LGS A-Level OCR Biology - Unit 3 - Mammalian Gas Exchange and Ventilation
It is not possible to expel all air from the lungs because the thorax cannot be completely flattened, leaving some air trapped inside. In addition, the trachea and bronchi are supported by cartilage, which prevents them from collapsing fully during exhalation.
Why is it not possible to expel all air from the lungs?
thorax cannot be completely flattened
- trachea/bronchi held open by cartilage
Key Terms
Why is it not possible to expel all air from the lungs?
thorax cannot be completely flattened
- trachea/bronchi held open by cartilage
Why are specialised exchange surfaces are needed by some organisms?
they have a low SA:V so exchange surfaces increase that
maximise efficiency of diffusion
ensure the demand for oxygen and glucose is me...
What are the 4 features of efficient exchange surfaces?
Increased surface area
Thin layers
Good blood supply
Ventilation to maintain a diffusion gradient
Why does an increased surface area make an exchange surface efficient?
Provides the area needed for exchange overcomes limitations of low SA:V ratio
Why do thin layers make an exchange surface efficient?
the distances that substances have to diffuse across is short making it fast and efficient
Why does a good supply make an exchange surface efficient?
the greater the difference in concentration the greater the rate of diffusion. A good supply means substances are constantly being delivered and re...
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| Term | Definition |
|---|---|
Why is it not possible to expel all air from the lungs? | thorax cannot be completely flattened - trachea/bronchi held open by cartilage |
Why are specialised exchange surfaces are needed by some organisms? | they have a low SA:V so exchange surfaces increase that maximise efficiency of diffusion ensure the demand for oxygen and glucose is met |
What are the 4 features of efficient exchange surfaces? | Increased surface area Thin layers Good blood supply Ventilation to maintain a diffusion gradient |
Why does an increased surface area make an exchange surface efficient? | Provides the area needed for exchange overcomes limitations of low SA:V ratio |
Why do thin layers make an exchange surface efficient? | the distances that substances have to diffuse across is short making it fast and efficient |
Why does a good supply make an exchange surface efficient? | the greater the difference in concentration the greater the rate of diffusion. A good supply means substances are constantly being delivered and removed, maintaining the steep concentration gradient |
Why does ventilation make an exchange surface efficient? | For gases ventilation helps to maintain concentration gradients |
How is the nasal cavity adapted for the gas exchange system? | good blood supply warms air to body temperature cells secrete muscus to trap dust and bacteria to protect lung tissue moist surfaces reduce evaporation from the exchange surfaces which increase humidity |
How is the trachea adapted for the gas exchange system? | supported by incomplete rings of strong, flexible cartilage to allow for movement and prevent the trachea from collapsing lined with ciliated epithelium and goblet cells |
What is the function of goblet cells? | Secrete mucus which traps dust and microogranisms |
What is the function of ciliated epithelial cells? | Cilia beat and move mucus away from the lungs, protecting them |
How are the bronchi adapted for the gas exchange system? | -supported by small rings of cartilage |
How are bronchioles adapted for the gas exchange system? | contain no cartilage contain smooth muscle smooth muscle contracts when bronchioles constrict and relaxes when they dilate |
How are the alveoli adapted for the gas exchange system? | very thin walls contain elastic fibres which allow alveoli to stretch as air is drawn n and when they return to size help squeeze air out good capillary blood supply coated in surfactant |
What is breathing? | The movement of air in and out of the lungs |
What is gas exchange? | the delivery of oxygen from the lungs to the bloodstream and the elimination of carbon dioxide from the blood stream |
Outline the steps in inspiration | diaphragm flattens and contracts external intercostal muscles contract making the ribs move up and out this increases the volume of the thorax so reduces pressure pressure is more negative than the atmosphere air air is drawn into the lungs to equalise the pressures inside and outside the chest |
Outline the steps in normal expiration | diaphragm relaxes and curves upwards external intercostal muscles relax so ribs move in decreases volume of the thorax pressure in the lungs is less negative than atmospheric air air moves out of the lungs until pressure inside and out is equal |
Outline the steps in forced expiration | abdominal muscles contract, pushing diaphragm upward quickly making lung pressure less negative internal intercostal muscles contract pulling ribs down hard and fast |
What is inspiration? | the movement of air into the lungs |
What is expiration? | the movement of air out of the lungs |
Does inspiration require energy? | Yes |
Does expiration require energy? | No, it is a passive process |
What are the 3 ways lung capacity can be measured? | peak flow metre vitalographs spirometer |