8.4 Gas exchange in fish

Question 1

What is the name given to the special respiratory surface of a fish?

Answer 1

• The gill

Question 2

What are the 3 features of a gill?

Answer 2

Gills have

1. a one way current of water, kept flowing by a specialised ventilation mechanism
2. Many folds providing a large surface area over which water can flow, allowing gaseous exchange
3. A large surface area, maintained as the density of the water flowing through prevents the gills from collapsing on top of each of other

Question 3

What are the two types of fish

How do you classify fish?

Answer 3

There are two types fish, classified by their skeleton:

1. Cartilagenous fish
2. Bony fish

The ventilated their gills in different ways

By the composition of their skeleton

Question 4

Example of a cartilagenous fish?

Answer 4

shark

Question 5

Where are the gills found in cartilaginous fish?

Answer 5

A shark has gills in 5 spaces on each of its sides,

They are called gill pouches which open to outside at gill slits

Question 6

Why is the gas exchange in cartilagenous fish, less effecient than that of boney fish.

Answer 6

Cartilagenous Fish do not have a special mechanism to force water over the gills and many must keep swimming for ventilation to happen .

Blood travels through the gill capillaries in the same direction as the water travels, this is what is known as a parallel flow.

Gas exchange in parallel flow does not occur across the whole gill lamella, only part of it, until the oxygen concentration in blood and water are equal.

Question 7

What is parallel flow?

Answer 7

Parallel flow occurs when blood and water flow in the same direction at the gill lamellae,

This maintains a concentration gradient which allows oxygen to diffuse into the blood

Upto the point where the concentration in the blood and water are equal

Question 8

What are the features of a bony fish?

Answer 8

A bony fish has an internal skeleton made up of bones

Its gills are covered with a flap called the operculum, rather than opening directly on the sides as in cartaliagenous fish

Question 9

What is the most common fish and in what two types of water?

Answer 9

Bony fish are the most common

They are found in freshwater + sea water

Question 10

What is the operculum

Answer 10

The covering over the gills of a bony fish.

Question 11

How does a fish maintain one directional flow?

Answer 11

• Water is forced over the gill filaments by pressure differences
• The water pressure in the mouth is higher than the water pressure in the opercular cavity
• This forces the water over the gills

Question 12

6 things

The Ventilation mechanism has divided into two:

Taking in water

Removing water

Question how does the ventilation mechanism take in water

Answer 12

1. Mouth opens
2. Operculum closes
3. Floor of mouth lowers
4. Volume inside the mouth cavity increases
5. Pressure decrease inside the mouth cavity
6. Water flows in, as the external pressure is higher than the pressure inside the mouth

Question 13

6 things

The Ventilation mechanism has divided into two:

Taking in water

Removing water

Question how does the ventilation mechanism removes water

Answer 13

1. Mouth closes
2. Operculum opens
3. Floor of mouth raises
4. Volume inside mouth cavity decreases
5. The pressure inside the mouth cavity increases
6. Water flows out over the gills

Question 14

How many gills are their in boney fish

Answer 14

4 pairs

Question 15

What is a gill suported by

Answer 15

gill arch / bar which is made of bone

Question 16

What are the projects found on gill arches?

Answer 16

gill filaments

Question 17

What are the gill filaments

Answer 17

Gill filaments are a gas exchange surface

Question 18

Why do fish die if out of water?

Answer 18

• The gills collapes because there is no water flowing through them
• Which means there is less surface area for gas exchange
• Which means that insufficient gas exchange occurs to sustain life

Question 19

What are gill lamela sometimes called?

How are these gill plates held apart?

What is the function of the gill lamella?

Answer 19

• Gill plates
• are held apart by water flowing between them
• The provide a large surface area for gas exchange

Question 20

what is counter current flow?

Answer 20

The counter current flow desribes the flow which occurs

when blood and water move in the oposite direction at the gill lamela.

This maintains a concentration gradients and therefore oxygen diffusion into the blood, along their entire length

Question 21

Why is the counter current flow more efficient than a counter current flow?

Answer 21

• Water always has a higher oxygen concentration that the blood
• O2 diffuses into the blood along the whole length of the gill lamela
• Unlike in parallel flow where the fish can only use part of the gill lamela
• The gills of bony fish, remove 80% of the O2 from water
• This high level of extraction is important to fish as water contains much less 02 than air
• Which is why counter flow is more efficient than parallel flow

Question 22

What is the difference in the way cartilagenous fish and bony fish remove CO2

Answer 22

• Co2 diffuses from the blood into the water in both Cartilagenous fish and bony fish
• In bony fish the process is more efficient because CO2 out of the blood along the whole length of the gill lamela whereas in cartilagenous fish it only diffuses across part of the gill lamella

Question 23

What do gills provide?

Answer 23

1. A specialised respiratory surface rather than using the whole body surface
2. A large surface extended by the gill filaments and gill lamela
3. An extensive network of capillaries, in which blood containing haemaoglobin allows the exchange of oxygen into the blood and carbon dioxide out of the blood.