Lesson 4 - Gaseous exchange systems in insects Flashcards
Why can’t insects use diffusion?
Exoskeleton through which no diffusion can occur
How is oxygen transported around insects?
Oxygen is delivered directly to cells and carbon dioxide is removed directly, as they have no blood pigments that can carry oxygen.
Spiracles
Small openings in the thorax and abdomen of insects. Air enters through them and water is lost.
How is water loss through spiracles prevented?
Sphincters open and close spiracles. Spiracles are closed as much as possible to prevent water loss.
What is the first tube after the spiracles?
Tracheae
Diameter of the tracheae?
1mm
Support for the tracheae?
Lined by spirals of chitin to keep them open when bent or pressed.
Does gaseous exchange occur in the tracheae?
Chitin makes up the cuticle. This is impermeable to gases, preventing diffusion.
What is after the tracheae?
tracheoles
Diameter of tracheoles?
0.6 - 0.8 micrometers
What are tracheoles?
Single elongated cells. They are very small, so spread throughout tissues of the insect and run between individual cells. Most gaseous exchange occurs here.
Where is tracheal fluid?
Near the ends of the tracheoles
What is the purpose of tracheal fluid?
Increases the surface area of the tracheoles for osmosis when lactic acid builds up in the tissues.
What does tracheal fluid limit?
Penetration of gases by diffusion. This is because O2/CO2 dissolve in moist lining of cells.
Two ways of increasing O2 and CO2 exchange in larger insects?
- Mechanical ventilation of tracheal system
- Collapsible or enlarged tracheae or air sacs
Large insects examples:
- Wasp
- Bee
- Grasshopper
- Locusts
- Beetles
- Flies
Mechanical ventilation of tracheal system:
Air is actively pumped into tracheal system by muscular pumping movements of the thorax and abdomen. These movements change the volume of the body and this changes the pressure in the tracheae and tracheoles. Air is drawn into the tracheae / tracheoles, or forced out, as the pressure changes.
Collapsible enlarged tracheae or air sacs
Act as reservoirs. Increase the amount of air moved through the gaseous exchange system. Inflated and deflated by the ventilating movements of the thorax and abdomen.
DGC
Discontinuous gas exchange cycle
Three states of discontinuous gas exchange cycle:
- Closed
- Open
- Fluttering
DGC - closed:
When the spiracles are closed no gases move in or out of the insect. Oxygen moves into the cells by diffusion from the tracheae and carbon dioxide diffuses into the bodily fluids where it is held in a process called buffering.
Buffering
When CO2 is stored in the bodily fluids of an insect
DGC - Fluttering
When spiracles flutter, they open and close rapidly. This moves fresh air into the tracheae to renew supply of oxygen, while also minimising water loss.
DGC - open
When carbon dioxide levels build up really high in the bodily fluids of the insects, spiracles open widely and carbon dioxide diffuses out rapidly. There may also be pumping movements of the thorax and abdomen when spiracles are open to maximise gaseous exchange.
