Another reason is because the surface area and volume ratio does not stay the same as their size increases. Because of this, it is harder for a large cell to pass materials in and out of the membrane, and to move materials through the cell.

Cells are limited in how large they can be.

Limits to Cell Growth

The larger a cell beomes, the more demands the cell places on its DNA. This is known as “DNA overload”

• 1. Calculate the total surface area for each cell model by the following formula:

• surface area = (Length X Width) X 6 sides  

• 2. Calculate the volumes for each cell model by the following formula:

• volume = length X width X height  

• 3. Calculate the surface area-to-volume ratio for each cell model by the following formula:

ratio =surface area

volume

Large surface area to volume ratio of microbes facilitates nutrients uptake.If the ratio is too low, the extracellular concentration of essential nutrients may be too low to rely on passive mechanisms of uptake.

DATA TABLE: Cell Size ComparisonCell Dimension

s (cm)

Surface Area (cm2)

Volume (cm3)

Ratio Surface area to Volume

1 1cm

2 2 cm

3 4cm

6 cm2 1 cm3 6:1

24 cm2 8 cm3 3:1

96 cm2 64cm3 1.5:1

How Cells Get Around the SA/V Problem

• Avoid the problem - stay small

• Elongate or flatten out • Fold the surface membrane

Extending the outer surface of a cell into folds, fingers or indentations can increase the total surface area by a factor of several times Villi of the Small Intestines

Root Hairs

Cristae

The Brain

Alveolus