Cornstarch & Iodine – In this lab you will observe the diffusion of a substance

13 Jun Cornstarch & Iodine – In this lab you will observe the diffusion of a substance

Question
You are required to take and upload 3 pictures during the lab: 1) a picture of all your materials, 2) part A: a picture of the baggie in iodine mixture after 15 minutes, 3) part B: a picture of the potato cubes cut in half showing iodine absorption. Include your face in the pictures!

Materials Needed:

Plastic baggie (like a sandwich baggie)
Cornstarch (only 1 teaspoon)
Iodine (at least 8 ounces — You can buy this at Walmart for a few $$!)
1 large potato
Ruler and calculator
Paper towel
PART A: Osmosis

Cornstarch & Iodine – In this lab you will observe the diffusion of a substance across a semi permeable membrane. Iodine is a known indicator for starch. An indicator is a substance that changes color in the presence of the substance it indicates.

Procedure:

Fill a plastic baggie with a teaspoon of cornstarch and half a cup of water and tie the bag.
Fill a cup halfway with water and add ten drops of iodine.
Place the baggie in the cup so that the cornstarch mixture is submerged in the iodine water mixture.
Wait fifteen minutes and answer the questions.
PART B: DIFFUSION & CELL SIZE

In this lab you will observe the relationship between cell size and extent of diffusion in potato cubes, and understand the necessity of microscopic cell size.

Math Formulas

* Surface area (mm2) = Length X Width X 6 (# of sides)

* Volume (mm3) = Length X Width X Height

Experimental Evidence:

1. Using a scalpel and paper towels, carefully cut 3 potato cubes using the dimensions in the calculations for Data Table 1 (0.5 cm3, 1 cm3, 2 cm3).

2. Submerge the potato cubes (cells) into the iodine solution for 20 minutes.

3. 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) in Data Table 1.

4. Carefully remove the potato cubes (cells) from the iodine solution and place them on absorbent paper towels.

5. Cut each cell in half and observe the inside. Note the color change from brown to clear that indicates the diffusion of diffusion medium (iodine) into the cube.

Using a metric ruler, measure the distance in centimeters that the diffusion medium diffused into each cube by measuring (in cm) how far the iodine penetrated into each cube. Record the data in Data Table 2. Next, record the total time of diffusion. Finally, calculate and record the rate of diffusion for each cube as centimeters per minute (divide centimeters/# of minutes).

Calculate the percentage of cell reached by diffusion for each cube.

a. Measure one side of the colored area of each cube. Calculate the volume of the colored area for each cube and record in Data Table 3.

b. Determine the volume of the cleared area of the cubes by subtracting the volume of the colored area from the total volume. Record in Data Table 3.

c. Finally, calculate the percentage of each cube into which the iodine diffused. Use this equation:

(total cube volume) – (volume of cube that has not changed color) X 100

(total cube volume)

1. In which cell (potato) did the iodine diffuse all the way to the center of the cube? Discuss the differences between the cells.

2. If each cube represented a living cell, and the iodine solution was a substance needed within the cell, what problem might the largest cell have?

3. As cell size increases, what happens to the surface area to volume ratio? Give examples from the lab.

4. 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.

Cube Size

Depth of Diffusion (cm)

Time (min)

Rate of Diffusion

0.5

1

2

Cube Size

Surface Area (cm2)

Volume (cm3)

Surface Area : Volume

0.5

1

2

Cube Size

Surface Area (cm2)

Volume (cm3)

Surface Area : Volume

0.5

1

2

Cube Size

Surface Area (cm2)

Volume (cm3)

Surface Area : Volume

0.5

1

2

Cube Size

Surface Area (cm2)

Volume (cm3)

Surface Area : Volume

0.5

1

2

Cube Size

Surface Area (cm2)

Volume (cm3)

Surface Area : Volume

0.5

1

2

Cube Size

Surface Area (cm2)

Volume (cm3)

Surface Area : Volume

0.5

1