Q.The Oxygen Dissociation Curve is

The Haldane effect describes how the oxygenation state of haemoglobin affects its ability to carry carbon dioxide — deoxyhaemoglobin binds CO2 more readily than oxyhaemoglobin.

As oxygen is released from oxyhaemoglobin at the tissues (where oxygen is being consumed by respiring cells), the resulting deoxyhaemoglobin has a greater affinity for carbon dioxide and hydrogen ions than oxyhaemoglobin does. This means deoxygenated blood can pick up and carry more CO2 (partly as carbaminohaemoglobin, and partly by buffering H+ ions produced from carbonic acid dissociation, which in turn favours more CO2 being converted to bicarbonate in the blood).

Conversely, in the lungs, as haemoglobin binds oxygen (becoming oxyhaemoglobin), its affinity for CO2 and H+ decreases, which helps release/unload the CO2 that was being carried, so it can diffuse out into the alveoli and be exhaled.

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The Haldane effect states that deoxygenated hemoglobin binds CO2 more readily than oxygenated hemoglobin, so the level of oxygen bound to hemoglobin directly controls how much CO2 it can carry — exactly the relationship the question statement describes.

In the tissues, cells continuously produce CO2 as a byproduct of aerobic respiration, and oxygen is being delivered from the blood to the tissues. As oxyhemoglobin (HbO2) releases its oxygen to the tissues, it becomes deoxyhemoglobin (reduced Hb). This reduced hemoglobin has a HIGHER affinity for CO2 than oxygenated hemoglobin — it can bind CO2 directly (forming carbaminohemoglobin) more effectively, and it also more effectively binds H+ ions (buffering the acid formed when CO2 combines with water to form carbonic acid/bicarbonate), which in turn allows more CO2 to be converted to bicarbonate and transported in the plasma. This is the Haldane effect: the deoxygenation of hemoglobin in the tissues increases its capacity to carry/transport CO2 away from the tissues.

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