Ventilation and Gas Exchange in Other Organisms
Gaseous Exchange in Insects:
- Exoskeleton means no gaseous exchange can take place at surface.
- Insects don't have oxygen carrying blood pigments.
- Spiracles are small openings on the thorax of the insect through which air enters and leaves, as well as water. They can be opened (during periods of high demand for oxygen) or closed (when the insect is inactive) by sphincters to control water loss.
- Tracheae are large tubes which lead off from spiracles, carrying air into the body. They are lines with chitin to give them mechanical strength, but are impermeable so no gaseous exchange can take place.
- Tracheoles come off of tracheae branches and are single elongated cells which run between tissues. They have no chitin lining so are permeable allowing gaseous exchange. Lots of tracheoles give a large area for diffusion. Moisture in tracheoles allows oxygen to diffuse into liquid before diffusing into tissues.
- Tracheal fluid limits penetration of oxygen down tracheoles, reducing area available for diffusion, but during periods of high activity the build up of lactic acid causes tracheal fluid to move out and expose more area for gaseous exchange,
- Some insects with higher energy demands (wasps, flies, locusts, large beetles etc) have other additional methods of increasing gaseous exchange.
- Mechanical ventilation - muscular movements of the thorax actively pump air into the respiratory system.[
- Air Sacs - which act as reservoirs during times of high activity, but can be deflated.
Discontinuous Gas Exchange Cycles in Insects:
- A pattern of methods by which gas exchange is aided in insects.
- For example the spiracles have three states in discontinuous gas exchange cycles:
- Closed - no gases move in or out, oxygen only diffuses into tissues from the air within the tracheoles. Carbon Dioxide diffuses into body fluids where it is stored (buffering).
- Fluttering - spiracles open and close rapidly moving fresh air into tracheae, but minimizing water loss.
- Open - when there are high levels of carbon dioxide in the body this allows it to diffuse out rapidly. Mechanical ventilation can maximise gaseous exchange.
- There is debate as to whether this behaviour is adaptive or evolved.
- Fish get their oxygen from water which is 1000x denser, 100x more viscous and has a much lower oxygen content than air, so have evolved different respiratory systems.
- Fish are often very active, so have a high demand for oxygen from respiring tissues.
- Most fish have a SA:V too poor for diffusion alone to be an effective method of getting oxygen, and their scaly outer covering means no gaseous exchange can happen at the surface.
- Gills are fish organs for gaseous exchange. Water flows over the gills and oxygen diffuses in.
- They have a large surface area so there is lots of space for exchange to occur.
- They have a good blood supply to take oxygen away and maintain a concentration gradient.
- They are very thin, so oxygen doesn't have to diffuse very far so diffusion occurs quickly.
- Because water is too dense to be pumped in and out, a constant flow of water is required over the gills either by ram ventilation (constant movement) or buccal pumping (opening and closing of the operculum and changing of pressure in the buccal cavity causing water to move in and out).
Effective Gaseous Exchange in Water:
- Large SA:V ratio (as above)
- Good blood supply (as above)
- Thin layers (as above)
- Overlapping gill filaments - this increases water resistance allowing more time for diffusion.
- Countercurrent flow - by moving the blood flow and water flow in opposite directions a steeper concentration gradient is set up, and equilibrium is never reached, allowing for more oxygen to be removed from water.
Dissection:
- Gives you a unique insight into the complexity of a living organism.
- It can be confusing, because most body systems do not exist in isolation.
- You need chopping boards, scalpels, scissors, tweezers and pins to display your dissection.
- In dissection you aim to be as precise and clean as possible, and your observations should be resented in a well labelled diagram.
- Some aspects of the respiratory system can not be seen with the human eye, instead microscopy must be used to observe detailed adaptations of exchange surfaces,
- E.g. Delicate air sacs that make up the surface area of alveoli can only be seen in light micrographs.
- E.g. Chitin rings of support in tracheae can only be seen in light micrographs.
- E.g. Gill structure of individual lamellae can only be seen in light micrograph.