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RESPIRATION AND
GAS EXCHANGE
Key concepts

Types of respiration
 Cellular Respiration is the chemical breakdown of food substances to yield ATP.
 Different organisms use different kinds of breathing mechanisms in order to transport oxygen
throughout their bodies.

Evolutionary adaptations of gas exchange systems and respiration
 Different plant adaptations in acquiring CO2 from the environment evolved: C3, C4, and CAM
pathways.
 Structural adaptations of respiratory apparatus depend on the animal’s habitat. The three
most common respiratory organs are gills, tracheae, and lungs.
 The respiratory system and circulatory system cooperate directly with each other.

Mammalian respiration
 The respiratory system is divided into the upper respiratory tract (nasal passages, mouth,
throat, larynx and trachea) and lower respiratory tract (bronchi and the lungs).
 Air enters (inhalation) the respiratory system due to a pressure drop inside the lungs (negative
pressure).
 Air exits (exhalation) the respiratory system due to an increase in pressure inside the lungs.
 Breathing is regulated by control centers in the brain (medulla oblongata and pons)
 Gases are transported via passive diffusion throughout the body.

Respiratory diseases and their prevention
 Respiratory disorders may be congenital or environmental.
 Respiratory disorders can be prevented through a combination of proper diet and lifestyle
change.
Vocabulary words
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aerobic respiration
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emphysema
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air sacs
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alveolus
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epiglottis
gas exchange
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anaerobic respiration
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gills
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asthma
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blood pH
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glottis
glycolysis
hemocyanin
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Bohr shift
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breathing
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bronchiole
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bronchus
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C3 pathway
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C4 pathway
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CAM pathway
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nasal cavity
negative pressure breathing
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cell respiration
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nose
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countercurrent exchange
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parabronchi
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cutaneous respiration
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partial pressure
pharynx
diaphragm
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photosynthesis
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dissociation curve
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hemoglobin
larynx (voicebox)
lung Cancer
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lungs

medulla oblongata
myoglobin
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pneumonia
pons
positive pressure breathing
residual volume
respiratory medium
respiratory pigments
respiratory surface
rib muscles
spiracle
surface tension
syrinx
thoracic cavity
tidal volume
trachea or windpipe
tracheae
tuberculosis
ventilation
vital capacity
vocal cords of the larynx
Cellular Respiration
- Transformation of chemical energy into ATP
- Overall Reaction: C6H12O6 +6O2 → 6CO2 +6H2O + 36 ATP
1 Glucose molecule
(6C) from digestion
Glycolysis in the
cytoplasm 
2 pyruvate molecules
(3C)
2 ATPs
Aerobic Respiration in the
mitochondria
Anaerobic Respiration in
Krebs Cycle (2 ATPs)
the cytosol 
Electron Transport Chain
ethanol/lactic acid/CO2
(32 ATPs)
 CO2+ H2O
NADH and FADH2 are
e- donors that enable the
formation of ATP
Photosynthesis
 Method of converting sun
energy into chemical
energy usable by cells
 Light reactions
 Dark reactions/Calvin
Cycle
6 CO2 + 6 H2O + light
energy → C6H12O6 + 6O2
Plant adaptations for
acquiring CO2 from the
environment

C3 (most abundant)
 CO2 converted to a 3C sugar, 3-phosphoglycerate
 RuBisCO (Ribulose-1,5-bisphosphate
carboxylase/oxygenase) enzyme catalyzes
carbon fixation
 prone to photorespiration, lessens efficiency of
food production during hot and dry days
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C4
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store CO2 in specialized compartments
convert CO2 into a 4C compound, oxaloacetate
converted into the 3C sugar and CO2 used in the C3
pathway/Calvin cycle
minimizes photorespiration and enhances sugar
production
CAM
 succulent plants
 f ix CO2 at night and store it as 4C organic acids
 minimizes water loss and enhances sugar
production
Gas exchange supplies oxygen for
cellular respiration and removes CO2
 Gas exchange – uptake of
O2 from environment and
discharge of CO2
 Mitochondria need O2 to
produce more ATP, CO2 is
the by-product
C6H12O6 + 6O2  6CO2 + 6H2O + 36 ATP
 Diffusion rate
 α SA  large
 α 1/d2  thin
 Moist so gases are dissolved
first
DIFFUSION
Respiratory surfaces and gas exchange
 Respiratory surface
 Simple invertebrates
 Size of organism
 Sponges, cnidarians,
 Habitat
flatworms, roundworms
 diffusion
 Metabolic demands
 Unicellular organisms
 Entire surface area for
diffusion
Respiratory surfaces and gas exchange
 More complex animals
 Thin, moist epithelium
 Separates medium from
capillaries
 Entire outer skin  small,
long, thin organisms
 Specialized respiratory
organs that are extensively
folded and branched
Gills in aquatic animals
 Outfoldings of the body
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surface suspended in
water
Sea stars
Segmented worms or
polychaetes
Molluscs and
crustaceans
Fishes
Young amphibians
Total surface area is
greater than the rest of
the body
Water as a respiratory medium
 Surfaces are kept moist
 O2 concentrations in water
are low
 Ventilation – increasing
flow of respiratory medium
over the surface
 Countercurrent exchange –
process in which two fluids
flow in opposite directions,
maximizing transfer rates
 Why are gills impractical
for land animals?
Just keep
swimming
swimming
swimming!
Air as a respiratory medium
 Air has a higher
concentration of O2
 O2 and CO2 diffuse
much faster in the air
 less ventilation
 Difficulty of keeping
surface moist
 Solution: respiratory
infolding inside the
body
 Tracheal system of insects –
network of tubes that bring O2
to every cell
Spiracles
Lungs
 Heavily vascularized
invaginations of the body
surface restricted to one
location
 Found in spiders, terrestrial
snails, vertebrates
 Amphibians supplement
lung breathing with skin
 Turtles supplement lung
breathing with moist
surfaces in mouth and anus
Mammalian
respiration
Lung ventilation through breathing
 Positive pressure
 Negative pressure breathing in reptiles and
breathing in frogs
 “Gulping in” air
 Rib muscles and diaphragm change lung volume
mammals
and pressure
Lung volumes
 Factors
 Sex
 Height
 Smoking
 Physical activity
 Altitude
 Tidal volume
 Volume of air inhaled and
exhaled with each breath
 Vital capacity
 Maximum volume inhaled
and exhaled during forced
breathing
 Residual volume
 Air left in alveoli after forced
exhalation
Avian breathing
•Air sacs - bellows to
keep air flowing
through the lungs
•Syrinx – vocal
organ of birds
Control
centers in
the brain
regulate
breathing
Gases
diffuse down
pressure
gradients
concentration and
pressure drives the
movement of gases into
and out of blood
Respiratory
pigments
 O2 transport
 Low solubility of O2 in
H2O
 Respiratory pigments
are proteins with metal
atoms
 Hemoglobin – Fe
 Hemocyanin – Cu
 Allow reversible binding of
O2
 Drop in pH results in a
lowered affinity of
hemoglobin for O2
 CO2 transport
Respiratory
pigments
 7% in plasma
 23% bound to
hemoglobin
 70% as HCO3 buffer
Fetal hemoglobin
HbF has greater affinity to O2 than Hb
 low O2% by time blood reaches placenta
 fetal Hb must be able to bind O2 with greater
attraction than maternal Hb
Deep-diving
mammals
 Seals, whales, dolphins are
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capable of long underwater
dives
Weddell seal  5% O2 in
lungs, 70% in blood
Huge spleen stores huge
volumes of blood
Large concentrations of
myoglobin in muscles
Heart rate and O2
consumption rate decrease
Blood is redirected from
muscles to brain spinal
cord and eyes