Monkemeier
Honors Biology
December 8, 2014 – December 12, 2014
Unit 4: Microscopes, Structure and Function of Cells
NAME__________________________ DATE _________________
What Limits Cell Size? Minilab Activity
This activity will answer the following questions:
- Why can't cells continue to grow larger and larger to become giant cells, like a blob?
- Why are most cells, whether from an elephant or an earthworm, microscopic in size?
- What happens when a cell grows larger and what causes it to divide into two smaller cells
rather than growing infinitely larger?
- What limits cell size?
Objective: Demonstrate that as a cell grows, the cell membrane does not increase in size as fast as
the volume of a cell.
Vocabulary: Define and / or provide mathematical models for the following terms.:
Cell Membrane:
Surface Area (of cell membrane):
Volume (of the cell):
Materials:
Sand
Scissors
Tape
Balance for measuring mass
Cube A (smallest cube) = 1 unit
Cube B = 2 units across
Cube C = 3 units across
Cube D = 4 units across
Procedure:
1. Examine the four cubes. Notice that cube A is the smallest cube that there is a relationship
between the four cubes.
2. Fill each of the four cubes to the top with sand. Place each cube on an electronic balance and
measure the mass of each cube. Record the mass of each cube in the data table attached.
3. Calculate the total surface area for each cube. Do this by using the formula:
Area = 6 x
2
(number of units across) . Record each area in the data table attached.
4. Calculate the total volume of each cube. Do this by using the formula:
Volume =
(number of units across)3. Record the volume of each cube in the data table attached.
5. Calculate the distance from the center of the cell to the center of each wall. Do this by using
the formula: Distance = (number of units across) / 2. Record this for each of the four cells in
the data table attached.
Data Table:
Cube
Number
of Units
across
1
1
2
2
3
3
4
4
Total Surface
Area:
Volume
Area = 6 x
(number of
units
across)2
Volume =
(number
of units
across)3
Distance
from
center to
edge
Distance =
(number of
units
across) / 2
Mass of
Cell Filled
with
Sand
Surface Area /
Volume
Surface Area /
mass
(grams)
Calculations:
1. Using the information in your data table, divide the total surface area by the volume for each
cube. Record your “ratios” in the data table above.
2. Using the information in your data table, divide the total surface area by the mass for each
cube, Record your “ratios” in the data table above.
Analyzing the Data:
1. Anything that the cell takes in, like oxygen and food, or releases, such as carbon dioxide, must
cross the cell membrane. Which measurement of the cells best represents how much cell
membrane the models have?
2. The cell contents, nucleus and cytoplasm, use the oxygen and food while producing the waste.
Which two measurements best represent the cell content?
3. As the cell grows larger and gets more cell content, will it need more or less cell membrane to
survive?
4. As the cell grows larger, what happens to the Total Surface Area -to- mass ratio?
5. Why can't cells survive when the Total Surface Area -to- Volume ratio becomes too small?
6. Which size cell has the greatest Total Surface Area -to- Volume Ratio?
7. Which size cell has the greatest chance of survival? Explain your reasoning.
Drawing Conclusions:
Which ratio limits the cell size? (In other words, what limits how large a cell can grow?)
Describe what happens when a cell grows and approaches the ratio mentioned in the prior question?
What is the benefit of being composed of many specialized cells working together to perform specific
functions rather than just being one big cell?
Some unicellular organisms are described as colonial. Colonial organisms can join together to share
common functions; however, each cell maintains its own identity. List some possible benefits to cells
when involved within a colony.
Scientists have evidence that multicellular organisms evolved from unicellular organisms. WHY is
there a need for organisms to be multicellular rather than one very large cell? HOW do you think
multicellular organisms evolved?