Many organisms have evolved specialised gas exchange surfaces to maximise efficiency. One crucial feature of these structures is their large surface area to volume ratio.
Describe how the structures of mammalian alveoli and fish gills provide a large surface area for gas exchange.
mammalian alveoli:
fish gills:
The axolotl, Ambystoma mexicanum, is an aquatic amphibian that retains its branching, feathery external gills into adulthood. Most other adult amphibians lose their gills and live on land, relying on lungs and skin for gas exchange.
Suggest why the axolotl has retained external gills as an adult.
Mammals use lungs for gas exchange. The following passage describes how the gas exchange system is maintained and ventilated.
Complete the passage using the most appropriate words or phrases.
In the trachea and bronchi, cells have tiny hair-like projections called .................................... that sweep mucus and trapped pathogens upwards towards the throat. Within the alveoli, a substance called pulmonary .................................... is secreted to reduce surface tension and prevent the alveoli from collapsing. During inspiration, the volume of the chest cavity increases when both the external intercostal muscles and the .................................... contract. In contrast, resting expiration is largely a passive process that relies on the elastic .................................... of the lung tissue.
