1. Cellular Reproduction
Chapter 9
Cellular Reproduction

2. THEME FOCUS
Cells go through several changes as they GROW and REPRODUCE

3. BIG Idea
Cells go through a life cycle that includes INTERPHASE, MITOSIS, and CYTOKINESIS

4. MAIN Idea
Cells grow until they reach their SIZE limit, then they either stop growing or DIVIDE

5. Cell Size Limitations
Most cells are less than 100 µm, which is smaller than the period at the end of this sentence.
The size of a cell is limited by its ratio of SURFACE AREA to its VOLUME
The SURFACE AREA is the area covered by the plasma membrane
The VOLUME is the space taken up by the inner contents of the cell

6. Ratio of Surface Area to Volume
To calculate the surface area of a cube shaped cell, the following formula is used:
LENGTH x WIDTH x number of SIDES (6)
To calculate the volume of a cube shaped cell, the following formula is used:
LENGTH x WIDTH x HEIGHT

7. Ratio of Surface Area to Volume
The surface area of the small cell shown above is 6 µm2 and the volume is 1 µm3. Therefore the ratio of surface area to volume is 6:1

8. Ratio of Surface Area to Volume
The surface area of the medium cell shown above is 24 µm2 and the volume is 8 µm3. Therefore the ratio of surface area to volume is 3:1

9. Ratio of Surface Area to Volume
The surface area of the large cell shown above is 96 µm2 and the volume is 64 µm3. Therefore the ratio of surface area to volume is 3:2

10. Ratio of Surface Area to Volume
As the cell grows, its VOLUME increases much more rapidly than the SURFACE AREA.
This means that the cell might have difficulty supplying NUTRIENTS (FOOD & OXYGEN) and expelling enough WAST PRODUCTS (CARBON DIOXIDE).
By remaining small, cells have a GREATER surface area to volume ratio and can therefore sustain themselves more easily.

11. Transport of Substances
The movement of substances can be managed more easily in a SMALL cell than in a LARGE cell.
Recall, it is the selectively permeable PLASMA MEMBRANE that controls cellular transport
Once inside, substances move by DIFFUSION or by motor proteins pulling them along the CYTOSKELTON
SMALL size maximizes the ability of diffusion and motor proteins to transport NUTRIENTS and WASTE PRODUCTS

12. Cellular Communications
Cell SIZE affects the ability of the cell to communicate instructions for cellular functions
If it becomes too LARGE, it becomes almost impossible for cellular communications to take place efficiently