Cell Size

Background:

Cell size and shape play a crucial role in determining the rate of diffusion. When cells reach a certain size, their growth slows, causing them to divide into smaller cells. This phenomenon is observed in specialized cells like epithelial cells. Building larger models of smaller cells can help investigate these processes.

Procedure:

1. With the knife, cut the block of phenolphthalein agar into cubes. The first cube should be 3cm on each side; the second, 2 cm on each side; and the third, 1 cm on each side. Measure carefully and trim away the waste. Examine the cubes. Think of them as giant models of tiny cells.

2. Calculate the total surface area of each of your three models using the following formula: Surface area = 6 × (length x width), that is; the total surface area is 6 times the surface area of one side. Remember to refer to Appendix A table for surface and volume calculations.

3. Record the total surface area for each cube in your table

4. The cells have different surface areas and they have different volumes (amounts of materials inside). Calculate the volume of each cube. Volume = length x width x height.

5. Record the volume of each cube in your data table

6.  Place all three cubes in a beaker along with enough. 1M HCl to cover all three of the cubs.  Allow the cubes to remain in the beaker for 10 minutes. Use the plastic spoon to turn the cubes often for 10 minutes. Be careful not to cut or scratch the surface of the cubes.

7. Remove the cubes from the acid solution, gently dry, and then slice each cube in half with the knife. Draw what you see in your lab book.

8. Measure the distance from the edge of the cube to the pink color. This represents the distance that the HCI diffused through the cell or cube.

9. Calculate the ratio of surface area to volume for each cube and record it in your data table. The number obtained should be expressed as a ratio. Then calculate the diffusion rate in cm/min.

Results/Analysis:

Discussion and Conclusions:

Claim: The surface area-to-volume ratio of a cell or cube affects the rate of diffusion.

Evidence: The lab experiment carefully outlines a process that provides compelling evidence for the claim. Initiating with the creation of three different-sized cubes from phenolphthalein agar, each symbolizing a cell of a distinct volume. These cubes, with their varying dimensions, present a range of surface area-to-volume ratios. Following this, the cubes are submerged into a beaker filled with 1M HCl, acting as a substance attempting to diffuse into the cells. This scenario aids in observing how the diffusion process is influenced by the size of the cell. The distance the HCl travels within each cube is then measured, providing a tangible measure of the diffusion rate. This step is crucial as it offers direct evidence of how far the substance can penetrate the cell within a specific timeframe. Finally, the surface area-to-volume ratio for each cube is calculated. By comparing these ratios with the measured diffusion rates, the significant impact of the surface area-to-volume ratio on the rate of diffusion is discerned. In essence, every step in this lab acts as a building block that contributes to supporting the claim, illustrating the relationship between a cell's size and the diffusion rate.

Reasoning: The evidence from the experiment shows how cell size impacts diffusion rate. The different-sized cubes represent cells of various volumes. When these cubes are placed in HCl, it simulates a substance diffusing into the cells. By measuring the distance the HCl travels into each cube, we can determine the diffusion rate. The smaller the cube (cell), the faster the diffusion because the surface area-to-volume ratio is higher. This means substances can enter and exit the cell more quickly. So, the claim that cell size impacts diffusion rate is supported. The smaller the cell, the more efficient the diffusion, which is crucial for cells to function properly.