Page 27 - Q & A STPM 2022 Biology

Biology STPM Chapter 7 Gaseous Exchange
Answer: B
The haemoglobin in a worm has the highest affinity for oxygen and does not
unload the oxygen until it reaches a very low partial pressure of oxygen. The
pigeon is an active animal, hence the rate of respiration is higher. This means
more oxygen is needed. There is a high level of CO , hence the affinity of
2
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haemoglobin for oxygen decreases. So, oxygen is released into the tissue readily.

Question 5
The graph below represents the oxygen dissociation curves of a mammal at
two different partial pressure of carbon dioxide. What is the advantage of the
effect shown by the two curves to the organism?

100
pCO 2 = 2 kPa
Semester
2 80
Percentage of saturation of haemoglobin with oxygen 60 pO 2 = 10 kPa

40

20

0
4 8 12 16 20
pO 2 /kPa
A Haemoglobin removes more carbon dioxide from active tissues.
B Oxyhaemoglobin is not denatured at low pH values.
C Oxygen is more easily released to the active tissues.
D Haemoglobin is saturated with oxygen at the lungs.

Answer: C
Active tissues require more oxygen and have a high partial pressure of CO since
2
it is a product of respiration. At higher pCO , the oxygen dissociation curve shifts
2
to the right. This shows carbon dioxide reduces the affinity of haemoglobin for
oxygen. This causes oxygen to be released into the active tissues. This is called
the Bohr effect.

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Chapter 7.indd 152 11/2/21 9:27 AM