The mechanism of ventilation in bony fish and insects

Question 1

What covers the opercular cavity?

Answer 1

The operculum

Question 2

How many pairs of gills do fish have?

Answer 2

5 pairs

Question 3

What is each gill made of?

Answer 3

Two rows of gill filaments

Question 4

What is on the surface of gill filaments?

Answer 4

Thin folded lamellae

Question 5

Explain how the gills of fish are adapted for gas exchange

Answer 5

• Gill filaments are thin so there is a short diffusion pathway which increases the rate and efficiency of gas exchange and diffusion
• The tips of adjacent gill filaments overlap which increases the resistance and slows down the flow of water over the gill surface. This increases the time for gas exchange to occur.
• The thin lamellae on the surface of the gill filaments have a large surface area which increases the rate of diffusion so that enough oxygen is supplied and carbon dioxide is removed
• water moves over the gills in the opposite direction to blood flow in a countercurrent exchange system.Water contains a higher concentration of oxygen than water and so this maintains asteep concentration gradient of oxygen which increases the rate and efficiency of diffusion and gas exchange

Question 6

How does counter-current flow work for gas exchange

Answer 6

• Water flows over the surface of the gills in the opposite direction to the flow of blood
• The water contains a higher concentration of oxygen than the blood and so a steep concentration gradient of oxygen is maintained which increases the rate and efficiency of diffusion and gas exchange

Question 7

Describe the mechanism of ventilation in fish

Answer 7

1. The fish’s mouth opens
2. The buccal cavity floor is lowered
3. The volume of the buccal cavity increases and the pressure inside the buccal cavity decreases so it is less than the pressure outside
4. Water rushes into the buccal cavity to equalise the pressure difference
5. The buccl cavity is raised and the opercular cavity expands
6. The pressure inside the buccal cavity is higher than in the opercular cavity so the water moves from the buccal cavity over the gills into the opercular cavity to equalise the pressure difference
7. The mouth is closed and the operculum opens
8. The sides of the opercular cavity move inwards, increasing the pressure
9. The water flows out of the fish through the operculum

Question 8

What is the exoskeleton of insects made of?

Answer 8

Chitin

Question 9

Chitin is a polysaccharide

TRUE OR FALSE

Answer 9

TRUE

Question 10

Is chitin permeable or impermeable to gases?

Answer 10

impermeable to gases

Question 11

What is on the surface of the exoskeleton of insects which allows gases to diffuse into the body of the insect?

Answer 11

Spiracles

Question 12

What is the function of spiracles?

Answer 12

They are small openings in the exoskeleton of insects which allow carbon dioxide and oxygen to diffuse into the insect body. They also allow the loss of water

Question 13

Which muscles prevent the loss of water from spiracles?

Answer 13

Sphincter muscles

Question 14

What do the spiracles lead to?

Answer 14

The tracheae

Question 15

Where are the tracheae found in insects?

Answer 15

In the abdomen

Question 16

What does the tracheae branch into in insects?

Answer 16

tracheoles

Question 17

What is the tracheae in insects made out of?

Answer 17

Spirals of chitin

Question 18

What is the function of chitin in the tracheae in the abdomen?

Answer 18

To prevent the tracheae from collapsing

Question 19

Describe the structure of the tracheoles

Answer 19

• single, elongated cell that is extended to form a hollow tube.
• No chitin as gas exchange happens here

Question 20

Give the features of the tracheoles which make it an efficient gas exchange surface

Answer 20

• Tracheoles have a thin surface layer and are very close to the surroudning cells which gives a short diffusion distance, allowing for a fast diffusion rate of oxygen into the cells
• There are a large number of tracheoles which means they have a large surface area which allows for the rate of diffusion to be fast enough to supply enough oxygen to cells
• Tracheoles contain tracheal fluid which inhibits gas exchange in normal conditions but during intense activity, cells undergo anaerobic respiration which produces lactic acid which reduces the water potential of the cells. Water moves into the cells from the tracheoles by osmosis. This exposes more of the surface of the tracheoles which increases the rate and efficiency of diffusion

Question 21

Describe how the tracheal fluid contributes to gas exchange in insects

Answer 21

• In normal conditions, the tracheal fluid at the ends of the tracheoles inhibits gas exchange
• In intense activity the cells surroding the tracheoles undergo anaerobic respiration and they produce lactic acid which lowers the water potential of the cells
• Water moves from the tracheoles to the cells by osmosis down the water potential gradient
• This exposes more of the surface of the tracheoles which increases the rate and efficiency of gas exchange

Question 22

Give the adaptations of spiracles which help with its function

Answer 22

• Lined with hairs which filter the air as it enters, this prevents dust or bacteria from getting into the gas exchange system
• The hairs prevet water loss by trapping water vapour tryiing to escape from the spiracles

Question 23

Describe the process of inspiration in insects

Answer 23

1. The thoracic spiracles open
2. The abdominal muslces relax
3. The volume of the abdomen increases and the pressure inside the bdomen decreases so it is less than the air pressure outside
4. Air is drawn into the tracheal system

Question 24

Describe the process of expiration in insects

Answer 24

1. The abdominal spiracles open
2. The abdominal muscles contract
3. This causes the volume of the adomen to decrease and the pressure inside the abdomen to increase so that it is more than the pressure outside
4. Air is pushed out of the tracheal system