PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Macromolecules, membranes and cell architecture · Macromolecules, membranes and cell architecture
Forces, Machines and Signals, Ch The fluid membrane: bending, flicker and shape
Problem
A red cell has fixed membrane area A=135μm2. In isotonic saline its volume is 90fL, giving the usual discocyte with reduced volume v≈0.61. It is now transferred to a solution containing a slowly permeating solute that lets it imbibe water until its volume rises to 120fL, with the area unchanged.
((a)) Find the new reduced volume v.
((b)) Predict, in words, whether the cell becomes more spherical or more sharply creased than the discocyte, and explain the prediction using the reduced-volume classification of shapes rather than the spectrin skeleton.
((c)) State how much further (in fL) the cell could swell before its membrane would have to stretch rather than merely change shape, and what limits that further swelling.