Question

Time to move 10 microns

(typical size of animal cell)

Object radius (nm) D(cm^2/s) time (sec)

oxygen 0.2 2*10-5 0.02

sucrose 0.5 5*10-6 0.13

insulin 1.4 1.6*10-8 0.3

hemoglobin 2.5 7*10-7 0.2

HIV 100 2.2*10-10 23

bead 250 8.9*10-9 56

bacteria 750 1.8*10-10 170

1b. What would be the appropriate units for the diffusion coefficient in this example? (2). Cm^2/s

1c. What would be another set of units that might also apply to diffusion coefficients? m^2/s

2. Cell Surface to Volume issues – this question asks students to become familiar with basic formulas used to calculate surface area and volume, and to understand how much surface area and volume change when the diameter of a cell (or organism) gets larger. It also gives practice in understanding the (confusing) concept of surface area to volume ratios. Finally, an important example of biological compensation for such matters is presented.