1. Settler
Gas exchange in humans – Why is this not an efficient system for fish??????
Chambers inside separate the oxygen and release the liquid so that the user can breathe comfortably in the ocean.
Read more: Follow on Twitter | DailyMail on Facebook

2. Why do fish gills need to be so efficient?
Oxygen not very soluble in water
Surface water = 5 ppm cf 210,000 ppm in air
Water contains about one-thirtieth as much oxygen per volume as the atmosphere above it.
Water more dense than air – more difficult to move over exchange surface than air
Fish countercurrent system ensures 80% absorption of oxygen from water
Our lungs can extract only 25% from air
If we were somehow able to "breathe" water, we would need to take about 450 "breaths" per minute just to get enough oxygen into our lungs!

3. Module 3 Exchange and transport
7. Exchange surfaces
7.4 Ventilation and gas exchange in bony fish

4. Breathing in and out Pressure in lungs decreases.
Volume of chest cavity decreases
Diaphragm relaxes and is pushed upwards by displaced organs underneath
External intercostal muscles relax and ribs fall
Pressure in lungs increases.
Air moves out of the lungs.
Diaphragm contracts to become flatter and pushes digestive organs down
Volume of chest cavity increases
External intercostal muscles contract to raise ribs
Air moves into the lungs.

5. Breathing in and out Breathing in Breathing out
1. External intercostal muscles contract to raise ribs
1. External intercostal muscles relax and ribs fall
2. Diaphragm contracts to become flatter and pushes digestive organs down
2. Diaphragm relaxes and is pushed upwards by displaced organs underneath
3. Volume of chest cavity increases
3. Volume of chest cavity decreases
4. Pressure in lungs decreases.
4. Pressure in lungs increases.
5. Air moves into the lungs.
5. Air moves out of the lungs.

6. Learning Objectives Success Criteria
Demonstrate knowledge, understanding and application of the mechanisms of ventilation and gas exchange in bony fish
Identify the gills as the site of gaseous exchange in bony fish
(Grade E - D)
Understand the mechanisms of ventilation and adaptations of gas exchange in bony fish
(Grade C –B)
Apply understanding to the examination and drawing of a bony fish gill
(Grade B – A)
FISH DISSECTION – 2 lessons

7. Structure of fish gills

8. Gas exchange in fish
There is a lower concentration of oxygen in water than in air. Fish have special adaptations to get enough oxygen.
The gills of a fish are found just behind the head. There are 4 pairs of gills in the opercular cavity. The flap over the gills is called the operculum.

9. http://www.pskf.ca/sd/#int Salmon dissection
Bond - The scaly texture on the arms conceal small holes in the material where water is sucked in.
Chambers inside separate the oxygen and release the liquid so that the user can breathe comfortably in the ocean.
Read more: Follow on Twitter | DailyMail on Facebook

11. Gills Gills are the gas exchange surfaces in fish
Gills provide a large Surface Area, mainly given by the filaments and secondary lamellae.
The gills are highly capillarised which gives a good blood supply.
Gills have a short diffusion distance; this is provided by flattened cells in capillaries and epithelium (surface of gill plates). This enables 02 to get into the bloodstream faster.
How does this help facilitate gas exchange?
Why will a fish suffocate if left out of water?

12. Single circulation

13. Structure of a gill
To allow efficient gas exchange, fish need to maintain a continuous flow of water over the gills, even when they are not moving, and to access oxygen when diffusion is slower in water than air.

14. Gills
The afferent blood vessel brings deoxygenated blood to the gill. A branch of it goes along the inside of each lamella towards the tip.
Blood then flows across the gill plates and into the capillaries inside the gill plates.
The efferent blood vessels then carry oxygenated blood away from the gill.

15. Gas exchange across gill lamellae

16. Why is a counter current flow a more efficient way for gas exchange in fish than a parallel/concurrent flow???? Discuss

18. Why is a counter current flow a more efficient way for gas exchange in fish than a parallel/concurrent flow???? Discuss

19. Countercurrent exchange principle
There is a lower concentration of oxygen in water than in air. So fish have adaptations :
1)Water containing oxygen enters the fish through its mouth and passes over the gills
2) Blood flows through the lamellae in one direction and water flows in the opposite direction = countercurrent flow blood is always coming into contact with water that has a higher dissolved oxygen concentration
The diffusion gradient for oxygen is therefore maintained along the entire length of the gill structure
This facilitates maximum possible gas exchange across gill lamellae
lesson 3\counter-current flow.swf

20. Parallel flow
In parallel flow the concentration gradient will level out when blood and water are both 50% saturated with oxygen
Diffusion therefore stops when the blood is only 50% saturated with oxygen
In the countercurrent system blood will continue absorbing oxygen from water as the concentration gradient does not level out lesson 3\parallel flow.swf

21. Plenary
Explain how the structure of the gas exchange system of a bony fish maximises the amount of oxygen that can be taken from the water (6 marks)
Gills have large stacks of gill filaments carrying gill lamellae that have a large SA (1); good blood supply (1);thin layers(1). Constant flow of water maintained over gills, so has diffusion gradient for gases (1); tips of gill filaments overlap – increasing resistance of flow of water, slowing it down for a more effective gas exchange (1); water and blood flow in opposite directions-countercurrent exchange system (1)

22. Complete the exam style questions on gas exchange in fish
(a) countercurrent mechanism; helps maintain diffusion gradient; 2
 (b) mackerel has shortest total distance; for diffusion; (activity requires) oxygen for respiration / ATP production; [5]
 Qu 1
(a)(i) Arrow from vein towards artery, across lamella. 1
(ii) Water with high oxygen conc. meets blood with low oxygen conc; (may be derived from correct diagram) Difference in concentration maintained (across lamella); Diffusion gradient maintained. 2
(b)(i) 79 (Allow 78-80) – gains 2 marks. Length of cycle calculated from graph ( s) - gains 1mark Correct method (60 divided by cycle time), but cycle wrong time - gains 1 mark 2
(ii) Floor of mouth cavity lowered (increasing volume) [6]

24. Jan 2009 markscheme