplicating its chromosomes within the nucleus (replication)  This must occur before cell division  The chromosomes contain all the important information needed for the cell to survive  This is also a period of interphase

10. The Cell Cycle – step 4  Another period of growth and preparation for cell division occurs  Again, this is a period of interphase

11. Mitosis  Most cells divide the same way  All cells divide into two cells – a mother cell produces two daughter cells  The division of information in the nucleus and the sharing of cytoplasm by moving to opposite ends of the cell is called mitosis

12. Cytokinesis  Cell division continues with the separation of cytoplasm and its contents into equal parts  This begins before mitosis is complete  Half of the cytoplasm, containing half of the organelles, goes to each daughter cell  This process differs between plants and animals

13. Cytokinesis – Plants and Animals  In plants, a cell wall forms along the middle of the cell, creating two new cells  In animals, the cell membrane pinches together in the middle, separating the cytoplasm into two equal parts  Both daughter cells grow and develop complete organelles during interphase  They will also make a copy of genetic material

14. The Phases of Mitosis  Interphase  cell grows and duplicates genetic material  Prophase  Individual chromosomes (two strands of information) becomes visible  Metaphase  Double-stranded chromosomes line up in the middle of the cell  Anaphase  Each chromosome splits and moves to opposite ends of the cell  Telophase  A nuclear membrane forms around each strand; cytokinesis begins  Interphase  Cell continues to grow and duplicates its genetic material

15. Videos The Cell http://www.youtube.com/watch?v=X6N82No4Nz8 Mitosis http://www.youtube.com/watch?v=L0k-enzoeOM