Page 30 - Q & A STPM 2022 Biology

Biology STPM Chapter 7 Gaseous Exchange

Question 9
Which of the following processes in the red blood cells is catalysed by an
enzyme?
A The reaction between water and carbon dioxide, forming carbonic acid.
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B The reaction between carbon dioxide and haemoglobin, forming
carbaminohaemoglobin.
C The reaction between hydrogen ions and haemoglobin, forming
haemoglobinic acid.
D The dissociation of oxyhaemoglobin, releasing oxygen.

Answer: A
Carbonic anhydrase is a very efficient enzyme found in the red blood cells. It
catalyses the combination of carbon dioxide and water to form carbonic acid,
as well as, the dissociation of carbonic acid, releasing hydrogen carbonate ions Semester
and hydrogen ions.
2
Question 10
Which of the following forms does carbon dioxide mainly transported in
blood?
A As hydrogen carbonate ions
B As carbonic acid
C In solution as dissolved carbon dioxide
D As carbaminohaemoglobin

Answer: A
About 85% of CO produced by tissues combine with water to form carbonic
2
acid. Carbonic acid dissociates to hydrogen and hydrogen carbonate ions. These
ions move out of the red blood cell into the plasma where they combine with
sodium to form sodium hydrogen carbonate.

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