Date | November 2016 | Marks available | 6 | Reference code | 16N.3.HL.TZ0.23 |
Level | Higher level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
Command term | Explain | Question number | 23 | Adapted from | N/A |
Question
Explain, using an oxygen dissociation curve, how hemoglobin supplies oxygen to respiring tissues and how the Bohr shift increases the supply.
Markscheme
How hemoglobin supplies oxygen to respiring tissues
a. properly labelled axes showing % saturation hemoglobin and partial pressure of oxygen
b. correct/sigmoid shape of «normal» oxygen dissociation curve
Do not accept concave curves. Curve should start at origin.
c. tissues use O2 for «cellular» respiration thus lowering pO2 at tissue level
OR
respiring tissues produce CO2
d. O2 dissociates more at lower pO2 from Hb «than at higher pO2» thus providing O2 to «respiring» tissues/OWTTE
How Bohr shift increases the supply
e. CO2 is converted to hydrogen carbonate ions/HCO3− and H+
f. increase in H+ lowers blood pH
g. H+ combines with Hb / conformational change in Hb «in red blood cell» freeing some O2
h. shifts the oxygen dissociation curve to the right «Bohr shift»
OR
shift to the right shown on diagram labelled Bohr shift
i. oxygen dissociation curve steeper at lower pO2 «corresponding to respiring tissues»
j. lowers the affinity of hemoglobin for oxygen
k. means less oxygen can be carried for same pO2 «as normal»
OR
«even» more oxygen available for respiring tissues for same pO2
Accept any of the marking points in a clearly annotated diagram. Values not required.