Outline the process of inhalation.

Explain the process of gas exchange taking place in the alveoli.

Discuss the relationship between atmospheric carbon dioxide concentration and global temperatures.

a. diaphragm contracts / moves downwards/flattens ✔

b. external intercostal muscles contract ✔

c. (muscle contraction) moves the rib cage upwards and outwards ✔

d. increases volume of the thorax / lungs ✔

e. difference in pressure/decreasing pressure causes air to flow into lungs / lungs inflate ✔

a. O₂ diffuses into blood and CO₂ diffuses out from blood ✔

b. blood entering the alveoli is high in CO₂/low in O₂ ✔
OR
air in alveolus is high in O₂/low in CO₂ ✔

c. diffusion (in either direction) take place due to concentration gradients ✔

d. concentration gradients maintained by ventilation/blood flow ✔

e. large surface area created by many alveoli/spherical shape of alveoli for more efficient diffusion ✔

f. rich supply of capillaries (around alveoli) allows efficient exchange ✔

g. type I pneumocytes are thin to allow easy diffusion/short distances ✔

h. gases must dissolve in liquid lining of alveolus in order to be exchanged ✔

i. type II pneumocytes secrete surfactants to reduce surface tension/prevent lungs sticking together ✔

j. type II pneumocytes create moist conditions in alveoli ✔

a. greenhouse effect keeps Earth warm ✔

b. (over-time) earth’s temperature has fluctuated naturally ✔

c. changes in human activities have led to increases in CO₂ concentration ✔

d. CO₂ absorbs infrared/long wave radiation / trapping heat ✔

e. increase in atmospheric CO₂ (concentration) correlates with/causes increased global average temperature ✔

f. use of fossil fuels increases atmospheric CO₂ ✔

g. deforestation removes a carbon sink / less CO₂ absorbed ✔

h. loss of polar ice causes less reflection of surface light/ more reradiation as heat contributing to (global) warming ✔

i. CO₂ is not the only greenhouse gas/ there are other greenhouse gases ✔

This question was attempted by approximately 56 % of candidates.

Done well by many. Diaphragm contraction and external intercostal muscle contraction was commonly known along with the idea that the rib cage moves upwards and outwards. Further understanding of the consequent pressure changes in the thorax was not clear.

This question was attempted by approximately 56 % of candidates.

Some coherent, clear answers were given earning the maximum marks. However, commonly, valid ideas were given but were jumbled. Coherent writing was usually missing. The term diffusion was missing in many answers. The idea that alveoli are surrounded by capillaries to enable exchange of gases between the air in alveolus and the blood did not seem to be a mental picture for many. Concentration gradients as a reason for diffusion of oxygen or carbon dioxide between the alveoli and the blood was rarely explained. However, it seemed that everyone knew about surfactants from type II pneumocytes.

This question was attempted by approximately 56 % of candidates.

This question was actually quite narrow as reflected in the number of marks it could earn. Some candidates understood which part of the global warming topic was being asked of them and stuck to the topic. Good applications to the carbon cycle were given. Strong responses avoided deviations into consequences and how humans should behave. Several misunderstandings surfaced. For example that CO₂ was responsible for the breakdown of the ozone layer. Many seemed to tie ozone layer destruction and global warming information together in their explanation. Atmospheric carbon dioxide and the ozone layer were confused. Some thought that the ozone layer traps heat.