2.2 Adaptations for gas exchange FISH Flashcards
What are the features of specialised respiratory surfaces (lungs, gills)?
Large surface areas
Moist to dissolve gases before diffusion
Mechanisms to maintain concentration gradients (eg. ventilation / circulatory systems)
Short diffusion pathways
How are fish adapted for efficient gas exchange?
Gills with multiple filaments and lamellae, = increase surface area
Countercurrent flow - water flows in opposite direction to the blood in the gills, maintaining the concentration gradient across the entire gill surface
Thin walls of capillaries in contact with water
Continuous unidirectional flow of water over gills
Describe inspiration in bony fish
Operculum (gill flap) closes
Mouth opens and buccal floor goes down
Volume increases, pressure decreases, water drawn in
Describe expiration in bony fish
Mouth closes and buccal floor raises
Volume decreases, pressure increases, water forced into operculum cavity and over gills
Why is a ventilation mechanism important in fish?
To ensure a concentration gradient is maintained at the respiratory surface (gills)
The water is pumped over gills in one direction only to maintain countercurrent flow
What is the job of the gill rakers?
To filter out debris and protect the gill filaments
What would happen to gills out of water?
They would dry out (dessicate) and clump together
Water supports the gill filaments, keeping them separate and maintaining a large surface area
The moist surface allows for dissolving of gases before diffusion
What is the benefit of countercurrent flow over parallel flow?
With parallel flow only 50% of the available oxygen is absorbed from the water due to equilibrium being reached.
In countercurrent flow, the concentration gradient is maintained, so oxygen is absorbed across the entire gill surface, due to blood always meeting water with a higher oxygen content
