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 prevent water loss from their gaseous exchange surfaces as land animals do, but there are other difficulties to overcome:
- Water is 1000x denser than air
- 100x more viscous
- & has a much lower oxygen content.
To cope w the slow rate of oxygen diffusion, fish have evolved specialised respiratory systems that are different from those of land animals
- 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
- Gill filaments are covered in lots of tiny gill lamellae
- Increases the SA even more.
- Have lots of blood capillaries & a thin surface layer of cells to speed up diffusion
What are gill filaments
- Each gill is made of lots of thin branches called gill filaments, which give a large SA for gaseous exchange
- 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)
How are fish ventilated
By OPENING & CLOSING their mouths
Ventilation in fish: What happens when bony fish OPEN their mouth
- The mouth is opened & the floor of the buccal cavity is lowered
- This increases the volume of the buccal cavity. As a result, this decreases the pressure in the cavity & water moves into the buccal cavity.
- At the same time, the opercular valve is shut & the opercular cavity containing the gills expand.
- This lowers the pressure in the opercular cavity containing the gills. The floor of the buccal cavity starts to move up, increasing the pressure there so water moves from the buccal cavity over the gills
Ventilation in fish: What happens when bony fish CLOSE their mouth
- The mouth closes, the operculum opens & the sides of the opercular cavity move inwards.
- All of these actions increase the pressure in the opercular cavity & force water over the gills & out of the operculum.
- The floor of the buccal cavity is steadily moved up, maintaining a flow of water over the gills.
Features of gills that make it effective for gaseous exchange in water
- Have a large SA for diffusion
- Rich blood supply to maintain steep concentration gradients for diffusion
- Thin layers so that diffusing substances have only short distances to travel
2 extra adaptations of gills that help to ensure the most effective gaseous exchange possible in water
- The tips of adjacent gill filaments overlap
- The water moving over the gills & the blood in the gill filaments flow in different directions
2 extra adaptations of gills that help to ensure the most effective gaseous exchange possible in water: the tips of adjacent gill filaments overlap
- This increases the resistance to the flow of water over the gill surfaces & slows down the movement of the water. As a result, there is more time for gaseous exchange to take place
2 extra adaptations of gills that help to ensure the most effective gaseous exchange possible in water: the water moving over the gills & the blood in the gill filaments flow in different directions
- A steep concentration gradient is needed for fast, efficient diffusion.
- Bc the blood & water flow in opposite directions, a countercurrent exchange system is set up. This adaptation ensures that steeper concentration gradients are maintained than if blood & 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, extract 80% of the oxygen from the water flowing over them. The cartilaginous fish have parallel systems & can only extract 50%)
Explain the parallel system
- Blood in the gills & water flowing over the gills travel in the same direction, creating a STEEP BUT INCONSISTENT oxygen concentration gradient between blood & water.
- Diffusion takes place until the oxygen concentration gradient of the blood & water are in equilibrium, then no net movement of oxygen into the blood occurs
Explain the countercurrent system
- Blood & water flow in opposite directions so a SHALLOW BUT CONSISTENT oxygen concentration gradient between the water & the blood is maintained all along the gill.
- The concentration of oxygen in the water is always higher than that in the blood, so a much higher level of oxygen saturation of the blood is achieved
Another advantage of the countercurrent system
Also enables bony fish to remove more CO2 from the blood than a parallel system
see diagram of parallel & countercurrent systems in images ss
16th nov, pg76
Dissecting an animal gives you a unique insight into the…
…complexity of a multicellular living organism.
The process of evolution over millions of yrs has resulted in internal systems of great efficiency & elegance
Specialist equipment for dissecting an animal
- boards & pins, with which to display dissection
- sharp scissors
- scalpels
- tweezers
- mounted needles, to lift & tease out tissues
Using microscopes to view adaptations of exchange surfaces
Key features of exchange surfaces - the large SA, short diffusion distances, proximity of blood supply - cannot be seen when looking at whole organ system
Using prepared slides w the light microscope can give you insight into the detailed adaptations of these surfaces for their roles in gas exchange
see images for examples of uses of microscopes to view exchange surfaces (be able to identify them)
16th nov
Vessels in fish carries
oxygenated blood from the gill
Artery in fish carries
deoxygenated blood to the gill
see diagrams of gill filaments/lamellae on pg76
