Lab title: Comparing the surface area to the volume of growing cells.
Experimental Question: Why are cells so small?
Materials:
 250mL beaker
 Potato
 Knife
 Metric ruler
 150 mL Lugol’s solution (I2KI – iodine)
 Forceps
 Graduated cylinder
 Dissecting tray
Procedure Day 1
1. Cut cubes of potato into the sizes below
2.5 cm
2.0 cm
1.5 cm
1.0 cm
0.5 cm
2. Place the cubes into a 250 mL beaker and add enough Lugol’s solution to cover the potato cubes.
3. Cover your beaker with foil and place it in the fume hood to soak overnight.
4. In the table below, calculate the surface area, volume and ratio between surface area and volume of each cube.
Length of one side of
Surface area of cube
Volume of cube
cube in cm
L X W X 6 sides (cm )
2
L X W X H (cm )
3
2.5 cm
2.0 cm
1.5 cm
1.0 cm
0.5 cm
Procedure Day 2
5. Using the forceps, remove the potatoes from the Lugol’s solution and place them on the tray.
6. Cut each cube in half and examine the cross-section
7. Measure how far into each potato cube the Lugol’s penetrated.
8. Record here:
Length of one side of
Penetration depth of Lugol’s
cube in cm
solution (cm)
2.5 cm
2.0 cm
1.5 cm
1.0 cm
0.5 cm
Ratio
Surface Area:Volume
9. Make a drawing of each cross section to scale, showing the penetration of Lugol’s solution here:
2.5 cm
2.0 cm
1.0 cm
0.5 cm
Cross section sketches of potato
cubes after soaking in Lugol’s
solution for 24 hours
1.5 cm
Analysis questions: Write your answers on this sheet.
1. Which cube has the greatest part of its total volume NOT penetrated by the stain? (In other words, which one has
the most white place remaining.)
2. Which cube has the greatest part of its total volume perpetrated by the stain?
3. Remember that nutrients are absorbed through the surface of a cell membrane. If Lugol’s solution was a nutrient
and these potato cubes were really cells, which cube would have been able to “feed” it’s volume the best? (Hint:
compare surface area to volume.)
4. Which is better equipped to feed itself: a large cell or a small cell?
5. Why are cells so small?