I/GCSE Biology - Breathing and Gas Exchange

In I/GCSE Biology, you should have clear concept of breathing and gas exchange. Let's get started!

a) To remove carbon dioxide from the body into the air outside.

• This carbon dioxide is generated from respiration. The greater the rate of respiration, the more carbon dioxide is generated so the faster the rate of breathing.

b) To move oxygen into the body from the air outside.

• The greater the rate of AEROBIC respiration, the higher the demand for oxygen

Do you remember the control of the rate of air flow in I/GCSE Biology?

The rate of air flow in and out of the lungs is controlled in 2 ways:

• Number of breaths per minute (breathing rate)
• The deepness of each breath (the deeper the breath, the greater the volume of air moved per breath).

Key structures

• Ribs, intercostal muscles, diaphragm, lungs.
• Trachea (windpipe), Bronchus (bronchi), Bronchioles, alveolus (alveoli)
• Pleural membranes, pleural cavity.
• Look at the schematic diagram of lungs and thorax below!

As shown in the diagram above,

• Larynx - speech and sound generation.
• Trachea or windpipe – carries air from the throat to the bronchi.
• Two tubes that are each known as a bronchus, plural bronchi – carry air into the bronchioles within the lungs.
• Bronchioles which are subdivisions of each bronchus.
• Alveoli which are sacs at the end of the airways, the sites of gas exchange.
• Pleural membranes – attached to inside wall of the thorax and the lungs and prevent friction as the lungs expand and contract.

In I/GCSE Biology, understanding the mechanism of breathing is crucial!

To inhale:

1. Create an area of lower pressure by enlarging the volume of the thorax.
2. Do this by CONTRACTING intercostal muscles (which moves the ribs up and out) and the diaphragm, which flattens from its relaxed domed shape.
3. Air will then rush in until the inside pressure is equal to the outside pressure.

To exhale:

1. Create an area of higher pressure inside the thorax by reducing the volume of the thorax.
2. Do this by RELAXING intercostal muscles (so ribs move down and in) and the diaphragm which resumes its domed shape.
3. The air inside will move out until the pressure inside is equal to the pressure outside.

Do you remember what alveolus is in I/GCSE Biology?

At the end of each bronchiole is an ALVEOLUS. These are adapted for their function:

• Very thin walled for fast diffusion into and out of the alveolus
• A very large surface area (the inside of each is folded to increase its surface area) which speeds up diffusion of gases.
• Rich blood capillary network for rapid gas exchange
• The inside surface is moist so that the gases dissolve . They can then diffuse across the membrane

References:

1. "2.44: Describe the Structure of the Thorax, Including the Ribs, Intercostal Muscles, Diaphragm, Trachea, Bronchi, Bronchioles, Alveoli and Pleural Membrane", https://lh5.googleusercontent.com/eHTOYd05iSC5Jwn1bWaBLPjr9dOJ147e3Q4-9z64R-XofiCfldODoTs5i2UhdZ_G-wpSRzwBzt7wIusAds7hvJJB9N29UJSsgyUWwp3TjZ56o8UM_p29iEyiWxeYraQ7O1hQy4xg
2. "Human respiratory system - The mechanics of breathing", https://cdn.britannica.com/36/92936-004-8881E781/diaphragm-air-paralysis-lungs-breathing-muscles-lung.jpg
3. "Why Is The Composition Of Inhaled And Exhaled Air Different", https://image.slidesharecdn.com/respiration-140724233645-phpapp01/95/respiration-igcse-15-638.jpg?cb=1502970390

And we're done with this topic! Well Done!

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Drafted by Alyssa (Biology)