Q46 / 200 · MHT CET - Medical 2026 (25 April Shift 2) · Biology

Before the formation of oxyhaemoglobin, the $\text{O}_2$ has to pass through _________ membranes from the alveolar air.

  • A
    $2$
  • B
    $7$
  • Correct answer
    C
    $3$
  • D
    $4$

Solution

To form oxyhaemoglobin, oxygen from the alveolar air must diffuse into the red blood cells (RBCs) where haemoglobin is present. During this process, the $\text{O}_2$ molecule has to pass through the following three cellular membranes:

1. Squamous epithelium of the alveoli (Alveolar membrane)
2. Endothelium of the alveolar capillaries (Capillary membrane)
3. Plasma membrane of the red blood cell (RBC membrane)

Note: The basement substance present between the alveolar epithelium and capillary endothelium is a non-cellular matrix layer and is not counted as a cellular membrane in this context.

Therefore, oxygen passes through $3$ membranes.

Answer: $3$

Hence, the correct answer is option: 'C'.

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