Organisms Exchange Substances with their Environment: Gas Exchange - Humans (Alveoli)

Question 1

Describe movement of oxygen and carbon dioxide through the gas exchange system

Answer 1

• Air moves down trachea, bronchi, bronchioles and into alveoli
• Oxygen moves into blood and is transported around body
• Carbon dioxide moves down its own diffusion and pressure gradients in opposite direction to oxygen

Question 2

Describe gas exchange in the alveoli

Answer 2

• Oxygen diffuses out of alveoli, across alveolar squamous epithelium and capillary endothelium
• Oxygen moves into haemoglobin
• Carbon dioxide diffuses into alveoli from blood

Question 3

Describe how alveoli are adapted to exchange gases efficiently

Answer 3

• Alveolar epithelium is one cell thick
- Short diffusion pathway

• There are millions of alveoli
- Large surface area

• Constant blood supply
- Maintains steep concentration gradient

Question 4

Describe how blood capillaries are adapted to exchange gases efficiently

Answer 4

• Pulmonary capillary wall endothelium is one cell thick
- Short diffusion pathway

• Constant blood circulation
- Maintains steep concentration gradient

• Capillary lumen is smaller than RBC diameter
- Slows movement of RBC, allowing time for diffusion