Chapter ( 3 ) Cell Division 1 Mr. Mohamed Mansoor (0533816341) Cell Division Mitosis - Meiosis - Happens in both Unicellular and Multicellular organisms. - Happens in Multicellular only - Produce Two Identical copies of Parent cell (Diploid 2N) - Produce Four cells with half chromosome number (Haploid N ) - Nucleus Divides only one time - Happens in Body Cells - Nucleus Divides two times meiosis I and meiosis II - Happens in Germ cells - Happens for Growth , Repair ,Reproduction - Happens for Reproduction only , to form Gametes (Sperm and Egg ) Chromosome structure : - A chromosome consists of a highly coiled and condensed strand of DNA. - A replicated chromosome consists of two sister chromatids, connected at centromere 2 Mr. Mohamed Mansoor (0533816341) - THE CELL CYCLE 1- Interphase ( G1, S , G2 ) , 90% Of cell cycle 2- Mitosis Nuclear division (Pro , Meta , Ana , Telo ) 3- Cytokinesis Cytoplasm Divides - Mitosis 1- Prophase : - chromosomes begin to condense and become visible. - The nucleoli disappear. - Spindle fibers begin to form - Centrioles begin to migrate to the poles. - The nuclear membrane begins to disintegrate. 2- Metaphase : - Chromosomes line up single file located on the - Centrosomes are at opposite poles of the cell. - Spindle fibers run from centrosomes to the centromeres 3- Anaphase : (Shortest phase) - The centromeres of each chromosome separate, and spindle fibers begin to pull the sister chromosomes apart. 4- Telophase : - Chromosomes are at cell pole - Nuclear membrane Re- form 3 Mr. Mohamed Mansoor (0533816341) - Cytokinesis - In animal cells, a cleavage furrow forms down the middle of the cell. - The Two cells Separate - In plant cells, a cell plate forms down the middle of the cell. - The two cells Don’t separate - sticky middle lamella cements adjacent cells together Meiosis I - Called Reduction division Because it reduces the no. of chromosomes to Half. A) Interphase happens as a preparation phase for meiosis - Synapsis : Two homologous pair (Tetrad) pair up precisely so , Crossing over happens - Crossing Over : is the process in which homologous chromatids exchange genetic material. ( It happens to increase genetic variety ) Note : Both Synapsis and crossing-over Happens during Prophase I 4 Mr. Mohamed Mansoor (0533816341) 2- Metaphase I :Tetrads Line up at the cell Equator 3- Anaphase I : Notice that Chromosome pairs (Half of the tetrad ) Will separate and start to move to the opposite poles of the cell Note : During Anaphase of mitosis (Single chromosomes ) separated 4- Telophase I : - The Homologous chromosome pairs move to cell poles and cell divide into two cells - cells have same number of chromosomes of mother cell (because of the interphase) - resulting cells with Unique genetic structure because of the crossing-over Meiosis II o o Note that interphase happens before meiosis I But no Interphase happens before Meiosis II Meiosis II is Identical to mitosis , and happens to the two cells produced from Meiosis I producing four Haploid cells - - Note that Anaphase I separates the two homologous chromosomes - But Anaphase II separates the sister chromatids 5 Mr. Mohamed Mansoor (0533816341) 6 Mr. Mohamed Mansoor (0533816341) Important points of Section (2 & 3) active transport adenosine triphosphate anaphase carrier proteins cell cell cycle cell division cell sap cell wall centrioles chloroplasts chromatids chromatin chromosomes cilia 7 Mr. Mohamed Mansoor (0533816341) cleavage furrow cytokinesis cytoplasm cytoskeleton diffusion endocytosis endoplasmic reticulum eukaryotic facilitated transport flagella fluid-mosaic model G1 phase G2 phase Golgi bodies homologues interphase 8 Mr. Mohamed Mansoor (0533816341) karyokinesis lysosomes M phase metaphase microfilaments microtubules mitochondria mitosis nucleolus nucleus organelles osmosis passive transport peroxisomes phagocytosis phospholipid bilayer 9 Mr. Mohamed Mansoor (0533816341) pinocytosis plasma membrane prokaryotic prophase ribosomes sodium-potassium pump S phase spindle fibers telophase vacuoles vesicles 10 Mr. Mohamed Mansoor (0533816341) MULTIPLE-CHOICE QUESTIONS Questions 1–6 (A) Mitotic cell division (B) Meiotic cell division 1. The human liver can be induced to regenerate when liver cells become damaged and need to be replaced. 2. An embryo grown into a fetus and then a baby during a nine-month gestation period. 3. Human males begin to produce sperm at puberty. 4. A fertilized ovum undergoes rapid cell division immediately after it is fertilized by a sperm cell. 5. A cut on your skin heals. 6. A cancerous tumor grows larger. ________________________________________ 7. Which of the following does NOT occur by mitosis? (A) Growth (B) Production of gametes (C) Repair (D) Development of an embryo (E) Cleavage furrow forms in animal cells 11 Mr. Mohamed Mansoor (0533816341) Questions 8–9 8. How many chromosomes are in this cell? (A) 0 (B) 2 (C) 3 (D) 4 (E) Cannot be determined (D) 4 (E) Cannot be determined 9. How many chromatids are in this cell? (A) 0 (B) 2 (C) 3 ________________________________________ 10. In which stage in the life of a cell is the nucleolus visible? (A) Prophase (B) Anaphase (C) Telophase (D) Cytokinesis (E) Interphase 11. Which of the following is NOT found in plant cells? (A) Cell plate (B) Cleavage furrow (D) Centromere (E) Chromatids (C) Middle lamella 12. If a cell has 12 chromosomes at the beginning of meiosis, how many chromosomes will it have at the end of meiosis? (A) 6 (B) 12 (C) 24 (D) 48 (E) It varies with the species. 13. If a cell has 12 chromosomes at the beginning of mitosis, how many will it have at the end of mitosis? (A) 6 (B) 12 (C) 24 (D) 48 (E) It varies with the species. 14. All of the following are true of meiosis in plants EXCEPT (A) Crossing-over occurs during prophase. (B) There is no replication of chromosomes between meiosis I and meiosis II. (C) Spindle fibers are attached to the centriole. (D) Synapsis occurs during prophase. (E) Homologous pairs of chromosomes line up on the metaphase plate in meiosis I. 12 Mr. Mohamed Mansoor (0533816341) Questions 15–18 Match the event of mitosis with stages listed below. 15. Which stage is metaphase I of meiosis? (A) A (B) B (C) C (D) D (E) E 16. Which stage is metaphase II of meiosis? (A) A (B) B (C) C (D) D (E) E (D) D (E) E 17. Which stage is anaphase II of meiosis? (A) A (B) B (C) C 18. Which stage shows non-disjunction? (A) A (B) B (C) C (D) D (E) E ________________________________________ 19. Chromosomes become visible for the first time during (A) interphase (B) prophase (D) anaphase (E) telophase (C) metaphase 20. Chromosomes replicate during (A) interphase (B) prophase (D) anaphase (E) telophase 13 Mr. Mohamed Mansoor (0533816341) (C) metaphase
