1. Cell Replication What is the purpose? What is mitosis? 1

2. Why do cells need to replicate? Nucleus to cytoplasm ratio – as sell matures this ratio gets larger i.e. nucleus gets smaller compared to size of cell. Growth – needed for multicellular organisms to increase in size Development – the ability of undifferentiated cells to become specialised. Maintenance and repair – replacement of those cells that have been damaged or lost.

3. Cell division INTERPHASECYTOKINESISMITOSIS

4. Stages of cell replication Interphase ◦ Organelles and DNA copied but NOT visible yet Mitosis ◦ Chromosomes separated into 2 identical nuclei but cell not divided yet Cytokinesis ◦ 2 daughter cells become independent ◦ Cleavage furrow (animal) ◦ Cell plate formation (plants) 4

5. 5 NUCLEUS Homologous Chromosomes Sister chromatids This cell has a : Diploid number = 4 Haploid number = 2 DNA is copied – still in long threads – chromosomes NOT yet completely visible Interphase

6. 6 CENTRIOLE Nuclear membrane breaks down Chromosomes condense so you can now see them Centrioles send out spindle fibres START MITOSIS - Prophase

7. 7 CENTRIOLE Centromeres and spindle fibres drive the chromosomes to the equator Metaphase – line up on equator

8. 8 CENTRIOLE Spindle fibres pull chromatids to opposite poles of the cell. Anaphase

9. 9 Centrioles break down Nuclear membrane forms around each set of chromosomes CENTRIOLE Telophase

10. Two daughter cells with exactly the same chromosomes as the original parent cell. Cytokinesis 10

11. Plant Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

12. Animal Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

13. some extras... some extras... 13

14. Division of the molecules and organelles of the cytoplasm Separation of new nuclei, to form two new identical daughter cells How do cells replicate? – Cytokinesis Plant New plasma membrane and cell wall are deposited in the centre of the cell Animal Plasma membrane moves inward, pinching the daughter cells apart