Download Name: Date:______ Period

Name:________________________________
Date:__________
Period: _____
LAB: Why Don’t Cells Grow Indefinitely?
OBJECTIVES: Students will be able to….
1. make a hypothesis that describes the relationship between surface area and volume of a cell.
2. determine the relationship between surface area and the volume of a model cell.
3. apply these mathematical relationships to living cells.
BACKGROUND:
Many cells grow until they reach a certain size and then divide. Why don’t cells grow indefinitely until they
become the size of basketballs? What problems arise when a cell grows larger? Why does a cell divide into
two smaller cells when it reaches a certain size? These are all questions that scientists have attempted to
resolve.
Cell division is a necessary part of the life of any multicellular organism and allows for growth, repair and
formation of cells for reproduction. Growth of an organism occurs mainly by an increase in the number of cells
rather than by the enlargement of individual cells. This process seems to be controlled by simple physical laws.
HYPOTHESIS: Make a hypothesis that answers the question ‘What will happen to the surface area-to-volume
ratio as a cell grows larger?’
MATERIALS:
Photocopy of 3 cell models
Tape
Scissors
Calculator
PROCEDURE:
1. Obtain a photocopy of the three cells models and cut out each of the 3 cell models. Do not cut off
the tabs.
2. Fold and tape together all sides of each model. You will have three structures that resemble open
boxes. Imagine that each cell model has a 6th side and is a closed box. These models represent a
cell at three different stages of growth. The youngest stage in growth is represented by the model
that is 1 cm to a side. The oldest stage in growth is represented by the model that is 4 cm to a side.
3. Examine Table 1. Next to the row marked ‘Formulas’, write in the mathematical formulas that can
be used to calculate the value described in the heading of each column. Use “s” as the length of one
side of your model.
4. Use your formulas to calculate values for each of the tree cell models. Record your values in Table
1.
5. Calculate the ratio of total surface area to volume for each model cell. To do this divide the cells
total surface area by its volume. Place your answers in Table 2.
Name: __________________________________________
Date: __________________
DATA SHEET: Surface Area to Volume Ratio Lab
Research Question:______________________________ ___________________________________
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HYPOTHESIS: ____________________________________________________________________
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PROCEDURE: (summarize in a list or paragraph what you are expected to do in this lab).
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DATA: Table 1:
Formulas
Cell size
(Length of one side)
1 cm
2 cm
4 cm
Area of one face
(square units)
Total Surface Area of cell
(square units)
Volume of Cell
(cubic units)
Table 2:
Cell Size
(Length of one side)
Total Surface Area to Volume Ratio
1 cm
2 cm
4 cm
ANALYSIS QUESTIONS:
1. Anything that the cell takes in, such as oxygen or food, or lets out, such as carbon dioxide, must
pass through the cell membrane. Which of the measurements (area, total surface area, or volume) of your
model cells best represents the
cell membrane? ___________________________________________________________
2. The cell contents, including the nucleus and cytoplasm, use food and oxygen and produce wastes.
Which measurements (area, total surface area, or volume) best represent the contents of one of your
model cells? ____________________
3. As the cell grows larger and accumulates more contents, will it need more or less cell membrane to
survive? EXPLAIN your answer. ______________________________________________________
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4. As the cell grows larger, does the surface area-to-volume ratio get larger, get smaller or remain the
same? ____________________________________________________________________________
5. Which cell model has the greatest surface area-to-volume ratio? ____________________________
6. Why don’t cells survive when the surface area-to-volume ratio becomes too small? EXPLAIN!
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7. Which cell model has the greatest chance of survival? ____________________________________
CRITICAL THINKING:
Why do cells need to divide? Why can’t cells grow indefinitely?
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Graph: Graph the results in order to show the relationship between the length of the side of each cell model
and its surface area-to-volume ratio. The side length in centimeters should be placed on the x-axis and the
surface area-to-volume ratio should be placed on the y-axis. Be sure to add a title and a key.