3. Fish and insect gas exchange Flashcards
To reduce water loss 3pts
Waterproof coverings
A smallish surface area to volume ratio
Spiracles closed most of time
Tracheae and Tracheoles
Insects have an internal network of tubes. The tracheae are strengthened by rings to stop them collapsing. The tracheae divide into smaller tubes called tracheoles. These extend through the whole of the insects body and bring the oxygen into contact with the respiring tissues.
Spiracles
Spiracles are tiny pores on the body surface which connect the tubes with the atmosphere
Spiracle can be opened or closed by a valve
When the spiracles are open the insect is in danger of losing too much water, therefore it will close its spiracles periodically.
Movement of gases in and out of the tracheal system
Along the diffusion gradient- As cells are respiring oxygen is used up. This creates a low concentration of oxygen in the cells. As carbon dioxide is produced this has a high concentration in the cells. Diffusion gradients are set up and as diffusion is more rapid in air than water gases can be exchanged efficiently
Ventilation mechanism- As the muscles contract, mass movement of air in and out of the tracheae takes place.
Summary
Internal network of trachea, strengthened to prevent collapse
Tracheoles permeate through body so there is a short diffusion pathway to cells as they need to reach respiring cells
Gradient maintained by the cells using oxygen and creating carbon dioxide by respiration – these gases diffuse into tracheoles in opposite direction down a diffusion gradient
Gas exchange in Insects
As insects are terrestrial they have to balance their gas exchange needs with reducing water loss. They have developed
Waterproof coverings
A smallish surface area to volume ratio
Insects can not obtain their gases by simple diffusion. They have developed a system of TRACHEAL TUBES to aid gas exchange.
Insects have developed a system of tracheole tubes to aid gas exchange.
They also have waterproof chitin exoskeletons to reduce water loss.
Their small SA:V ratio also helps reduce water loss (reason insects can’t maintain gas exchange directly through membranes)
Movement of gases in and out of the tracheal system is brought about in 2 ways:-
Along the diffusion gradient- As cells are respiring oxygen is used up. This creates a low concentration of oxygen in the cells. As carbon dioxide is produced this has a high concentration in the cells. Diffusion gradients are set up and as diffusion is more rapid in air than water gases can be exchanged efficiently
Ventilation mechanism- As the muscles contract, mass movement of air in and out of the tracheae takes place.
Why do we not get insects the size of elephants?
it is important that all cells are close to a tracheal tube for the diffusion pathway to remain short. This is why we do not see insects which are the size of elephants!
Gas Exchange in Fish
Their scales are waterproof and fish are quite large. This means they cannot exchange gases over their body surface. They have developed a specialised internal gas exchange mechanism:- The gills
The gills are in the fish body, behind the head. They are covered with the gill flap (operculum) and are made up of gill filaments.
Gills structure summary
Gill filaments stacked in a pile
Gill lamellae at right angles to the filaments – huge surface area created
Good bloody supply to move internal medium and maintain concentration gradient
countercurrent flow
Water is taken in through the mouth and pushed over the gills. The flow of water over the gill lamellae and the flow of blood within them are in opposite directions. This is called countercurrent flow.
With counter current flow the concentration gradient is maintained along the whole length of the gill lamellae
In the gills of a fish, blood flows through the lamellae in one direction and water flows over in the oppositedirection. This is called a counter- currentsystem. The counter-current system means that the water with a relatively high concentration of oxygen always flows next to blood with a lower concentration of oxygen. This means that a steep concentration gradient is maintained along the whole length of the lamellae.
Ventilation in fish
As volume increases, pressure decreases
To increase volume, fish may open their mouths, lower the buccal cavity floor and close the operculum – causing a decrease in pressure so water flows in.
To force water over the operculum, fish close their mouths, raise the buccal cavity floor and the operculum moves inwards.
This increases pressure by decreasing the volume and so water flows out over the operculum
