1. Why are cells so small?
Cells are found in every living organism, ranging from unicellular (one-celled) organisms, such as amoebas, to multicellular (many-celled) organisms, such as human beings. Even though each organism is very unique, their cells are typically about the same small size.
This similarity then leads to the questions:
1. Why are cells so small?
2. Why are we composed of billions of
tiny cells instead of a few large cells?

2. Getting Through
Materials move through cells by diffusion. Oxygen and food move into cells, while waste products move out of cells. How does the size of a cell affect how efficiently materials get to all parts of a cell?
Work with a partner to complete this activity.
1. On a sheet of paper, make a drawing of a cell that has the following dimensions: 5 cm x 5 cm x 5 cm. Your partner should draw another cell about one half the size of your cell on a separate sheet of paper.
2. Compare your drawings. How much longer do you think it would take to get from the cell membrane to the center of the big cell than from the cell membrane to the center of the smaller cell?
3. What is the advantage of cells being small?

3. Cell Growth
Chapter 10.1

4. Reasons For Cell Division
The larger a cell becomes, the more demands the cell places on its DNA.
 In addition, the cell has more trouble moving enough nutrients and wastes across the cell membranes

5. DNA Overload
DNA  contains the information that controls a cell’s functions
Eukaryotes DNA is found in the nucleus
Prokaryotes DNA is found in the cytoplasm
As cell increases in size, DNA does not have enough information to maintain it and service the needs of the cell

6. Exchanging Materials: Surface Area
Rate at which exchange of wastes, nutrients, and gases takes place depends on the surface area of the cell
Surface area = length x width x # of sides 5
What is the surface area of the cube?
Surface area = l x w x # sides
 Surface area = 5 x 5 x 6 = 150

7. Exchanging Materials: Volume
Rate at which nutrients and gases are used up and wastes are made depends on volume of the cell
Volume = length x width x height 5
What is the volume of the cube?
Volume = l x w x h
 Volume = 5 x x 5 = 125

8. Exchanging Materials
Volume increases much faster than surface area when a cell is growing
Exchange of materials cannot keep up with the demand
 Materials have to travel farther to get to all parts of cell

9. Surface Area-to-Volume ratio
Smaller cells have a larger surface area to volume ratio
Means there is more surface area for materials to fit into

10. Ratio of Surface Area to Volume in Cells
Section 10-1
Ratio of Surface Area to Volume in Cells
Cell Size
Surface Area (length x width x 6)
Volume
(length x width x height)
Ratio of Surface Area to Volume