Gas Exhange In Other Organisms 7.4 Flashcards
Why do insects need gas exchange?
They are very active so have high metabolic demand, however, no gas exchange happens on their tough exoskeleton and they don’t have blood that carries their oxygen so they use gas exchange in a different way.
How does gas enter an insect?
There are openings in the abdomen of the insect called spiracles. They allow air to enter but also can lose water so they have sphincters controlling the openings of the spiracles. When the metabolic activity is low, the spiracles close so there isn’t a lot of oxygen intake. When the metabolic activity increases, the spiracles will open and allow gas exchange.
Trachea
These are the biggest airways in the insect and lead the air away from the spiracles. They are lined with chitin which makes them strong and keeps them open if they are bent, and impermeable to gases, so no gas exchange can occur on them
Tracheoles
These are the tiny tubes that come off the trachea. They don’t have chitin so gas exchange occurs here and it is only one cell long and spreads out around the tissues of the bug.
How does the gas move around in the insect?
It moves by diffusion and the oxygen will dissolve in the moisture on the tracheoles. There is also tracheal fluid which stops diffusion. When the metabolic demand is high, lactic acid builds up in tissues and the moisture will take the oxygen in by osmosis, which also makes more surface area.
What do insects with really high metabolic demands do?
They can have an adapted gas exchange system like mechanical ventilation where the air is actively pumped into the spiracles or the trachea can be collapsible and act as air reserves.
What are the troubles for aquatic animals?
They get their oxygen from water which is far too dense and viscous and doesn’t have a high oxygen content for it to be the same as the land animal gas exchange system. Instead, they have gills.
Gills
They are the gas exchange organs in fish. They use the flow of water in one direction as a way for them to take in oxygen and release CO2. They have a good blood supply, big surface area and are thin so are specialised for gas exchange.
The anatomy of the fish gill
The gills are covered by a protective bony flap called the operculum. There are gill filaments which are stacked on top of each other and allow the flow of water to keep them apart for increased SA. There are also gill lamellae which are the main site of gas exchange.
Water flow over gills
There has to be a continuous movement of water over the gills at all times so fish have adapted to keep their mouth and their operculum open. Other aquatic animals like shark rely on continuous movement which is called ram ventilation as that is the only way to keep water flowing over their gills.
How fish breathe
Their mouth is open and the floor of the buccal cavity lowers. This decreases the pressure in the buccal cavity so water moves in. The opercular valve is still closed and the opercular cavity with the gills will expand. This lowers the pressure in the opercular cavity so the operculum will open and water will flow in and over the gills. The mouth will close and the sides of the opercular cavity will move inwards which increases the pressure inside, making the water move out.
Two adaptations of gills
Their filaments overlap which increases the resistance to the flow of water and slows it down so more gas exchange can take place.
The water moving over the gills and the blood moving through the gill filaments are going in opposite directions which is called the countercurrent system so will increase the concentration gradient and diffusion.
