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Size:  459.4 KB for this question please can someone explain how to tackle it. How do you know that u need to describe the trend instead one describing one thing specifically? Also any idea for part ii)?? I really don't get it. Many thanks.
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    This is my answer for part 1 but the mark scheme describes the trend instead. This is the new eduqas specimen questions. Name:  1460244693862-909329399.jpg
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    It'd be CO2, the data shows that if you increase oxygen and decrease CO2 then the ventilation rate decreases, if oxygen had a greater effect on ventilation rate than CO2, then increases the % oxygen from 21 to 83 should have decreased the ventilation rate, but instead it almost doubles. Something a long those lines anyway.
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    Scientist who did the experiment did not know their stuff. Only one variable should ever be changed. Otherwise there are confounding variables.
    Chemoreceptors do not respond to %of air CO2 and O2, they respond to pCO2 and pO2.
    It would have been a far better and more interesting experiment to keep pO2 constant, but increasing the gas pressure while increasing the % CO2.
    In humans we have a CO2 drive which is mainly via the peripheral chemoR and an indirect CO2 drive in the central chemoR (indirect via changes in CSF pH).
    We also have a O2 drive but this is normally not well developed but can be in chronic CO2 retainers (eg long term bronchitics).

    The answer to this one is CO2. The reason for that is rows 1 to 4 of the gas mixtures table there is a relatively small fractional change in o2% but a larger fractional change in co2%. There is a trend whereby decreasing %co2 from 17 results in decreased frequency of breathing movements. Having 100% O2 results in very few breathing movements and this is probably due to residual o2 drive.

    The second question is actually far more interesting and forms the basis of a famous physiology experiment. Rebreathing air results in an increase in both resp rate and tidal volume in humans, both these things increase minute ventilation (which is a product of the two things, TV x RR) There is also a rebreathing experiment where soda lime is used to absorb the CO2 from the rebreathed air. However it is very dangerous as it can result in loss of consciousness as humans respond more to CO2 drive and if the CO2 in the inhaled air is zero, this can result in not enough oxygenated haemoglobin in the blood.
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    (Original post by AortaStudyMore)
    It'd be CO2, the data shows that if you increase oxygen and decrease CO2 then the ventilation rate decreases, if oxygen had a greater effect on ventilation rate than CO2, then increases the % oxygen from 21 to 83 should have decreased the ventilation rate, but instead it almost doubles. Something a long those lines anyway.
    That's what I had written. However, the mark scheme only awards a mark for describing the trend but I talked about a specific data. How do you know when you need to describe the trend of the data? thanks.
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    (Original post by benion)
    Scientist who did the experiment did not know their stuff. Only one variable should ever be changed. Otherwise there are confounding variables.
    Chemoreceptors do not respond to %of air CO2 and O2, they respond to pCO2 and pO2.
    It would have been a far better and more interesting experiment to keep pO2 constant, but increasing the gas pressure while increasing the % CO2.
    In humans we have a CO2 drive which is mainly via the peripheral chemoR and an indirect CO2 drive in the central chemoR (indirect via changes in CSF pH).
    We also have a O2 drive but this is normally not well developed but can be in chronic CO2 retainers (eg long term bronchitics).

    The answer to this one is CO2. The reason for that is rows 1 to 4 of the gas mixtures table there is a relatively small fractional change in o2% but a larger fractional change in co2%. There is a trend whereby decreasing %co2 from 17 results in decreased frequency of breathing movements. Having 100% O2 results in very few breathing movements and this is probably due to residual o2 drive.

    The second question is actually far more interesting and forms the basis of a famous physiology experiment. Rebreathing air results in an increase in both resp rate and tidal volume in humans, both these things increase minute ventilation (which is a product of the two things, TV x RR) There is also a rebreathing experiment where soda lime is used to absorb the CO2 from the rebreathed air. However it is very dangerous as it can result in loss of consciousness as humans respond more to CO2 drive and if the CO2 in the inhaled air is zero, this can result in not enough oxygenated haemoglobin in the blood.
    Hi, thanks for the reply, the answer for the second part of the question is 43-49 but how is that estimated? Thanks.
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    at 6% CO2 it is 45 and at 3% CO2 it is 43.
    as the figures show nearly all the drive to breathing is CO2 I would say the drive from CO2 is somewhere between the 2 figures, so 44
    taking into account the lower % O2 than in the gas mixtures, perhaps you could add one or two and make it around 45. However it is difficult to give an accurate figure as you are being asked to account for differences in both %CO2 and %O2. Hence the experiment is not very good as pO2 should have been fixed and only one variable changed.
 
 
 
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