<prompt> The biconcave shape of the RBCs is useful for all exceptPassing easily through smaller capillariesIncreased surface area for diffusionAllows considerable alteration in cell volumeResist hemolysis  <response>: Biconcave shape provides large surface area to volume ratio necessary for rapid exchange of gases and diffusion of other substances across the RBC membrane. This flexible shape helps RBC to squeeze through very small capillaries. Considerable alteration in the cell volume is possible because of biconcave shape. This prevents RBCs from rupturing when increase in volume of cell occurs. Ref: Textbook of medical physiology by N Geetha, 3rd edition, page no. 76 