7.4b - Ventilation & Gas Exchange in other Organisms

Question 1

What differences between water and air make it more difficult for fish to exchange gas?

Answer 1

Water is…

• More dense/viscous
• Water moves slower than air
  
  • requires more muscular effort Water flows in one direction, not ‘water in/water out’

Question 2

What issues do fish have that cause respiratory difficulty?

Answer 2

• Low SA:V ratio, diffusion wouldn’t be able to cope with O2 demands
• Scaly outer covering doesn’t allow gaseous exchange

Question 3

What have fish developed to overcome the issue of ineffective gas exchange? (Give gill adaptations)

Answer 3

Fish have developed a ventilatory system to perform gas exchange in the direction of the flow of water.

Gills: Large SA, good blood supply, thin layers

Operculum is a protective flap covering gills.

Question 4

What is the structure of the gills?

Answer 4

• Series of bony gill arches, with 2 stacks of gill filaments
• Each gill arch has vascular vessels running through the gill arches
• Gill filaments have protruding rows of thin lamellae
  
  • ​has a network of capillaries, covered by a single layer of epithelial cells (thin diffusion pathway)
• Operculum: bony plate protecting the gills

Question 5

What are the challenges gills of gas exchange face?

Answer 5

• Continuous water flow must be maintained, even when immobile
• Gas exchange must be efficient as diffusion is slower in water than air

Question 6

How do different fish types keep water flowing over their gills whilst immobile?

Answer 6

MOBILE: fish swim, water is flowing as mouth and operculum is open

IMMOBILE: Primitive cartilaginous fish use ram ventilation to ram water past gills

Bony fish don’t rely on movement based water flow, they use buccal pumping

Question 7

Describe the process of buccal pumping.

Answer 7

1. Mouth opens, the buccal cavity (mouth) floor lowers

• Increases cavity volume, dropping cavity pressure - this draws water IN
• Opercular valves shut, opercular cavity expands, lowering pressure
• Buccal cavity floor rises, increasing its pressure, forcing water to gills.

2. Mouth closes, operculum opens.

• Operculum sides and cavity gets smaller
  
  • increasing pressure of opercular cavity, forcing water over gills and out of body

Question 8

Give 2 adaptations of gills that help effective gas exchange in water.

Answer 8

• Tips of adjacent gill filaments overlap, causes water resistance (slowing water down)
  
  • more time for gas exchange
• Countercurrent flow - blood flows in opposite direction to water to maximise oxygen removal from water (80% of water removed)
  
  • maintains concentration gradient between oxygen in water and blood capillaries
    
    • in a parallel system, equilibrium is reached quickly