The oxygen dissociation curve
"The oxygen dissociation curve" is a free, interactive Class 11 Biology simulation for NEET, built on the lesson "Transport of oxygen" in Breathing and Exchange of Gases. Slide the pO₂ from the lungs (104 mmHg) down to the tissues (40 mmHg). Watch how the seats empty, and how steep the curve is in the middle. The S-shape comes from cooperative binding: each O₂ that binds makes the next one bind more easily. High pCO₂, H⁺ and temperature shift the curve right (the Bohr effect), so O₂ is unloaded where it is being used; in the lungs the curve shifts back and haemoglobin refills to about 98 %. At rest, 100 mL of blood gives up roughly 4-5 mL of O₂ to the tissues (this model: 4.3 mL; NEET quotes the rounded figure, about 5 mL).
From the lesson Transport of oxygen in Breathing and Exchange of Gases. Change the values and watch what happens.
The idea behind it
NCERT §14.4, §14.4.1
- Blood carries O₂ and CO₂. About 97 per cent of O₂ travels bound to haemoglobin in RBCs; the remaining 3 per cent is dissolved in plasma.
- Haemoglobin is a red, iron-containing pigment in RBCs. O₂ binds it reversibly to form oxyhaemoglobin, and each haemoglobin molecule can carry at most four molecules of O₂.
- Binding of O₂ depends mainly on pO₂; pCO₂, hydrogen ion concentration and temperature also affect it.
- Plotting percentage saturation of haemoglobin against pO₂ gives a sigmoid curve, the oxygen dissociation curve, which is very useful for studying how pCO₂, H⁺ concentration and other factors affect O₂ binding.
- In the alveoli, high pO₂, low pCO₂, lower H⁺ concentration and lower temperature all favour formation of oxyhaemoglobin.
- In the tissues, low pO₂, high pCO₂, higher H⁺ concentration and higher temperature favour dissociation of O₂ from oxyhaemoglobin.
- Under normal physiological conditions, every 100 mL of oxygenated blood delivers around 5 mL of O₂ to the tissues.
Questions
2 answers
- What does the "The oxygen dissociation curve" simulation show?
- Slide the pO₂ from the lungs (104 mmHg) down to the tissues (40 mmHg). Watch how the seats empty, and how steep the curve is in the middle.
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Transport of oxygen" in Breathing and Exchange of Gases (Class 11 Biology).
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