3.3.2 Gas Exchange

Question 1

Where is the site of gas exchange in a fish?

Answer 1

gills

Question 2

What are the 4 adaptations of fish to ensure efficient gas exchange?

Answer 2

1. Large surface area of gills
2. Thin lamellae
3. Counter-current flow
4. Constant water flow

Question 3

How do fish gills have a high surface area?

Answer 3

-high number of gill filaments
-each filament is covered with lamellae
-increases area available for gas exchange

Question 4

Why does fish having a thin lamellae increase efficiency of gas exchange?

Answer 4

reduces diffusion distance between water and blood

Question 5

What is counter-current flow and how does it increase efficiency of gas exchange?

Answer 5

-water and blood flow in opposite directions across the gill lamellae
-maintains a concentration gradient along the entire length of the gill
-maximises oxygen uptake by fish

Question 6

Why does a constant water flow increase efficiency of fish gas exchange?

Answer 6

-water is continuously moved over fish’s gills
-ensures a constant supply of oxygen

Question 7

Describe and explain how fish maintain a flow of water over their gills (4 marks)

Answer 7

-mouth opens, operculum valves shut
-floor of mouth lowers
-water enter due to decreased pressure (due to increased volume)
-mouth closes, operculum valves open
-floor of mouth is raised, which increases the pressure
-increased pressure forces water over gills

Question 8

Explain how the ventilation mechanism of a fish and the structure of its gills result in the efficient uptake of oxygen from water (6 marks)

Answer 8

1. Filaments/ lamellae - large surface area
2. Large number of capillaries - removes oxygen/ maintains concentration gradient
3. Thin epithelium - short diffusion distance
4. Pressure changes - maintains gradient/ brings in more water
5. Countercurrent flow - exchange along whole length of gill, blood always meets water with higher oxygen concentration (conc. gradient is maintained)