1. Biology 103 - Main points/Questions
How do your lungs work?
How do gasses get to your cells?
What gasses do plant cells need to transport?

2. Remember Circulation …
Plants and animals push extracellular fluids
Plants generate flow w/o muscle tissue
Animals generate flow with pumping muscles
Fungi move intracellular fluids
Use cytoplasmic streaming
Proteins in the cell “stir” the cytoplasm moving nutrients etc. to rapidly growing hyphae.
Protists use diffusion & streaming

3. Why exchange gases? Cellular respiration - summarized as:
Glucose + oxygen  carbon dioxide + water
Look! This consumes oxygen and gives off CO2
And, of course, produces ATP!
So - Gas exchange supplies oxygen for cellular respiration and disposes of carbon dioxide

4. Gas Exchange
All the complex multicellular critters use oxygen to produce ATP in mitochondria
So all cells need gas exchange for this
Many plant cells also need a supply of carbon dioxide for photosynthesis
We look at animals first

5. In vertebrates gases are transferred via the circulatory system!
Gas exchange occurs between an organism and the environment, often in specialized respiratory organs.
In vertebrates gases are transferred via the circulatory system!
Figure: 35-1
Title:
Skeletal muscle structure
Caption:
A muscle is surrounded by connective tissue and attached to bones by tendons. It contains from a few to 1000 muscle cells called muscle fibers, often packaged into bundles within the muscle. Each fiber is packed with cylindrical subunits called myofibrils, which contain thick and thin filaments of protein.

6. Ultimately exchange happens between cells and the interstitial fluid that surrounds them!
Figure: 35-1
Title:
Skeletal muscle structure
Caption:
A muscle is surrounded by connective tissue and attached to bones by tendons. It contains from a few to 1000 muscle cells called muscle fibers, often packaged into bundles within the muscle. Each fiber is packed with cylindrical subunits called myofibrils, which contain thick and thin filaments of protein.

7. Types of Respiratory Systems
The simplest animals obtain oxygen directly from their environments through diffusion

8. Fig. 40-3
Mouth
Diffusion works well as long as distances are small and surfaces are permeable
Gastrovascular
cavity
But as organisms become more complex they need specialized exchange organs
Exchange
Exchange
Exchange
Figure 40.3 Contact with the environment
1.5 mm
(a) Single cell
Cnidarians

9. All organisms use diffusion at the cellular level but…
Fig. 40-3
Mouth
Diffusion works well as long as distances are small and surfaces are permeable
Gastrovascular
cavity
All organisms use diffusion at the cellular level but…
Exchange
Exchange
Exchange
Figure 40.3 Contact with the environment
1.5 mm
(a) Single cell
Cnidarians

10. Types of Respiratory Systems
As organisms get more complex they need specialized organs to exchange gases with the environment
different phyla have different organs:
Gills in fish, some arthropods, mollusks,
Tracheae in insects,
and lungs mostly in terrestrial chordates

11. Why do gases move?
Gases diffuse down pressure gradients in the lungs and other organs
In the lungs and tissues, O2 and CO2 diffuse from where their concentrations are higher to where they are lower

12. Remember diffusion Movement from high concentration to low
Doesn’t require any energy expenditure to make happen
Works very quickly over short distances
Important transport mechanism of cellular material

13. Factors controlling diffusion rate:
Can you remember what some are?

14. Factors controlling diffusion rate:
Temperature
Size of molecule:
Concentration gradient:
Surface area:
Distance:
Medium
set by organism
set
constantly maintained
Increased as much as possible
Decrease as much as possible
Gas as often as possible

15. Respiratory Medium
Animals can use air or water as a source of O2, or respiratory medium
In a given volume, there is less O2 available in water than in air
Obtaining O2 from water requires greater efficiency than air breathing

16. Respiration in Aquatic Vertebrates
Water moves past a fish’s gills in one direction
this permits countercurrent flow

17. Respiration in Aquatic Vertebrates
Countercurrent flow
extremely efficient way of extracting oxygen
blood flows through a gill filament in an opposite direction to the movement of water
the blood always encounters water with a higher oxygen concentration (constant gradient for diffusion)

18. Figure 30.3 Countercurrent flow
Because the two fluids flow in opposite directions blood can continue to pick up oxygen well past the 50% mark.
Figure 30.3 Countercurrent flow

19. Figure 30.3 Countercurrent flow
If blood flowed in the same direction as water the system could exchange at most 50% of the gas dissolved.
Figure 30.3 Countercurrent flow

20. Terrestrial gas exchange
For organisms on the land gas exchange poses a new problem
The exchange must happen on living cells bathed in fluid – but fluid loss can be a huge problem so…
Gas exchange organs are moved into the body & adaptations to prevent water loss are common.

21. Tracheal Systems in Insects
The tracheal system of insects consists of tiny branching tubes that penetrate the body
The tracheal tubes supply O2 directly to body cells

22. Fig c

23. Lungs Lungs - an infolding of the body surface
The circulatory system transports gases between the lungs and the body
The size and complexity of lungs correlate with an animal’s metabolic rate

24. In humans: A system of branching ducts conveys air to the lungs
Air inhaled through the nostrils passes through the pharynx via the larynx, trachea, bronchi, bronchioles, and alveoli, where gas exchange occurs
Exhaled air passes over the vocal cords and can create sounds

25. Fig. 30.6

26. Fig c

27. How a Mammal Breathes
Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs
Lung volume increases as the rib muscles and diaphragm contract

28. Figure 30.7 How breathing works

29. Blood arriving in the lungs has a low amount of O2 and a high concentration of CO2 relative to air in the alveoli
In the alveoli, O2 diffuses into the blood and CO2 diffuses into the air
In tissue capillaries, gradients favor diffusion of O2 into the interstitial fluids and CO2 into the blood

30. When it leaves this has reversed
Alveolus
Alveolus
PCO2 = 40 mm Hg
PO2 = 100 mm Hg
PCO2 = 46
PO2 = 40
PCO2 = 40
PO2 = 100
Blood arriving in the lungs has a low O2 and a high CO2 relative to air in the alveoli
When it leaves this has reversed
Then in body tissue the situation is the opposite
Circulatory
system
Circulatory
system
PO2 = 40
PO2 = 100
PCO2 = 46
PCO2 = 40
Figure Loading and unloading of respiratory gases
PO2 ≤ 40 mm Hg
PCO2 ≥ 46 mm Hg
Body tissue
Body tissue
(a) Oxygen
(b) Carbon dioxide

31. To move more gas they are carried in several ways
Alveolus
Alveolus
PO2 = 100 mm Hg
PCO2 = 40 mm Hg
PO2 = 40
PO2 = 100
PCO2 = 46
PCO2 = 40
Circulatory
system
Circulatory
system
PO2 = 40
PO2 = 100
PCO2 = 46
PCO2 = 40
PO2 ≤ 40 mm Hg
PCO2 ≥ 46 mm Hg
Body tissue
Body tissue
In tissue capillaries, O2 moves out of the blood and CO2 moves into the blood… why?
To move more gas they are carried in several ways
Figure Loading and unloading of respiratory gases

32. hemoglobin molecules contain iron - oxygen binds in a reversible way
Figure 30.8 The hemoglobin molecule

33. hemoglobin acts like little sponges for oxygen
at high O2 levels (like in the lungs), most hemoglobin carry a full load of O2
in the tissues, the O2 levels are much lower and hemoglobin gives up its bound oxygen
The vast majority (> 90%) of oxygen you use was carried to your cells on hemoglobin

34. CO2 must also be transported by the blood
about 8% simply dissolves in the plasma
20% is bound to hemoglobin
rest is carried as HCO3- in blood cells & plasma
This is highlighted on figure from your book…

35. Figure 30.9 How respiratory gas exchange works

36. What about plants? Do they transport gasses in circulatory system?
No! – they rely only on diffusion
specialized anatomy makes this work…
CO2 O2
Light
H2O
Sugar
Figure 36.2 An overview of resource acquisition and transport in a vascular plant O2
H2O and minerals
CO2

37. Leaf cross section shows…
Cells packed in top layer - photosynthesis
Open “spongy” layer below for exchange
But cuticle blocks gas exchange…

38. Lots of open spaces inside but…
Plant leaf anatomy:
Lots of open spaces inside but…
Must open stomata (pores) to get gasses in
Opened
Closed

39. This causes leaf to lose water so…
plants need to balance water loss and gas exchange
Guard cells control opening/closing
How…?
changes in the water pressure of guard cells

40. When the guard cells lose water, the stoma closes
Figure guard cells open and close stomata
When the guard cells are plump and swollen with water, they are said to be turgid and the stoma is open
When the guard cells lose water, the stoma closes

41. Controlling stomata opening:
Most plants keep closed at night open during the day. Why?
Some specially adapted plants keep closed during day & open at night… Why would you do that?
Hint: ➔