Chapter 7 p 4 Flashcards
Respiratory systems in bony fish
- Animals that get their oxygen from water do not need to try and prevent water loss from their gaseous exchange surfaces as land animals do, but there are other difficulties to overcome.
- Water is 1000 times denser than air.
- It is 100 times more viscous (thick) and has a much lower oxygen content.
- To cope with the viscosity of water and the slow rate of oxygen diffusion, fish have evolved very specialised respiratory systems that are different from those of land-dwelling animals.
- It would use up far too much energy to move dense, viscous water in and out of lung-like respiratory organs.
- Moving water in one direction only is much simpler and more economical in energy terms.
Bony Fish
Bony fish such as trout and cod are relatively big, active animals that live almost exclusively in water.
Because they are very active, their cells have a high oxygen demand.
Their SA: V ratio means that diffusion would not be enough to supply their inner cells with the oxygen they need, and their scaly outer covering does not allow gaseous exchange.
Gill Ventilation in Bony Fish:
bony fish have evolved a ventilatory system adapted to take oxygen from the water and get rid of carbon dioxide into the water.
They maintain a flow of water in one direction over the gills, which are their organs of gaseous exchange.
Gills have the large surface area, good blood supply, and thin layers needed for successful gaseous exchange.
In bony fish they are contained in a gill cavity and covered by a protective operculum (a bony flap), which is also active in maintaining a flow of water over the gills
Challenges of Gaseous Exchange in Water:
The gills make up the gaseous exchange surface of the fish.
They have many features in common with both mammalian and insect gaseous exchange surfaces.
However, they also have particular challenges. To allow efficient gas exchange at all times, fish need to maintain a continuous flow of water over the gills, even when they are not moving.
They also need to carry out gaseous exchange as effectively as possible in water, a medium where diffusion is slower than in air.
diagram of Gill Ventilation in Bony Fish
Water flow over the gills
When fish are swimming they can keep a current of water flowing over their gills simply by opening their mouth and operculum.
However, when the fish stops moving, the flow of water also stops.
The more primitive cartilaginous fish such as the sharks and rays often rely on continual movement to ventilate the gills.
This is known as ram ventilation - they just ram the water past the gills.
However, most bony fish do not rely on movement-generated water flow over the gills; They have evolved a sophisticated system involving the operculum, which allows them to move water over their gills all the time
diagram Water flow over the gills
gills
Gills have a large surface area for diffusion, a rich blood supply to maintain steep concentration gradients for diffusion, and thin layers so that diffusing substances have only short distances to travel.
Gills have two extra adaptations that help to ensure the most effective possible gaseous exchange occurs in the water
Two extra adaptations of gills:
The tips of adjacent gill filaments overlap.
The water moving over the gills and the blood in the gill filaments flow in different directions.
The tips of adjacent gill filaments overlap.
This increases the resistance to the flow of water over the gill surfaces and slows down the movement of the water.
As a result there is more time for gaseous exchange to take place.
The water moving over the gills and the blood in the gill filaments flow in different directions.
- A steep concentration gradient is needed for fast, efficient diffusion to take place.
- Because the blood and water flow in opposite directions, a countercurrent exchange system is set up.
- This adaptation ensures that steeper concentration gradients are maintained than if blood and water flowed in the same direction (known as a parallel system).
- As a result, more gaseous exchange can take place.
- The bony fish, with their countercurrent systems, remove about 80% of the oxygen from the water flowing over them.
- The cartilaginous fish have parallel systems and can only extract about 50% of the oxygen from the water flowing over them
diagram of countercurrent system
Dissecting, examining, and drawing gaseous exchange systems:
You cannot see the gas exchange system, for example, without getting through the body wall.
You will need specialist equipment including boards and pins with which to display your dissection.
The tools needed for successful dissections include sharp scissors and scalpels along with tweezers and mounted needles to lift and tease out tissues.
When you carry out a dissection the aim is to be as precise and clean in your work as possible.
You should observe and display the relevant features of an organism to the best of your ability, and then record what you have seen in a clear and well-labelled diagram.
It may be useful to take a photograph of your dissection and so preserve what it actually looked like alongside your labelled diagram.
In Figure 3 and Figure 6 you can see examples of dissections of the gas exchange system of an insect and the gas exchange system of a bony fish.
Drawings from dissections are always done in pencil - suggest why.
Easy to make alterations and corrections (1); won’t run if it gets damp/splashed
