Download SURFACE AREA TO VOLUME RATIO LAB Why Do Cells Divide?

Name __________________________________ Date ___________________ Period _______
SURFACE AREA TO VOLUME RATIO LAB
Why Do Cells Divide?
Background:
The materials a cell needs for maintenance and growth move into the cell through the cell
membrane. Waste materials leave through the cell membrane. As the cell grows, its volume
increases at a greater rate than its surface area. If growth were unchecked, the surface area
would become too small to accommodate the transfer of materials in and out of the cell. To
maintain a workable ratio of volume to surface area, a cell must divide or stop growing.
When a cell reaches a certain size, it divides into daughter cells. The daughter cells in turn grow
and increase in size until they too divide. The daughter cells produced during cell division are
similar in structure to the parent cell. The daughter cells receive portions of the cytoplasm and
information possessed by the parent cell.
Large organisms are composed of many cells. Your body contains billions of cells. Wouldn’t it be
easier to be just one big cell? The size of cells is limited by a factor called the Surface-to-Volume
Ratio. Cells can only get so large until they lose the ability to efficiently get nutrients into and
remove wastes from the various parts of the cell. As the size of a cell increases, the rate of
increase for the surface area does not increase as rapidly as the volume increases. This means
there is proportionally less surface area available to get more needed nutrients in and more wastes
out. This is really not a good situation for the cell.
Purpose:
In this activity, you will determine the relationship between the surface area and the volume of a
cell as the cell grows larger.
Materials:
String
Meter stick
Three balloons of varying size
Calculator
Formulae:
Use the following formulas to calculate surface area and volume:
C (circumference) = 2πr
V (volume of a sphere) = 4πr3
3
Surface area of a sphere = 4πr2
where π = 3.14159 (pi)
r = radius (cm)
1cm3 = 1mL = 1cc
Procedure:
1. Use a piece of string to mark the circumference of each “cell” (balloon).
2. Measure the length of string against a meter stick to determine the length of the circumference in
centimeters
3. Use the circumference to determine the radius of the “sphere”. (hint: solve for “r” in formula)
Analysis: Answer questions in lab journal.
1. Describe the factors that limit cell size.
2. What could the cell do to increase its surface to volume ratio?
Lab Journal Format
Title
Graph
Purpose
Materials
Data Table 1
(leave space for calculations)
Analysis
1.
2.
Cut out data table and paste into lab journal. (Remember to include the correct unit in your measurements
and calculations)
Data Table 1:
Balloon
Circumference
(in centimeters)
Radius
(In centimeters)
Surface Area
(in cm2)
Volume
(in cm3)
1
2
3
Now draw a line graph below showing the change in surface area to volume as the cell size (volume)
increases. (x-axis: surface area; y-axis: volume). Remember to include the correct units.
Graph 1