Define:
Gas Exchange
Process of absorbing one gas from the environment and releasing another.
☆ All organisms do it.
☆ Large SA and shortened distance (to diffuse across) are needed for effective gas exchange.
Define:
Diffusion
(Net) Flow of matter from a region of high concentration to a region of low concentration.
☆ Molecules move randomly, therefore diffusion is a relatively slow process.
How Does Diffusion in Small Organisms Occur?
Small Organisms have:
* Large SA to V Ratio
* Small Internal Distance
Therefore, Gas Exchange is via Outer Surface.
How Does Diffusion in Large Organisms Occur?
Large Organisms have:
* Small SA to V Ratio
* Large Internal Distance
Therefore, Gas Exchange via Specialized Gas-Exchange Surfaces.
List:
Gas-Exchange Surface Properties
- Permeable: O and CO2 can diffuse across easily.
- Large: Total SA is large in relation to the V of the organism.
- Moist: Covered by film of moisture (in terrestrial organisms) so gases can dissolve.
- Thin: Shortened distance, mostly one-cell thick.
Define:
Concentration Gradient
Gradual change in concentration of a substance within a particular region.
☆ Needed for diffusion.
How Does Diffusion Affect Concentration Gradients?
Diffusion evens out concentration gradients, which could slow and then stop gas exchange. Therefore, concentration gradients must be maintained.
Describe:
Diffusion in Alveoli
- O diffuses from air in the alveoli to the adjacent capillaries because the O concentration of blood in the capillaries is lower than in air.
- CO2 diffuses from the blood to air in the alveoli because the CO2 concentration is lower in air.
For small, aerobically respiring organisms that use their outer surface for gas exchange:
Cell respiration maintains concentration gradients, as it continually uses O and produces CO2.
For large organisms such as fish or mammals:
Blood flows continuously through dense capillary networks in organs specialized for gas exchange. Aerobic respiration causes the blood to have a low O concentration and high CO2 concentration.
Define:
Ventilation
Movement of air in and out of lungs; Movement of water across gills.
☆ Maintains concentration gradients.
Describe:
Ventilation in Mammals
Periodically expel air from alveoli by exhaling, then replace it by inhaling air. As a result:
* Prevents O concentration from dropping too low for diffusion from air to blood.
* Prevents CO2 concentration from rising too high for diffusion from blood to air.
☆ Rate of ventilation adjusted according to CO2 concentration of blood.
Describe:
Air Travel in Lungs
Trachea → Bronchus → Bronchiole → Alveolar Duct → Alveoli
