Diffusion experiments of a small molecule drug in tissue samples are performed. The drug has a radius 2.24 nm and a pure water-diffusivity of 2.75 *10^-6 cm^2/s. Cells occupy approximately 72% of the tissue by volume. The molecule is very hydrophilic and does not readily cross cellular membranes. If you assume that the interstitial space is gel-like with a microstructure parameter k=3.7*10^-3 nm^-1, what is the effective diffusivity in the tissue.

According to Fick’s diffusion equation, what variables determine a molecule’s rate of diffusion in bulk solution? When considering diffusion across membranes, what other factor(s) will influence the rate of diffusion of the molecule across that membrane?

The molecule shown below is atrazine, another commonly used herbicide. Describe the difference between passive (or simple) diffusion and facilitated diffusion, and explain why it could be more difficult for glyphosate to cross the cell membrane by passive diffusion than atrazine. Assume that bonds with an electronegativity difference of 0.5 are non-polar.