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Page 1

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All aerobic organisms require a constant supply of oxygen to release energy in the form of
ATP during respiration.
The carbon dioxide produced in the process needs to be removed as its build-up could be
harmful to the body.

The volume of oxygen that has to be absorbed and…

Page 2

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Part Function
- Pair of lobed structures
Lungs -
Made up of a series of branched tubules, called bronchioles
Bronchioles end in tiny air sacs call alveoli

- Flexible airway
Trachea -
Supported by rings of cartilage
Cartilage prevents the trachea collapsing as the air
pressure inside falls…

Page 3

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The Mechanism of Breathing
To maintain diffusion of gases across the alveolar epithelium, air must be constantly
moved in and out of the lungs.

We call this process breathing, or ventilation.

When the air pressure of the atmosphere is greater than the air pressure inside the
lungs, air is forced…

Page 4

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Breathing is an active process; it uses energy and occurs as follows:

The external intercostal muscles contract
The internal intercostal muscles relax

The ribs are pulled upwards and outwards
Volume of the thorax increases

The diaphragm muscles contract causing it to flatten
Volume of the thorax increases

The increased…

Page 5

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Breathing out is a largely passive process ­ it does not require much energy and occurs as

The internal intercostal muscles contract
The external intercostal muscles relax

The ribs move downwards and inwards
Volume of the thorax decreases

The diaphragm muscles relax causing it to return to its…

Page 6

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Pulmonary Ventilation
To know how much air is taken in and out of the lungs in a given time we use a measure
called pulmonary ventilation.

Pulmonary ventilation is the total volume of air that is moved into the lungs during one

To calculate it we multiply together two…

Page 7

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Exchange of Gases in the Lungs
The site of has exchange in mammals is the epithelium of the alveoli.

These alveoli are minute air sacs and are situated in the lungs.

To ensure a constant supply of oxygen to the body, a diffusion gradient must be
maintained at the alveolar…

Page 8

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Role of the Alveoli in Gas Exchange
Each alveolus is lined mostly with epithelial cells.

Around each alveolus is a network of pulmonary capillaries, so narrow that red
blood cells are flattened against the thin capillary walls in order to squeeze through.

These capillaries have walls that are only a…


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