Gas Exchange (Core)

Assessment Statements Obj.

6.4.1 Distinguish between ventilation, respiration and gas exchange. 2

6.4.2 Explain the need for a ventilation system. 3

6.4.3 Describe the features of alveoli that adapt them to gas exchange. 2

6.4.4 Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli. 1

6.4.5Explain the mechanism of ventilation of the lungs, in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles.

3

MrT says…I pity the fool

who thinks breathing is respiration.

Why do we need a ventilation system? We are large organisms. Oxygen cannot diffuse into all our cells directly from the air, nor can waste products be directly ejected from the body. We have specialised organ systems, which are efficient, but need delivery of nutrients and removal of waste. The ventilation system ensures the blood can be the medium for this.

We are land-borne. Gases need moist surfaces (membranes) in order to diffuse. Our lungs are moist membranes, allowingoxygen to diffuse into the blood and carbon dioxide to diffuse out.

The ventilation system maintains a large concentration gradient between the alveoli and the blood. The constant flow of past the alveoli brings blood with a high CO2 concentration and low O2 concentration. Breathing out keeps the CO2 concentration in the alveoli low, so it diffuses out of the blood. Breathing in keeps O2 concentration in the alveoli high, so it diffuses into the blood.