This document discusses gas exchange in four animal groups - mammals, fish, birds, and insects. It describes how each group has adapted to efficiently take in oxygen and release carbon dioxide through specialized gas exchange surfaces and circulatory systems. Fish respire through gills with countercurrent flow to enhance gas diffusion. Mammals and birds use lungs with alveoli that have a large surface area and short diffusion distance. Birds additionally have air sacs that facilitate one-way airflow through the lungs. Insects transport gases directly to cells through a tracheal system.

1. GAS EXCHANGE
IN ANIMALS
We will be studying the diversity of adaptations
for this process in four animal groups:
MammalsFish Birds Insects

2. AN OVERVIEW
• Cellular respiration
requires O2 and produces CO2 :
C6H12O6 + 6O2  6CO2 + 6H2O
• Gas exchange provides a means of
supplying an organism with O2 and
removing the CO2
glucose + oxygen  carbon dioxide + water

3. Organism level
Cellular level
Respiration
ATP
Gas exchange medium (air or water)
Fuel molecules
from food
CO2
Gasexchangesurface
O2
CO2
Circulatorysystem

4. THE SOURCE OF OXYGEN
Air
• about 21% oxygen
• thinner at higher altitudes
• easy to ventilate
Water
• amount of oxygen varies but is always
much less than air
• even lower in warmer water
• harder to ventilate

5. GAS EXCHANGE SURFACES
Gases move by diffusion. Diffusion
Diffusion is greater when:
• the surface area is large
• the distance travelled is small
• the concentration gradient is high
Gas exchange also requires a moist surface
• O2 and CO2 must be dissolved in water to
diffuse across a membrane

6. GAS EXCHANGE SURFACES
Therefore, an efficient gas exchange surface will…
• have a large surface area
• provide a small distance for gases to diffuse
across
• be moist
…and will be organised or operate in a way that
maintains a favourable concentration gradient
for the diffusion of both gases.
A circulatory system may operate in
tandem with the gas exchange system
to maintain the concentration gradient

7. Depends on:
• the size of the organism
• where it lives – water or land
• the metabolic demands of the
organism – high, moderate or low
STRUCTURE OF THE GAS
EXCHANGE SURFACE

8. TYPES OF GAS EXCHANGE
SURFACE

9. WATER AS A
GAS EXCHANGE MEDIUM
No problem in keeping the cell membranes
of the gas exchange surface moist
BUT
O2 concentrations in water are low,
especially in warmer and/or saltier water
SO
the gas exchange system must be very
efficient to get enough oxygen for respiration

10. GETTING OXYGEN FROM WATER:
FISH GILLS
• Gills covered by an
operculum (flap)
• Fish ventilates gills by
alternately opening and
closing mouth and
operculum
 water flows into mouth
 over the gills
 out under the operculum
• Water difficult to ventilate
 gills near surface of body

11. GETTING OXYGEN FROM WATER:
FISH GILLS
• Each gill made
of four bony
gill arches.
• Gill arches
lined with
hundreds of
gill filaments
that are very
thin and flat.

12. GETTING OXYGEN FROM WATER:
FISH GILLS
• Gill filaments are
have folds called
lamellae that
contain a network
of capillaries.
• Blood flows
through the blood
capillaries in the
opposite
direction to the
flow of water.

13. ENHANCING THE EFFICIENCY
OF FISH GILLS
• Gills have a very large surface area:
four arches with flat filaments with lamellae
folds
• Gills are thin-walled and in close contact
with water: short distance for diffusion
• Gills have a very high blood supply to
bring CO2 and carry away O2  dark red
colour
• Gills are moist: fish live in water!

14. ENHANCING THE EFFICIENCY
OF FISH GILLS
Fresh water flows over gills in one direction.
COUNTER-CURRENT FLOW: water and blood in
the gills flow in opposite directions
 maintains a favourable concentration gradient
for diffusion of both gases
Concurrent
flow animation
Countercurrent
flow animation

15. CONCURRENT FLOW

16. COUNTER-CURRENT FLOW

18. GETTING OXYGEN FROM AIR:
MAMMALS, BIRDS & INSECTS
As a gas exchange medium, air has many
advantages over water:
• Air has a much higher oxygen
concentration than water
• Diffusion occurs more quickly so less
ventilation of the surface is needed
• Less energy is needed to move air
through the respiratory system than water

19. BUT
as the gas exchange surface must be
moist, in terrestrial animals water
is continuously lost from the gas
exchange surface by evaporation
SO
the gas exchange surface is folded
into the body to reduce water loss.
GETTING OXYGEN FROM AIR:
MAMMALS, BIRDS & INSECTS

20. WARM-BLOODED ANIMALS
Warmth speeds up body’s reactions
 enables faster movement etc
BUT
increases evaporation of water from lungs
AND
increases demand for energy to stay warm
SO
higher demand for gas exchange to provide O2
for and remove CO2 from respiration

21. MAMMAL LUNGS: VENTILATION
Two lungs ventilated by movement
of diaphragm and ribs

22. MAMMAL LUNGS: STRUCTURE
• Air enters via trachea
(windpipe)
• Trachea branches into
two bronchi (one
bronchus to each lung)
• Bronchi branch into
bronchioles
System of tubes (held open by rings of
cartilage) allow air to flow in and out of lungs

23. MAMMAL LUNGS: STRUCTURE
Rubber cast of human lungs

24. MAMMAL LUNGS: STRUCTURE
Healthy lungs Smoker’s lungs

25. MAMMAL LUNGS: STRUCTURE
Many alveoli at the end of the bronchioles
• walls made of flat cells; only one cell thick
• each alveolus lined with moisture
• surrounded by capillary network carrying blood

26. GAS EXCHANGE IN MAMMALS
Inhaled air: 21% O2 and 0.04% CO2
Blood arriving: low in O2 and high in CO2
O2 in
lung air
dissolves in
moist lining
diffuses into
blood
CO2 in
blood
diffuses into
moist lining
diffuses into
lung air
Exhaled air: 17% O2 and 4% CO2
Blood leaving: high in O2 and low in CO2

27. GAS EXCHANGE IN MAMMALS
Gas exchange
animation

28. GAS EXCHANGE IN MAMMALS

29. Large surface area
• many tiny alveoli
• area as big as a tennis court in humans!
Short distance for diffusion
• alveoli and capillary walls only one cell thick
• cells are flattened so very thin
• capillaries pressed against alveoli
Moist
• wet lining of alveolus
• system internal to reduce water loss by evaporation
ENHANCING THE EFFICIENCY
OF MAMMAL LUNGS

30. Maintaining a concentration gradient
• air (with depleted O2 and excess CO2) is
exhaled  replaced with fresh inhaled air
• blood (having lost CO2 and been enriched
with O2) returns to heart to get pumped
around body replaced with blood collected
from body
ENHANCING THE EFFICIENCY
OF MAMMAL LUNGS

31. BIRD LUNGS
Birds have a high demand for oxygen:
• warm-blooded so metabolism is high
• flight requires a lot of energy
Additional challenge:
• air at higher altitude is
thinner  lower in O2
…yet some species have
been seen flying over
Mt Everest!
Birds have a very efficient gas exchange system to
cope with low O2 supply & high O2 demand

32. BIRD LUNGS
Birds have lungs
and air sacs:
• air sacs are not
sites of gas
exchange
• air sacs enable a
one-way flow of
air through lungs

33. BIRD LUNGS: VENTILATION
Passage of air through lungs:
in trachea rear air sacs rear bronchi
parabronchi in lungs
out trachea front air sacs front bronchi

34. BIRD LUNGS
Main air tubes through lungs are the parabronchi.
Tiny air capillaries loop away from and back to
parabronchi  one way flow of air
Blood capillaries run alongside air capillaries
BUT
blood flows in opposite direction to air flow
 COUNTER-CURRENT EXCHANGE of gases

36. ENHANCING THE EFFICIENCY
OF BIRD LUNGS
Large surface area
• many tiny air capillaries
Short distance for diffusion
• air and blood capillary walls made of
flattened, thin cells
• air & blood capillaries alongside each other
Moist
• lining of air capillaries is wet
• system is internal to conserve moisture

37. ENHANCING THE EFFICIENCY
OF BIRD LUNGS
Maintaining a concentration gradient
• Air flows in one direction through lungs
regardless of whether the bird is inhaling or
exhaling
• One way passage in both parabronchi and
air capillaries; other way in blood
capillaries
 COUNTER-CURRENT EXCHANGE

38. INSECT TRACHEAL SYSTEM
Completely different system!
Air tubules (trachea & tracheoles) throughout the
body which open to the environment via spiracles

39. INSECT TRACHEAL SYSTEM
• Trachea kept open by circular bands of chitin
• Branch to form tracheoles that reach every cell
• Ends of the tracheoles are moist
• Oxygen delivered directly to respiring cells –
insect blood does not carry oxygen

40. • Oxygen delivered
directly to
respiring cells
• Can pump body to
move air around in
tracheal system
BUT
• Size of animal
limited by relatively
slow diffusion rate
ENHANCING THE EFFICIENCY
OF INSECT TRACHEAE

41. DIVERSITY
fish
gills
mammal
lungs
bird
lungs
insect
tracheae