1. THE IMPORTANCE OF CELL DIVISION
Cell Rap
THE IMPORTANCE OF CELL DIVISION
SNC 2PI April 2011

2. In the beginning ... You started life as a single cell:
Now your body is made up of TRILLIONS of cells
How does a single cell become a full-grown multicellular organism?
A fertilized egg

3. Why do cells divide? Cells divide for three reasons: Reproduction
Growth
Repair

4. Cell Division for Reproduction
All cells, including single-celled organisms use cell division to reproduce
Single-celled organisms reproduce by the process of asexual reproduction:
Involves only one parent
Offspring are exact genetic copies of the parent
Multi-cellular organisms reproduce by the process of sexual reproduction:
Two parents involved
Cell from one parent joins with cell from another parent
Offspring inherit characteristics from both parents

5. Cell Division for Growth
As multi-cellular organisms grow, the number of cells increases
Why does the number of cells increase instead of simply increasing the size of the cells?
The answer lies in how a cell uses chemicals to function

6. Cell Division for Growth
All cells require a few things to survive:
A source of energy
Nutrients
Water
Certain gases (such as oxygen)
How do these chemicals that are needed travel into the cell to where they are used?
Diffusion is the transport mechanism by which chemicals move into and out of the cell
Chemicals move from areas of high concentration to low concentration

7. Cell Division for Growth
Concentration is the amount of substance (solute) in a given area
Water enters and leaves the cell by the process of osmosis
Osmosis is the movement of water towards an area of high solute concentration

8. Cell Division for Growth
So back to the question ...
Why does the number of cells increase as an organism grows?
Diffusion and osmosis take time
If a cell get too large, important chemicals and water may not move through the cell fast enough for the cell to function properly

9. Cell Division for Repair
Your body must continually replace cells in order to survive:
Every day you shed MILLIONS of dead skin cells
All of your red blood cells are replaced approximately every 120 days
If you break a bone, your cells divide to heal the break
If you cut yourself, new cells need to be made to fill the gap

10. Textbook Questions Answer ‘Check Your Learning’ questions
1 – 6 on page 37

11. Pg. 37 # 1 – 6 Name three reasons for cell division.
Cell division for reproduction
Cell division for growth
Cell division for repair
A cleaning product claims to kill ‘99.9% of all bacteria.’ Will a cleaned surface stay bacteria-free forever? Explain your answer.
The surface will not stay bacteria-free forever, because if a single bacterium is left alive, it can reproduce to a large number in a short period of time.

12. Pg. 37 # 1 – 6
List three differences between asexual and sexual reproduction.
Asexual Reproduction
Sexual Reproduction
One parent
Two parents
Offspring identical to parents
Offspring share characteristics of both parents
Does not involve cells joining together
Involves two ‘half-cells’ joining together

13. Pg. 37 # 1 – 6
What processes are responsible for chemicals moving into, throughout and out of cells?
Diffusion and osmosis are responsible for moving chemicals into, throughout and out of cells.
Why do cells divide instead of just getting bigger, as an organism grows?
Important chemicals must be available to all parts of the cell. If a cell gets too large, the chemicals may not be able to move fast enough for the cell to survive.

14. Pg. 37 # 1 – 6
A minor wound heals over time. Explain how this happens.
Cell division creates new cells that replace those in the wounded area to close and heal the wound.