ap biology 2005-2006 chapter 42. gas exchange gills alveoli elephant seals
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2005-2006 AP Biology
Chapter 42.
Gas Exchange
gills
alveoli
elephantseals
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2005-2006AP Biology
Gas exchange O2 & CO2 exchange
exchange between environment & cells
provides O2 for
aerobic cellular respiration need moist
membrane need high
surface area
Respiration for
respiration!
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2005-2006AP Biology
Optimizing gas exchange Why high surface area?
maximizing rate of gas exchange CO2 & O2 move across cell membrane by
diffusion rate of diffusion proportional to surface area
Why moist membranes? moisture maintains cell membrane
structure gases diffuse only dissolved in water
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2005-2006AP Biology
Gas exchange in many forms…
one-celled amphibians echinoderms
insects fish mammals
endotherm vs. ectothermwater vs. landwater vs. land
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2005-2006AP Biology
Evolution of gas exchange structures
external systems with lots of surface area exposed to aquatic environment
Aquatic organisms
moist internal respiratory surfaces with lots of surface area
Terrestrial
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2005-2006AP Biology
Gas Exchange in Water: Gills
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2005-2006AP Biology
Function of gills out-foldings of body surface suspended
in water
Just keep swimming…
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2005-2006AP Biology
Counter current exchange system Water carrying gas flows in one direction,
blood flows in opposite direction
What is the adaptive value?
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2005-2006AP Biology
water
blood
How counter current exchange works Blood & water flow in opposite directions
Maintains diffusion gradient over whole length of gill capillary maximizing O2 transfer from water to blood
front back
blood
100%15%
5%90%
70% 40%
60% 30%
100%
5%
50%
50%
70%
30%
watercounter-current
concurrent
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2005-2006AP Biology
Gas Exchange on Land Advantages of terrestrial life
air has many advantages over water higher concentration of O2
O2 & CO2 diffuse much faster through air respiratory surfaces exposed to air do not have to
be ventilated as thoroughly as gills
air is much lighter than water & therefore much easier to pump expend less energy moving air in & out
Disadvantages keeping large respiratory surface
moist causes high water loss
Why don’t land
animals use gills?
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2005-2006AP Biology
Terrestrial adaptations
air tubes branching throughout body
gas exchanged by diffusion across moist cells lining terminal ends, not through open circulatory system
Tracheae
How is this adaptive?
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2005-2006AP Biology
Lungs exchange surface, but also creates risk: entry point for environment into body
spongy texture, honeycombed with moist epithelium
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2005-2006AP Biology
Alveoli Gas exchange across thin epithelium of
millions of alveoli total surface area in humans ~100 m2
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2005-2006AP Biology
Mechanics of breathing Air enters nostrils
filtered by hairs, warmed & humidified sampled for odors
Pharynx glottis larynx (vocal cords) trachea (windpipe) bronchi bronchioles air sacs (alveoli)
Epithelial lining covered by cilia & thin film of mucus mucus traps dust, pollen, particulates beating cilia move mucus upward to pharynx,
where it is swallowed
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2005-2006AP Biology
Negative pressure breathing Breathing due to changing pressures in lungs
air flows from higher pressure to lower pressure pulling air instead of pushing it
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2005-2006AP Biology
Positive pressure breathing Frogs
draw in air through nostrils, fill mouth, with mouth & nose closed, air is forced down the trachea
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2005-2006AP Biology
Autonomic breathing control Medulla sets rhythm & pons moderates it
coordinate respiratory, cardiovascular systems & metabolic demands
Nerve sensors in walls of aorta & carotid arteries in neck detect O2 & CO2 in blood
Don’t have to think to breathe!
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2005-2006AP Biology
Medulla monitors blood Monitors CO2 level of blood
measures pH of blood & cerebrospinal fluid bathing brain CO2 + H2O H2CO3 (carbonic acid)
if pH decreases then increase depth & rate of breathing & excess CO2 is eliminated in exhaled air
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2005-2006AP Biology
Diffusion of gases Concentration & pressure drives
movement of gases into & out of blood at both lungs & body tissue
blood lungs
CO2
O2
CO2
O2
blood body
CO2
O2
CO2
O2
capillaries in lungs capillaries in muscle
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2005-2006AP Biology
Pressure gradients
Lungs
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2005-2006AP Biology
Hemoglobin Why use a carrier molecule?
O2 not soluble enough in H2O for animal needs hemocyanin in insects = copper (bluish) hemoglobin in vertebrates = iron (reddish)
Reversibly binds O2
loading O2 at lungs or gills &unloading in other parts of body
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2005-2006AP Biology
Hemoglobin Binding O2
loading & unloading from Hb protein depends on cooperation among protein’s subunits
binding of O2 to 1 subunit induces remaining subunits to change shape slightly increasing affinity for O2
Releasing O2 when 1 subunit releases
O2, other 3 quickly follow as shape change lowers affinity for O2
Heme group
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2005-2006AP Biology
O2 dissociation curves for hemoglobin
drop in pH lowers affinity of Hb for O2
active tissue (producing CO2) lowers blood pH& induces Hb to release more O2
Bohr shift
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2005-2006AP Biology
Dissolved in blood plasma Bound to Hb protein Bicarbonate ion (HCO3
-) & carbonic acid (H2CO3) in RBC enzyme: carbonic anhydrase reduces CO2
Transporting CO2 in blood
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2005-2006AP Biology
Fetal hemoglobin
What is the adaptive advantage?
2 alpha & 2 gamma units
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