1. Exchange Systems
F211

2. Explain, in terms of surface-area-to-volume ratio, why multicellular organisms need specialised exchange surfaces and single-celled organisms do not.
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3. Exchange surfaces What do cells need to keep them alive?
Oxygen for aerobic respiration
Glucose for energy
Proteins
Fats to make membranes
Minerals- to maintain water potential and help action

4. Exchange surfaces What waste do cells need to get rid of?
Carbon dioxide
Oxygen
Other wastes such as ammonia or urea which contain excess nitrogen

5. Larger organisms need a larger area to exchange more substances
1cm3 organism
Surface area : volume ratio = 6:1
8cm3 organism surface area:volume ratio = 3:1
27 cm3 organism surface are : volume ratio = 2:1
1cm3
Larger organisms need a larger area to exchange more substances
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6. What makes an exchange surface efficient?
Feature
How it helps
Large surface area
Larger area for molecules to diffuse
Thin barrier
Shorter distance for diffusion
Permeable membrane
Allow molecules through
Good supply/removal of molecules required
Maintain diffusion gradient

7. Examples
Small intestine
Liver
Lungs
Root hairs
Hyphae of fungi

8. Week 7
Describe the features of an efficient exchange surface with reference to diffusion of oxygen and carbon dioxide across an alveolus.
Describe the features of the mammalian lung that adapt it to efficient gas exchange.
Outline the mechanism of breathing (inspiration and expiration) in mammals, with reference to the function of the rib cage, intercostal muscles and diaphragm.
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9. Lungs and breathing
Label as many parts as you can.

10. Lungs and breathing Larynx Trachea Right lung Left lung Left bronchus
Right bronchus
Bronchioles
Intercostal
Muscles
Heart
Alveoli
Ribs
Pleural cavity
Pleural Membrane
Diaphragm
Label as many parts as you can.

11. Video Clip

12. Lungs and breathing

13. Week 7
Capillary network over the surface of alveoli and details of gaseous exchange
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14. Can you say what is happening at each stage8. 7. 6. 5. 4. 1. 2. 1. 3. 2.

15. Feature that make the lungs adapted to exchange
Week 7
Feature that make the lungs adapted to exchange
Large surface area - An average adult has about 600 million alveoli, giving a total surface area of about 70m² (Half size of tennis court)
Permeable to O2 and CO2
Thin barrier to reduce diffusion distance
The walls of the alveoli are composed of a single layer of flattened epithelial cells, as are the walls of the capillaries, so gases need to diffuse through just two thin cells (less than 1µm thick)
Both cells made of squamous cells (meaning flattened or very thin cells)
Capillaries very close to alveolus wall
Narrow capillaries- RBCs squeezed against cell wall
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16. Feature that make the lungs adapted to exchange
Week 7
Feature that make the lungs adapted to exchange
Water diffuses from the alveoli cells into the alveoli so that they are constantly moist.
Oxygen dissolves in this water before diffusing through the cells into the blood, where it is taken up by haemoglobin in the red blood cells.
The water also contains a soapy surfactant which reduces its surface tension and stops the alveoli collapsing.
The alveoli also contain phagocyte cells to kill any bacteria that have not been trapped by the mucus
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17. 1) by blood flow on one side by air flow on the other side.
The steep concentration gradient across the respiratory surface is maintained in two ways:
1) by blood flow on one side
by air flow on the other side.
This means oxygen can always diffuse down its concentration gradient from the air to the blood, while at the same time carbon dioxide can diffuse down its concentration gradient from the blood to the air.
The flow of air in and out of the alveoli is called ventilation and has two stages: inspiration (or inhalation) and expiration (or exhalation). Lungs are not muscular and cannot ventilate themselves, but instead the whole thorax moves and changes size, due to the action of two sets of muscles: the intercostal muscles and the diaphragm.

18. The flow of air in and out of the alveoli is called ventilation and has two stages: inspiration (or inhalation) and expiration (or exhalation). Lungs are not muscular and cannot ventilate themselves, but instead the whole thorax moves and changes size, due to the action of two sets of muscles: the intercostal muscles and the diaphragm.

19. Describe the stages of Inhalation and exhalation
Must give reference to
Diaphragm
Intercostal muscles
Volume of chest cavity
pressure
Exhalation is a passive process, We breathe out when our muscles relax

20. Breathing is a passive process
Inhalation
Exhalation
Diaphragm Contracts, moving downwards increasing the volume of the chest cavity and displacing the organs beneath
The diaphragm relaxes, the organs below move back into place
The intercostal muscles contract moving the ribcage up and out
The intercostal muscles relax, the ribcage moves down and in
The volume of the chest cavity increases decreasing the pressure in the thorax below atmospheric pressure
The volume of the chest cavity decreases causing air pressure in the lungs to increase above atmospheric pressure
Air is sucked into the lungs as a result
Air is forced out of the lungs as a result

21. Week 7
Describe the distribution of cartilage, ciliated epithelium, goblet cells, smooth muscle and elastic fibres in the trachea, bronchi, bronchioles and alveoli of the mammalian gaseous exchange system.
Describe the functions of cartilage, cilia, goblet cells, smooth muscle and elastic fibres in the mammalian gaseous exchange system.
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22. What is the role of each tissue? Cartilage Smooth Muscle
Week 7
(a) Bronchiole and (b) trachea in transverse section
What is the role of each tissue?
Cartilage
Smooth Muscle
Elastic fibres
Goblet cells and glandular tissue
Cilliated epithelium
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24. Week 7
Explain the meanings of the terms tidal volume and vital capacity.
Describe how a spirometer can be used to measure vital capacity, tidal volume, breathing rate and oxygen uptake.
Analyse and interpret data from a spirometer.
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25. Removes CO2

27. Total Lung Capacity- The maximum amount of air that the lungs can hold
Residual Volume- The volume of air that remains in the lungs after breathing approx 1.5dm3
Vital Capacity- The maximum usable lung volume (total lung capacity minus the residual volume). The average vital capacity is dm3 for men and for women.
Tidal Volume- The volume of air that moves in and out of the lungs in each breath (during normal breathing). In a normal adult this is about 0.5 dm3.
Inspiratory Reserve Volume- The amount of air that the lungs will hold after a normal expiration (i.e. inspiratory reserve + tidal volume).
Expiratory Reserve Volume- The amount of air remaining in the lungs after a normal quiet expiration (i.e. expiratory reserve volume + residual volume).

29. Exam questions
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