gas exchange in fish and insects

Question 1

what are spiracles

Answer 1

• small openings along the thorax and abdomen
• air enters and leaves through them
• water loss
• spiracles can open/close by sphincters to minimise water loss

Question 2

what are tracheae

Answer 2

• leading away from the spiracles
• largest tubes of insects’ respiratory system
• carry air into body
• lined by chitin spirals
• chitin is impermeable to gases, and it keeps tubes open

Question 3

what are tracheoles

Answer 3

• tracheae branch to form narrower tubes
• single, elongated cell
• no chitin lining so permeable to gases
• spread throughout tissues of insects
• where gas exchange between air and respiring cells happens

Question 4

how does air move through tracheae and tracheoles

Answer 4

• diffusion
• lots of tiny tracheoles give high SA
• oxygen dissolves in moisture on walls of the tracheoles and diffuses into surrounding cells
• end of tracheoles–> tracheal fluid which limits penetration of air for diffusion
• lactic acid build up in tissues results in water moving out of tracheoles by osmosis so more SA is exposed

Question 5

insects alternative methods for supplying oxygen

Answer 5

• using rhythmic abdominal movements to change volume of their bodies (thorax) so change the pressure

Question 6

features of gills

Answer 6

• large SA
• good blood supply
• thin layers
• operculum (protective bony flap) covers them

Question 7

structure of gills

Answer 7

• each gill is supported by a gill arch
• gill filaments/primary lamellae are thin stacked up plates that make up the gills
• they are covered in gill plates/secondary lamellae
• continuous water flow needs to be maintained over gills to carry out gas exchange

Question 8

what happens when the fish mouth opens

Answer 8

• floor of buccal cavity is lowered
• increases volume in buccal cavity
• pressure decreases in buccal cavity
• water moves in
• opercular valve is shut and opercular cavity expands
• lowers pressure in opercular cavity
• floor of buccal cavity starts to move up
• increases pressure
• water moves from buccal cavity over the gills

Question 9

what happens when fish mouth closes

Answer 9

• floor of buccal cavity is raised
• volume decreases in buccal cavity
• pressure increases in buccal cavity
• operculum is open and sides of opercular cavity move inwards
• forces water over the gills and out the operculum

Question 10

counter-current system

Answer 10

• blood flows through gill plates in 1 direction and water flows over in the opposite direction
• water with high O2 conc. always flows next to blood with a low O2 conc.
• steep conc. gradient is maintained between water and blood