GAS EXCHANGE IN ANIMALS
Biology ATAR Unit 2
Chapter 11
275-277
Keywords
Tracheal system
 Spiracles
 Lungs
 Air sacs
 Alveoli
 Gills
 Diffusion
 Concentration
gradient
 Counter-current
system

Making connections



All multicellular
organisms need systems
for gas exchange
The type of system an
organism has is
dependent its size and
on the environment it
lives in
All systems have
common characteristics
that increase the
efficiency of gas
exchange
GAS EXCHANGE
Gas exchange in
animals is by
diffusion
 The 2 main gases
exchanged is O2 into
the body and CO2 out
of the body
 A high concentration
of CO2 is more
dangerous to
organisms than a low
concentration of O2

Oxyge
n
Carbon dioxide
GAS EXCHANGE SURFACES
Characteristics of
effective exchange
surfaces:
1.
2.
3.
4.
Large surface area to
volume ratio
Thin & permeable
Moist – enables the
dissolution of O2 for
diffusion into the
blood stream
High concentration
gradient is
maintained across the
membranes
TYPES OF GAS EXCHANGE SYSTEMS
System
Animal
Example
Moist skin
Adult amphibians
Cnidarians
Insects
Arachnids
Frogs
Jellyfish
Grasshopper
Redback spider
Tracheal
system
Lungs
Mammals
Reptiles
Lungs with Birds
air sacs
Humans
Lizards
Chickens
Gills
Goldfish
Crabs
Tadpoles
Fish
Crustacean
Juvenile
amphibians
MOIST SKIN
CNIDARIANS
Cnidarians are
aquatic animals
 Gases continually
diffuse across the
membranes

AMPHIBIANS (FROGS)
Tadpoles have
external gills
 Frogs rely on their
lungs and their moist
skin for gas exchange

TRACHEAL SYSTEMS
 Insects
have holes (spiracles) which lead into
tubes (tracheas)
 The O2 diffuses through these from the outside
air and CO2 leaves by diffusion in the opposite
direction
GILLS
The amount of dissolved
O2 in water is a lot less
than it is in air
 Therefore, gills have a
greater surface area as
compared to the lungs of
a similarly sized mammal
 Gills are highly
convoluted structures
with a very high surface
area.

Blood flows in the
opposite direction to the
water (counter-current)
increasing the efficiency
of gas exchange
 Gills rely on water flowing
over them to ensure
maximum O2 uptake
 Gills are the most
efficient gas exchange
system out of all 3 types
of systems

LUNGS WITH AIR SACS
Birds have lungs
with air sacs
 They are inflated and
deflated by the
muscles of the rib cage
 The air sacs force air
through very fine
tubes where the gas
exchange takes place

LUNGS
Mammals and reptiles
have lungs.
 The air travels:
1. In through the nostrils
2. Down the trachea
3. Into the alveoli of the
lungs
 Gas exchange takes
place in the alveoli
 Alveoli dramatically
increase the surface
area of the lungs
