Gas exchange - Fish

Question 1

Describe what happens when a fish opens its mouth

Answer 1

• Pressure decreases
• Volume increases
• Water enters via mass flow

Question 2

Describe what happens when a fish closes its mouth

Answer 2

• Volume decreases
• Pressure increases
• Water is pushed over gills

Question 3

Describe and explain how fish maintain a flow of water over their gills

Answer 3

1. mouth opens, operculum / opercular valve shuts;
2. floor of mouth lowered
3. water enters due to decreased pressure / increased volume;
4. mouth closes, operculum / opercular valve opens;
5. floor raised results in increased pressure / decreased volume;
6. high / increased pressure forces / pushes water over gills;

Question 4

Explain how the gas exchange system of a fish is adapted

Answer 4

• Many gill filaments with lamellae to give a large surface area, increasing the rate of diffusion
• The walls of the gills are thin (the epithelial layer is one cell thick). reducing the diffusion distance
• There are a high number of capillaries to ensure movement of the internal transport medium, maintaining a concentration gradient

Question 5

Fish that swim fast have larger gills than fish that swim more slowly.
Suggest and explain why

Answer 5

• Fish that swim faster have a higher rate of muscle contraction
• Therefore, they need more ATP
• As a result, they need more oxygen to carry out more aerobic respiration
• Therefore they have larger gills to increase the surface area for exchange
• This increases the rate of diffusion of oxygen into the blood

Question 6

Describe what is meant by parallel flow

Answer 6

Blood in the capillaries flow in the same direction as water

Question 7

Explain why parallel flow would NOT be an efficient method of exchange in fish

Answer 7

Parallel flow would not be an efficient method of exchange as equilibrium would be reached, reducing the concentration of oxygen that can diffuse into a fish’s blood

Question 8

Describe what is meant by counter current flow

Answer 8

Blood flows in the opposite direction to the water

Question 9

Why is counter current flow important

Answer 9

A diffusion gradient is maintained

Question 10

Explain why counter current flow provides a higher metabolic rate than parallel flow

Answer 10

• Counter current flow allows for a higher metabolic rate as a greater concentration of oxygen can diffuse into the blood.
• Therefore, a greater concentration of oxygen can diffuse into respiring cells, meaning that more aerobic respiration can take place, producing more ATP for the cell to carry out more metabolic reactions.