Page 35 - Q & A STPM 2022 Biology

Biology STPM Chapter 7 Gaseous Exchange

(b) State the tissue where myoglobin is found. (1 mark)
(c) With reference to the graph,
(i) state the percentage saturation of myoglobin and haemoglobin when
partial pressure of oxygen is 2 kPa. (1 mark)
(ii) explain the significance of the difference in percentage of saturation
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that you have shown in (i). (1 mark)
(d) When a person exercises vigorously, the partial pressure of carbon
dioxide in the blood increases. Draw on the graph a dissociation curve for
haemoglobin when the partial pressure of carbon dioxide has increased.
(1 mark)

Answer:
(a) (i) – Haem
– able to combine loosely with a molecule of oxygen
(ii) – When an oxygen molecule combines with the ferrous iron atom of
a single haem unit, it distorts the shape of the haem unit slightly.
Semester
2 – This distortion causes the whole haemoglobin molecule to change
its shape accordingly.
– When oxygen molecule attaches to the second and third haem
groups, more structural changes occur.
– Each change facilitates a much faster uptake of oxygen than the
one earlier.
(b) Skeletal muscle
(c) (i) Myoglobin- 90%
Haemoglobin- 25%
(ii) – Myoglobin has a high affinity for oxygen, hence it retains its oxygen
in the resting cell.
– It only begins to release oxygen when pO is below 20 mmHg,
2
which is during vigorous muscle activity.
– It acts as a store of oxygen in muscles, only releasing the oxygen
when the supplies of oxyhaemoglobin have been exhausted.
(d) The curve is to be drawn to the right of the haemoglobin curve (H).

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Chapter 7.indd 160 11/2/21 9:27 AM