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```					                                              Cell Size Lab
Name                                                 Block ______           Date ______________

INTRODUCTION:
It is through the cell membrane that food, oxygen, and water enter the cell and waste
products leave the cell. How quickly this exchange takes place depends on the surface area of the cell
membrane. The amount of food and oxygen needed and the amount of waste produced
depends on the volume of the cell. When cells grow to a certain size, their rate of growth slows
down and then stops. They have reached their size limit. When one of these larger cells divides
into two smaller cells, the rate of growth again increases. In this investigation you will experiment to determine
why this is so.

EQUIPMENT AND MATERIALS:
250 ml beaker    agar w/indicator                        Plastic spoon
millimeter ruler razor blade/knife                      .4% Sodium Hydroxide (NaOH)
paper towels

PRE-LAB

Answer the following questions by using the information discussed in the introduction above, procedure
below and information you have learned in class.

1. What determines how quickly a cell will exchange food, oxygen, and water with it’s environment?

2. What determines how much food and oxygen are needed as well as waste that is produced?

3. What happens when a cell has reached its “size limit”?

4. You will be provided with a 6x3x3 block of agar. Describe how you will get each cube size requested in
procedure step #2.
3cm

6cm

5. What safety measure must be taken with the Sodium Hydroxide?

6. What formula is used to determine surface area of a cube?
7. What formula is used to determine volume of a cube?

8. You have two cubes, one has a side that is .5cm and one has a side that is 1.5cm. Determine the SA/V
ratio for each and explain which cube (cell) would be more efficient at taking in nutrients and getting rid
of waste products by using the SA/V ratio in your explanation.

PROCEDURE:

1. Obtain an agar block from your teacher.

2. With a razor blade/knife, cut your block into 3 cubes. One cube should be 3cmx3cmx3cm, the next cube
should be 2cmx2cmx2cm, and the third cube 1cmx1cmx1cm.

3. As you cut the blocks, measure and record their length, width, and height on the data table.

4. When all the blocks have been measured and recorded place them into the 250ml beaker of .4% Sodium
Hydroxide.

Use caution with sodium hydroxide. If sodium hydroxide gets on you, wash it off immediately.

5. Allow the cubes to soak for 5 minutes. After 5 minutes, remove the cubes with your spoon and rinse the
cubes in running water. Return the Sodium Hydroxide to your instructor.

6. Blot the cubes dry with a paper towel.

7. With your razor blade/knife, cut the agar cubes in half and measure the depth of the pink area. This is known
as the “amount of absorption” and should be recorded in the mm absorbed column.

8. Using your measurements, determine the surface area, volume, and surface area to volume ratio of each
block and record it on the data table.

DATA TABLE

Cube Dimension        Surface Area (cm2)          Volume (cm3)        SA / V ratio       mm absorbed (PINK)
1.
2.
3.
Graph #1
GRAPHING

Now, graph the following situations:

Graph #1: on one graph:
a. cube dimension vs. surface area
b. cube dimension vs. volume
Graph #2: cube dimension vs. SA/V ratio
Graph #3: cube dimension vs. mm absorbed

Graph #2

Graph #3
QUESTIONS:

1. Describe what happens to the surface area as the cell grows.

2. Describe what happens to the volume as the cell grows.

3. Describe what you notice in Graph #1 when comparing the rate of growth between the surface area and
volume of the cell.

4. Describe what happens to the surface area to volume ratio as the cell grows?

5. How can you tell that sodium hydroxide is being absorbed by the agar cubes?

6. From our last unit on cells, explain how cells obtain nutrients.

7. If the sodium hydroxide were some vital substance, such as food, and the agar cubes were cells,
which cell would be fed the most efficiently?

8. What happens to the cell’s ability to feed itself and get rid of waste as it grows?

9. What happens to the surface area to volume ratio if you divide the cell in half?

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