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In this topic of IBDP Biology, we will learn about gas exchange in fish.
Gas exchange in fish
- There is very little dissolved oxygen in the water.
- Air contains 30 times more.
- Oxygen concentration in water decreases further with increasing temperature.
Gill structure
When it comes to IBDP Biology,
- 4 gill arches either side of head.
- Separate buccal and opercular cavities.
- Each arch has 2 rows of filaments in a V shape.
- Each filament is flattened with an upper and lower row of lamellae (gill plates).
- Lamellae are covered in a thin layer of epithelial cells .
- Lamellae are in close contact with those of neighbouring filaments.
- Excellent blood supply.
- The tips of the filaments overlap.
- Whole thing forms a sieve like structure.
- This provides resistance to flow of water.
- This increases time for gaseous exchange.
- Gill slits are the spaces between gill arches.
- Approx. 0.05mm wide.
- Operculum is the bony flap that covers gills in the opercular cavity.
- This protects gills and moves to aid ventilation
The counter-current mechanism
- When it comes to IBDP Biology, a countercurrent system occurs when two substances flow through the same body part in opposite directions.
- Blood in lamellae flows in opposite direction to water.
- Blood always meets water with a relatively higher concentration of dissolved oxygen.
- This maintains the concentration gradient between the blood and water for the whole length of the lamellae.
- 80% of oxygen in water can be extracted.
Water flow pathway
When it comes to IBDP Biology,
- Some fish achieve this by swimming forwards with mouth open.
- Slow swimmers or fish in still water use pumping system to move water.
- Coordinated activity of both chambers ensures continuous flow of water.
This is the end of this topic
