Question 19N.2.SL.TZ0.6c
| Date | November 2019 | Marks available | [Maximum mark: 7] | Reference code | 19N.2.SL.TZ0.6c |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Explain | Question number | c | Adapted from | N/A |
Explain how ventilation and lung structure contribute to passive gas exchange.
[7]
a. air carried through trachea AND bronchi/bronchioles AND alveoli ✔ All three required in correct order.
b. alveoli increase the surface area/thin walled for gas exchange ✔
c. gas exchange carried out through type I pneumocytes ✔
d. type II pneumocytes secrete surfactant to reduce surface tension ✔
e. moist surface/surfactant allows gases to diffuse in solution ✔
f. ventilation/moving blood maintains concentration gradients of oxygen and carbon dioxide ✔
g. between air in alveoli and blood in «adjacent» capillaries
OR
oxygen diffuses from alveoli to capillaries and carbon dioxide from capillaries to alveoli ✔ OWTTE
h. external intercostal muscles/diaphragm contract during inspiration ✔
i. lowering air pressure «in lungs»/increasing thorax volume ✔
j. relaxation of external intercostal muscles/diaphragm enable «passive» expiration ✔
k. internal intercostal «and abdominal muscles» contract «to force» expiration ✔
l. expiration due to increasing air pressure «in lungs»/decreasing thorax volume ✔
Accept correctly annotated diagram.
