PMDC Verified Question 5 of 34
Most of the carbon dioxide in blood is transported as by bicarbonate ions. Choose the event not taking place during gaseous exchange at tissue level.
A
Formation of HHb
B
Formation of sodium bicarbonate
C
Chloride shift
D
Formation of oxyhaemoglobin
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Formation of oxyhaemoglobin
Concept: Gas exchange events differ completely based on the location: systemic tissues vs. pulmonary capillaries (lungs).

Solution:
  • At the tissue level, oxygen is desperately needed for cellular respiration. Therefore, hemoglobin must release its oxygen.
  • Because oxygen is being released, oxyhaemoglobin (\( \text{HbO}_2 \)) is breaking down, NOT forming.
  • The formation of oxyhemoglobin exclusively happens in the lungs where oxygen is abundant.


Why other options are incorrect:
  • Formation of HHb (reduced hemoglobin): Occurs at the tissues as hemoglobin drops oxygen and buffers hydrogen ions.
  • Formation of sodium bicarbonate & Chloride shift: Occur actively at the tissues as massive amounts of \( \text{CO}_2 \) enter the RBCs, convert to bicarbonate, and exit into plasma in exchange for Chloride.

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