gas exchange in fish

Question 1

why do fish require a gas exchange surface?

fish’s gas exchange surface is the gills

Answer 1

• because they are waterproof
• have small surface area: volume ratio

Question 2

Explain how the counter current exchange mechanism improves effieciency of gas exchange (3 marks)

this is a typical exam question !!!

Answer 2

• **blood and water flow in opposite directions **(1 mark)
• **along the full length of gill filament **(1 mark)
• which maintains concentration gradient (1 mark)

Question 3

how is rate of diffusion calculated?

hint: using ficks law

Answer 3

diffusion = surface area x concentration difference/ length of diffusion pathway

Question 4

what are the adaptations of fish for gas exchange?

Answer 4

• large number of filaments and lamellae –> increases surface area for gas exchange
• large number of capillaries around lamellae –> maintains conc gradient, as circulation constantly removes oxygen blood
• gill lamellae is very thin –> short diffusion distance for gas exchange
• ventilation by operculum–> mainstains conc gradient, as fresh water flow over gills replaces lost oxygen

Question 5

explain why the counter current flow system so important

Answer 5

• countercurrent flow= water flows over gills in opposite direction to blood flow in capillaries
• ensures equilibrium is not reached
• ensures diffusion gradient is maintained across ENTIRE length of lamaellae