Describe the loading and unloading of oxygen.

Loaded in the lungs at high pO₂ (haemoglobin nearly fully saturated) and unloaded in respiring tissues at low pO₂.

What does the oxyhaemoglobin dissociation curve show?

The percentage saturation of haemoglobin with oxygen at different partial pressures of oxygen.

What is cooperative binding?

Binding of the first oxygen changes the shape of haemoglobin, making it easier for further oxygen molecules to bind.

Why is the dissociation curve S-shaped?

The first oxygen binds with difficulty, then cooperative binding makes further binding easier, so the curve is steep, then it flattens as sites fill.

What is the Bohr effect?

A higher carbon dioxide concentration (lower pH) reduces the affinity of haemoglobin for oxygen, shifting the curve to the right.

What is the benefit of the Bohr effect to active tissues?

More oxygen is unloaded at a given pO₂, where it is needed most for aerobic respiration.

What does a curve shifted to the left mean?

Haemoglobin has a higher affinity for oxygen: it loads at lower pO₂ but unloads less readily.

Why does fetal haemoglobin have a higher affinity than adult haemoglobin?

So that it loads oxygen from the mother's haemoglobin in the placenta, where pO₂ is low.

How is llama haemoglobin adapted to high altitude?

Higher affinity for oxygen, so it loads more oxygen at the low pO₂ of the lungs at altitude.

Why does a small mammal with a high metabolic rate have haemoglobin with a lower affinity?

It unloads oxygen more readily to tissues, supplying the fast aerobic respiration needed.

Haemoglobin and oxygen transportAQA A-Level Biology: Flashcards

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What is the quaternary structure of haemoglobin?

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What is the quaternary structure of haemoglobin?: Four polypeptide chains, each with a haem group containing an iron ion (Fe²⁺).
How many oxygen molecules can one haemoglobin molecule carry?: Four, one at each haem group.
Where is haemoglobin found?: Inside red blood cells.
Describe the loading and unloading of oxygen.: Loaded in the lungs at high pO₂ (haemoglobin nearly fully saturated) and unloaded in respiring tissues at low pO₂.
What does the oxyhaemoglobin dissociation curve show?: The percentage saturation of haemoglobin with oxygen at different partial pressures of oxygen.
What is cooperative binding?: Binding of the first oxygen changes the shape of haemoglobin, making it easier for further oxygen molecules to bind.
Why is the dissociation curve S-shaped?: The first oxygen binds with difficulty, then cooperative binding makes further binding easier, so the curve is steep, then it flattens as sites fill.
What is the Bohr effect?: A higher carbon dioxide concentration (lower pH) reduces the affinity of haemoglobin for oxygen, shifting the curve to the right.
What is the benefit of the Bohr effect to active tissues?: More oxygen is unloaded at a given pO₂, where it is needed most for aerobic respiration.
What does a curve shifted to the left mean?: Haemoglobin has a higher affinity for oxygen: it loads at lower pO₂ but unloads less readily.
Why does fetal haemoglobin have a higher affinity than adult haemoglobin?: So that it loads oxygen from the mother's haemoglobin in the placenta, where pO₂ is low.
How is llama haemoglobin adapted to high altitude?: Higher affinity for oxygen, so it loads more oxygen at the low pO₂ of the lungs at altitude.
Why does a small mammal with a high metabolic rate have haemoglobin with a lower affinity?: It unloads oxygen more readily to tissues, supplying the fast aerobic respiration needed.

Exam questions on Haemoglobin and oxygen transport

Haemoglobin is carried inside red blood cells. A student is studying the structure of human haemoglobin and how it takes up oxygen in the lungs. She notes that the oxyhaemoglobin dissociation curve for haemoglobin is S-shaped, with a shallow start and then a steep rise as the partial pressure of oxygen increases.
Explain why the oxyhaemoglobin dissociation curve is S-shaped, with a shallow start and then a steep rise.2 marks
During vigorous exercise, the muscle cells of a runner respire rapidly and release large amounts of carbon dioxide. This lowers the pH of the blood in the muscle capillaries. A sports scientist is investigating how this affects the way haemoglobin loads and unloads oxygen.
Explain how the effect of carbon dioxide on haemoglobin benefits the exercising muscle.2 marks
In the placenta, oxygen passes from the mother's blood to the blood of the fetus. Adult haemoglobin is 50% saturated at a partial pressure of oxygen of 3.5 kPa, whereas fetal haemoglobin is 50% saturated at 2.4 kPa. At a partial pressure of oxygen of 4 kPa, similar to that in the placenta, adult haemoglobin is about 59% saturated and fetal haemoglobin is about 80% saturated. After birth, fetal haemoglobin is gradually replaced by adult haemoglobin over the first few months of life.
Use the information to explain how fetal haemoglobin allows the fetus to obtain oxygen from its mother's blood.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).