1. Cell Size, Division and Potency

2. Cell Size Cell size is directly related to the cell membrane
Ideally, a cell needs a large surface area (cell membrane) with a small volume
Surface Area/volume Ratio:
6 to 1
Surface Area/volume Ratio:
3 to 1

3. Why do cells need a lot of surface area?
Cells need a large surface area to allow needed nutrients to enter and wastes to exit.
If a cell gets too big, then there isn’t enough membrane to allow for the exchanges and the cell dies.

4. Cell Size Experiment
Pink agar is prepared and cut into three different sizes; these 3 cubes represent 3 different sized cells
The agar is placed in an acidic solution.

5. Cell Size Experiment (cont.)
The acid diffuses into the “cells” and changes the pink color to white.
In the small cell, the acid was able to get through to the center. In the big cell, it could not. This big cell would die.

6. Why do cells need to have small volume?
As the cell increases in size it does not make an extra copy of DNA so the DNA that it has will no longer be able to control the growing cell.
It’s like a teacher with a small class…she can control the class better than a teacher with a large class.

7. Cell Division
Cell division is defined as the splitting of a single cell into 2 daughter cells
A cell must divide when:
A cell has grown so much that the nucleus can no longer control all of the cytoplasm
The surface area to volume ratio is too low

8. 3 Life Processes that Depend on Cell Division
Growth- Increase in size
Repair- Accomplished by cell regeneration at the site of injury
Reproduction- Either asexually (requires one parent) or sexually (requires two parents)

9. Cell Differentiation
Differentiation is defined as the changes that take place in cells as they develop

10. Cell Potency
At first cells have the potential to become any other type of cell, but as cells become more specialized, they lose this ability
The levels of cell potency are:
Totipotent
Pluripotent
Multipotent
Unipotent

11. Totipotent
These cells have TOTAL potential…thus the name, totipotent. They have the ability to become any cell in the body and even the extra embryonic tissues (ex: placenta).
This totipotent cell might become part of the baby, part of the amniotic sac, part of the umbilical cord, etc. It has total potential.

12. Pluripotent
These cells can become any cell in the body, but have lost the ability to become an extraembryonic tissue cell
These cells will form the placenta and amniotic sac.
These pluripotent cells will form the baby.

13. Multipotent
These cells are committed to give rise to only one group of cells (ex: blood cells).
This multipotent cell can become any BLOOD cell, but it can’t become any other type of cell like muscle or nerve.

14. Unipotent
These cells are so specialized that they can only give rise to cells like themselves.
This unipotent skin cell can only give rise to another skin cell.