This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
The biconcave shape of the RBCs is useful for all except 
Select and explain. 
A. Passing easily through smaller capillaries, B. Increased surface area for diffusion, C. Allows considerable alteration in cell volume, D. Resist hemolysis
B: Increased surface area for diffusion
Answer: B: Increased surface area for diffusion 
Explanation: 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