Course Content
Biology Form 2
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Amphibians: Lungs

Frogs have a pair of lungs hanging in the cavity.

Air from the buccal cavity is received into the lungs through a structure called glottis.

It open into a larynx, which is connected to a trachea.

The trachea branches into short tubes called bronchi (sing-bronchus) which extends into each lung.

The lungs comprises of airspaces referred to as alveoli.

Adaptation of the alveoli to gaseous exchange

  • Thin lining to shorten diffusion distance.
  • Highly vascularised for faster transport of respiratory gases.
  • It is moist lining to allow diffusion of gases in solution form.
  • Numerous to increase surface area for gaseous exchange.



The nostrils open while mouth and glottis are closed.

The floor of the mouth is lowered increasing the volume of the mouth cavity while the pressure is reduced.

Air rich in oxygen enters through nostrils into the mouth cavity.

The nostrils and mouth then closes.

The floor of the mouth cavity is raised forcing open the glottis and air is forced into the lungs. Oxygen diffuses into the blood across the membranes of the alveoli and blood capillaries. Oxygen is used up in respiration and Carbon (IV) oxide is produced and diffuses out of capillaries into the alveolar space.


Occurs when nostrils are closed and air is sucked from the lungs into the mouth cavity.

The glottis closes, nostrils open while the floor of the mouth is raised forcing air out of the mouth cavity into the atmosphere through the nostrils.

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