Cell Size Lab
Class Set – PLEASE RETURN!
Background Information:
• Iodine is an indicator for starch and turns dark purple/black.
• Cells require nutrients in order to survive.
• Cells must eliminate waste in order to survive.
• Pretend that each potato cube is a single cell and the iodine is the nutrients
(food) for the cell.
Purpose: To provide evidence for why cells are so small.
Hypothesis: Make a statement as to which potato (cell) will have the nutrients
diffuse the farthest proportionally (closest to the center of the cell) in 20 minutes, and
why do you think so.
Materials: ruler, calculator, scalpel, potato pieces, paper towels, and iodine solution.
Math Formulas:
* Surface area (mm2) = Length X Width X 6 (# of sides)
* Volume (mm3) = Length X Width X Height
* Surface area to volume ratio (mm2)/(mm3)
= Surface area (mm2)
Volume (mm3)
•
Double the cell size (from 1 mm to 2 mm), and the surface area ↑ 4-fold or
(increases 4 times)
•
Double the cell size (from 1 mm to 2 mm), and the volume ↑ 8-fold or
(increases 8 times)
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2 mm
1 mm
1 mm
2 mm
1 mm
2 mm
1 mm
1 mm
2 mm
1 mm
1 mm
1 mm
2 mm
1 mm
Surface area = 6 mm 2
Volume = 1 mm3
2
2
Surface
area
= 6=
mm
Surface
area
6
mm
Surface:Volume
= 6:1
Volume = 1 mm3
1 mm
3
Surface : Volume = 6:1
Volume = 1 mm
Surface:Volume = 6:1
2
2 mm
Surface area = 24
mm
2
Surface area = 24 mm3
Volume = 8 mm
Volume = 8 mm3
2
Surface
area
=
24
mm
Surface:Volume
=
3:1
Surface: Volume = 24:8 = 3:1
Volume = 8 mm 3
Calculations: Determine the following for allSurface:Volume
3 cells (potatoes). = 3:1
1) 0.5 cm cell
A) Surface Area (cm2) =
B) Volume (cm3) =
C) Surface Area to Volume Ratio =
2) 1 cm cell
A) Surface Area (cm2) =
B) Volume (cm3) =
C) Surface Area to Volume Ratio =
3) 2 cm cell
A) Surface Area (cm2) =
B) Volume (cm3) =
C) Surface Area to Volume Ratio =
Experimental Evidence:
1. Using a scalpel and paper towels, carefully cut 3 potato cubes using the
dimensions from above.
2. Obtain TEACHER’S SIGN-OFF BEFORE you proceed!
3. Submerge the potato cubes (cells) into the iodine solution for 20 minutes.
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4. While you are waiting for 20 minutes, calculate the surface area, volume, and
surface area to volume ratio for each of the 3 potato cubes (cells).
5. Carefully remove the potato cubes (cells) from the iodine solution and place
them on absorbent paper towels.
6. Cut each cell in half and observe the inside.
7. Draw each cell in detail showing the pattern of iodine throughout the potato.
Conclusion Questions: Use complete sentences for FULL credit!
1. What does the iodine used in the lab represent in the cell?
2. As the size of the cell increases, which increases faster: cell surface area or
cell volume?
3. As cell size increases, what happens to the surface area to volume ratio? Give
examples from the lab.
4. According to your drawings, in which cell (potato) did the iodine diffuse all
the way to the center of the cube? Discuss the differences between the cells.
5. Based on your understanding of cell size and the rate (speed) of diffusion,
explain why there are NO GIANT CELLS! Discuss diffusion in your answer.
Conclusion:
Restate your Hypothesis and state whether or not if it is correct and why. Refer to
your data and give numbers.
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