B7 - gas exchange in insects & bony fish

Question 1

Why do insects need a gas exchange system? (2)

Answer 1

• very active, so have high O2 demand
• BUT have tough exoskeleton (made of chitin) impermeable to gases

Question 2

What is a spiracles and sphincters?

Answer 2

• small opening along abdomen
• air enters & leaves but also lose H2O, therefore sphincters control opening & closing
• sphincters mostly closed to reduce H2O lost, they open at higher demands of O2.

Question 3

spiracle -> tracheae -> tracheoles (structure)

Answer 3

tracheae:
- made of chitin spirals to keep held open
- impermeable chitin = little gas exchange

tracheoles:
- single, elongated cell w/ no chitin
- small & run between cells
- gas exchange between air in tracheoles & cells

Question 4

How does O2 travel spiracle -> tracheae -> tracheoles -> cells ?

Answer 4

• diffuses along tracheae to tracheoles
• O2 dissolved in moisture in tracheole lining, then diffuses into cells
• Tracheal fluid at end of tracheoles reduces air availability for diffusion (controls O2 amount absorbed)
• lactic acid builds up in tissues of active insects
• water leaves tracheoles by osmosis
• removal of tracheal fluid creates more SA for O2 to dissolve in

Question 5

Why is a gas exchange system needed in bony fish?

Answer 5

• (30x) less O2 in water than air
• water = more viscous = less O2
• skin impermeable to O2
• small SA:V
• use lots of energy moving through viscous water
• adapted to absorb O2 from water

Question 6

GILLS

Answer 6

• gas exchange surface in fish
• large SA, good blood supply, thin
• contained in gill cavity & covered by operculum (bony flap)
• gill lamellae project at right angles to increase SA & have blood capillaries = rich blood supply

Question 7

gill lamellae

Answer 7

• project at right angles to gills
• water flow between lamellae
• have capillaries = rich blood supply
• afferent blood vessel brings blood into system
• efferent blood vessel carries blood leaving gills

Question 8

water flow over gills mechanism

Answer 8

MOUTH OPEN:
- opercular valve closed
- buccal cavity lowers = more volume
- pressure drops, water moves in
- opercular cavity expands = lowers pressure
- buccal cavity floor raises = increases pressure so water flows to the gills

MOUTH CLOSED:
- operculum opens & opercular cavity moves inwards
- Increase pressure forces water flow over the gills & out of the operculum
- Buccal cavity raises steadily to maintain water flow over gills

Question 9

Gill adaptations for effective gas exchange

Answer 9

Large SA
rich blood supply
thin layers
- tips of adjacent gill filaments overlap, increasing resistance to water flow over gills & slows water movement to allow more time for gas exchange
- countercurrent flow: maintains concentration gradient as O2 diffuses from water into blood

Question 10

countercurrent flow

Answer 10

• water moving over gills flows in opposite direction to blood in gill filaments
• blood always meets water with higher O2 concentration = O2 diffuses into blood

Question 11

problems w/ parallel system:

Answer 11

• initial steep concentration gradient
• O2 in blood & water eventually reaches equilibrium