Chapter 13 Gas exchange in humans (Revised)
HOMEWORK
4. a cartilage ring 1m
to prevent collapse of the trachea/ to allow free passage of air 1m
b (i) pleural membranes 1m
(ii) because air leaks in/ increases pressure between pleural membranes, 1m
the lung collapses due to its own elasticity 1m
c muscle C relaxes 1m
d (i) to provide a short distance for diffusion 1m
(ii) to provide a large surface area for diffusion 1m
(iii) to dissolve the respiratory gases for diffusion to occur 1m
e dust particles cannot be removed from the respiratory tract/ more dust particles enter the lungs 1m
thereby reducing the surface area for gas exchange 1m
5. a ventilation rate = 1000 x 36 cm3 per minute 1m
= 36000 cm3 per minute
b To supply more oxygen 1m
to the skeletal muscles 1m
for faster respiration/ for more energy supply 1m
To remove carbon dioxide more rapidly 1m
c Dust particles are trapped by the hair in the nose and 1m
mucus along the lining of the air passage/ nasal cavity/ trachea 1+1m
d large, clear, accurate diagram 1m
labels and title 2m
6. a Oxygen in the tidal air diffuses through the residual air 1m
and dissolves in the water film lining the air sac 1m
It then diffuses across the walls of the air sac and the capillary into the blood 1m
b (i) The volume of tidal air will increase 1m
(ii) The oxygen uptake in the blood becomes faster 1m
because the distance of diffusion of oxygen from the tidal air to the water film is reduced
or because the surface area of the air sac for diffusion of oxygen is increased 1m
c Particles / tar deposit on the wall of the air sac 1m
thus reduce the rate of diffusion of oxygen 1m
7. a rate of breathing = 12 breaths per minute 1m
depth of breathing = 500 cm3 1m
b between 0 and 2.5 second 1m
c Intercostal muscles relaxed, so that the ribs moved downward and inward 1m
Diaphragm muscles relaxed, so that the diaphragm recoiled to the dome-shape 1m
The thoracic/ lung volume decreased 1m
Leading to an increase in air passage in the lungs 1m
The lungs recoil due to their own elasticity. 1m
Max. 4 marks
d (i) The breathing movements would become faster 1m
(ii) In the left lung, air flow would decrease 1m
