1. Biology 12 Cell Division Intro

3. Review: Cell Theory 1. All living things are composed of one or more cells 2. The cell is the smallest entity that retains the properties of life 3. New cells arise from existing cells.

4. Extensions and Implications: Living things come in a variety of sizes but all cells are roughly the same size, the difference is the number of cells. vs. Different cells have different life spans Human skin cells: 20 days Human brain cells: 30-50 years

5. Extensions and Implications cont`d: All organisms must grow and divide as part of their life cycle There are 25 million cell divisions occurring every second in a human adult!

6. Think about it!

7. Review: Two type of cell reproduction: Asexual vs. sexual Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells Examples: Mitosis & binary fission Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells Example: meiosis

8. Purpose of cell division: 1. Growth Early in the development of an organism, cells are dividing to increase the overall number of cells (i.e. Human fetus) 2. Differentiation Cells divide to produce different types of cells 3. Repair damaged tissue 4. Replace cells from outer surfaces (i.e. Skin) 5. Immune functions (i.e. Memory T cells)

9. What cells divide often? What cells rarely/never divide? Skin Stomach lining Red Blood cells Embryo Plant roots Hair Nails Nervous System Liver

10. Some important vocabulary (“C” Terms): 1. Chromosomes Long threads of genetic material Found in nucleus 2. Chromatid One side of a duplicated chromosome

11. 3. Centromere  Structures that hold sister chromatids together  NOTE: 2 sister chromatids = 1 duplicated chromosome

12. 4. Chromatin DNA tangled around a histone (a protein) Condensed chromatin = chromosome

13. Once more… B. Chromatin A. DNA histone C. Duplicated chromosome

14. The Cell Cycle: The cell cycle is the series of events that take place in a cell leading to its division and replication. It consists of 3 major stages 1. Interphase 2. Mitosis 3. Cytokinesis Note: it is a continuous process!

15. 1. Interphase In this phase DNA is copied in preparation for cell division This is a non-reproducing stage A cell spends most of the time in this phase

16. 2. Mitosis Nuclear division Two identical sets of chromosomes are allocated to the 2 daughter nuclei

17. 3. Cytokinesis Cytoplasmic division The cytoplasm is equally divided between the two daughter cells

18. Short clip: cell division http://www.youtube.com/watch?feature=player_detailpag e&v=Q6ucKWIIFmg http://www.youtube.com/watch?feature=player_detailpag e&v=Q6ucKWIIFmg

19. To do: Cell Cycle colouring sheet If time permits: read pg 82-90 and start questions 1-10 on page 90