gas exchange in fish

Question 1

how does gas exchange in fish occur?

Answer 1

• mouth opens, buccal cavity lowered so the increase in volume decreases the pressure.. opercular valve is still closed
• water moves from outside to inside the buccal cavity down pressure gradient
• buccal cavity starts to rise and opercular cavity also expands so water moves down pressure gradient
• the mouth closes
• buccal cavity constricts and so does the opercular cavity
• the increase in pressure in opercular cavity pushes open the operculum and water is forced out over the gills

Question 2

what increases the surface area in the gills?

Answer 2

• there are many stacks of filaments on the gill arch

- there are many microscopic lamellae on the filaments, perpendicular

Question 3

how are the gills adapted to be an efficient gaseous exchange system?

Answer 3

• the tips of the gill filaments overlap which increases the resistance for the flow of water so water flows more slowly giving more time for gaseous exchange to take place
• there are many lamellae and filaments which provide a large surface area
• there is a rich capillary network within the lamellae which maintains the concentration gradient
• the lamellae and filaments are thin so short diffusion distance
• the water and blood flow in different directions in the filament.. countercurrent multiplier system

Question 4

why is the countercurrent multiplier system advantageous?

Answer 4

• it maintains a concentration gradient between the blood and water so as much oxygen as possible can diffuse into the blood

Question 5

why so fish need this respiratory exchange system?

Answer 5

• the oxygen content in water is very low and water is very viscous
• the system helps cope with the viscosity and the slow rate of diffusion of oxygen
• moving water in one direction is more reasonable in terms of energy needs

Question 6

Why do gill filaments require water?

Answer 6

• the gill filaments require water to keep them apart and only then can they expose a large surface area for gas exchange

Question 7

Do bony fish require on movement generated flow of water over the gills?

Answer 7

• no
• they have adapted this sophisticated system that allows water to continuously flow over the gills without them having to move

Question 8

what is ram ventilation?

Answer 8

• when primitive cartilaginous fish like sharks ram water over their gills because they often rely on continual movement to ventilate the gills

Question 9

What is important to take into consideration when cutting with a scalpel?

Answer 9

• cut away from your body and make sure your fingers are not near

Question 10

What can scissors be used for in dissections?

Answer 10

• to cut larger pieces of tissue

Question 11

Why do we need tweezers, forceps and pins?

Answer 11

• to move other structures out of the water to leave the desired structures exposed