3 - MZH - Gaseous exchange in fish & insects

Question 1

Lable the diagram

Answer 1

1. Operculum
2. Gill filaments
3. Gill arch
4. Gill rakes

Question 2

Descibe how fish ventilates

Answer 2

1. Floor of buccal cavity drops, mouth opens.
2. Pressure inside mouth is less than pressure outside mouth so water is forced into mouth.
3. Floor of buccal cavity rises, mouth closes.
4. Pressure inside mouth is greater than pressure outside, gills open and water is forced outwards

Question 3

What type of gaseous exhcange system so fish have?

Answer 3

Countercurrent flow.

• Water always passes over the gills in the opposite direction to the blood flowing through the gills.
• Ensures the blood always being next to water containing a slightly higher O₂ conc.
• O₂ conc never reaches equilibrium.
• Ensures that oxygen absorption occurs over the whole gill plate.

Question 4

What about terrestrial organisms?

Answer 4

The cells of the body surface is modified to reduce water loss but this also prevents gaseous exhcange.

Water loss isn’t a problem for organisms like fihs but is for insects that live on land.

Question 5

How does the gaseous exchange system of insects work?

Answer 5

Waterproof cuticle covers insect’s body, redce water loss + gaseous exchange is impossible through this surface.

They have a system of breathing tubes called tracheae from which branch into thinner treacheoles.

Tracheae have ridgit rings n their walls made of chitin to keep them open.

Tracheoles penetrate between cells andright into muscle cells. Gaseous exchange takes place in the tracheoles.

Tracheae connect with the insect’s environment via spiracles (this is where water is lost)

Question 6

What happens when an insect is at rest?

Answer 6

• Not much oxygen is needed for respiration, spiracles are almost closed to reduce water loss.
• Tracheoles are partially filled with fluid which reduces the SA in contact with air in te tracheole system.
• Air in tracheole is almost saturated with water vapour, reducing the evaporation from the surfaces of tracheoles.

Question 7

What happens when an insect is active?

Answer 7

• Rate of respiration and conc of CO₂ increases (carbon dioxide is the trigger).
• Spiracles open, increase gaseous exchange and water loss.
• Fluid is absorbed from the tracheoles, exposing a greater SA for gaseous exchange.

Question 8

What about very active insects e.g. when flying?

Answer 8

Spiracles close and contraction of the muscles cause abdominal movements.

These movements squeeze the tracheae frcing air into the tracheoles.