When there is a cell wall, there is no added resistance to diffusion
1 of 3
Gas exchange in insects
Increasing their surface area for better exchange of gases can cause insects to lose water quickly as water will evaporate
Insects conserving water is topic 6.5 (limiting water loss)
For gas exchange, insects have tracheae
Tracheae are supported by rings to prevent them from collapsing
Tracheae divide into dead-end tubes called tracheoles
Tracheoles extend through the tissues
Atmospheric air is brought directly to the respiring tissues due to the short diffusion pathway
Gas enters and leaves through small pores called spiracles
Spiracles can be opened and closed by valves
When open, water vapour can evaporate out of the insect which is bad
Therefore, spiracles are mainly kept shut to prevent water loss
The tracheal system is an extremely efficient method of gas exchange
However, it relies heavily on diffusion and so the size of insects is limited as the bigger the insect, the larger the diffusion distance
2 of 3
Gases move in and out in 3 ways
Along a diffusion gradient
When cells respire, oxygen is used up decreasing the concentration of oxygen at respiring tissues creating a diffusion gradient
Oxygen diffuses down the tracheae and tracheoles to the respiring tissues along this concentration gradient
Carbon dioxide is produced during respiration so respiring tissues cause an increase in carbon dioxide concentration making a concentration gradient of carbon dioxide
Carbon dioxide therefore diffuses along the diffusion pathway out of the insects
This causes rapid transport of gases
Mass Transport
Contraction of muscles in the insect can squeeze the tracheae
This creates the mass movement of gas in and out of the insect
This increases the speed of exchange of respiratory gases
Water filled tracheoles
Anaerobic respiration produces lactate which decreases the water potential of muscle cells
Water moves into the cells by osmosis from the tracheoles bringing oxygen with it
The final diffusion pathway is in a gas not liquid state making it faster
However, this method increases the rate of evaporation increasing water loss
Comments
No comments have yet been made