Fish

Question 1

Difficulty obtaining oxygen from water

Answer 1

• Water contains less oxygen than air
• Diffusion rates much slower
• Dense and viscous so more difficult to move

Question 2

Cartilaginous fish (cartilage skeleton)

Answer 2

• Less efficient ventilation system as no mechanism to force water over gills
• Must keep swimming

Question 3

Parallel flow

Answer 3

• Blood travels in same direction as water
• Equilibrium reached part way across lamellae so conc gradient not maintained
• Less diffusion of oxygen (only 50% saturation with oxygen)

Question 4

Bony fish (bone skeleton)

Answer 4

• 4 pairs of gills in pharynx
• Gill supported by bony gill arch
• Gill filament (2 in each gill) = large SA and filled with capillaries
• Gill rakers- filter water and trap prey to prevent damage to filaments
• Filament has gill plates/ lamellae = SA (exchange site)

Question 5

Ventilation I

Answer 5

• Mouth opens, operculum closes
• Floor of mouth/ buccal cavity is lowered
• Volume of cavity increases and pressure falls
• Water flows/ pilled in due to the pressure difference (greater out)

Question 6

Ventilation II

Answer 6

• Mouth closes
• Floor of buccal cavity is raised
• Volume decreases and pressure increases
• Water forced across the gills
• Operculum forced open and water flows out as greater inside

Question 7

Countercurrent flow

Answer 7

• Blood flows across gill plates in opposite direction to water
• Conc/ diffusion gradient of oxygen maintained across the entire gill as water has higher conc than blood along entire length
• Higher saturation of blood with oxygen
• More efficient- equilibrium never reached

Question 8

Heat exchanger

Answer 8

• Cold blood in arteries from gills passes close to warm blood in veins in opposite direction
• Heat from warm blood raises temp of cold blood before reaching capillaries
• Temperature gradient maintained across the entire length of the heat exchanger

Question 9

Out of water

Answer 9

• Water separates gill filaments so gills dry out
• Filaments stick together and gills collapse
• Lower SA for gas exchange and diffusion
• Water needed for diffusion of gases
• Not enough exchange to survive = die