What Is The Connection?

http://www.asknature.org/media/image/1380

A conceptual problem…

• Q = How do cells feed and excrete?

• A = Via their cell membranes

• So therefore, shouldn’t cells require MORE surface area?

Lab: Assessing the Rate of Cellular Diffusion v. Differing Surface Area to Volume Ratios

• Purpose: To determine how the size of a cell is related to its ability to perform diffusion

• Method: Measurement of conductivity of the solution. The greater the rate of diffusion, the greater the rate of change in conductivity (as measured in µS/cm/sec)

Calculating S.A.: Vol Ratios

• From block of sodium-infused agar, cut 3 2x2x2 blocks

• Cut 2nd block into eight cubes

• Cut 3rd block into 64 cubes

• Calculate cumulative S.A.: Vol. ratios for each set of cubes

Collecting the data

• Place the first 2cm3 cube into 300 mL of tap water

• Immerse the conductivity probe into the tap water bath

• Collect data, while STIRRING CONSTANTLY for 300 seconds

• Determine the slope in µS/cm/sec

Processing/Interpreting The Data

• Graph the rate (y-axis) vs. ratio of S.A.: Vol. (x-axis)

• Answer the analysis questions in your lab notebook