Lesson 3

Question 1

Describe problems for gas exchange by being in water

Answer 1

• Water has lower conc. of O2 than air
• Rate of diffusion is slower
• Water is dense so doesn’t flow as freely

Question 2

What are features of cartilaginous fish?

Answer 2

• Skeleton made of cartilage
• Live in saltwater usually
• 5 gill clefts
• Uses parallel flow

Question 3

What are features of bony fish?

Answer 3

• Bone skeleton
• Gills covered with flap called operculum
• Counter-current flow
• 4 gills

Question 4

Explain ventilation system of bony fish

Answer 4

• Mouth opens and buccal cavity opens, increasing volume so pressure inside decreases
• So water flows in
• Mouth closed and buccal cavity rises so volume inside decreases
• So water flows over gills and out through operculum

Question 5

What is ram ventilation ?

Answer 5

Cartilaginous fish constantly swim with mouth open to allow water to pass through gills

Question 6

Describe structures of gills

Answer 6

• Each gill has many filaments
• Filaments have many lamellae
• Creates large surface area

Question 7

What is benefit of counter-current flow?

Answer 7

Blood will always meet water with higher oxygen conc. meaning conc. grad. is always maintained and oxygen diffuses across whole length of gill lamellae

Question 8

Describe parallel flow

Answer 8

• Gas exchange very efficient when water first meets blood as water very high conc. and blood very low conc.
• But once water and blood have equal conc. of O2, diffusion stops

Question 9

Why is counter-current more efficient than parallel?

Answer 9

• Oxygen diffusion is not constant as it doesn’t occur across whole length of lamellae
• It does in parallel flow
• So high blood saturation level in bony fish