Page 41 - Q & A STPM 2022 Biology

Biology STPM Chapter 7 Gaseous Exchange
Answer:
(a) J : medulla oblongata
K : vagus nerve
L : carotid body
M : aortic body
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(b) J : Has respiratory centre that contains the central chemoreceptors which
are stimulated by the high concentration of hydrogen ion (H ). It then
+
sends impulses to the diaphragm and intercostal muscles to increase
the rate of breathing.
M : These are specialised cells with chemoreceptors that detect the increase
in carbon dioxide or hydrogen ion (H ) concentration in the blood and
+
sends impulses to the respiratory centre.
(c) – Concentration of carbon dioxide.
– Concentration of hydrogen ions (H ).
+
(d) – As we exercise, the breathing rate increases.
– Exercise increases cellular respiration.
– This increases the concentration of carbon dioxide or hydrogen ion (H )
+
Semester
2 in the blood which is then detected by the chemoreceptors.
– Nerve impulses from the chemoreceptor are then sent to the respiratory
centre that will increase the rate of breathing.
– Excess carbon dioxide is expelled.
(e) – As more carbon dioxide diffuses from the blood into the alveoli, the
concentration of CO in the blood decreases.
2
– When the concentration of CO returns to normal and less H ions
+
2
are produced, the chemoreceptors will not be stimulated, hence the
breathing rate returns to normal.

Section C Essay Questions

Question 1
(a) Describe briefly the adaptations of the alveolus for gaseous exchange in
the lungs. (3 marks)
(b) Explain how the mechanism of breathing is controlled in a human.
(12 marks)

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Chapter 7.indd 166 11/2/21 9:27 AM