Page 36 - Q & A STPM 2022 Biology

Biology STPM Chapter 7 Gaseous Exchange

Question 4
The diagram below shows the chemical reactions which occur in the blood
during the transportation of carbon dioxide.

Cell/ Tissue
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S
P + O 2 CO 2+ H 2 O
IV
I V R
III
CO 2 + H 2 O HCO 3 – H + Hb O 2

II
Q HbO 2
H 2 CO 3 Semester

(a) State the part of haemoglobin molecule that binds to carbon dioxide.
(1 mark) 2
(b) State the substances labelled P, Q, R and S. (2 marks)
P :
Q :
R :
S :
(c) Explain the events that occur at the stages I, II, III, IV and V. (5 marks)
I:
II:
III:
IV:
V:

Answer:
(a) Amino groups in haemoglobin
(b) P : Glucose
Q : Carbonic anhydrase
R : Haemoglobinic acid
S : Chloride ions
(c) I : Carbon dioxide produced during cellular respiration diffuses out from
the cell into the blood plasma. The carbon dioxide then diffuses into
the red blood cell where it combines with water to form carbonic acid.
This reaction is catalysed by the enzyme carbonic anhydrase.
II : The carbonic acid dissociates into hydrogen ions (H ) and hydrogen
+
carbonate ions (HCO ). This action is catalysed by carbonic anhydrase.
-
3
III : The haemoglobin releases the oxygen. The haemoglobin produced
combine with the hydrogen ions (H ) to form haemoglobinic acid.
+
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Chapter 7.indd 161 11/2/21 9:27 AM