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)
Tracheal & cuticular gills def
- Gills = consists of organ that allows dissolved O2 from water to diffuse into body
- in insects - normally extensions of tracheal system & covered by thin cuticle (permeable to O2 & CO2)
Breathing tubes & siphons def
- aquatic insects - intake air straight from water surface thru hollow breathing tube (siphons)
Breathing tubes & siphons eg.
- Mosquito larvae
- Water scorpions (Hemiptera: Nepidae)
- Rat-tailed maggots (Diptera)
Breathing tubes AKA?
Siphons
Plastron & air bubbles def
- Plastron = special array of rigid, closely spaced hydrophobic hairs - create airspace next to body
- Air gets trapped btwn hairs & acts as physical gill (obtains O2 from trapped air (Like O2 tank))
- Volume of air trapped does not change during GE - O2 consumed = lowers pp inside = quickly compensated by dissolved O2 from water that enters plastron
- N diffuse out of plastron = little N in water = corrected by O2 uptake
Where are plastrons found? (insect type)
- Aquatic insects that are permanently submerged (rifle beetles) OR
- lack ability to reach surface (floodwater mosquitos larvae)
Where is the bubble trapped? (plastrons)
Under the elytra (wing cover) OR against body with specialized hair
How do the air bubbles work?
The air bubble covers one or more spiracles and the insect can “breathe” from the air in the bubble
What is the main difference between plastrons & air bubbles?
When O2 in the bubble is consumed, its volume changes: this is the major distinction from a plastron.
Why is an air bubble a limited “physical gill”?
There is passive diffusion of O2 from the water into the bubble,
In the long run, the oxygen uptake cannot match the O2 demand and the bubble’s volume decreases as O2 is depleted
Gills def
Feathered surfaces that contain membranes that bind dissolved oxygen in the water when water passes over these structures
Where are gills found in crustaceans?
Within thoracic cavity or appendages
Flow of O2 in crustaceans
(Circulatory system contains hemolymph (fluid))
1. From heart, the hemolymph is transported to the dorsal vessel towards organs that need oxygen
2. Then to the sternal sinus and gills where it picks up oxygen
3. Then transported to the pericardial sinus and back to the ostium in the heart
What about gills in larger species?
In hemolymph O2 is carried by respiratory pigments - HEMOCYANIN
Book lungs def
- Made of slits that are open in the ventral abdomen and a chamber (atrium) expands to many leaf-like air pockets
- A very thin cellular layer allows gas exchange by simple diffusion as hemolymph circulates through the book lungs
What optimizes oxygen uptake and gas exchange in book lungs?
The folds of the ‘book’ increase the surface area exposed to air
Diving bell spiders scientific name
Argyroneta aquatica
How do diving bell spiders work?
- Creates a bell with its web attached across aquatic plants
- Fills the bell with air from the surface which is transported and held with the abdomen and fine hairs on the rear legs.
- The diving bell takes a role of a ‘physical gill’ by maintaining and providing oxygen to the spiders for long periods
- As it gets depleted, spiders need to return to the surface and carry large air bubbles to replenish the diving bell
Book gills are though to be?
Modified legs
Main difference btw cyclic & discontinuous gas exchange?
Continuous gas exchange is constantly releasing CO2 while DGE undergoes periods of no CO2 release.
