3.1.1f Gas Exchange in Fish Flashcards
Difficulties of animals that get their oxygen from water PART 1
Animals that get their oxygen from water do not need to try & prevent water loss from their gaseous exchange surfaces as land animals do, but there are other difficulties to overcome:
Difficulties of animals that get their oxygen from water PART 2
- Water is 1000x denser than air. It is 100x more viscous & has a much lower oxygen content. To cope w the viscosity & slow rate of oxygen diffusion, fish have evolved specialised respiratory systems that are different from those of land animals
Difficulties of animals that get their oxygen from water PART 3
It would use up far too much energy to move dense, viscous water in and out of respiratory organs. Moving water in one direction only is much simpler & more economical in energy terms
Size significance of bony fish
- Bony fish (trout & cod) are relatively big, active animals, that live almost exclusively in water.
- Bc 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, & their scaly outer covering doesnt allow gaseous exchange
How have bony fish evolved fro effective gaseous exchange
Bony fish have evolved a ventilatory system adapted to take oxygen from the water & get rid of CO2 into the water. They maintain a flow of water in one direction over the GILLS
What are gills
The organs of gaseous exchange in fish
What makes gills an effective gaseous exchange surface
- Large SA: more area for oxygen & CO2 to diffuse across
- Good blood supply: O2 is delivered & removed efficiently, providing a steep concentration gradient
- Thin layer or cells: short diffusion distance
- Close proximity of capillaries to the exchange surface: short diffusion distance
Location and surroundings of gills
In bony fish, gills are contained in a gill cavity & covered by a protective operculum (a bony flap), which is also active in maintaining a flow of water over the gills
see images ss for diagram of fish head + gills
16th nov
What are the gill lamellae
With their rich blood supply & large SA, are the Ian site of gaseous exchange in fish
What are gill filaments
Occur in large stacks (gill plates) & need a flow of water to keep them apart, exposing the large SA needed for gaseous exchange
What do fish need to maintain to allow efficient gas exchange at all times + difficulties
- Fish need to maintain a continuous flow of water over the gills, even when they are not moving
+ They need to carry out gaseous exchange as effectively as possible in water, a medium where diffusion is slower than in air
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 & operculum.
- However, when the fish stops moving, the flow of water can also stop.
What is ram ventilation
The more primitive cartilaginous fish (sharks & rays) often rely on continual movement to ventilate the gills. This is know as ram ventilation - they just ram the water past the gills
How do bony fish deal with difficulties moving water over their gills at all times
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 (opening and closing mouth)
