1. Cell Division

2. What do you think??? Do we have the same skin as we were born with?
What happens when we cut ourselves?
What happens when we burn our skin?
Why does our hair grow when we cut it?

3. Recall: The Cell Theory
Cells are the basic fundamental units of life.
All living things are composed of one or more cells.
All cells come from pre-existing cells.

4. FUNCTIONS OF CELL DIVISION
Healing & Tissue Repair
Growth & Development
Reproduction
NOTE: In humans, 1 & 2 divide through mitosis & 3 divides through meiosis

5. 1. Healing & Tissue Repair
Millions of cells in our bodies die or are damaged every second and they need to be replaced, otherwise we would disappear!!!
E.g. Scraping your knee, burning skin
Video Leopard Gecko

6. 2. Growth & Development Cells divide so that we can grow
Single cells get bigger and eventually divide
Materials such as nutrients and water are more easily controlled in smaller cells
Eg. Getting taller

7. 3. Reproduction Enables organisms to survive, otherwise species
would die out
Applies to unicellular (body cells) & multicellular organisms (sex cells)through different processes of cell division
Eg. An amoeba will divide into two identical cells
Video Seahorse

8. Sexual vs Asexual Reproduction
Occurs in complex organisms
Two parents
Each parent donates ½ the genetic information required
Cell is different from either parent
Greater variety of offspring
Slower process
Asexual
One parent
Results in two cells
Cells identical to parent
Simple Organisms (Bacteria)
Fast Process
No genetic variation – susceptible to disease
Produces body cells in humans
Sexual vs Asexual Reproduction
Produces New Cells

9. Cell Division & the Nucleus
The nucleus is the “control centre” of the cell. It contains chromosomes, which are made of DNA and proteins.
When a cell divides the genetic material must replicate and divide as well.
Q: Why does the genetic material have to replicate?

10. Chromosome number is species dependent
humans dog chimps ferns

11. Terms to describe DNA
Each chromosome is a long DNA molecule, typically containing 1000’s of genes
Chromatin – 95% of the time the genetic material appear like this
“Spaghetti like”, uncoiled, long, thin & stringy
Found during interphase
Chromosomes – 5% will appear like this in an actively growing cell
Coiled, short & thick, can be seen under the microscope
Found during Mitosis (cell division)

13. Variation in Genetic Material
Depending on the stage of the Cell Cycle, chromosomes will have different appearances, and have different names.
Unreplicated
chromosome
centromere
Replicated/
double stranded
chromosome

15. THE CELL CYCLE: Interphase + Cell Division
A) Interphase:
is a stage of growth & development
B) Cell Division:
Includes both Mitosis (nuclear division) & Cytokinesis (division of organelles and cytoplasm)
There are four phases of Mitosis
Prophase
Metaphase
Anaphase
Telophase
To Remember all the Stages: I-PMAT!!!

16. THE CELL CYCLE: Interphase + Cell Division

17. Interphase
Cell grows & prepares itself for mitosis by building proteins
Duplicates genetic material called CHROMATIN, now double stranded
Centrioles are also replicated, more organelles form
Parent Cell

18. Prophase Genetic material now called CHROMOSOMES
chromosomes shorten & thicken, now visible in light microscope
Nuclear membrane & nucleolus breakdown, freeing the chromosomes
centrioles move away from each other & form spindle fibres
Prophase
Cytoplasm
Cell Membrane

19. Metaphase Nuclear membrane has disappeared
Centrioles have reached opposite poles
Chromosomes line up in the middle of the cell or EQUATOR
They are attached to the spindle fibres by their CENTROMERES.
Cytoplasm
Cell membrane

20. Anaphase
Spindle fibres shorten to pull and separate duplicated chromosomes to opposite poles of the daughter cells
The chromosomes are now referred to as DAUGHTER CHROMOSOMES.
Cytoplasm
Cell Membrane
Daughter Chromosome

21. Telophase
Daughter chromosomes have reached opposite poles & begin to uncoil
Nuclear membrane & nucleolus reform
Spindle fibres disappear
DAUGHTER CELLS are genetically identical
Cytokinesis begins
Daughter Cells

22. Cytokinesis (animal vs. plant)
Clevage Furrow Cell Plate

23. And…..It All Begins Again!!!
Two new ‘daughter’ cells in interphase

24. Mitosis Overview