8.2.2
Oxygen Dissociation
Dissociation Curves
Dissociation Curves
The relationship between the percentage saturation of haemoglobin and oxygen partial pressure of the surrounding tissues can be shown in a dissociation curve.


Low pO2
Low pO2
- When partial pressure is low, haemoglobin has a low affinity for oxygen.
- The percentage saturation of haemoglobin is low because oxygen dissociates from the haemoglobin.


Increasing pO2
Increasing pO2
- As pO2 increases, affinity of haemoglobin for oxygen increases slightly.
- When the first molecule of O2 binds to haemoglobin, the protein undergoes a conformational change.
- The change in shape allows the other O2 molecules to bind to haemoglobin more easily.
- The percentage saturation of haemoglobin increases quickly.


Plateau in percentage saturation
Plateau in percentage saturation
- As more molecules of O2 bind to haemoglobin, it becomes more difficult for more O2 molecules to bind.
- The percentage saturation of haemoglobin begins to plateau.


S-shaped curve
S-shaped curve
- The increasing affinity of haemoglobin with increasing pO2 in this way creates an S-shaped curve.
- The S-shaped curve is called the dissociation curve.


Higher altitudes
Higher altitudes
- The partial pressure of oxygen is lower at higher altitudes. This makes it difficult to saturate haemaglobin with oxygen. It can be difficult to deliver enough oxygen to tissues.
- To compensate for this, people who live at higher altitudes have a higher red blood cell count. This increases the amount of haemoglobin in blood.
- The hormone erythropoietin stimulates red blood cell production at low partial pressures of oxygen. (You do not need to remember the name of this hormone).
- This process is called acclimation.
The Bohr Effect
The Bohr Effect
The partial pressure of carbon dioxide (pCO2) also influences the affinity of haemoglobin for oxygen. This is called the Bohr effect.


High pCO2
High pCO2
- Respiring cells use oxygen in respiration and produce carbon dioxide.
- The respiring cells have low pO2 and high pCO2.
- When pCO2 is high, the rate of oxygen dissociation increases.


Bohr effect
Bohr effect
- The increased dissociation of oxygen causes a shift in the oxyhaemoglobin dissociation curve to the right.
- The shift in the dissociation curve means that oxygen will dissociate from haemoglobin at a lower pO2 than normal.
- This is called the Bohr effect.
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
Jump to other topics
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
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