1. mass
transport
systems

2. Mass transport systems
Move substances to & from excahnge surfaces
Substances are dissolved or suspended in fluid
Fluid travels in vessels
Prevents accumulation of waste

3. Mass flow transport occurs within larger organisms and more active organisms because their SA:VOL can never be large enough to provide all the cells with the necessary metabolites.
Pressure differences within the organism move the materials from and area of high concentration, called the source, to an area of lower concentration, called the sink.

4. Gas exchange in flowering plants & mammals
It is necessary to supply all cells with oxygen for respiration and to excrete carbon dioxide.
Gas exchange surfaces are specialised to maximise the rate of gas exchange:
Large surface area
Moist surface for respiratory gases to dissolve
Diffusion gradients for both O2 & CO2
Permeable to both O2 & CO2
Short diffusion path

5. Surface area x difference in concentration
Fick’s Law expresses the relationship between the rate of diffusion, surface area, concentration gradient & membrane thickness.
RATE OF
DIFFUSION
Surface area x difference in concentration =
Membrane thickness

6. A good exchange surface needs to be adapted to allow a high rate of diffusion.
It needs to have:
large SA
method to maintain a high conc. gradient
short diffusion distance
e.g alveoli in the lungs to pick up oxygen and remove carbon dioxide, root hair cells to take up minerals such as nitrates by AT, leaf for gas exchange for photosynthesis.

7. A poor exchange surface needs to be adapted to reduce the rate of diffusion.
It needs to have:
small SA
method to reduce a high conc. gradient
large diffusion distance
e.g leaf to reduce transpiration

8. the rate of gas exchange
Factors affecting
the rate of gas exchange
in a mammal

9. Mammals have highly specialised exchange surfaces because they have a small surface area to volume ratio and an impermeable body covering.
The alveolar wall forms the gas exchange surface.

10. Adaptations of the lung surface
Thin respiratory surface creates a short diffusion distance
Single layer of squamous epithelium of the alveoli
Single layer of squamous endothelium of blood capillary wall
The capillaries sit tight against the alveoli and the capillaries are so narrow that the red blood cells )erythrocytes) must squeeze through, ensuring contact with the endothelial wall and reducing the diffusion pathway

11. Squamous epithelium lining the alveoli
lumen of alveolus

12. squamous endothelium lining blood capillary wall.

13. Adaptations of the lung surface
Large surface area provided by alveoli
Approximately 700 million alveoli with a surface area of 75m2, 30 times larger than the surface of the body.
Moist outer surface of alveoli

14. Adaptations of the lung surface
Steep concentration gradients are created by
Mass flow of air to the respiratory surface i.e. ventilation
Brings oxygen into the lungs and removes carbon dioxide
Rich vascular supply through the capillaries
Brings carbon dioxide rich blood to the alveoli and removes oxygen rich blood
Together these maintain a steep diffusion gradient of oxygen from the alveoli into the blood and carbon dioxide from the blood into the alveoli.

15. Diffusion gradient for O2
Breathing movements ensure that there is always a high concentration of O2 in the alveoli
Good blood supply constantly removes O2 (which combines with haemoglobin in RBC) ensuring the concentration is low
Large difference between O2 concentration creates steep concentration gradient for efficient gas exchange

16. Adaptations of the lung surface
Moist outer surface of alveoli, deep inside the body to reduce water loss by evaporation
gases dissolve for diffusion across the surfaces
Surfactant in the moisture layer of alveoli reduces surface tension
This prevents the alveoli collapsing which would reduce the SA for gas exchange
Macrophages
Protect against infection by digesting microorganisms by phagocytosis

17. Diffusion gradient for CO2
Breathing movements ensure that there is always a low concentration of CO2 in the alveoli
Good blood supply constantly brings CO2 (released in cell respiration) from the body ensuring the concentration is high
Large difference between CO2 concentration creates steep concentration gradient for efficient gas exchange

18. Concentration gradient
circulation
diffusion
diffusion
Lungs
Respiring cell
Blood transports gases and metabolites
Large SA for gas exchange
Large SA for gas exchange
circulation
Deoxygenated
Oxygenated

19. Lung surfactant
The watery film lining the lungs creates a surface tension which would cause the alveoli to collapse and stick together when air is exhaled.
Surfactant is a mixture of phospholipid molecules found between the watery film on the inner surface of the alveoli and the air inside them
It reduces the surface tension so that the alveolar surfaces do not stick together, they remain open for gas exchange
IMPORTANT AT BIRTH. First breath very difficult, but causes surfactant to line alveoli; subsequent breaths easier. Premature babies do not have sufficient to keep alveoli open.

20. Air exhaled Hydrophobic head immersed in water next to alveolar wall
Walls of the alveolus
drawn inwards
Surfactant prevents
alveolar membranes
sticking together
Hydrophobic head
immersed in water
next to alveolar wall
Hydrophobic tail
in air space
Water lining the
inner surface of
alveolus

23. Past paper essay question
Give an account of the features of the gas exchange surface in a mammal and explain how these result in efficient gas exchange. (13 marks)

24. https://pbs.twimg.com/tweet_video/B-30NonUAAER7Yf.mp4
breathing
The term used to describe the processes involved in ventilating the lungs and the alveoli.

25. The respiratory system

26. The breathing mechanism
Breathing involves the alternate increase and decrease
of air pressure in the lungs relative to that outside.
A fall in air pressure in the thorax causes inspiration
A rise in air pressure in the thorax causes expiration

27. Inspiration/inhalation (breathing in) ACTIVE PROCESS
external intercostal muscles contract & internal intercoastal muscles relax
ribs and sternum move up and out
width of thorax increases front to back and side to side
diaphragm contracts
diaphragm moves down, flattening
depth of thorax increases top to bottom
volume of thorax increases.
pressure between the pleural surfaces decreases. 
air pressure in alveoli is less than atmospheric pressure. 
air is forced in by the higher external atmospheric pressure
lungs expand to fill thoracic cavity. 

28. expiration (breathing out) PASSIVE PROCESS
External intercostal muscles relax internal intercostal muscles contract
ribs and sternum move down and in
width of thorax decreases front to back and side to side
diaphragm relaxes
diaphragm moves up & returns to a dome shape
depth of thorax decreases top to bottom. So the … 
volume of thorax decreases. 
pressure between the pleural surfaces increases. 
lung tissue recoils from sides of thoracic cavity 
air pressure in alveoli is more than atmospheric pressure. 
air is forced out.

29. inspiration

30. expiration

31. Use class text books to BRIEFLY outline the following conditions
The effects of smoking
Use class text books to BRIEFLY outline the following conditions
Lung cancer
Emphysema
Cilia damage
Bronchitis

32. PRACTICALS: The respirometer The J tube