1. Cell Growth & Reproduction

2. Cell Sizes
*usually micrometers in diameter (whale & mouse cells are about the same size- how?)
*cell range in size from 8 micrometers to 1 meter long to 8 centimeters
 size related to function, not organism (nerve cells long to relay messages, blood cells fit through arteries)
*cells don’t just increase in number, they become specialized

6. Cell Size Limitations - #1 Why diffusion limits cell size:
a. cells need plenty of glucose & oxygen to make energy & to get rid of CO2 & waste
b. it takes a fraction of a second for oxygen to travel about 20 nanometers to innermost mitochondrion
c. if a cell were too big, diffusion of needed nutrients would take too long.
Ex: if a cell were 20 cm, it would take months for a molecule of oxygen to get to the mitochondria & the cell would die

7. Cell Size Limitations - #2 Why a cells DNA content limits cell size:
a. most cells contain only one nucleus that contains DNA. If a cell doesn’t have enough DNA to control it, the cell will die
b. if a cell is very large, it must have more than one nucleus so it has enough DNA

8. Cell Size Limitations - #3 Surface area to volume ratio:
a. as a cell size increases, volume increases faster than surface area
Ex: If cell surface area = 6mm2 (1mm sides), volume = 1mm3
If cell surface area = 24mm2 (2mm sides), volume = 8mm3
b. Is big better? If a cells surface area does not increase in proportion to volume there would not be enough surface area through which nutrients & oxygen to enter

9. Why Most Cells Are Small:

10. four
surface area
eight
volume
The surface area of the cell will increase by four.
The volume will increase by eight.
it divides