Gaseous Exchange – S3 Biology Notes

These Senior 3 Biology notes cover gaseous exchange. They start by explaining how gaseous exchange differs from ventilation and why organisms need it. They then describe the factors that affect how fast gases diffuse, the features of respiratory surfaces, and how air and water compare as exchange media. The notes show how gases are exchanged in amoeba, insects, bony fish, amphibians and humans. Topics include tracheal ventilation, the structure of gills and countercurrent flow, breathing through the skin, mouth lining and lungs, and the human breathing system and how breathing works. They also describe a bell-jar model of the lungs and exchange at the alveolus. Exam-style questions with marks are included throughout.