Respiration
Gases move from areas of high concentration to areas of low
concentration. They will always try and balance out. Moving from one
area to another is called diffusion. The gases will diffuse through
structures. In this instance the structures will be the walls of the
alveoli, capillaries and muscle.
The concentration of gas within a mixture of gases is known as the
partial pressure of the gas e.g. O2 within air. As described above
gases will diffuse from areas of high partial pressure to areas of low
partial pressure.
External respiration - This refers to the exchange of gases
between the Alveoli (lungs) and the Capillaries (blood).The partial
pressure of O2 within the alveoli is high compared with the partial
pressure of O2 in the blood, which has come from the heart to be
oxygenated. The O2 diffuses across through the walls of the alveoli
and capillaries and into the blood. (see transport of O2 and CO2)
Meanwhile the partial pressure of CO2 is relatively high in the blood
compared to the partial pressure of CO2 within the alveoli.
Therefore the CO2 diffuses through the walls of the capillaries and
alveoli and into the lungs (then breathed out).
Remember that this is both O2 and CO2.
The O2 from the alveoli to the blood.
The CO2 from the blood to the alveoli.
Internal respiration – This refers to the exchange of gases
between the blood and the muscle tissue. The partial pressure of O2
in the blood is high in comparison to the partial pressure of O2
within the muscle tissue. The O2 diffuses across into the muscle
tissue from the blood, bonding with the myoglobin.
The partial pressure of CO2 is higher within the muscle tissue (as a
result of energy production) than the blood, where the Partial
pressure is low. The CO2, therefore moves from high concentration
to low, diffusing from the muscle tissue into the blood. (See O2 and
CO2 transport)
The difference between the Partial pressures of O2 and CO2 within
two areas i.e. lungs and blood is called the diffusion gradient. The
bigger the difference - the bigger the diffusion gradient.
The bigger the diffusion gradient – the more readily the gases
diffuse. (as during exercise)
The O2 from the Blood to the muscle tissue.
The CO2 from the muscle tissue to the blood.
Key words
Internal respiration
External respiration
O2 and CO2
Diffusion
Partial pressure
Diffusion gradient
Note -Questions could ask that you describe Internal or External
respiration, or both – If both, then how the O2 and CO2 was
transported between the two points of respiration could be included.