Distinguish between ventilation, gas exchange and cell respiration.

Outline the process of aerobic respiration.

Respiration and other processes in cells involve enzymes. Explain the factors that can affect enzymes.

ventilation is moving air into and out of lungs/inhalation and exhalation;
involves (respiratory) muscle activity;
gas exchange involves movement of carbon dioxide and oxygen;
between alveoli and blood (in capillaries) / between blood (in capillaries) and cells;
cell respiration is the release of energy from organic molecules/glucose;
(aerobic) cell respiration occurs in mitochondria;
To award [4 max] responses must address ventilation, gas exchange and cell respiration.

during glycolysis glucose is partially oxidized in the cytoplasm;
(small amount/yield of) ATP produced;
(two) pyruvate formed by glycolysis;
pyruvate absorbed into/broken down in the mitochondrion;
requires oxygen;
carbon dioxide is produced;
water is produced;
large amount/yield of energy/ATP molecules (per glucose molecule);

collisions between enzyme/active site and substrate;
enzyme activity increases as temperature rises;
more frequent collisions at higher temperatures;
each enzyme has an optimum temperature / enzymes have optimal temperatures;
high temperatures (above optimum) denature enzymes;
each enzyme has an optimum pH / enzymes have optimal pHs;
increase or decrease from optimum pH decreases rate of reaction/activity;
extreme pH alters/denatures the tertiary/3D protein/enzyme structure;
increasing substrate concentration increases the rate of reaction;
higher substrate concentration increases chance of collision;
until plateau;
when all active sites are busy;
Accept clearly annotated graph.

As candidates distinguished between ventilation, gas exchange and cell respiration (A.S. 6.4.1), certain ideas keep reappearing and others were infrequently expressed. Among the former were inhalation and exhalation; movement of carbon dioxide and oxygen; and release of energy from organic molecules. Less common were involvement of muscle activity for ventilation; exchange between alveoli and blood or between blood and cells; and that cell respiration occurs in mitochondria. “Ventilation is moving air into the lungs” was not enough for a mark, nor was “cell respiration is release of energy from food” which was too general.

With this question on aerobic respiration (A.S. 3.7.2, 3.7.3), many candidates easily earned four of the six available marks. These were that aerobic respiration requires oxygen, produces carbon dioxide, produces water and produces a large yield of energy/ATP. Additional marks were earned with commentary on glycolysis, since it produces the pyruvates that are eventually broken down aerobically. 

Factors that affect enzyme activity (A.S. 3.6.1-3.6.4) is another topic that has appeared repeatedly on past IB exams. Furthermore, the topic is often visited during IA investigations. Details on how changes in temperature and pH affect enzyme activity formed the heart of most answers. Denaturation of enzyme structure that alters the active site was usually included in those answers. The effect of substrate concentration on enzyme activity was less common. Higher quality answers mentioned collisions between enzyme and substrate and linked enzyme activity to the frequency of collisions at different temperatures or substrate concentrations. Many written passages were supported with annotated graphs that also earned marks. However, some candidates confused the graph for enzyme activity vs temperature with the graph of enzyme activity vs. substrate concentration. They show a plateau in the temperature curve and declared that the plateau represented denaturation of the enzyme at that temperature.