The membrane that surrounds a certain type of living cell has a surface area of
ID: 2255422 • Letter: T
Question
The membrane that surrounds a certain type of living cell has a surface area of 5.9 x 10-9 m2 and a thickness of 1.5 x 10-8 m. Assume that the membrane behaves like a parallel plate capacitor and has a dielectric constant of 4.3. (a) The potential on the outer surface of the membrane is +54.8 mV greater than that on the inside surface. How much charge resides on the outer surface? (b) If the charge in part (a) is due to K+ ions (charge +e), how many such ions are present on the outer surface?
Explanation / Answer
C=A*epsilon/d
C=(5.9*10^-9)*(4.3)/(1.5*10^-8)
Q=CV=(54.8*10^-3)*(5.9*10^-9)*(4.3)/(1.5*10^-8)=0.09268coulomb
b)
No. of ions=Q/e=0.09268/(1.6*10^-19)
Ions K+ present=5.79*10^17