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Chapter 21

Chapter 21. Cell Division. 21.1 How do cells divide?. All organisms will eventually die. 21.1 How do cells divide?. However, life continues because organisms are able to produce offspring. 21.1 How do cells divide?. The process of producing offspring is called. Reproduction ( 生殖作用 ).

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Chapter 21

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  1. Chapter 21 Cell Division

  2. 21.1 How do cells divide? All organisms will eventually die ...

  3. 21.1 How do cells divide? However, life continues because organisms are able to produce offspring ...

  4. 21.1 How do cells divide? The process of producing offspring is called ... Reproduction (生殖作用) which involves the processes of cell division

  5. 21.1 How do cells divide? Cell division Mitotic cell division (有絲細胞分裂) Meiotic cell division (減數細胞分裂) … both involves replication of genetic material

  6. 21.1 How do cells divide? Chromosome  Genetic information is carried in … Deoxyribonucleic acid (去氧核糖核酸) DNA

  7. DNA molecule when highly coils special protein 21.1 How do cells divide? one chromosome Chromosome

  8. one chromosome chromatid chromatid (染色單體) 21.1 How do cells divide? Chromosome

  9. Brief Revision ~ Word corner ~ Chromosome ** Chromo-  Coloured

  10. 21.1 How do cells divide? Chromosome  exist in pairs  homologous chromosome(同源染色體)

  11. 21.1 How do cells divide? Chromosome  number of pairs varies with different species e.g. 23 pairs humans

  12. 21.1 How do cells divide? Chromosome  number of pairs varies with different species e.g. 39 pairs dogs

  13. 21.1 How do cells divide? Chromosome  number of pairs varies with different species e.g. 7 pairs peas

  14. 21.1 How do cells divide? Chromosome  with 2 sets of chromosomes : diploid(二倍體) (2n)  with 1 set of chromosomes : haploid(單倍體) (n)

  15. Brief Revision ~ Word corner ~ Diploid, Haploid ** Di-  Two ** Haplo- Single

  16. Extension 21.1 How do cells divide? Mitotic cell division  two identical cells produced  same chromosome no. as parent Mitotic cell division mitosis (nuclear division) cytoplasmic division

  17. Extension Mitosis Just before mitosis • DNA molecules are replicated chromosomes nuclear membranes cell membrane

  18. Extension Mitosis Stage 1 Chromosomes become visible Nuclear membranes disintegrate

  19. Extension Mitosis Stage 2 Chromosomes line up at the middle of the cell

  20. Extension Mitosis Stage 3 Chromatids separate and move to the opposite ends

  21. Extension Mitosis Stage 4 New nuclear membranes are formed Chromosomes become invisible again Mitosis is now complete!

  22. Extension Cytoplasmic division In animal cells cell membrane constricts at the middle

  23. Extension Cytoplasmic division In plant cells new cell walls and cell membranes form between two nuclei

  24. Extension Meiotic cell division four identical cells produced  reduce the chromosome no. by half  consists of two divisions Meiotic cell division meiosis (nuclear division) cytoplasmic division

  25. Extension Meiosis First meiotic division 1) Chromosomes shorten and thicken nuclear membranes cell membrane

  26. Extension Meiosis First meiotic division 2) Homologous chromosomes pair up

  27. Extension Meiosis First meiotic division 3) Nuclear membranes disintegrate Each chromosome consists of two chromatids

  28. Extension Meiosis First meiotic division 4) Homologous pairs line up at the middle of the cell

  29. Extension Meiosis First meiotic division 5) Members of each homologous pairs separate and move to the opposite ends of the cell Cytoplasm starts to divide

  30. Extension Meiosis First meiotic division 6) New nuclear membranes are formed

  31. Extension Meiosis Second meiotic division 7) Chromosomes line up again

  32. Extension Meiosis Second meiotic division 8) Chromatids separate Cytoplasm starts to divide

  33. Extension Meiosis Second meiotic division 9)4 daughter cells are formed (each has a haploid number of chromosomes) Nuclear membranes are formed

  34. Significance of cell division Mitotic cell division 3) As a way of asexual reproduction 1) Growth 2) Repairing damage

  35. meiosis fertilization Significance of cell division Meiotic cell division 1) Formation of haploid gametes (in gametes, i.e. sperm and egg) 2n n sperm (n) + egg (n) zygote (2n)  the diploid number of chromosomes can be restored after fertilization

  36. A a B b A a A a B b b B Significance of cell division Meiotic cell division 2) Creation of genetic variations among gametes homologous chromosomes arrange randomly at the middle of the cell 2 pairs of homologous chromosomes

  37. A a A a members of each homologous pair separate B b B b A a A a b B b B Independent assortment (獨立分配) OR OR Gametes with different genetic combinations

  38. Mitosis Meiosis 1Place of occurrence 2Pairing of homologous chromosomes 3Separation of homologous chromosomes 4Number of divisions Extension Brief Revision What is the difference between mitosis and meiosis? Body cells Sex organs Does not occur Occurs Does not occur Occurs 1 2

  39. Mitosis Meiosis 5Number and types of daughter cells 6Chromosome number of each daughter cell 7Significance Extension Brief Revision What is the difference between mitosis and meiosis? 1Place of occurrence 2, body cells 4, gametes 2Pairing of homologous chromosomes Diploid (2n) Haploid (n) 3Separation of homologous chromosomes Forms cells for growth, repair and asexual reproduction Forms haploid gametes so that the diploid condition can be restored in the zygote after fertilization

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