# Homework Help: Biophysics equation

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1. Jan 16, 2015

### charlielow

1. The problem statement, all variables and given/known data
Consider a simple, physical model of a cell in which the cell is regarded as a spherical bag with radius r, bounded by a membrane permeable to alcohol with permeability, P=20μms-1. Show the concentration of alcohol in the cell is governed by this equation.

2. Relevant equations
-d(Δc)/dt = (3P/r)Δc

3. The attempt at a solution
I don't really know what to do with this, I don't really know where to start. The second bit of the question asks to solve the equation which I guess you can do by bringing dt over to the other side and dividing by Δc and integrating both sides, but I have no idea how to get the equation really.

2. Jan 16, 2015

### Ygggdrasil

Have you learned any equations to find the flux of molecules across a membrane? Or, have you learned Fick's laws of diffusion? Either one could serve as a starting point for the derivation. (If not, here's a website with some explanations)