GAS EXCHANGE IN FISH

Question 1

Gills properties (3)

Answer 1

• one-way current
• many folds increase SA
• flowing water prevents gills collapsing

Question 2

Cartilaginous fish - example and gills (4)

Answer 2

• Sharks
• five spaces on each side = gill pouches
• open at gill slits
• cartilage skeleton

Question 3

Ventilation in cartilaginous fish (3)

Answer 3

• no special mechanism
• must keep swimming to force water over gills
• blood and water travel in the same direction

Question 4

Parallel flow (2)

Answer 4

• diffusion only occurs until equilibrium (50%)

- only occurs on part of the lamellae

Question 5

Bony fish properties (3)

Answer 5

• bone skeleton
• gills covered by flap = operculum
• fresh & seawater

Question 6

Ventilation in bony fish (2)

Answer 6

• continuous unidirectional flow

- water forced over gill filaments by pressure difference

Question 7

Bony ventilation mechanism mnemonic (2)

Answer 7

• Most Observant Flamingos Value Pretty Wafers

Mouth Operculum Floor Volume Pressure Water

Question 8

Bony ventilation mechanism (in) (6)

Answer 8

• Mouth opens
• Operculum closes
• Floor of mouth lowers
• Volume (in mouth) increases
• Pressure (in mouth) decreases
• Water flows in because pressure is higher outside than inside

Question 9

Bony ventilation mechanism (out) (6)

Answer 9

• Mouth closes
• Operculum opens
• Floor of mouth is raised
• Volume in mouth decreases
• Pressure in mouth decreases
• Water flows out because pressure internally is higher than externally

Question 10

Bony fish gills (2 + 3 & explanation)

Answer 10

• Each gill supported by gill arch/bar
• Small projections across arch = gill filaments
• Gill lamellae (resp surface) held apart by water flow increasing S/A

Question 11

Why do fish die outside water? (5)

Answer 11

• Need water to hold gill lamellae apart
• if not they collapse
• less surface area
• therefore less respiration
• therefore death

Question 12

Counter-current flow (3)

Answer 12

• Across entire lamellae
• blood & water flow in opposite directions
• more efficient than parallel (80%)

Question 13

Why is efficient gas exchange important in fish? (1)

Answer 13

• much less o2 in water than air

Question 14

Bony fish CO2 exchange (2)

Answer 14

• occur along entire lamellae

- more efficient than cartilaginous fish

Question 15

Gills in bony fish are… (3)

Answer 15

• specialised respiratory surface
• large surface extended by gill filaments & lamellae
• extensive network of capilliaries