1. Mitosis

2. Why do cells divide? (Purpose of Mitosis) Growth Repair and replace dead cells asexual reproduction

3. What cells divide often? Skin Stomach lining Red Blood cells Embryo Plant roots Hair Nails

4. What cells rarely/never divide? Nervous System (nerve cells) Liver (liver cells)

5. Interesting Fact: Why do we age? Eventually cells stop being replaced “Apoptosis” –Cell death “We die because our cells die.” –William R. Clark

6. “C” Terms Chromosomes –Long threads of genetic material –Found in nucleus Chromatid –One side of a duplicated chromosome

7. “C” Terms Centromere –Structures that hold sister chromatids together NOTE –2 sister chromatids = 1 duplicated chromosome

8. DNA is broken into long strands and wrapped around proteins to form structures called chromosomes.

10. “C” Terms… Centrioles –Small protein bodies –In cytoplasm –Animal cells only –Spindle fibres extend from centrioles.

11. Micrograph of a Chromosome

12. Cell Reproduction Cells must divide to increase the number of body cells (not egg or sperm) in an organism There are two parts to it: –mitosis - the division of the nuclear material –cytokinesis - the division of the cytoplasm and organelles

13. Cell Division in a Nutshell Before: –Chromosome duplicates = 2 sister chromatids (DNA replication ) During: –Sister chromatids separate After: –2 “daughter” cells –Genetically identical

14. Mitosis Phases Interphase Prophase Metaphase Anaphase Telophase

15. Stages of Mitosis: Interphase resting phase (period between divisions) centrioles are just outside the nuclear membrane nucleolus is present and DNA appears as fine threads called chromatin DNA replicates and appears as double chromosomes and centrioles begin to move apart near the end of this phase

16. Interphase membrane

17. Stages of Mitosis: Prophase nucleolus disappears centrioles move to opposite sides of nucleus asters and spindle fibers form around each centriole nuclear membrane disappears chromosomes are visible as two sister chromatids held together at the centromere

18. Prophase Spindle fiber membrane

19. Stages of Mitosis: Metaphase chromosomes line up along equator (middle) of cell spindle fibers extend from centrioles (poles) to centromeres of the paired chromatids

20. Metaphase

21. Stages of Mitosis: Anaphase chromatids separate and move toward opposite poles

22. Anaphase

23. Stages of Mitosis: Telophase chromosomes disappear; chromatin reappears spindle fibers and asters disappear nucleolus reappears and nuclear membrane reforms cell membrane pinches inward to split cytoplasm (cytokinesis)

24. Telophase & Cytokinesis

25. Cytokinesis…

26. Concept Map

27. Mitosis Animation

28. Mitosis in Plants Mitosis in plants is very similar to animals with 2 exceptions: –plant cells lack centrioles –plant cells form a cell plate between the two daughter cells in telophase.

30. Cytokinesis in Plants

31. Cytokinesis Why would it occur differently in animal and plant cells? Plant cells have a rigid cell wall!

32. Cytokinesis Animal Cells Plant Cells Cell membrane pinches inward Creates cleavage furrow Think: –Pull a string around a balloon Cell Plate forms between two new nuclei Becomes cell wall

33. What phases do you see? A D B C

34. What phase? Interphase

35. What phase? Prophase

36. What phase? Metaphase

37. What phase? Anaphase

38. What phase? Telophase

39. What phase? Interphase

41. Understanding Concepts 1)Go to page 90 in BIOLOGY 11 BOOK - Answer questions 2, 3, 4, 5, 6, 7, 9, 10 2) Complete Mitosis Review Worksheet