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2. In Stentor, a narrow elongate shape permits faster diffusion.
In Stentor, a narrow elongate shape permits faster diffusion.
Myonemes along body wall allow shape contraction to mix cell contents.
Exterior circulation by cilia helps move fresh water for gas exchange, nutrients closer to body, for exchange by diffusion.

3. Gas Exchange in Unicellular Organisms
Size matters: microorganisms use simple diffusion for gas exchange
Altering shape may make diffusion uptake a shorter, faster path
diffusion

4. Size Matters: Surface/Volume Ratio
unfold the cube’s surfaces
1 cm
volume = 1 cm3
S/V=6.0
surface = 6 cm2
unfold the cube’s surfaces
2 cm
DB25020.jpg
volume = 8 cm3
S/V=3.0
surface = 24 cm2
Larger organisms have less surface area relative to volume than do smaller organisms. Materials inside the larger multicellular body have less contact with surface, so something more than diffusion is needed!
Conclusion?
Circulation!

5. Geometry Matters: Surface/Volume Ratio
unfold the cube’s surfaces
2 cm
volume = 8 cm3
S/V=3.0
surface = 24 cm2
unfold the cube’s surfaces
1 cm
DB25020.jpg
volume = 8 cm3
S/V=3.5
Larger organisms depending on diffusion for gas exchange get better gas exchange if the body is thinner rather than blockier
surface = 28 cm2
Conclusion?

6. Unicellular animals use diffusion
Simple aquatic multicellular animals exchange gas through skin with capillary exchange with blood system…evaginated
Unicellular animals use diffusion
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..or invaginated
Air breathers use lungs or tracheal systems

7. Invaginated or Evaginated?
Bristleworms (Nereis) have capillary beds in the parapodia for gas exchange
Invaginated or Evaginated?
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8. Mexican Axolotl Ambystoma mexicanum
See Fig pg 906

9. Nudibranch Flabellina verrucosa

10. Argopecten gibbus the Calico scallop, a bivalve mollusc
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Ciliated surfaces move water across gills for gas exchange
Mucilage surface traps and accumulates food particles
Cilia move food-laden mucilage to mouth for digestion

11. Scallop respiration and feeding
(shown with one valve removed)
The soft tissue anatomy of the calico scallop, Argopecten gibbus, visible following removal of one of the shell valves. Key: AM - adductor muscle; G – gills; O – ovary; T – testis; L – ligament; M – mantle. The inhalant and exhalant chambers of the mantle cavity are identified as IC and EC respectively.

12. Exploring the incurrent and excurrent siphons of a clam:

13. Evaginated gills surrounded by water bearing oxygen
Architeuthis Giant squid
Evaginated gills surrounded by water bearing oxygen
Mesonychoteuthis hamiltoni
Colossal squid

14. Perca flavescens oxygenated water deoxygenated, carbonated water
oxygenated
water
operculum
deoxygenated,
carbonated water
Muscular operation of operculum system moves water into mouth, over evaginated gills, and out from trailing edge of operculum
See Fig pg 907

15. How do evaginated gills work?
oxygenated
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filament enlarged…
deoxygenated

16. Gill filament shows counter-current exchange design:
oxygenated water
water and blood flow in opposite directions
blood return to heart
blood from heart
deoxygenated water
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See Fig pg 907

17. Counter-current is more efficient than concurrent exchange water water
blood
blood
100 50
Percent O2 Saturation
water
blood
100 50
Percent O2 Saturation
water
blood
Countercurrent flow maximizes:
Oxygen removal from water
Blood oxygen content
This efficient system is needed because oxygen solubility is very low in water (10 mg/L) compared to in air (286 mg/L).
See Fig pg 907

18. Delicate gills need protection from predators: shells, opercula
Other species evolved internalized respiratory trees…
Sea cucumber body systems
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evaginated or invaginated?

19. Tidal flow through anus into respiratory tree of sea cucumber:

20. The tidal flow gas supply is enough to support a friend too…

21. And now for a look inside our gastropod mollusc…
Trochophore larva:
And now for a look inside our gastropod mollusc…
Veliger larva:
The shell obviously provides a hard covering for the visceral mass.
The snail shown here is a pulmonate, with a vascularized mantle cavity serving as a lung. Vascularizing this led to loss of the gills in most gastropods.
The gastropods, are clearly hermaphroditic, and some are self-fertile.
Free-living larval stages are the dispersal mechanisms in water (diffusion?)

22. Adult Sea elephant (snail)… trochophore larva
its radula
gas exchange by simple diffusion
veliger larva
its proboscis

23. The slug shows the pneumostome in the mantle for breathing.
foot
mantle
optical tentacles
skirt
sensory tentacles

24. book gills

25. Chelicerata Considerable diversity within a single taxonomic category
book lungs
trachea
book gills
diffusion

26. Argyroneta aquatica, the water spider, traps air with body hairs at surface and brings the air down to the hydrophobic web for later use…sometimes called the “water bell” spider.

27. Centruroides vittatus (bark scorpion) has a book lung
(an evaginated surface like a gill for terrestrial gas exchange)
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28. In an insect respiratory tree, the tracheoles contact every cell.
trachea
tracheoles
spiracles
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See Fig pg 908

29. Tobacco hornworm: Manduca sexta larva

30. The abdominal exoskeletal plates an insect, mostly rigid, move relative to each other by muscle contraction inside, to drive the tidal flow through the spiracles (on the side of the body)
See also:

31. The Cicada Killer Wasp Sphecius speciosus pumps his abdominal segments like a bellows to produce tidal flow through the spiracles on the side of his body.

32. An insect gas exchange--an invaginated tracheolar system
This is not particularly different from the respiratory tree model
But the segmented abdomen and musculature permit tidal air flow
trachea
spiracle
tracheoles
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33. Here are two spiracles, one open with sensors functioning.
The other is closed to avoid desiccation/predation, etc.
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The convergence with stomata in plant leaves is interesting!

34. Could this be another example of “ontogeny recapitulating phylogeny”?
In larval aquatic stages of arthropod metamorphosis, larvae may demonstrate evaginated gills rather than invaginated tracheoles.
Could this be another example of “ontogeny recapitulating phylogeny”?
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35. Vertebrates evolved an invaginated gas exchange system:
The alveolate lung
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Notice in this sequence how exchange surface area increases!

36. Tidal flow in “blind pouch” exchange system
warms, humidifes,
traps particles
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closes glottis for swallowing
exhaled air vibrates cords for voice
mucus, particles swallowed
cartilage ridges keep airway open
cilia lift mucus with particles upward

37. Bronchoscopy: Vocal cords, Cartilage ridges, Mucus!

38. The human breathing system: the larger structures
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39. The mammalian lung gas exchange fine structure: the alveolus
Note the convergence of the oxygen contact feature with spongy mesophyll of plants
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See Fig pg 910

40. Respiratory Pigments Function: deliver O2 to the cells
Hemerythrin – red color but no heme group Fe, low oxygen binding, few inverts, Methylococcus (methanotropic bacterium)
Hemocyanin – blue color, Cu group, moderate oxygen binding, most molluscs
Hemoglobin – red color, heme Fe group, high oxygen binding, 4 polypeptides, vertebrates and some invertebrates
Some organisms have none of these: high surface to body area ratio so exchange occurs at body surface by simple diffusion
wikipedia/commons/7/79/
Hemerythrin.jpg
Wikipedia/commons/f/fb/
Hemocyanin2.jpg
commons/d/d2/Hemoglobin.gif

41. How the alveolate lung works inhalation exhalation
“Artificial respiration” is possible because of this!
inhalation
exhalation
Notice this is not a counter-current mechanism and is inefficient compared to gills
Terrestrial animals do not need efficient exchange because air holds much oxygen compared to water
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42. contracts to drop floor
The ventilation movement in vertebrates with lungs has two parts
lungs nearly empty
lungs nearly full
rib muscles lift
contracts to drop floor
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For many singers and public speakers, the first lesson is re-learning how to breathe!
See Fig pg 911

43. Bird lungs have additional air sacs attached to their lungs
anterior sacs
lung
posterior sacs

44. What is the advantage of this apomorphy? lung
Bird Lung Function:
What is the advantage of this apomorphy?
lung
anterior air sac
posterior air sac
inhalation
blood flow
anterior air sac
posterior air sac
lung
exhalation
blood flow
See Fig pg 911

45. SEM of bird lung: note-cells are close to gas exchange surfaces
Just as observed in plant leaves
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46. Gas Exchange Path for Cooling: Canine Panting
cool inspired air
evap cool expired air
cooled arterial blood to brain
arterial blood from heart
cooled venous blood
exg rete
What kind of exchange is found in this rete?
arterial blood in nose and tongue
air
temperature
venous blood to heart
arterial blood to brain
exchange rete
venous blood in nose and tongue

47. In wintering aquatic birds, the feet isolate body from cold water
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Feathers provide body insulation

48. Gas Exchange between the environment and the film of body fluid coating body cells is only the first step in gas exchange for large multicellular animals.
The rest of the story involves getting gas exchange between the exchange surfaces and the blood stream and then between the blood stream and the internal body tissues.
The rest of the story relates to animal circulation systems which we shall hold off for now...