1. Cell Division
Chapter 9

2. Why do you think cells in all plants and organisms need to divide?
To replace damaged tissue
To increase in size
To reproduce

3. Repair Cells are constantly repairing themselves
If a cell can’t be repaired new ones are produced to fill the void

4. Growth Cells are also what create our size
As we grow our cells are constantly reproducing
If the reproduction rate is faster than normal we grow

5. Reproduction Asexual Sexual Done by somatic or body cells
Done also by unicellular organisms
Creates identical daughter cells
Done by gametes or sex cells
Creates genetically different daughter cells

6. What do we need for cell division?
Chromatin: a mass of DNA found in the nucleus

7. What do we need for cell division?
Sister chromatids
Centromere
TEM 36,600
Chromosome: a compacted piece of chromatin that is used for cell division
Sister Chromatids: A pair of identical Chromosomes
Centromere: The center section where the sister chromatids are connected

8. DNA supercoil

9. Chromosome distribution to daughter cells
LE 8-4
Sister chromatids
Centromere
TEM 36,600
Sister
chromatids
Chromosome
distribution to
daughter
cells
duplication

11. How do cells divide?
Cell Cycle: an orderly sequence of events where cells divide
The cell cycle consists of two major phases
Interphase (90% of the time)
Mitotic Phase (10% of the time)

12. The Cell Cycle
In humans and other mammals, cells that reproduce daily have a cell cycle that usually lasts 10 to 20 hours.

13. The Cell Cycle: series of events that cells go through from “birth” to reproduction

14. Interphase Phase where all metabolic processes and functions happen
Ex:
Cellular respiration
Protein creation
Movement
Growth
Other desired function

15. Interphase Interphase is also when the cell prepares for cell division
Ex:
Increases proteins
Duplicates organelles
Grows in size
Duplication of DNA

16. Mitotic Phase The division phase of the cell
There are two main parts of M phase
Mitosis
Cytokinesis

17. Mitotic phase Mitosis Cytokinesis
The division of a cells nucleus and DNA into two equal parts
Creates two daughter nuclei
Cytokinesis
The division of the cells cytoplasm
Together they create two identical daughter cells

18. Mitosis Prophase: Metaphase: Sister chromatids are formed
Formation of spindle
Nuclear envelope breaks down
Metaphase:
Sister chromatids line up
Spindle is formed and attaching to chromosomes

19. LE 8-6a LM 250  INTERPHASE PROPHASE PROMETAPHASE Early mitotic
spindle
Fragments
of nuclear
envelope
Centrosomes
(with centriole pairs)
Centrosome
Chromatin
Kinetochore
Nucleolus
Nuclear
envelope
Plasma
membrane
Chromosome, consisting
of two sister chromatids
Centromere
Spindle
microtubules

20. Mitosis Anaphase: Telophase: Cytokinesis:
Separation of sister chromatids
Spindle pulls chromosomes to either side of the cell
Telophase:
Spindle breaks down
Nuclear envelopes form (2)
Chromosomes loosen to become chromatin
Cytokinesis:
Cell pulls apart to create two identical cells

21. LE 8-6b Metaphase plate Cleavage furrow Nucleolus forming Nuclear
ANAPHASE
TELOPHASE AND CYTOKINESIS
Metaphase
plate
Cleavage
furrow
Nucleolus
forming
Nuclear
envelope
forming
Daughter
chromosomes
Spindle

22. Cytokinesis in animal cells
Cleavage furrow
Cleavage
furrow
Daughter cells
Contracting ring of
microfilaments
SEM 140
Animal
Plants
Formation begins with indentation
Cell is pulled/ pinched until it breaks apart
Formation begins with a disc containing cell wall materials
A cell plate forms between the two nuclei

23. Cytokinesis in plant cells
Formation begins with a disc containing cell wall materials
A cell plate forms between the two nuclei
Cell wall
New cell wall
Daughter cells
Cell plate
Vesicles containing
cell wall material

25. Benign vs. malignant tumor
Benign tumor:
abnormal mass of normal cells
Malignant tumor:
Masses of cells that result from the reproduction of cancer cells
Cancer
Disease caused by cells that loose their ability to control rate of division

28. Meiosis
Organisms that reproduce sexually have specialized cells called gametes (sex cells)
Gametes are the result of a type of cell division called meiosis

29. Diploid and haploid
Almost all human cells are diploid or containing two homologous sets of chromosomes
2n = 46
Eggs and sperm cells (gametes) are haploid or containing a single set of chromosomes
n = 23

30. HUMAN KARYOTYPE
A display of all the 46
chromosomes of an
Individual.

31. 9.5 page 2

32. ORGANISM (Genus species) NUMBER OF CHROMOSOMES
Homo sapiens (human)______________________________46
Mus musculus (house mouse)_________________________40
Drosophila melanogaster (fruit fly)_____________________8
Caenorhabditis elegans (microscopic roundworm)_________12
Saccharomyces cerevisiae (budding yeast) ______________32
Arabidopsis thaliana (plant in the mustard family) ________10
Xenopus laevis (South African clawed frog)______________36
Canis familiaris (domestic dog)________________________78
Gallus gallus (chicken) ______________________________28
Zea mays (corn or maize)____________________________20
Muntiacus reevesi (the Chinese muntjac, a deer) _________23
Muntiacus muntjac (its Indian cousin) __________________6
Myrmecia pilosula (an ant) ___________________________2
Parascaris equorum var. univalens (parasitic roundworm)___2
Cambarus clarkii (a crayfish)__________________________200
Equisetum arvense (field horsetail, a plant)______________216

33. Horsetail

34. MITOSIS

37. Meiosis

38. haploid egg and sperm
diploid zygote
In the human life cycle a haploid egg and sperm fuse and form a diploid zygote. Mitosis produces an embryo with numerous cells that continue to multiply and develop.

39. 2 diploid daughter cells
MEIOSIS
MITOSIS
Original diploid cell 2n 2n 2n
2 diploid daughter cells

40. Genetic variation is a result of two processes that occurs during meiosis:
Independent assortment of chromosomes, and
Crossing over

41. During metaphase I, the independent assortment of chromosomes that end up in the resulting cells occurs randomly

42. Crossing over: exchange of genetic material between homologous chromosomes during prophase I of meiosis

43. Genetic recombination: new combination of genetic information in a gamete as a result of crossing over during prophase I of meiosis

45. MITOSIS MEIOSIS TYPE OF CELL (that undergoes this division)
(pages 195, 200, & 201)
MITOSIS
MEIOSIS
TYPE OF CELL (that undergoes this division)
# OF CELL DIVISIONS
Starts/ends as diploid or haploid cell
# OF DAUGHTER CELLS
# OF CHROMOSOMES AFTER DIVISION
EXCHANGE OF DNA (Y/N)
UNIQUE OR IDENTICAL CELL AFTER DIVISION

46. Development of egg and sperm

47. Onion Root Cell Observations
Using the largest magnification (X400), find a section of the onion root (towards the tip works better).
Count only the cells in one of the quadrants.
Try to find the different stages of cell division, and fill out the table bellow as accurately as you can.
Phase
# of cells %
Time/min.
Interphase
Prophase
Metaphase
Anaphase
Telophase
Total # of cells

48. Onion root tip