HKDSE Biology – a modern approach 2A
Answers to Coursebook exercises
11 Gas Exchange in Humans
Check your progress
11.1 The need for gas exchanges in humans
True or false
1.
F
2.
T
3.
T
4.
T
(1 mark each)
(Total: 4 marks)
11.2 General plan of the breathing system
A. True or false
1.
F
2.
T
3.
F
4.
T
5.
F
(1 mark each)
(Total: 5 marks)
B. Question
1.
(a)
vocal cord
(b)
bronchi
(c)
epiglottis
(d)
pleural membrane
(e)
diaphragm
(f)
rib cage
(1 mark each)
(Total: 6 marks)
11.3 Gas exchange in alveoli
Question
1.
(a)
The oxygen dissolves in the moisture of the alveoli.
(1 mark)
It diffuses across the walls of the alveoli and the capillaries into the blood.
(1 mark)
© Aristo Educational Press Ltd. 2009
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HKDSE Biology – a modern approach 2A
Answers to Coursebook exercises
It then diffuses through the cell membrane into the red blood cell.
(b)
Any three of the following:

(1 mark)
(3 marks)
The walls of the alveoli are very thin which provide a short distance for diffusion
of gases.

There are numerous alveoli which provide a large surface area for diffusion of
gases.

The alveoli are surrounded by a network of capillaries. They provide a rich blood
supply to transport gases to and from respiratory surface, which maintains a steep
gradient for diffusion.

The walls of the alveoli are moist. Thus the oxygen can dissolve in this fluid and
diffuse across the walls of the alveoli.
(c)
The blood in region A contains more carbon dioxide and
(1 mark)
less oxygen than that in region B.
(1 mark)
(Total: 8 marks)
11.4 Transport of respiratory gases
Fill in the blanks
1.
2.
(a)
red blood cells
(b)
oxyhaemoglobin
(c)
plasma
(d)
hydrogencarbonate ion
(1 mark each)
(Total: 4 marks)
11.5 The mechanism of ventilation in humans
Questions
1.
A, C
(1 mark)
2.
(a)
contracted
(b)
upwards and outwards
(c)
flatten the diaphragm
(d)
increased
(e)
decreased
(f)
atmosphere
(1 mark each)
(Total: 7 marks)
© Aristo Educational Press Ltd. 2009
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HKDSE Biology – a modern approach 2A
Answers to Coursebook exercises
Revision Exercise
A.
Multiple choice
1.
C
2.
B
3.
B
4.
A
5.
B
6.
B
7.
D
(1 mark each)
(Total: 7 marks)
B.
Short questions
1.
Large dust particles are first filtered by the hairs in the nostrils.
(1 mark)
Dust particles which enter the nasal cavity are trapped by the mucus,
(1 mark)
secreted by mucus-secreting cells.
(1 mark)
The trapped dusts are then swept away by the beating cilia
(1 mark)
on the ciliated epithelial cells.
(1 mark)
Finally, the mucus is swallowed or coughed out as sputum.
(1 mark)
(Total: 6 marks)
2.
We cannot breathe and swallow at the same time
(1 mark)
because it will result in choking / food will enter the trachea and block the respiratory
pathway.
(1 mark)
(Total: 2 marks)
C.
Structured questions
1.
(a)
(b)
In the normal lung the bronchioles are wider and
(1 mark)
the alveoli are more deeply folded than the affected lung.
(1 mark)
The narrow bronchioles in the affected lung will slow down the airflow into the lung.
(1 mark)
Besides, the foldings in the alveoli are less deep and this will decrease the surface area
for gas exchange.
(1 mark)
(c)
The breathing rate of the person with the affected lung is higher.
(1 mark)
(d)
The soot particles increase the thickness of the barrier for diffusion of gases
(1 mark)
and also they reduce the effective surface area for gas exchange.
(1 mark)
(Total: 7 marks)
© Aristo Educational Press Ltd. 2009
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HKDSE Biology – a modern approach 2A
Answers to Coursebook exercises
2.
(a)
(b)
(i)
Graph B
(1 mark)
(ii)
Graph A
(1 mark)
(i)
The baby breathes faster but not as deeply.
(1 mark)
(ii)
The baby possesses a higher metabolic rate due to rapid growth.
(1 mark)
A faster rate of breathing can ensure an adequate supply of oxygen to support the
(c)
metabolism.
(1 mark)
(i)
The adult on a very high mountain breathes faster and more deeply.
(1 mark)
(ii)
Since the oxygen level at a very high mountain is lower than that at sea level,
(1 mark)
less oxygen is obtained in a single breath compared with that at sea level.
(1 mark)
Therefore, the adult has to breathe faster and more deeply in order to get
sufficient oxygen.
(1 mark)
(Total: 9 marks)
© Aristo Educational Press Ltd. 2009
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