Describe the structure of a single gill.

Each gill has a bony gill arch that bears two rows of thin gill filaments, and the surface of every filament is thrown into many thin plates called gill lamellae set at right angles to it.

Why is a gill filament divided into lamellae?

The lamellae multiply the surface area available for diffusion enormously, so a large quantity of oxygen can be absorbed in a small space.

How thin is the barrier between the water and the blood at a lamella?

The wall of the lamella and the wall of the capillary within it are each one cell thick, so the whole barrier is only about two cells across and gases cross it very quickly.

Describe how the water is then driven over the gills and out.

The mouth closes and the floor of the buccal cavity is raised, so the pressure inside rises and water is forced over the gill filaments, and the opercular valve opens to let it escape behind.

Eduqas A-Level Biology A400QS

Biological Molecules

Topic overview Inorganic ions and the properties of water Monosaccharides and disaccharides Polysaccharides, storage and structure Lipids, triglycerides and phospholipids Amino acids and protein structure Condensation, hydrolysis and the food tests

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Adaptations for Gas Exchange

Topic overview Surface area to volume ratio and gas exchange in small organisms Specialised respiratory surfaces and the need for ventilation Gills and counter current flow in bony fish The human breathing system and its histology Ventilation and gas exchange in humans The insect tracheal system The angiosperm leaf, stomata and gas exchange

Adaptations for Transport

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Adaptations for Gas Exchange

Gills and counter current flow in bony fish

3 things to know
Component 3

Overview

Structure of a single gill, how a bony fish draws water into its mouth and role of the operculum as a valve.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Describe how a bony fish draws water into its mouth.

Key term

Describe how a bony fish drives water over its gills and out.

Key term

Where are the gills of a bony fish, and what covers them?

Questions from this subtopic

Each one with the model answer underneath.

1
Where are the gills of a bony fish, and what covers them?
Model answer
The gills lie in a chamber on each side of the pharynx, and each chamber is covered by a bony flap called the operculum.
2
Describe the structure of a single gill.
Model answer
Each gill has a bony gill arch that bears two rows of thin gill filaments, and the surface of every filament is thrown into many thin plates called gill lamellae set at right angles to it.
3
Why is a gill filament divided into lamellae?
Model answer
The lamellae multiply the surface area available for diffusion enormously, so a large quantity of oxygen can be absorbed in a small space.
4
How thin is the barrier between the water and the blood at a lamella?
Model answer
The wall of the lamella and the wall of the capillary within it are each one cell thick, so the whole barrier is only about two cells across and gases cross it very quickly.
5
Describe how a bony fish draws water into its mouth.
Model answer
The fish opens its mouth and lowers the floor of the buccal cavity, so the volume inside increases and the pressure falls below that of the surrounding water, and water flows in.
6
Describe how the water is then driven over the gills and out.
Model answer
The mouth closes and the floor of the buccal cavity is raised, so the pressure inside rises and water is forced over the gill filaments, and the opercular valve opens to let it escape behind.

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