Gas Exchange In Fish And Insects

Question 1

How is the gas exchange system of an insect efficient?

Answer 1

The high number of tracheoles and the high degree of branching results in a large surface area for gas exchange.
The ends of the tracheoles penetrate deep into the muscle and no cell is far away from a source of oxygen
The ends of the tracheoles are fluid filled and this gives the insect some control over the rate of gas exchange. In high activity respiration increases, oxygen is not sufficient lactic acid will begin to build up, lowering the water potential of the tissues, so fluid is drawn out of the tracheoles and this increases the surface area for gas exchange, so diffusion is faster.

Question 2

What are the openings of the tracheoles called?

Answer 2

Spiracles

Question 3

How does a fish ventilate the gills?

Answer 3

Mouth opens, whilst opercular valve shuts;
The floor of mouth lowers
Volume increases and pressure lowers so water
Mouth closes, opercular valve opens
floor raised results in increased pressure due to decreased volume;
High pressure forces water over gills;

Question 4

Explain how the gills of a fish are adapted to form a specialised exchange surface.

Answer 4

Structure of filaments with a large number of lamellae; and secondary lamella provide a large surface area for exchange
The lamellae have a thin surface, a single layer of flattened epithelial cells provide a short distance between water and blood / short diffusion pathway
Counter-current flow of water and blood across lamella maintains a diffusion gradient along length of lamellae and prevents oxygen concentrations reaching equilibrium;
Ventilation mechanism in producing water flow over gills and circulation of blood maintains a diffusion gradient.

Question 5

How does the countercurrent system in fish work?

Answer 5

Fish has ventilation system which replaces water, which is high in oxygen
The circulatory system brings in blood with low concentration of oxygen and removes oxygenated blood Water flows in opposite direction to blood across (gill) lamellae; so difference in concentration maintained and Diffusion occurs over full length of lamellae.