Page 29 - Q & A STPM 2022 Biology

Biology STPM Chapter 7 Gaseous Exchange
Answer: B
In the lungs, when the partial pressure of oxygen is high, haemoglobin readily
combines with oxygen. In active tissues, when the partial pressure of CO
2
increases, the affinity oh haemoglobin for oxygen is decreased and more oxygen
is readily released. This is the Bohr effect.
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Question 8
The graph below shows the oxygen dissociation curves for fish and human.

Percentage of saturation of haemoglobin with oxygen (%)

Semester
2 Fish Human

0 Partial pressure of oxygen/ kPa
Which of the following is the reason the oxygen dissociation curve for fish is
more to the left compared to the curve for human?
A The concentration of oxygen in water is lower than in air.
B At a low partial pressure of oxygen, human haemoglobin is more
saturated compared to fish haemoglobin.
C At a low partial pressure of oxygen, oxygen uptake of fish haemoglobin is
less compared to human haemoglobin.
D Fish haemoglobin has a higher affinity for oxygen.

Answer: D
The fish haemoglobin has an increased affinity for oxygen than human
haemoglobin. This would displace the curve to the left. The initial uptake of
oxygen for fish haemoglobin is higher, till saturation.

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Chapter 7.indd 154 11/2/21 9:27 AM