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haemoglobin question aqa help

I do not understand how to do the calculation . I obtained 3.6 dm3 per minute but do not know how to continuehaemoglobin 2.jpghaemoglobin 1.jpg
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dasda
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Original post by dasda
I do not understand how to do the calculation . I obtained 3.6 dm3 per minute but do not know how to continuehaemoglobin 2.jpghaemoglobin 1.jpg

answer should be between 280-367
At the pO2 in the tissues [5.2 kPa], the saturation of Hb with O2 is about 50% [follow the vertical arrow on the left down to the sigmoid curve and read off on the y axis where it crosses. So 50% of the oxygen picked up in ythe lungs was released in the tissues.

Happy so far?

OK, next step. amount of blood pumped out per minute [cardiac output = 60 X 60 = 3600 cm3 = 3.6 dL [as you correctly say, but you must spell out in words what you are doing to earn full marks].

the Hb conc in his blood is 150 g/dL. So the amount of Hb in the blood pumped to tissues per minute = 150 X 3.6 = 540 g

We are told that 100% saturated Hb carries 1.35 cm3 O2 per g so if 50% of this is released (see 1st step) = 0.5 X 1.35 = 0.67 cm3 of O2/g is released.

If 1g of Hb releases 0.67 cm3 then 540 g of Hb will release = 0.67 X 540 = 360 cm3 approx [as the graph is nearly vertical at this point, it is very difficult to pinpoint a particular %age saturation hence the wide range in the possible correct answer - an unfair Q in my view].

If you show the logical method as above, then even if your answer is slightly out, you will earn good marks.

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