How do little elephants grow up to be BIG elephants?

1. How do little elephants grow up to be BIG elephants?

2. Why do animals shed their skin?

3. The process of asexual reproduction begins after a sperm fertilizes an egg.

4. Three reasons why cells reproduce by asexual reproduction: 1. Growth 2. Repair 3. Replacement Skin cancer - the abnormal growth of skin cells - most often develops on skin exposed to the sun. Cell that reproduce by asexual reproduction reproduce constantly.

5. The Cell Cycle • Interphase: • G1, S, G2 • Mitotic Phase • Mitosis: • Prophase/Pro-Metaphase • Metaphase • Anaphase • Telophase • Cytokinesis

6. Interphase 1st Phase of Cell Cycle • G1 is the main growth stage when cells grow from small daughter cells into into full-sized cell and carries out normal cell activities. • During the S-phase, chromosomes in the nucleus are copied (the # of chromosomes doubles) to produce sister chromatids. • During G1 and S-phases, chromosomes appear as threadlike or spaghetti-like strands called chromatin. • By the END of G2, each chromosome and its copy (the sisterchromatids) will become condensed and appear as thick, worm-like chromosomes! • During G2, the mitochondria in plant and animal cells and the chloroplasts in plant cells replicate. CELL MEMBRANE Nucleus Cytoplasm

7. Interphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

8. Prophase 1st step in Mitosis (1st Step in Mitotic Phase) • Mitosis begins (cell begins to divide) • DNA appears as condensed, worm-like chromosomes(not spaghetti-like chromatinseen in Interphase). • Chromosomes consist of two identical sister chromatids joined at the centromere. • Two pairs of centriolesappear and begin to move to opposite ends (poles) of the cell. • Centrioles occur in pairs; each centriole in a pair is oriented at a right angle to its partner. • Spindle fibers form between the two pairs of centrioles. Centrioles Sister chromatids Spindle fibers

9. Prophase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

10. Pro-Metaphase • The NEW step in the cycle that occurs between Prophase and Metaphase. • Activities formerly considered to mark the last part of Prophase: • Nuclear envelope disintegrates. • Centrioles reach the poles of the cell. • Activities formerly considered to indicate the beginning of Metaphase: • Spindle fibers attach to the centromeres linking two sister chromatids together. • Chromosomes (sister chromatids) begin migrating/moving towards center of cell.

11. Metaphase 2nd(or 3rd) step in Mitosis • Spindle Fibers attach to the chromatids (sister pairs of chromosomes) at the centromere. • Spindle fibers are usually visible under a microscope in this stage. • Sister Chromatids migrate until they are all lined up at the cell “equator” along the metaphase plate. • The location of the equator or metaphase plate is determined by WHERE the chromosomes line up. • Meta = Middle • Organization of sister chromatids along metaphase plate helps ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome. Centrioles Spindle fibers

12. Metaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

13. Anaphase 3rd(or 4th) step in Mitosis • The paired chromosomes (sister chromatids) separate and begin to move/migrate towards the opposite ends (poles) of the cell. • “Ana” = opposite • The migrating chromatids may appear V-like as they migrate. Centrioles Spindle fibers

14. Anaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

15. Telophase 4th (or 5th) step in Mitosis(Last step in mitosis, but NOT the last step in the Mitotic Phase) • The chromatids arrive at the poles of the cell. • A new nuclear envelopebegins to form around each of the two clumps of chromatids, eventually forming two new nuclei. • Chromosomes gradually become uncondensed and appear as chromatin (threadsrather than rods). • Acleavage furrow or cell platemay become visible towards the end of telophase. • This is the end of Mitosis. Nuclei Nuclei Chromatin

16. Telophase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

17. Cytokinesis2nd Stage in the Mitotic Phase • Cytokinesis is the division of the cytoplasm. • Cytokinesis usually begins during Telophase. • In animal cells, the cleavage furrowpinches inward. • In plant cells, a cell plate forms along the metaphase plate region and grows towards the cell walls. • Cytokinesis results in two daughtercells – each with its own nucleus with identical chromosomes. • Each daughter cell will end up with half of the cytoplasm and about half of the organelles—there are usually enough in the original cell that each daughter cell will end up with some.

18. Animal Mitosis -- Review

19. Plant Mitosis -- Review

20. Cell Cycle

21. 1 2 3 4 - Cell Division The Cell Cycle 6 5 22

22. MitosisAnimation http://www.cellsalive.com/mitosis.htm

23. Mitosis Discussion Question: Mitosis is the process in which the nucleus divides to form two new nuclei. How does mitosis differ in plants and animals? 24