7 Gas Exchange in Human
2nd Term WS 02
(a) Nasal cavity / trachea / bronchi / bronchioles
(b) The cells need to carry out respiration to release energy
for the movement of cilia.
(c) Mucus-secreting cells secrete mucus
to trap bacteria.
The cilia beat to sweep mucus towards the pharynx. The mucus is then swallowed or
coughed up. 1m
(a) Refreshing the air in the air sacs increases the concentration of oxygen in the air sacs.
This helps maintain a higher oxygen concentration than in the blood.
It also decreases the concentration of carbon dioxide in the air sacs.
This helps maintain a lower carbon dioxide concentration than in the blood.
(b) The continuous blood flow in the capillaries
brings in more carbon dioxide / takes away more oxygen. 1m
Oxygen combines with haemoglobin
to keep the oxygen concentration in blood / plasma low. 1m
(d) hydrogencarbonate 1m
(e) water 1m
(a) The lungs contain a large number of air sacs. 1m
(This provides a large surface area for diffusion of gases.)
(b) The walls of air sacs are one-cell thick / very thin. 1m
(This reduces the diffusion distance of gases.)
(c) Ventilation brings fresh air to the lungs to maintain a high oxygen content
in the lungs and to remove carbon dioxide from the lungs. /
The lungs are richly supplied with capillary
(which allows oxygenated blood to be carried away from the air sacs
and deoxygenated blood to be carried to the air sacs.) 1m
(d) The lungs are deep inside the body. 1m