Biology 102 Chapter 48
Gas Exchange in Animals
1. List the respiratory gases and the factors that affect gas
exchange.
---oxygen and carbon dioxide
---cells need O2 from environment to produce adequate ATP
through oxidation of nutrient molecules
---one of the end products of aerobic respiration is CO2
--must be lost to environment to prevent toxic effects
---diffusion is only means by which respiratory gases are
exchanged between internal body fluids and outside medium
of air or water
--diffusion based on concentration gradient
---air is better respiratory medium than water
--oxygen content higher
--oxygen diffuses more rapidly in air than water (8000x)
--less work to move air over respiratory surfaces because
density and viscosity (800x/50x)
---higher temps create respiratory problems for aquatics
---oxygen availability decreases with altitude
2. Describe the general requirements for a respiratory surface
and list the variety of respiratory organs adapted for the
purpose.
---respiratory surface is portion of animal surface where
gas exchange with the respiratory medium occurs
--oxygen diffuses in and carbon dioxide diffuses out
---these gases can only diffuse through membrane if they
are first dissolved in water that coats the respiratory
surface
--this surface must be large enough to provide O2 and
expel CO2
---protozoa (other unicellular organisms) exchange gases
over entire surface area
---sponges, cnidarians, and flatworms have body structures
such that plasma membrane of each body cell contacts
outside environment & can function in exchange
---three-dimensional body plan requires most of body
cells isolated from environment and respiratory
surfaces generally thin, most epithelial cells with
rich blood supply
--usually only single cell layer separates respiratory
medium from blood or capillaries
---some small animals/long, thin animals with high surface
area to volume ratio, use outer skin as respiratory
organ
--earthworms and some amphibians
-must live in water or damp places
---most other animals lack sufficient body surface area
to exchange gases for entire body
--possess region of body surface extensively branched
or folded providing enough respiratory surface area
for gas exchange
---gills are outfoldings of body surface specialized for
gas exchange
---tracheal systems are air tubes that branch throughout an
insect’s body
---lungs are highly vascularized invaginations of body
surface that are restricted to one location
3. Describe respiratory adaptations of aquatic and terrestrial
animals.
---gills are respiratory adaptations of most aquatic
animals
---some invertebrates (echinoderms) have gills of simple
shapes and distributed over entire body
---other invertebrates (annelids) gills are flap-like and
extend over each body segment/clustered at one end and
long and feathery
---others (mollusks/fish) have gills localized on a body
region where surface is finely subdivided to provide
large amount of surface area
--gills must be efficient because water has lower oxygen
[] than does air
---lungs are internal cavities for respiratory gas exchange with
air
--have large surface area because they are highly divided
--are elastic so can be inflated and deflated with air
---insects have highly branched network of air-filled tubes
called tracheae
4. Describe countercurrent exchange, and explain why it is more
efficient that concurrent flow of water and blood.
---countercurrent exchange: blood flows opposite direction
in which water passes over gills
--maintains constant [] gradient for oxygen between
blood and water passing over gill surface
--remove more than 80% of O2 dissolved in water
---concurrent flow (with blood and water moving in same
direction) would result in drop to 50% or < removal
-occurs because of [] gradient
5. For the human respiratory system, describe the movement of
air through air passageways to the alveolus, listing the
structures it must pass through on the journey.
---lungs located in thoracic cavity, enclosed in sac of two
layers that are held together by surface tension of
fluid between them
---air entering nostrils is filtered by hairs, warmed,
and moistened
---air travels through pharynx, through glottis, & into
larynx (possesses vocal cords/functions as voice box)
---air enters cartilage-lined trachea that forks into
two bronchi which further branch into finer bronchioles
that dead-end in alveoli
--alveoli lined with thin layer of epithelium which
serves as respiratory surface
---O2 dissolves in moist film covering epithelium & diffuses
across to capillaries covering each alveolus
--CO2 moves in opposite direction by diffusion
6. Define negative pressure breathing, and explain how
respiratory movements in humans ventilate the lungs.
---negative pressure breathing works like a suction pump
pulling air, instead of pushing it, into the lungs
---during inhalation, contraction of rib cage causes it to
expand while diaphragm contracts and descends
--lungs expand and pressure inside them is lowered
--air pressure now lower than in atmosphere
--air rushes into nostrils and down breathing tubes
---during exhalation, rib muscles and diaphragm relax
--lung volume is decreased and pressure inside them >
--air forced out of lungs
7.
Define the following lung volumes, and give a normal range
of capacities for the human male:
a. tidal volume
b. vital capacity
c. residual volume.
---tidal volume is volume of air inhaled and exhaled with
each breath during normal quiet breathing; 500 mL
---vital capacity is maximum air volume that can be inhaled
and exhaled during forced breathing; 4800 mL
---residual volume is amount of air remaining in lungs
even after forced exhalation; 1200 mL
8. List the barriers oxygen must cross from the alveolus into
the capillaries, and explain the advantage of having millions of
alveoli in the lungs.
---oxygen must cross the squamous epithelium cell lining
of alveolus; cross the endothelial lining of an
adjacent capillary, and cross the fused basement
membrane that lie between the alveolar and
endothelial cells
---all gas exchange occurs by simple diffusion
--pressure gradient needed to insure diffusion
---each alveolus is very small but combined surface area
of the 300 million (or so) alveoli is about 70 m2 (size
of badminton court
9.
Describe how oxygen moves from the alveolus into the
capillary, and explain why a pressure gradient is necessary.
---blood arriving at lungs via pulmonary arteries has
lower PO2 and higher PCO2 than air in the alveoli
---blood exchanges gases with air in alveoli and the
PO2 of the blood increases while the PCO2 decreases
---in tissue capillaries, gradients of partial pressure
favor diffusion of oxygen out of blood and diffusion
of CO2 into it, since cellular respiration rapidly
depletes interstitial fluid of O2 and adds CO2
---simple diffusion based on movement of molecules from
where they are more highly []ed to where they are
less []ed
10. Describe the structure of hemoglobin, explain the result of
cooperative binding, and state how many oxygen molecules a
saturated hemoglobin molecule can carry.
---four subunits with heme group that binds O2
---iron atom at center of each heme group is binder
---binding of oxygen to hemoglobin is reversible
---binding of O2 to 1 subunit induces shape change that
increases affinity of other 3 subunits for oxygen
--known as cooperativity
---unloading of oxygen from 1 heme group results in
conformational change that stimulates unloading from
other 3 subunits
---hemoglobin can carry 4 molecules of O2
11. Draw the Hb-oxgyen dissociation curve, explain the
significance of its shape, and explain how the affinity of
hemoglobin for oxygen changes with oxygen concentration.
---where curve has steep slope, even slight change in POs
causes hemoglobin to load or unload substantial amount
of oxygen
---slight drop in POs is enough to cause relatively large
increase in amount of oxygen the blood unloads
12. Describe the Bohr effect, and explain how the oxygen
dissociation curve shifts with changes in carbon dioxide
concentration and changes in pH.
---pH decreases (becomes more acidic) in very active
tissues because CO2 produced by respiration reacts
with water to form carbonic acid
---Bohr shift is lowering of hemoglobins’ affinity for
O2 upon drop in pH
--occurs in active tissues due to entrance of CO2 into
the blood
---as pH decreases in tissues, hemoglobin gives up more its
oxygen
13. Describe how carbon dioxide is picked up at the tissues and
deposited in the lungs, describe the role of carbonic anhydrase,
and state the form most of the carbon dioxide is in as it is
transported.
---carbon dioxide produced by body tissues diffuses into
interstitial fluid and into plasma within a capillary
---less than 10% remains in plasma as dissolved CO2
---over 90% diffuses into red blood cells
---some is picked up and transported by hemoglobin
---most of CO2 reacts with H2O in erythrocyte to form
carbonic acid (H2CO3)
---red blood cells contain carbonic anhydrase which
catalyzes this reaction
---carbonic acid dissociates into a bicarbonate ion (HCO3-)
and a hydrogen ion (H+)
---hemoglobin binds most of H+s from carbonic acid
--prevents them from acidifying the blood
---most of bicarbonate ions diffuse into plasma
--carried by blood stream to lungs
---reverse scenario occurs in the lungs
14. Explain how hemoglobin acts as a buffer.
---reversibility of carbonic acid-bicarbonate conversion
helps buffer the blood, releasing or removing H+
depending on pH