Name: _____________________________________

Ritika Gogna Period: _____

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Cell Size
What determines the size of a cell?

Why?
Sometimes bigger is better—tall basketball players, more closet space, and savings accounts may come to
mind. What about cells? Does having big cells make an organism bigger or better? Would having larger
cells be an advantage to an organism? If so, why do cells divide rather than continue growing? Maybe
there is an advantage to being small.

Model 1 – Investigating Cell Size

Black small dots are ribosomes

<-- Vacuole

Cytoplasm --> <-- Cell Membrane

Mitochondria --> <-- Nucleus

Cell A Cell B

1. Are the cells shown in Model 1 plant or animal cells? Explain your answer.
The cells shown in Model 1 are animal cells because there is no central vacuole in the cell which shows that it's not a
plant cell since the vacuole is the largest component in a plant cell.

2. Label Cell B in Model 1 with the following structures.

cell membrane cytoplasm nucleus
ribosomes vacuole mitochondria
3. Compare the smaller cell in Model 1 to the larger cell in Model 1.
a. Which cell has a larger surface area (more cell membrane surface)?
Cell B has a larger surface area because it is able to contain more organelles and still have more space, which
means there's more cytosol, and thus, more surface area.

b. Which cell has more channels in its cell membrane that can transport molecules (nutrients,
oxygen, and waste products) in and out of the cell?
Cell B has more channels because it has more gaps and spaces within the cell membrane, allowing for more
space for molecules to be transported inside and outside the cell.

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 4. Compare the smaller cell to the larger cell in Model 1.
a. Which cell has more mitochondria?
Cell B has more mitochondria.

b. Propose an explanation for why the cell in part a would need more mitochondria for proper
functioning of the cell.
Cell B would need more mitochondria in order to be able to function properly because there are more organelles
in Cell B which require energy which is formed in the mitochondria. Thus more mitochondria would produce
more ATP to help the entire cell.
5. What would be the consequences for a cell if the cell membrane was not large enough to have
adequate channels for bringing in nutrients and removing waste?
If the cell membrane was not large enough to have adequate channels, it would die because the waste would build
up with no way of removal and there would be a lack of nutrients which would prevent certain functions from
taking place. It would also not be able to maintain homeostasis and would be unable to produce energy from the
nutrients such as oxygen required from outside the cell and proteins won't be possible due to the lack of amino
acids.

6. Compare the smaller cell to the larger cell in Model 1.

a. Which cell has a larger volume?
Cell B has a larger volume.

b. Imagine a glucose molecule entering the cell membrane. Would that molecule be able to
reach the mitochondria faster if the cell had a smaller volume or a larger volume? Explain.
That molecule would be able to reach the mitochondria if the cell had a smaller volume because there would
be less distance to travel, preserving energy and saving time.

c. As the mitochondria metabolize the glucose, they produce carbon dioxide waste. Would the
CO2 molecules be able to leave the cell faster if the cell had a smaller volume or larger vol-
ume? Explain.
The CO2 molecules would be able to leave the cell with the smaller volume faster because the travel distance
is less, requiring less time to reach the cell membrane and leave the cell.

7. Consider your answers to the previous questions. Is bigger always better for a cell? Explain.
Bigger is not always better for a cell because bigger cells require higher maintenance and smaller cells have
higher diffusion rates, allowing the environment to remain more stabilized in a shorter amount of time. A smaller
volume is better as it is more efficient in transporting molecules throughout the cell in a relatively shorter amount
of time.

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Model 2 – Comparing Shapes

Side 1 cm 2 cm 4 cm
Surface area 6 cm2 24 cm2 96 cm2
Volume 1 cm3 8 cm3 64 cm3
Surface Area-to- 6:1 = 24:8 = 96:64 =
6:1 3:1
Volume Ratio 1.5:1

Diameter 1 cm 2 cm 4 cm
Surface area 3 cm 2
13 cm 2
50 cm2
Volume 0.5 cm3 4.2 cm3 34 cm3
Surface Area-to- 3:0.5 = 13:4.2 = 50:34 =
6:1 3.1:1 1.5:1
Volume Ratio

Diameter ×
1 cm × 1 cm 1 cm × 2 cm 1 cm × 4 cm
Height
Surface area 4.7 cm2 7.9 cm2 14 cm2
Volume 0.8 cm3 0.6 cm3 3.1 cm3
Surface Area-to- 4.7:0.8 = 7.9:1.6 = 14:3.1 =
5.9:1 4.9:1 4.5:1
Volume Ratio

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 8. Label the sets of shapes in Model 2 with each of the following: cubes, spheres, cylinders.
9. Calculate the surface area and volume values that are missing in Model 2. Divide the work
among the members of your group and check each other’s work.

10. Consider the data in Model 2.

a. Describe the change in the surface area of the cube when the length of the side doubles.
For the cube, the surface area quadruples when the length of the side doubles.

b. Describe the change in the volume of the cube when the length of the side doubles.
The volume of the cube is multiplied by 8 when the length of the side doubles.

c. When a shape gets larger, which increases at a faster rate, surface area or volume?
When a shape gets larger, the volume increases at a faster rate.

12. Calculate the surface area-to-volume ratio for each shape in Model 2. One example is given in
Model 1 for this calculation.
13. For all three of the shape sets, describe the change in the surface area-to-volume ratio as the size
of the shape increases.
The change in the surface area-to-volume ratio decreases as the size of the shape increases, as is seen with the
decreasing numbers in the table.

14. Considering your answer to Question 7, is it more desirable for a cell to have a small surface
area-to-volume ratio or a large surface area-to-volume ratio? Explain your answer in terms of the
functions of a cell.
It is more desirable for a cell to have a large surface area-to-volume ratio because the cell can perform more
functions due to the increased surface area which would be beneficial in transporting molecules across the cell
and for the significant surface area there would be a small volume which would help because the molecules can
diffuse throughout the cell at a much faster rate and much more efficiently.
15. Circle two figures in Model 2 that have a similar surface area (within 1 cm2 of each other).
a. Do the two figures have the same volume?
The sphere has a greater volume even though it has a slightly smaller surface area (1 cm^2 smaller) than the
cylinder.
b. Which shape has a more desirable surface area-to-volume ratio?
The cylinder has the more desirable surface area-to-volume ratio because it has a greater surface area for 1
cm cubed in comparison to the sphere.

16. In multicellular organisms some cells need to be large because of the functions they perform (i.e.
nerve cells, muscle cells). What shape would be most desirable for these larger cells?
A long, cylindric shape would be most desirable for these larger cells because they have a significantly greater
surface area-to-volume ratio than the other shapes which means that it can move molecules more efficiently and
faster across a cell and the surface area needs to be greater to make up for the significant increase in volume
required for larger cells.

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Extension Questions
17. Propose, by means of a sketch, geometrical shapes of cells that would allow a balance of function
and materials movement for each of the following situations. (Hint: Think about which aspect of
shape would help the cell best carry out its given function.)
a. Long-distance communication.
A long and thin cylinder would have a large surface area and the small diameter would ensure a smaller
volume.

b. Stretching.
An example of stretching is seen with muscle cells and they need a greater surface area-to-volume
ratio which would help them remain in homeostasis and transport energy and ATP throughout the cell
to the varying organelles to perform functions efficiently and quickly.

c. Storage.
A sphere shape would be ideal for storage because it allows for a larger amount of volume which
would provide space for molecules to be stored.

d. Covering and protecting.

Skin cells protect and cover an organism and they require a shape that is more flat so that they have
a greater surface area in comparison to volume because more surface area allows for the possibility
of more space for the molecules to go into and outside the cell.

e. Importing large quantities of material for transfer to other cells.

Any of the shapes are ideal for this situation if they are small and symmetrical because they have the greatest
surface area-to-volume ratio which allows for the import of large quantities of material into the cell as well as for
transfer to other cells quickly and efficiently.

18. Among unicellular eukaryotes, cell sizes differ greatly. Amoeba and Paramecium organisms are
animal-like protists that are heterotrophic, have no cell wall, and are several times larger than
most human cells. What might be some reasons why these unicellular organisms have larger cells
than cells with similar traits (heterotrophic, lacking cell walls) that are found in multicellular
organisms?
These unicellular organisms have larger cells than cells with similar traits that are found in multicellular organisms
because they are not specialized, unlike those found in the multicellular organism. Also, because they are not
specialized, these unicellular organisms must carry out all functions that can be separated into different specialized
cells in a multicellular organism. Such functions include food transport, reproduction, and movement.