Fish Gas Exchange

Question 1

Describe and explain how the countercurrent system leads to efficient gas exchange across the gills of a fish.

Answer 1

1. Water and blood flow in opposite directions
2. Maintains concentration gradient
3. Along whole length of lamellae

Question 2

AGD reduces efficiency of gas exchange in fish. Give two reasons why.

Answer 2

1. Longer diffusion pathway

2. Smaller surface area

Question 3

Calculate the volume of water that would have to pass over the gills each hour to supply the oxygen required by the fish.

Answer 3

90/7 = 12.85….. x 0.4 = 5.142….

Ans = 5.1

Question 4

The volume of water passing over the gills increases if the temperature of the water increases. Suggest why.

Answer 4

1. Increased metabolism

2. Less oxygen (dissolved in water)

Question 5

Calculate the minimum distance that a molecule of oxygen would have to travel from the water to a red blood cell.

Answer 5

10/20 x measurement

Question 6

Explain how the relationship between the direction of slow of water and of blood shown in the micrograph is useful to a fish

Answer 6

1. Maintains concentration gradient over whole length of gill
2. More oxygen enters blood
3. More aerobic respiration

Question 7

Describe the features of fish gills that give them a large surface area

Answer 7

Gills have lots of lamellae on both filaments

Question 8

Describe the relationship between gill surface area, mass and swimming speed shown in the diagram

Answer 8

All 3 go up

Question 9

Explain the relationship between gill surface area and swimming speed

Answer 9

1. More oxygen can be supplied

2. For more respiration

Question 10

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange.

Answer 10

1. Large surface area provided by lamellae, filaments increases diffusion, makes diffusion efficient.
2. Thin epithelium, distance between water and blood
3. Water and blood flow in opposite directions
4. Maintains concentration gradient along gill, equilibrium not reached as water always next to blood with lower concentration of oxygen.
5. Circulation replaces blood saturated with oxygen
6. Ventilation replaces water as oxygen removed

Question 11

The concentration of oxygen is higher in the surface waters than it is in water close to the seabed. Suggest why.

Answer 11

Concentration is higher in surface waters because surface waters closer to the air which has more oxygen.
Diffusion occurs where oxygen moves from air (with high concentration) to waters (low concentration).

Question 12

Explain how the shape of the curve for toadfish haemoglobin is related to where toadfish is normally found.

Answer 12

1. Not much oxygen near seabed

2. Toadfish haemoglobin has higher affinity for oxygen at low partial pressure of oxygen.

Question 13

Explain how ventilation mechanism of a fish and the structure of its gills result in the efficient uptake of oxygen from water.

Answer 13

1. Filaments/lamellae = large SA
2. Gill plates = more SA
3. Large number of capillaries = to remove oxygen/to maintain a gradient
4. Thin epithelium = short diffusion pathway
5. Pressure changes = to bring in more water/to maintain gradient
6. Countercurrent flow

Question 14

Fish has body mass of 0.2kg. Calculate volume of water it will need to pass over its gills each hour to supply the oxygen required when resting .

Answer 14

100 - 80 = needs 20
1dm3 = 80% of 9 (=7.2)
20/7.2 = 2.7

Question 15

Explain why is is easier to move water over the gas exchange surface of a fish in one direction rather than in a tidal pattern.

Answer 15

1. High density

2. Requires large input of energy as difficult to push back out

Question 16

As the water temperature rises, the rate of ventilation in a fish also rises. Explain the advantage of this .

Answer 16

1. To provide same amount of oxygen,

2. Need to have more water flowing over gills