gas exchange fish

Question 1

Explain two ways in which the structure of fish gills is adapted for efficient gas exchange.

Answer 1

Many lamellae / filaments so large surface area;

2. Thin (surface) so short diffusion pathway;

Question 2

Explain how the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills.

Answer 2

Water and blood flow in opposite directions;

Allow diagram showing counter-flow

2. Blood always passing water with a higher oxygen concentration;
3. Diffusion gradient maintained throughout length (of gill)

Question 3

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

____________________________

Answer 3

Increased metabolism / respiration / enzyme activity;

Accept: enzymes work more efficiently

2. Less oxygen (dissolved in water);

Neutral: references to increased kinetic energy (of water molecules)

Question 4

Gas exchange in fish takes place in gills. Explain how two features of gills allow efficient gas exchange.

Answer 4

Filaments / lamellae provide large surface area;

Thin / flattened epithelium / one / two cell layers so short diffusion pathway (between water and blood);

Countercurrent / blood flow maintains concentration / diffusion gradient;

Question 5

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange. 6 marks

Answer 5

Large surface area provided by lamellae / filaments increases diffusion / makes diffusion efficient;;

Q Candidates are required to refer to lamellae or filaments. Do not penalise for confusion between two

2. Thin epithelium / distance between water and blood;
3. Water and blood flow in opposite directions / countercurrent;
4. (Point 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 6

Mackerel live in the surface waters of the sea. Toadfish live on the seabed in deep water.

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

Answer 6

Mixing of air and water (at surface);

Air has higher concentration of oxygen than water;

Diffusion into water;

Plants / seaweeds near surface / in light;

Produce oxygen by photosynthesis;

Question 7

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

Answer 7

increased metabolism / respiration / enzyme activity;

Accept: enzymes work more efficiently

2. Less oxygen (dissolved in water);

Question 8

The table below shows some features of gas exchange of a fish at rest.

Volume of oxygen absorbed by the gills from each dm3 of water / cm3

7

Mass of fish / kg

0.4

Oxygen required by fish / cm3 kg–1 hour–1

90

(i) Calculate the volume of water that would have to pass over the gills each hour to supply the oxygen required by the fish. Show your working.

leran this qu

Question 9

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

Answer 9

Maintains concentration gradient (over whole length of gill) / diffusion
can occur over whole gill;

More oxygen enters blood ( / more CO2 leaves);

More (aerobic) respiration / more energy release in muscle / for
swimming;

Question 10

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

Answer 10

(gills have) lamellae on filaments;
lots of both;

Question 11

The diagram represents the flow of water and blood through the gills of a fish. The figures give relative oxygen concentrations.

Use the information in the diagram to explain the advantage of the countercurrent flow.

Answer 11

diffusion) gradient will be maintained all the way along the gill / the amount of oxygen in the water is always higher than in the blood / the numbers in the water are always higher than in the blood;

more oxygen will diffuse into the blood;

Question 12

Explain how the structure of the gill makes oxygen uptake efficient.

Answer 12

(many) filaments / lamellae / secondary lamellae;

so large surface area;

large number of capillaries; (NOT “good blood supply”)

maintains a diffusion gradient / removes oxygen;

/ lamellae wall;

short diffusion pathway;

Question 13

(b) There is a one-way flow of water over the gills of a fish whereas there is a two-way flow of air in the lungs of a mammal. Suggest one advantage to a fish of this one-way flow of water over its gills.

Answer 13

less energy needed / continuous flow of water or O2;

Question 14

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

Answer 14

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 15

A rise in the temperature of water decreases the amount of oxygen dissolved in the water. As the water temperature rises, the rate of ventilation in a fish also rises. Explain the advantage of this.

Answer 15

to provide same amount of oxygen;
need to have more water flowing over gills;
OR
metabolic rate / respiration increases (with increase in temperature);
so more oxygen required;