In this lab activity, you will use agar cubes as cell models. You will investigate how increasing a cell’s size affects the time for diffusion to move material across the cell. The agar for the cubes has been dyed with bromothymol blue—a pH indicator. When the agar cubes are placed in an acidic solution, they will begin to turn yellow as the acidic solution diffuses into the agar. You will time this diffusion process for 3 different sized cells and compare them. Diffusion will be considered complete when the blue color completely disappears from the center of the cell. Using a dull knife or a thin strip of hard plastic, cut three blocks of agar of different sizes (sizes are listed in data table below). These three blocks will be your models for cells. Place model cells into a 400mL beaker and cover model cells with acidic solution. Begin timing. Periodically, gently stir the solution or turn the cubes over. Record the time for complete diffusion. This will be once the blue color completely disappears. Table 1. Cell Dimensions and Time for Diffusion Time for Cell Size SA : V Surface Area Volume Complete (cm) ratio Diffusion 1 x 1 x 1 2 x 2 x 2 1 x 1 x 8 1. As the cube increases in size, what happens to the surface area to volume ratio? Explain. (2) 2. Which cell had the fastest diffusion time? Explain why. (2)
In this lab activity, you will use agar cubes as cell models. You will investigate how increasing a cell’s size affects the time for diffusion to move material across the cell. The agar for the cubes has been dyed with bromothymol blue—a pH indicator. When the agar cubes are placed in an acidic solution, they will begin to turn yellow as the acidic solution diffuses into the agar. You will time this diffusion process for 3 different sized cells and compare them. Diffusion will be considered complete when the blue color completely disappears from the center of the cell. Using a dull knife or a thin strip of hard plastic, cut three blocks of agar of different sizes (sizes are listed in data table below). These three blocks will be your models for cells. Place model cells into a 400mL beaker and cover model cells with acidic solution. Begin timing. Periodically, gently stir the solution or turn the cubes over. Record the time for complete diffusion. This will be once the blue color completely disappears. Table 1. Cell Dimensions and Time for Diffusion Cell Size (cm) Surface Area Volume SA : V ratio Time for Complete Diffusion 1 x 1 x 1 2 x 2 x 2 1 x 1 x 8 1. As the cube increases in size, what happens to the surface area to volume ratio? Explain. (2) 2. Which cell had the fastest diffusion time? Explain why. (2)
surface-area-to-volume-ratio-lab.docx