Question 18N.2.HL.TZ0.c
| Date | November 2018 | Marks available | [Maximum mark: 7] | Reference code | 18N.2.HL.TZ0.c |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Explain | Question number | c | Adapted from | N/A |
Adult humans may absorb more than five hundred litres of oxygen per day. Explain how gas exchange is maintained in the human respiratory system.
[7]
a. ventilation/inhaling brings fresh air/air with high oxygen concentration to the lungs
OR
ventilation/exhaling gets rid of stale air/air with high concentration of carbon dioxide ✔
b. ventilation due to muscle contractions causing pressure/volume changes in the thorax ✔
c. contraction of external intercostal muscles AND diaphragm occurs during inspiration
OR
contraction of internal intercostal muscles/abdomen wall muscles during «forced» expiration ✔
d. alveoli surrounded by «many» capillaries ✔
e. blood flow/pumping of heart «brings blood to/takes blood away from alveoli/lungs» ✔
f. concentration gradients «of oxygen/ CO2» maintained «by ventilation/blood flow» ✔
g. O2 AND CO2 diffuse ✔
h. CO2 from capillaries/blood/vessel to alveolus/air AND O2 from alveoli into capillaries/blood/vessel ✔
i. large numbers of alveoli increase surface area ✔
j. short distance so rapid diffusion/gas exchange ✔
k. type I pneumocytes/alveolus wall/capillary walls are one cell thick/very thin ✔
l. alveoli «lining» moist for dissolving of gases/rapid diffusion
OR
type II pneumocytes keep the «lining of» the alveolus moist ✔
m. type II pneumocytes secrete surfactant to reduce surface tension/prevents alveoli from collapsing ✔
