so this is the last video and we're going to look at myoglobin first um and then we're going to look at um a scenario where uh we link surface area to volume ratio of organisms to um the the position of their oxygen dissociation curves so uh myoglobin then uh this is um a protein that's found in muscles and it has a very very high affinity for oxygen so high that it actually stores oxygen within muscle tissue all right so The Binding of oxygen to myoglobin is incredibly strong because of the high affinity and that then makes myoglobin a storage uh protein and it stores oxygen within muscles now in terms of its uh oxygen dissociation curve so if we look at the graph on the left uh we've got the adult hemoglobin line for comparison okay now the myoglobin curve is almost vertical so that tells you it's got a very very high affinity for oxygen and in fact it becomes fully saturated at about uh8 kilopascals of oxygen okay so uh um why does it have this High Affinity why is it there to store oxygen well it's there to supply oxygen to the muscles when they're undergoing extreme physical activity so something like riding a bike running uh a long distance sprinting when your muscles are very active the circulatory system uh cannot deliver enough oxygen to the muscles okay so they could eventually start to respire anerobic and uh when that happens you get um lactic acid accumulating okay that's a product of anerobic respiration in humans you would have also have got a lot of carbon dioxide made when respir aerobic respiration was occurring in so you you ultimately get a lot of CO2 a lot of lactic acid accumulating in the muscles and it's those two things that actually lower myoglobin's affinity for oxygen and when that happens you get oxygen dissociation occurring and it h it then supplies oxygen to the muscles um to to allow them to carry out a bit more aerobic respiration so you you won't use the oxygen on the myoglobin and normal uh low activity levels it's only when you're exercising extremely that um myoglobin's Affinity will lower so that's why myoglobin uh is present in uh muscle uh tissues okay uh lastly then this graph on the right is looking at um animals with different uh surface area to volume ratios so in this graph I've chosen um a mouse I think it is and an elephant now again you may not get these animals in a in an exam question but you need to just apply the principle that I'm going to go through now so um the mouse has an oxygen dissociation curve to the right of the elephant now from previous videos I've said whenever a curve is to the left sorry to the right the hemoglobin has a low affinity for oxygen when the curve moves to the left the hemoglobin has a slightly higher Affinity uh for oxygen so the situation is this that these two animals generally have the the the same access to oxygen to 21% oxygen in the atmosphere um they they don't live in low level uh of oxygen so why do they have hemoglobin with different affinities if they're in the same environment where there's the same level of oxygen well it's to do with the surface area to volume ratio of the organism so if you look at the mouse because it is very small it has a high surface area to volume ratio the elephant because it's really big it has a low surface area to volume ratio now we talked about surface area to volume ratios in the gas exchange topic all right so that's where everything was explained so I'll assume that you understand uh surface area to volume ratio so why does the mouse with a high surface area to volume ratio have a hemoglobin with a lower Affinity well with the mouse because of its large surface area to volume ratio it loses a lot of heat so a lot of heat will be radi ating out from uh its body surface and that heat has to be replaced and the only way that it can be replaced is for the mouse to do more aerobic respiration all right so because this Mouse has a very high rate of respiration it needs to have oxygen delivered more readily to its cells so you need a hemoglobin with a slightly lower affinity for oxygen so it can dissociate more readily and provide the oxygen needed for the high respiration rate in the uh in the mouse so that's why it has a lower Affinity uh hemoglobin with the elephant because it doesn't lose as much heat from its body surface it doesn't have to do as much aerobic respiration to generate and to generate heat to replace the heat that's lost all right so that doesn't have to have um a lower Affinity uh hemoglobin okay so that's the key idea when you're asked about animals of different sizes okay uh is to do with surface area to volume ratio generally and the fact that a smaller animal will lose more heat than a larger one okay and uh that's why you get a different position of the oxygen dissociation uh curves okay so uh that's the end of this uh video and it's the last video um for gas transport