▪️Surface tension is the force by which molecules on the surface are held in position. ▪️Organic substances decrease surface tension. ▪️ while Inorganic substances increase it . ▪️ Example:- *Bile salts reduce ST by emulsifying lipids this aiding in their digestion and absorption. *A phospholipid (Dipalmitoyl lecithin) is responsible for maintaining low ST in lung alveoli keeping them patent .This enables efficient exchange of oxygen and carbon dioxide in the lungs .It's deficiency results in respiratory distress syndrome in preterm babies .