1. Module F211 1.2.1 Exchange surfaces and breathing
Lesson objectives:
To describe the features of an efficient exchange surface
Describe the diffusion of oxygen and carbon dioxide across an alveolus.

2. The need for an exchange system in multicellular organisms
Why doesn’t an amoeba need lungs or gills?
Amoeba

3. Practical – the effect of surface area on efficiency of exchange surfaces
You need – tile, scalpel, 3 small beakers, block of stained agar, stop clock
Use scalpel to cut block into 3 equally sized pieces (use a ruler)
block 1 stays complete,
block 2 cut into 4 equally sized pieces,
block 3 cut into 8 pieces (use a ruler)
Put each set of blocks into each of the 3 beakers with 10cm3 hydrochloric acid - start the stop clock immediately
Measure width, length and height of 1 block (mm)
calculate the total surface area for the smaller blocks,
(S.A .of 1 block x number of blocks)= total S.A.
While you are waiting –
Draw a suitable table to record the side measurements of the blocks
Describe relationship shown by your graph

4. Block
Width
(mm)
Length
Height
Surface area
(mm2)
Number of blocks
Total surface area of blocks (mm2)
Time taken for pink colour to disappear
(s) 1 2 3

5. Make a list of at least 5 errors in the construction of this table
Block
Width
Length
Height
(mm)
Surface area
Number of blocks
Total surface area of blocks
Time taken for pink colour to disappear 1
1cm
2cm 2
16cm2
1min 34sec
1.0 10 20
1min 10s 3
0.5
7.00 4 28
54.05s

6. Block
Width
(mm)
Length
Height
Surface area
(mm2)
Number of blocks
Total surface area of blocks (mm2)
Time taken for pink colour to disappear
(s) 1 10 20
1600 94 2 5
700 4
2800 70 3
400 8
3200 54

7. Calculating surface area : Volume ratio
Smaller animals have higher SA:V ratios V
Task:
Complete worksheet on SA:V ratio relationship

9. Plenary question
Q1; Jan 2007

10. Plenary question
Q1; Jan 2007

11. Exchange surfaces: Large surface area Short diffusion path
Concentration gradient maintained
(by good blood supply)
What do all exchange surfaces have in common?

12. Images

13. The alveoli & diffusion
(Produces a surfactant)

14. Arrangement of cells and tissues in the alveolus Label your diagram
Epithelial cells making up the wall of the alveolus (Type I pneumocyte)
Alveolar air space
Blood capillary
Special type of epithelial cell which produces a surfactant that reduces the surface tension of the alveolus lining (Type II Pneumocyte)
Red blood cell
Blood plasma
Phagocyte (macrophage) in an alveolus – helps destroy foreign material drawn into the lungs with the inspired air.
Supporting tissue + elastic fibres
Endothelial cell of blood capillary

15. Images

16. Task:
Fill in your sheet for the adaptations of the alveoli for gas exchange.

17. Adaptations for efficient gas exchange
Feature
Structure / Adaptation
Short diffusion path
Large surface area
Concentration gradient
(big difference in concentration either side of surface )
Thin walls ( one cell thick) of alveoli and capillaries
Made from tissue called squamous epithelium)
Capillaries close to alveoli walls
Large numbers of alveoli
Vast capillary network
Folded surface of alveoli
Concentration gradient maintained as fluid is moved away from exchange surface by circulation
Ventilation (breathing) removes stale air and fills lungs with fresh air

19. Name Lisa Simpson E Grade Female Describe Young Red dress Yellow skin
D,E Grades
Explain
B,C,D Grades
Sister of Bart
Cartoon character
Suggest, with reasons, which parent has influenced her development the most ( A*, A , B grades)

22. Tasks:
Fill in your sheet for the adaptations of the alveoli for gas exchange. Highlight key terms on worksheet “Fine structure of the lung”

23. Why is diffusion of gases so efficient in the alveoli?
The RBC are slowed as they pass through the pulmonary capillaries, allowing more time for diffusion.
The distance between the alveolar air and the RBC is reduced as the RBC are flattened against the capillary walls.
The walls of both alveoli and the capillaries are very thin and therefore the distance over which diffusion takes place is very short.
The alveoli and blood capillaries have a very high total surface area.
Breathing movements constantly ventilate the lungs, and the action of the heart constantly circulates the blood around the alveoli. Together these ensure that the steep concentration gradient of gases to be exchanged is maintained.

26. Try not to fall into traps...
Don’t just focus on familiar words
Don’t pick a term you understand and write all that you know about that
Don’t forget to include information requested by the question stem
Describe when you should explain (and vice versa)

27. Answers:

28. Plenary task:
Exam question 5 parts a & b
(6 mins)