GAS EXCHANGE IN ANIMALS - Sciencepoint...
Transcript of GAS EXCHANGE IN ANIMALS - Sciencepoint...
GAS EXCHANGE
IN ANIMALS We will be studying the diversity of adaptations
for this process in two animal groups:
Mammals Fish
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
THE SOURCE OF OXYGEN Air
• about 21% oxygen
• thinner at higher altitudes
Water
• amount of oxygen varies but is always much less than air
• even lower in warmer water
• harder to ventilate
GAS EXCHANGE SURFACES
Gases move by diffusion.
Diffusion is greater when:
• the surface area is l_____
• the distance travelled is s______
• the concentration gradient is h_____
Gas exchange also requires a m____ surface
• O2 and CO2 must be dissolved in water to
diffuse across a membrane
GAS EXCHANGE SURFACES
…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
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
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
GETTING OXYGEN FROM WATER:
FISH GILLS • Gills covered by an
operculum (flap)
• Gas exchange occurs at gills
• alternately opening and
closing mouth and operculum
water flows into mouth
over the gills
out under the operculum
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.
GETTING OXYGEN FROM WATER:
FISH GILLS • Gill filaments
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.
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!
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
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 Less
energy is needed to move air through the
respiratory system than water
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
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
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
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