Breathing and gas exchange

 Breathing

This topic is taught at Key stage 3, IGCSE and A level biology
Breathing is a series of muscle movements that allow ventilation to occur. Ventilation is the movement of air into and out of the lungs. Air moves in and out of the lungs due to pressure differences. These pressure differences are caused by muscle movements.
air1
This video will guide you through the process of inhalation and exhalation.
This video is supplied by Alila Medical media. Click on the link to see more breathing videos.

Gas Exchange

Once the air is inside the alveoli of the lungs gas exchange needs to occur.
The alveoli have several adaptations that make them efficient at gas exchange:
1. Large surface area
2. Thin walls (OCR-short diffusion distance, AQA-Short diffusion pathway)
3. Good blood supply to take away the oxygenated blood. This helps to maintain the concentration gradient so that the blood around the alveolus always has a lower concentration of oxygen. This means that oxygen will always diffuse from the alveolus into the blood.
4. Ventilation ensures that the air in the alveoli is replenished. This maintains the concentration gradient always making sure that the air in the alveoli has a high oxygen concentration and that it has a low carbon dioxide concentration.
Below is a diagram of the alveolus and is shows how the gas exchange occurs.
Structure of an alveolus
Image supplied by Alila Medical media. Click on the link to see more images of the respiratory system.