breathing and gas exchange

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Breathing and Gas Exchange
Things you must know
Describe the structure of the thorax, including the:
intercostal muscles,
alveoli and
pleural membranes
understand the role of the intercostal muscles and the diaphragm, in ventilation
Explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and
blood in capillaries.
Understand the biological consequences of smoking in relation to the lungs and the
circulatory system.
Describe a simple experiment to investigate the effect of exercise on breathing in humans.
The Purpose of Breathing
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
The rate of air flow in and out of the lungs is controlled in 2 ways:
Number of breaths per minute (breathing rate)

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The deepness of each breath (the deeper the breath, the greater the volume of air moved
per breath).
Anatomy of Lungs
Key structures
Ribs, intercostal muscles, diaphragm, lungs.
Trachea (windpipe), Bronchus (bronchi), Bronchioles, alveolus (alveoli)
Pleural membranes, pleural cavity.
The zone of the body between the neck and the bottom of the ribs is known as the
thorax. The major organs in the thorax are the heart and lungs. The lungs and
associated airways allow us to breathe.…read more

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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.
The Mechanism of Breathing
To inhale:
1. Create an area of lower pressure by enlarging the volume of the thorax.
2.…read more

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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.
Oxygen/ Carbon Nitrogen/ Water content Temperature/°C
% dioxide/% %
Inhaled 21 0.…read more

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Investigation to show how the rate of exercise affects breathing rate
Key Variables to Control
Same subjects for each exercise regime then take an average
same age
same sex
same level of fitness
same food intake
Or you could use a range of subjects BUT THEN they must all do the same exercise at
every level
Same type of exercise
Same time for exercise period
Example number of star jumps per minute (6 different rates).
Every exercise period lasting for exactly 5 minutes.…read more



This set of notes contains useful information on what you need to know, and clear explanations of the mechanism of breathing and gas exchange. Adding a line to the diagram  to show the position of the diaphragm at rest and when breathing in would be useful as this can be asked in questions.

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