gas exchange - insects

what specialised gas exchange and transport systems do insects use?

spiracles

gas exchange in insects

1. gas enters and leaves through tiny pores: spiracles which can open and close with a valve
2. this leads to a trachea, supported and strengthened by rings to prevent collapse
3. these divide into tracheoles which extend through body tissue and lead to muscle
4. tracheoles have water filled ends

adaptations of the gas exchange surface in the tracheal system of an insect

1. tracheole is one cell thick so rapid diffusion into cells
2. tracheoles enter and supply the cells and tissues so short diffusion pathway
3. tracheoles are highly branched so short diffusion pathway

what is the conflict of needing a large surface area for gas exchange in insects?

the need for insects to conserve water

what is spiracles’ evolved gas exchange system?

the tracheal system:
1. gas enters and leaves through tiny pores: spiracles, which can open and close with a valve
2. this leads to a trachea, supported and strengthened by rings to prevent collapse
3. these divide into tracheoles which extend through body tissue and lead to muscle, tracheoles have water filled ends

movement in and out of the tracheal system

1. along a diffusion gradient
2. mass transport
3. ends of tracheoles filled with water

movement in and out of the tracheal system: 1. along a diffusion gradient

- muscle cells aerobically respire, oxygen is used up and the concentration falls
- this creates a diffusion gradient so gaseous oxygen can diffuse in
- carbon dioxide is being produced by muscle cells, and diffuses down its concentration gradient out of the tracheole

movement in and out of the tracheal system: 2. mass transport

- CO2 is produced during aerobic respiration
- “abdominal pumping” increases pressure in the body
- muscle contraction squeezes trachea enabling mass movement of air in and out

movement in and out of the tracheal system: 3. ends of tracheoles filled with water

- major active muscle cells around tracheoles may carry out some anaerobic respiration, producing soluble lactate
- lowers water potential of muscles
- water moves into cells from tracheoles by osmosis, decreasing its volume
- this further draws air into the tracheoles
- so the final diffusion pathway is gas rather than liquid which is quicker, but this leads to greater water evaporation

Explain how an insect’s tracheal system is adapted for efficient gas exchange.

1. tracheoles have thin walls so short diffusion distance to cells;
2. highly branched so short diffusion distance to cells;
3. highly branched so large surface area for gas exchange;
4. tracheae provide tubes full of air so fast diffusion into insect tissues;
5. fluid in the end of the tracheoles that moves out into tissues during exercise so faster diffusion through the air to the gas exchange surface;
6. body can be moved by muscles to move air so maintains concentration gradient for oxygen;