Question

With reference to the oxyhaemoglobin dissociation curve, select the INCORRECT statement / statements.
I. 100 % saturation is very common.
II. 95 - 97 % saturation takes place at \(ppO_2 = 100\) mm Hg in alveoli.
III. At 30 mm Hg of \(ppO_2\), only 50% saturation can be maintained.
IV. The oxyhaemoglobin dissociation curve is J-shaped.

• A. I and IV only
• B. II and III only
• C. I, II and III only
• D. IV only

Hint:

The curve is sigmoid (S shaped), and 100 percent saturation is not common.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
The oxyhaemoglobin dissociation curve is a plot of percent saturation of haemoglobin against \(p\text{O}_2\).

Step 2: Check each statement
I is incorrect because 100% saturation is not very common.
II is correct. At about 100 mm Hg in the alveoli, saturation is 95-97%.
III is taken as correct in the textbook, since about 50% saturation is reached at a low \(p\text{O}_2\) near 30 mm Hg.
IV is incorrect because the curve is sigmoid, not J shaped.

Step 3: Match
The incorrect statements are I and IV only, option (A).

Final Answer:
Statements I and IV are incorrect. \[ \boxed{\text{(A) }\text{I and IV only}} \]