Which of the following statement is true about Hb-O2 dissociation curve?
**Core Concept**
The hemoglobin-oxygen (Hb-O2) dissociation curve is a graphical representation of the relationship between the partial pressure of oxygen (pO2) in the blood and the saturation of hemoglobin with oxygen. This curve is crucial in understanding how hemoglobin binds and releases oxygen in the body.
**Why the Correct Answer is Right**
The Hb-O2 dissociation curve is sigmoidal in shape due to the cooperative binding of oxygen to the four subunits of hemoglobin. As the pO2 increases, more oxygen binds to the hemoglobin, causing a sigmoidal increase in oxygen saturation. The curve is also influenced by factors such as pH, temperature, and the presence of 2,3-bisphosphoglycerate (2,3-BPG) in red blood cells. The Bohr effect describes how a decrease in pH (increase in acidity) shifts the curve to the right, facilitating the release of oxygen to tissues.
**Why Each Wrong Option is Incorrect**
* **Option A:** This statement is incorrect because the Hb-O2 dissociation curve is sigmoidal, not linear.
* **Option B:** This statement is incorrect because the curve is not flat, indicating that the binding of oxygen to hemoglobin is not independent of the other subunits.
* **Option D:** This statement is incorrect because the curve is not symmetrical, reflecting the cooperative binding of oxygen to hemoglobin.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the Bohr effect is responsible for the increased release of oxygen to tissues in conditions of acidosis, such as during intense exercise or in cases of lactic acidosis.
**Correct Answer:** C. The Hb-O2 dissociation curve is sigmoidal in shape due to cooperative binding of oxygen to hemoglobin.