Describe the features of a red blood cell that facilitate oxygen transport.
This question was best answered by considering form and then function. Detailing red cell size, that it is a biconcave disc, contains haemoglobin A (Hb F in-utero), has a central Fe moiety and demonstrates positive cooperativity in binding oxygen would be a good start. Additionally, noting that the RBC has a flexible membrane with shape maintained by structural proteins and that it lacks a nucleus, organelles and mitochondria, but contains carbonic anhydrase would pass this question. A complete answer would mention the3 shunts that come off the anaerobic glycolytic pathway (RBC’s only means of ATP generation), namely the production of 2-3 DPG via the RapoportLuebering shunt, generation of NADPH by the hexose monophosphate shunt (protects RBC from oxidative damage) and the reduction of metHb back to Hb by way of the NADH. Many answers lacked sufficient information to pass this question. Many answers included lengthy discussions about the production of RBC’s, the Oxyhaemoglobin dissociation curve or calculated the oxygen content of blood. RBC metabolic adaptations (e.g. 2, 3-DPG, NADPH production by the HMP shunt/ G6phosphatase to regenerate glutathione and metHb reductase) were rarely mentioned, as were vasodilatory mediators released by RBCs.
The college answer brought out a lot of RBC features which, though interesting, are only tenuously connected to the functions of the red cell which "facilitate oxygen transport". It appears the examiners wanted the candidates to answer the question, "what are the metabolic, structural and functional features of red cells?" Thus:
Gordon-Smith, Ted. "Structure and function of red and white blood cells." Medicine 41.4 (2013): 193-199.
Diez-Silva, Monica, et al. "Shape and biomechanical characteristics of human red blood cells in health and disease." MRS bulletin 35.5 (2010): 382-388.
Snyder, Gregory K., and Brandon A. Sheafor. "Red blood cells: centerpiece in the evolution of the vertebrate circulatory system." American zoologist 39.2 (1999): 189-198.