When cells reach a certain size, their rate
of growth slows down. They then stop growing. Usually mitosis (cell
division) follows, and the daughter cells continue to grow. Cells are
small (usually microscopic) because of the ratio of surface area to volume in a
cell.
In order for materials to get into or out of
a cell, they must pass through a cell membrane. Thus, the amount of
membrane available to the cell is very important. The membrane is essentially
the surface area and the contents of the cell is its volume.
Hypothesize - which of the three do you think would be most
likely to survive? Why?
Which one will do the best job of moving materials in and out
of the cell? Why?
Procedure:
1. You have been given three model "cells"
represented by cubes.
Calculate the surface area of each of you three model
"cells' in cm2.
Use the following formula: surface area of a cube = length X
width X #of surfaces
2. Calculate the total volume of the three "cells"
using the following formula:
volume
of cube (cm3) = Length X width X height
3. Complete the following table.
side length (cm)
surface area (cm2)
volume (cm3)
surface area/volume
0.5
.5 X .5 X 6 = 1.5
.5 X .5X .5 = .125
1.5/.125 = 12
Follow-Up:
1. Was your hypothesis correct? Why or why not.
2. Based on the information you obtained from this exercise, explain why
individual cells tend not to grow very large.
3. A worm has a long smooth skin through which is absorbs all the oxygen
needed by its cells. Does the amount of oxygen needed depend on the worm's skin
area or on the volume of its cell material?
