GCSE Biology Revision "Gas Exchange in the Lungs"

Gas Exchange in the Lungs

Overview of the Respiratory System

• Blood is pumped from the heart to the lungs to collect oxygen.

• Oxygen is then delivered to body cells by the circulatory system.

Structure of the Lungs

• Humans have two lungs.

• Air enters through the tube ‘trachea’ which contains rings of cartilage to prevent collapse of trachea during inhalation.

• The trachea splits into bronchi, which further divide into bronchioles.

• The bronchioles end in tiny air sacs called alveoli where gas exchange occurs.

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Alveoli and Gas Exchange

• Alveoli are microscopic structures that allow the exchange of gases. Where gases diffuse in and out of the bloodstream(sites of gas exchange)

• Gas Exchange Process:

  • Oxygen diffuses from the air into the bloodstream.

  • Carbon dioxide diffuses from the bloodstream back into the air.

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Adaptations of Alveoli for Gas Exchange

1. Large Surface Area

• Millions of alveoli provide a huge surface area for gas exchange.

2. Thin Walls

• Alveoli have very thin walls, making a short diffusion path for gases.

3. Good Blood Supply

• Once the oxygen diffuses into the blood, it's rapidly removed. ensuring that oxygen is rapidly transported away after diffusion.

• This maintains a steep concentration gradient for efficient gas exchange.

4. Role of Breathing

• Breathing helps increase the rate of diffusion by:

  • Bringing fresh oxygen into the alveoli.

  • Removing carbon dioxide.

• This action sustains high concentration gradients for both gases, increasing rate of diffusion.