Gas exchange and respiration
Gas exchange and respiration tests respiratory surfaces, ventilation, ATP production and the stages of aerobic and anaerobic respiration. Expect questions on lung structure, gills, tracheae, glycolysis, Krebs cycle and oxidative phosphorylation.
Gas exchange
- Mammalian alveoli have a large surface area, thin walls, surfactant and a good blood supply. Ventilation maintains concentration gradients.
- Fish gills use countercurrent flow so water and blood maintain a gradient. Insects use tracheae and spiracles; plants use stomata and lenticels.
Respiration
Glycolysis occurs in the cytoplasm and produces pyruvate, net 2 ATP and reduced NAD. The link reaction and Krebs cycle occur in the mitochondrial matrix and produce reduced NAD, reduced FAD and carbon dioxide. Oxidative phosphorylation occurs on the inner mitochondrial membrane and produces most ATP.
Worked example
Respiratory quotient (RQ) = carbon dioxide produced / oxygen consumed. For carbohydrate, RQ is about 1.0. For lipid, RQ is about 0.7 because more oxygen is used to oxidise hydrogen-rich fatty acids. An RQ of 0.85 suggests a mixture.
Traps
Glycolysis does not produce carbon dioxide. Anaerobic respiration yields only 2 ATP per glucose. ATP totals vary with shuttle and tissue, so use the value given in the question. Do not place Krebs cycle on the inner membrane.