At this stage from the alveoli carbon-dioxide comes out of the body of toad. Release of air or Expiration occurs in two steps:
(A) First step: At the first step of expiration the two lungs contract, external nasal apertures and mouth aperture remain closed and the floor of the buccal cavity is lowered. As a result volume of the buccal cavity increases and carbon-di-oxide mixed air returns to the buccal cavity.
(B) Second step: The floor of the buccal cavity is raised. The volume of buccal cavity reduce. At this time the glottis remains closed and the nasal apertures remain open. As a result through nasal apertures the carbon-dioxide enriched air comes outside.
Internal respiration: We have learnt earlier that internal respiratior basically cell respiration. In this process exchange of oxygen and carbon-dioxide takes place in the blood of capillaries. At the cellular level energy produced through oxidation of glucose.