6 - Gas exchange (2) Flashcards
Peer
Types of ventilatory systems
- Open ventilatory system
- Closed ventilatory system
Open ventilatory system def
- Spiracles are found dorsally and/or laterally, e.g. grasshopper
- Some insects just have two posterior spiracles, e.g. mosquito larva
Closed ventilatory system
- The insect has trachea but no spiracles as in aquatic larvae; e.g Mayfly larvae
Ventilatory processes
- Passive
- Active
Passive ventilation def
- Works with simple diffusion and is driven by gas concentration gradients
- Requires open spiracles
- Follows Fick’s law of diffusion
What is the spiracle represented as in the passive ventilation equation?
As a small cylindrical tube
Active ventilation def
- Requires rhythmic pumping actions, facilitated by muscles
- Needs elasticity of the insect cuticle
Basic types of gas exchange
- Continuous gas exchange
- Cyclic gas exchange
- Discontinuous gas exchange
Continuous gas exchange
- Primarily driven by diffusion
- Convection and spiracles are open
Cyclic gas exchange def
- Continuous trace of CO2 production with some cyclic variation (and random noise)
Discontinuous gas exchange
O2 uptake and CO2 release from the whole insect follow a cyclical pattern characterized by periods of little to no release of CO2 to the external environment
Phases of discontinuous gas exchange
- Closed phase
- Flutter phase
- Open phase
What does phylogeny indicate about GE?
– The cyclic pattern is the ancestral condition
– Discontinuous gas exchange cycles (DGCs) have been observed in only 5/30 orders of insects
– Continuous and cyclic patterns have been observed in all of the orders examined.
DGC hypothesis
- Hygric Hypothesis
- Chthonic Hypothesis
- Hygric-chthonic
- Oxidative damage hypothesis
- Strolling arthropods
- Emergent property
Hygric hypothesis
DGC would reduce water loss
Chthonic hypothesis
DGC would increase partial pressure for gas exchange
Hygric-chthonic hypothesis
DGC would enhance both increase in partial pressure & reduce water loss
Oxidative damage hypothesis
DGC would allow protection from oxidation
Strolling arthropods hypothesis
Protection against arthropods
Emergent property hypothesis
Interaction btwn O2 & CO2 feedback
What do the DGC hypotheses question?
The function of discontinuous gas exchange (DGC) in insects: closing spiracles = lower water loss. However, there is debate!
How would we test the hygric hypothesis?
See if species with DGC live in arid areas
Adaptions of aquatic insects
- Cuticular gas exchange
- Tracheal and cuticular gills
- Breathing tubes and siphons
- Plastrons and air bubbles
Cuticular gas exchange def
- very thin integument
- found in small, inactive insects / live in highly O2 environments (cold, fast moving stream = (O2 demand is less then O2 in water)