Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

8.2.58 · Transport in Mammals

The Bohr Shift — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 8 parts Lesson 15 of 21 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

8.2.5 The Bohr Shift — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain how carbon dioxide shifts the oxygen dissociation curve to the right and why this helps respiring tissues.Definition — the Bohr shift is the shift of the oxygen dissociation curve to the ri…

  • On a graph
  • Size of shift
  • Temperature
  • Steep part
  • No control needed
  • Linked chemistry

Part 1 of 6The Bohr effect

Definition
  • Definition the Bohr shift is the shift of the oxygen dissociation curve to the right when pCO2 rises.
Result
  • Result at a given pO2 haemoglobin is less saturated, so it has a lower affinity for oxygen and unloads more.
Origin
  • Origin it was described by Christian Bohr in 1904.
On a graph
  • On a graph at any given pO2, percentage saturation is lower at higher CO2 levels.

Part 2 of 6Mechanism

1
Respiring tissues produce more CO2, which enters red blood cells.
2
Carbonic anhydrase converts it to carbonic acid, which dissociates to H+ and HCO3-.
3
H+ combines with haemoglobin, forming haemoglobinic acid.
4
The lower pH slightly changes the shape of haemoglobin and reduces its affinity for oxygen.
5
Oxyhaemoglobin releases oxygen and the curve shifts right.

Part 3 of 6Biological significance

LocationpCO2Effect on haemoglobin
Active muscleHighCurve shifts right; more oxygen unloaded where it is needed
LungsLow (CO2 is exhaled)Curve shifts back left; haemoglobin loads oxygen efficiently
Signal
  • CO2 and H+ act as signals that a tissue is active and needs more oxygen.
Size of shift
  • Size of shift the greater the respiration rate, the more CO2 and lactic acid, and the greater the shift.
Exercise
  • Exercise haemoglobin gives up up to 90 per cent of its oxygen in the most active muscle.

Part 4 of 6Other factors and where the shift acts

Other factors and where the shift acts
Temperature
  • Temperature a rise shifts the curve right; active muscle is warmer because respiration releases heat.
BPG
  • BPG more 2,3-bisphosphoglycerate in red cells shifts the curve right.
Lungs
  • Lungs cooler temperature and lower CO2 favour loading.
Steep part
  • Steep part the shift mostly affects the steep part;
    • at high pO2 (lungs) the curves overlap, so loading is not impaired.
No control needed
  • No control needed the response happens immediately to local conditions without nervous or hormonal control.

Part 5 of 6Related effects

Linked chemistry
  • Linked chemistry the H+ formed when CO2 becomes hydrogencarbonate is the H+ that promotes oxygen unloading.
Haldane effect
  • Haldane effect oxygen loading in the lungs promotes release of CO2, the reverse side of the Bohr effect.
Root effect
  • Root effect in some fish, blood pH changes the maximum saturation of the pigment.

Part 6 of 6More from the specification

More from the specification
Allosteric oxygen binding sites and pH
  • Allosteric oxygen binding sites and pH carbon dioxide accumulation alters hemoglobin binding sites affinity, providing an efficient means to deliver oxygen during exertion.
Plasma
  • The liquid part of blood.
Partial pressure
  • The pressure exerted by one gas in a mixture.
Binding site
  • The region of a protein with a shape complementary to a ligand.
Chloride shift
  • Chloride shift hydrogencarbonate leaving red cells is swapped for chloride ions entering, keeping the cell electrically balanced;
    • it differs from the Bohr shift.

Key terms

TermMeaning
Bohr shiftShift of the dissociation curve to the right when pCO_{2} is high.
AffinityHow readily haemoglobin binds oxygen.
Haemoglobinic acidHaemoglobin combined with H^{+}.
Haldane effectOxygen loading promotes release of CO_{2}.
2,3-bisphosphoglycerate (BPG)A compound in red cells that lowers haemoglobin affinity for oxygen.

Avoid these mistakes

1
Saying the curve shifts left when CO_{2} rises — it shifts right, lowering affinity.
2
Saying the Bohr shift reduces oxygen loading in the lungs — the curves overlap at high pO_{2}.
3
Describing only the shift — a full answer gives cause, mechanism, result and benefit.
4
Confusing the Bohr shift with the chloride shift — the chloride shift is Cl^{-} moving into red cells.

Last updated: