Diffusion and cell size agar lab GEN DATA PDF

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general biology diffuesion and cell size data...

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Diffusion and Cell Size Lab Biology Name: ____________________________________________ Period: _________________ Diffusion and Cell Size Lab Background: The absorption of nutrients, excretion of cellular wastes, and the exchange of respiratory gasses are life processes, which depend upon the efficient transport of substances into, out of, and throughout living cells. Many important substances move into and out of cells via diffusion. Diffusion is the movement of substances from areas of high concentration to low concentration (with their concentration gradient). It is an example of passive transport because it requires no energy. For this reason, diffusion is one of the most common and efficient means by which substances are transported between cells and their environment. This occurs via the cell membrane, a selectively permeable barrier whose total surface area is important in regulation of the substances that diffuse into or out of the cell. As a cell grows in size, its volume increases at a greater rate than its surface area. Consequently, the surface area of the growing cell soon becomes inefficient for effective diffusion throughout the cell. The relationship between surface area and the volume of a cell can be expresses as a ratio (SA:V). The need for an effectively large surface area to volume ratio is considered to be the most significant factor in triggering a cell to divide (and therefore, determining cell size). Materials: 3cm x 3cm x 6cm phenolphthalein (indicator) agar block plastic knife plastic cup plastic ruler diffusion medium Procedure: 1. Obtain an agar block. Using a plastic knife, trim this piece into the following three cubes: a. 30mm x 30mm x 30mm b. 20mm x 20mm x 20mm c. 10mm x 10mm x 10mm 2. Place the three cubes into a plastic cup. Add diffusion medium until the cubes are submerged. Keep the cubes submerged in the diffusion medium. Be sure to keep the cubes submerged in the diffusion medium. 3. As the cubes soak, calculate the surface area, volume, and surface area to volume ratio for each cube. Record these values in table 1. Use the following formulas: a. SA = L x W x # of sides b. V = L x W x H

Table 1: Surface area to volume ratio Cube size Surface area (mm2) (SA= L x W x # of sides)

Volume (mm3) (V= L x W x H)

Surface Area to Volume Ratio

30mm x 30mm x 30mm 20mm x 20mm x 20mm 10mm x 10mm x 10mm

4.

After 10 minutes, remove the agar cubes and carefully blot dry on a paper towel. Then cut the cubes in half. Note the color change from clear to red or pink indicates the diffusion of the diffusion medium into the cube.

Diffusion and Cell Size Lab Biology

5.

Calculate the percentage of cell reached by diffusion for each cube. a. Measure one side of the clear area of each cube. i. 30x30x30: _______________ ii. 20x20x20: _______________ iii. 10x10x10: _______________ b. Calculate the volume of the clear area for each cube and record in table 2. c. Determine the volume of the pink area of the cubes by subtracting the volume of the clear area from the total volume. Record in table 2. d. Finally, calculate the percentage of each cube into which the diffusion medium diffused. Divide the volume of the pink area by the total volume and multiply by 100. Record in table 2. Table 2: Efficiency of Diffusion

Cube size

Total volume of cube (mm3) (from table 1)

Volume of clear area (mm3) (V=L x W x H)

Volume of pink area (mm3) (total volume-volume of clear area)

Percentage of cube reached by diffusion (vol. pink/total vol.) x100

30mm x 30mm x 30mm 20mm x 20mm x 20mm 10mm x 10mm x 10mm

Post-lab questions: 1. The agar used to make your cubes contained phenolphthalein (an indicator) and had a pH of greater than 9. The diffusion medium had a pH of 3. Explain how the use of a pH indicator allowed you to visualize the extent of diffusion into the agar cubes.

2. Which cube had the highest percentage of the cube reached by diffusion?

Diffusion and Cell Size Lab Biology 3. Make a generalized statement about the relationship between cell size and the percentage reached by diffusion. Make sure to support your statement with your data.

4. If each cube represented a living cell and the diffusion medium represented a substance needed within the cell, what problem might exist for the largest cell?

5. Compare the surface area to volume ratio and the percentage of cell reached by diffusion. Is it more efficient to have a high surface area to volume ratio, or a low surface are to volume ratio?

6. How do you think the percentage of cell reached by diffusion would compare for a thin, flat cell (shaped like a pancake) compared to a cube-shaped cell? Why?

7. Describe a cell that would be most efficient in terms of volume and surface area....