Animal transport system - gas exchange

Question 1

Organs of gas exchange

Answer 1

The lungs are a mammal’s organ of gas exchange.

Question 2

Air entry into the lungs

Answer 2

Air enters the nose or mouth and passes through a system of tube of decreasing diameter – the trachea, bronchi and bronchioles. The larger airways are supported and held open by rings of cartilage.

Question 3

Cilia and mucus

Answer 3

The trachea and bronchi are lined with tiny hair –like cilia and cells that secrete sticky mucus. The mucus traps dirt and germs in the incoming air and the rhythmic beating of the cilia sweeps the mucus containing the dirt and micro-organisms upwards and away from the lungs.

Question 4

Alveoli

Answer 4

Air passing along the narrow bronchioles ends up in tiny air sacs called alveoli.
The alveoli are so numerous that they provide a very large surface area for gas exchange.
Each alveolus is surrounded by a dense network of blood capillaries. The lining of the alveolus is very thin, has a film of moisture on its inner wall and is in close proximity to the walls of the blood capillaries which themselves are only one cell thick.
This combination of:
• Large surface area
• Short distance
• Thin moist walls
• Good blood supply

Question 5

Gas exchange

Answer 5

Since air breathed into the alveoli contains a higher oxygen concentration than the blood arriving in the lungs, diffusion occurs.
Oxygen dissolves in the moisture on the inner surface of the thin lining of the alveolus and then diffuses into the blood in the surrounding capillaries. The blood becomes oxygenated before leaving the lungs and passing to all parts of the body.
Deoxygenated blood entering the lungs contains a higher concentration of carbon dioxide than air entering the alveoli so carbon dioxide diffuses from the blood into the alveoli from where it is exhaled.