Tracheal system

Question 1

Why are insects so small?

Answer 1

•tracheal system - cuticular tubes running length of body
•haemolymph not involved in transport of O2 (don’t have respiratory pigmements to bind to O2, except some living in O2 depleted environments like FW)
•unique to insects
•gas exchange can only occur over 1.5cm = constrains their size
-widest dimension at 1 point is 3cm (rarely that big though)

Question 2

Tracheal system

Answer 2

•abdominal segments have pair of appendages and spiracles
-connected to tracheal system
•made of thin specialised cuticle
•tubes become smaller further into body - can penetrate individual cells and muscle fibres
•has corrugated structure
•insect orders show variation - locusts have large air sacs as reservoirs

Question 3

Spiracles control what?

Answer 3

• rate of release of CO2
• intake of O2
• loss of water

Question 4

Factors affecting rate of diffusion

Answer 4

1. Temperature
2. Conc gradient - interested in partial pressure of gases
3. Molecular weight - smaller MW = faster diffusion
4. Permeability of substrate - vacuum compared to water

Question 5

Gas laws relating to the insects system

Answer 5

• only needs a 2% difference between insects outside and inside in pO2 for transport of sufficient speed
• travels faster through gas phase than liquid 10xe5 faster
• rate limiting step = liquid phase

Question 6

Following O2 in system

Answer 6

1. Get O2 into system - via gas
2. Get O2 from spiracles to tracheoles - via gas
3. Get O2 from tracheoles into cells and mitochondria - via liquid

Question 7

Following CO2 in system

Answer 7

CO2 32x more soluble than water than O2
1. Initially dissolved in liquid of bodies (cytoplasm, interstitial fluid and haemolymph)
2. Builds up there and is released from system in 1 big breath
=negative pressure in system, helping O2 enter

Question 8

Aquatic insects?

Answer 8

Have a closed tracheal system filled with gas and connected to their gills
•gas exchange from liquid phase to gas across gills and into gas exchange system
•underwater = higher pressure
•could potentially collapse when come under stronger pressure

Question 9

A passive system?

Answer 9

• can expand and constrict - having some thinner and thicker parts so need to make through
• not such a passive system, can expand and contract in some species

Question 10

Respiratory physiology

Answer 10

•tracheal cuticle thin = permeable to gas
•gas exchange is often facilitated by ventilatory movement - needs to be strong
•overcome by having thinner and thicker areas of cuticle
•opening and closing of spiracles stimulated by levels of O2
-lack of O2 stimulated CNS to open spiracles