Lesson slides for instant use - A level Biology, Gas exchange Part 1 (Ssusume Patrick) Slides are helpful to students for self study and home revision

1. GASEOUS EXCHANGE AND
RESPIRATION
Ssusume Patrick
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2. Subtopic 1: Principles of
gas exchange systems
OBJECTIVES
Explain the relationship between
size, surface area to volume ratio
Explain the role of diffusion in gas
exchange
Explain how a respiratory surface
is modified to speed up diffusion
State the characteristics of a gas
exchange surface.
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3. Relationship between size
and surface area to
volume ratio
Surface area to volume ratio is an
important aspect in gaseous
exchange. It is obtained by
calculating the total surface area
and dividing it by the volume of
the object in question. Consider
two boxes A and B below
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4. Activity
Explain the above relationship in reference to organisms
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5. Distinguishing
Gaseous exchange
• The diffusion of gases especially
respiratory gases oxygen and carbon
dioxide from higher to lower
concentration between the external
media and the organism where oxygen
enters the tissues and carbon dioxide is
released into the external media.
Ventilation
• The mechanisms by which air or
water rich in oxygen is taken into
the organism and carbon dioxide
expelled out of the organism.
inspiration/inhalation and
exhalation/expiration
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6. RESPIRATORY SURFACE
• This is where gaseous exchange takes place.
Examples of organisms, their respiratory/gaseous
exchange surfaces and adaptations of these
surfaces are shown below.
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7. unicellular e.g. amoeba, paramecium,
plasmodium
Cell surface membrane Adaptations
• Large surface area to volume ratio for
efficient diffusion of gases.
• Being aquatic, the cell membrane is always
moist to dissolve respiratory gases to
enable their rapid diffusion.
• The cell surface membrane is permeable
to respiratory gases.
• The membrane is thin which reduces the
distance across which gases diffuse thus
rapid diffusion.
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8. coelenterates like starfish. earthworm
Entire body surface Adaptations
• ▪ Skin surface is moist to enable
dissolving of respiratory gases for
efficient diffusion.
• ▪ Skin is thin to reduce the diffusion
distance such that there is increased
rate of diffusion of respiratory gases.
• ▪ The epidermal tissue is highly
vascular to deliver and carry
respiratory gases such that a high
concentration gradient for the gases is
maintained
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9. Platyhelminthes like flat worms, liver flukes
Flattened body surface Adptations
The flatness increases the
surface area to volume ratio
to increase the rate of
diffusion of respiratory
gases.
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10. spiders
Book Lungs
Adaptation
• The internal cavity increases the
surface area for exchange of
respiratory gases.
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11. Insects like grasshoppers, houseflies.
Tracheoles Adaptations
• Tracheae are kept open by circular
bands of chitin to enable continued
movement of air in and out of
tracheoles.
• Tracheoles reach every cell to deliver
oxygen directly to respiring cells and
take away Carbon dioxide.
• Ends of the tracheoles are moist to
enable dissolution of respiratory gases
for increasing their diffusion
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12. Amphibians
Young i.e. tadpoles. Lugworms
Gas exchange surfaces features
• External gills These are epidermal
outgrowths suspended in water
unprotected and therefore easily get
damaged.
• There is increased surface area for
diffusion of respiratory gases.
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13. Adult i.e. frogs, toads.
Moist skin (cutaneous
respiration Adaptation
• Moist by mucus secretions to dissolve
gases for rapid diffusion.
• Skin is thin to reduce the diffusion
distance such that there is increased
rate of diffusion of respiratory gases.
• highly vascular to deliver and carry
respiratory gases such that a high
concentration gradient for the gases is
maintained
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14. Adult amphibians
Buccal cavity Adaptation
• Moist to dissolve gases for rapid
diffusion
• highly vascular to deliver and carry
respiratory gases such that a high
concentration gradient for the
gases is maintained.
• Thin buccal cavity lining reduces
diffusion distance increasing
diffusion of respiratory gases.
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15. Adult amphibians
Lungs (pulmonary respiration) Adaptation
• Moist to dissolve gases for rapid
diffusion
• Highly vascular to deliver and carry
respiratory gases such that a high
concentration gradient for the gases
is maintained.
• Thin reducing diffusion distance
increasing diffusion of respiratory
gases
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16. Fish e.g. Nile perch, tilapia
Gill filament Adaptation
• Gill filaments have folds called
lamellae that increase the surface area
for gas exchange
• Gills are moist to enable dissolution
of respiratory gases for efficient
diffusion.
• Gills are thin-walled and in close
contact with water to provide a short
distance for diffusion of respiratory
gases hence rapid diffusion.
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17. Fish
Gill filament Adaptation
• . The gill lamellae contain a network of
capillaries for carrying away oxygen or
bringing in Carbon dioxide for
expulsion thereby maintaining a steep
concentration gradient.
• There is counter current flow i.e. water
and blood in the gills flow in opposite
directions to maintain a favorable
concentration gradient for diffusion of
respiratory gases.
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18. I hope you hard a good morning
back there
Lets kick off
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19. Mammals e.g. man, whale
Alveoli in lung Adaptation
• alveoli are numerous which
provides a large surface area for gas
exchange.
• Diffusion of respiratory gases is
made faster by the shortened
distance due to
• (1) alveoli and capillary walls being
only one cell thick
• (2) epithelial cells are flattened so
are very thin
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20. Mammals e.g. man, whale
Alveoli in lung Adaptation
• (3) capillaries are pressed against
alveoli.
• 4)The moistened alveolar surface
enables dissolution of respiratory
gases to increase the rate of
diffusion.
• 5) There are high concentration
gradients of the gases, maintained
by ventilation and flow of blood in
the capillaries
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22. Plants
Cell walls of leaf mesophyll cells Adaptation
• When the stomata open, production
and consumption of oxygen and
carbon dioxide in the leaf is sufficient
to maintain a concentration gradient
steep enough to facilitate gas exchange
with the atmosphere.
• Large intercellular air filled spaces in
the spongy mesophyll act as a reservoir
for gaseous exchange.
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25. Plants
cortex of root and stem Adaptation
• The cortical air spaces of roots and stems
are continuous up and down and also in a
sideways direction, thus allowing gas
transport throughout the stem and root
tissues
• Root hairs lack a waxy cuticle and have moist
surfaces to facilitate rapid diffusion of gases
through the cell wall.
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26. Breathing roots of mangrove
• Mangrove species that grow in water
logged soils with less air content
develop breathing roots above the
ground level to increase gas
exchange.
• Root hairs are numerous to increase
the surface area for gas exchange.
• In the stem, lenticels consist of
loosely packed cells at the opening to
enable diffusion of respiratory gases.
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29. Moving to fast ? ooooh yeah
•Let’s pause a bit
•A student once
asked the
teacher…………
•Guess the student
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30. CONDITIONS NEEDED FOR GAS
EXCHANGE
• a) The supply of oxygen
• (1) Air - About 21% of air is oxygen. There is however less air at higher
altitudes.
• (2) Water - Amount of oxygen in water varies
• (about 1.03% in fresh water and 0.85% in sea water)
• but is always much less than in air,
• being even lower in warmer water than colder water.
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31. CONT’D
• b) Diffusion
• Diffusion is faster when the
• (1) surface area to volume ratio is large
• (2) distance travelled is small
• (3) concentration gradient of the diffusing substance is high.
• c) A moist surface is required because oxygen and carbon dioxide must be
dissolved in water to diffuse across a membrane.
• d) Permeable membranes
• (e) large surface area to volume ratio
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32. An efficient gas exchange surface
• (1) Have a large surface area relative to the volume of the organism to ensure
a faster diffusion rate of respiratory gases
• (2) provide a short distance (be thin) for gases to diffuse across
• (3) have a good blood supply that maintains a steep concentration gradient
for the diffusion of respiratory gases
• (4) permeable to the respiratory gases to enable their diffusion
• (5) be moist to enable dissolving of respiratory gases.
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33. Adolf Eugen Fick & the Fick’s law
• Adolf Fick was a German
physiologist, born in Kassel in
1829, who studied medicine at the
University of Marburg and
graduated in 1851.
• In 1855, he introduced Fick's laws
of diffusion, which governs
the diffusion of a gas across a fluid
membrane.
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34. Fick’s law
• The first four characteristics are summarized in a law that
considers how maximum diffusion rate can be achieved
i.e.
• Fick’s law which states that; diffusion of a respiratory gas
through a respiratory surface is proportional to;
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35. Fick’s law
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36. NOTE
• The factors that affect diffusion affect the rate of
gaseous exchange such factors include;
• concentration gradient
• distance over which diffusion takes place
• size and nature of diffusing molecules.
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37. RESPIRATORY MEDIA
• These are air and water and as gas exchange media present comparative
advantages and disadvantages to the organisms concerned because they
differ in properties as shown below.
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39. Lets first have an academic interphase !!!!
•By the way, have you ever found out the
definition of life ?...........
Well that might be hard, but…. Where do you
find a cow with no legs ?
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40. Well, here is the answer…….
•Right where you left it
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41. SELF CHECK !!
Assignment 9
Outline reasons why organisms need transport and gaseous exchange
mechanisms.
State the parameters listed in Fick’s law of diffusion
Explain how each parameter in Fick’s law of diffusion is reflected in the
structure of the mammalian lung
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43. MECHANISMS OF GASEOUS
EXCHANGE
Small organisms
Have a small surface area to volume ratio and their external membranes are
fully permeable to gases which diffuse rapidly over the body surface.
Cells are not far from the surface hence a short diffusion distance which
enhances faster gaseous exchange.
Have a low metabolic rate so their demand for oxygen is very low. Examples
include; amoeba, hydra, planarian.
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44. Large organisms
With increase in size, the distance of their cells from the body surface
become larger
Lowering diffusion rate and adequate supply and removal of gases by
diffusion cannot be achieved because large sizes decrease the surface area to
volume ratio.
Increased metabolic rate which increases their oxygen demand and carbon
dioxide production.
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45. Large organisms
In some larger organisms
The body becomes hardened and impermeable to gases,
The body is enclosed in a protective shell.
All this justifies the need for a specialized gaseous exchange mechanism which
has these features;
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47. GAS EXCHANGE IN VARIOUS
ORGANISMS
• In unicellular (single-celled) organisms
such as protozoa e.g. amoeba
• Measures less than 1mm in diameter and
possesses a big surface area to volume
ratio, gas exchange occurs by diffusion
across their membranes.
• Along their concentration gradients,
dissolved oxygen diffuses from the water
across the cell membrane into the
cytoplasm while dissolved carbon dioxide
diffuses in the opposite direction.
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48. cnidarians like hydra and obelia
• All cells are in contact with the
aquatic environment and each
cell is able to exchange gases
for its self-sufficient for its
needs through the cell
membrane adjacent to the
surrounding water.
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49. free living Platyhelminthes such as
planarian
• have a flattened body surface that
increases area of the body hence rapid
rate of diffusion. Sufficient oxygen is
supplied to the organism because they
live in well aerated environments.
• Many others such as taenia sp are
internal parasites surviving in low
oxygen tension and operate as
anaerobes.
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50. Annelids e.g Earth worms
• body surface is cylindrical in shape
increasing surface area for rapid
diffusion of gases across the whole body
surface.
• Annelids are also generally inactive and
their demand for oxygen is generally low.
• They possess a blood vascular system
which contains respiratory pigment
haemoglobin in solution. The contractile
pumping activity by the blood
• vessels facilitates the passage of blood
and dissolved gases around the body and
maintains a steep concentration gradient.
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52. Earth worms
• gaseous exchange occurs through the
skin whose epidermis is made of very
tiny cuticle covered by mucus for
dissolution of respiratory gases.
• Within the skin blood capillaries bring
blood containing haemoglobin close
the environment. Hemoglobin binds
loosely to oxygen and carries it
through the animal's bloodstream.
• Carbon dioxide is transported back to
the skin by the hemoglobin from
which it detaches and diffuses out. The
cuticle is thin and permeable to
respiratory gases and allows rapid
diffusion of gases in and out of the
capillaries beneath the skin.
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54. Organisms such as green algae
• In organisms such as green algae, the
cells may be close to the environment, and
gas exchange can occur easily by diffusion.
• (i) In the dark, no photosynthesis occurs
in the chloroplast, no oxygen is made.
Dissolved oxygen diffuses from the water
across the cell membrane into the
mitochondria while dissolved carbon
dioxide diffuses in the opposite direction,
along their concentration gradients.
• (ii) In the light, photosynthesis in
chloroplasts releases oxygen, some of
which diffuses into the mitochondria, the
excess diffuses out.
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55. LARGE ORGANISMS
• 1. GARDEN SNAIL
• A large part of its body is covered by a
protective shell. Within the body is a
lung which consists of a chamber with
a ribbed lining which provide an
increased surface area for gaseous
exchange.
• The blood transports oxygen around
the body being assisted by copper
containing respiratory pigment called
haemocyanin.
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57. ARTHROPODS E.G. INSECTS
• The body of an insect is impermeable
to gases. Air reaches the cells through
the tracheal system.
• The insect’s integument on either side
of the thorax and the abdomen is
perforated by a series of segmentally
arranged pores called spiracles which
open into a system of tracheal tubes
which permit entry of air into and
exist of waste air from the tracheal
system of the insect.
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59. SPIRACLES OF INSECTS
• The spiracles are closed by valves with
hairs to retain water vapour and prevent
excessive evaporation of water through
them.
• The size of aperture of the valves that
close spiracles is adjusted according to
levels of carbon dioxide inside the body
whose production is brought about by
increased activities and is detected is by
chemoreceptors which stimulate opening
of spiracles accordingly.
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61. Tracheal system
• The tracheae are definitely arranged
with some running longitudinally
and others transversely. Larger
tracheae are kept open permanently
spiral annular thickenings of
hardened chitin that prevent
tracheae from collapsing due
changes in pressure.
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63. Tracheoles
• Tracheae divide to form tracheoles
which lack rings of chitin making
them permeable to gases which
freely diffuse across their walls. The
ends of the tracheoles are filled
with a watery fluid for easy
diffusion of gases.
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64. Tracheoles at rest
• At rest the insect’s tissue is
hypotonic to the fluid in the
tracheoles, so air is drawn from
tissues to tracheoles by osmosis and
displaces air from the tracheoles
and tracheae and expelled to the
exterior through spiracles.
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65. Tracheoles during activity
• During activity, lactic acid is produced
due to anaerobic muscular respiration.
This increases osmotic pressure of cells
of tissues which becomes hypertonic to
the fluid in the tracheoles causing water
to move into the body by osmosis
resulting into further withdraw of air into
cells making more oxygen available for
respiration.
• After the activity lactic acid is oxidized
lowering osmotic pressure in the tissues
causing the fluid to re-enter the tissues.
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67. TERRESTRIAL INSECTS E.G.
GRASSHOPPER
INSPIRATION/INHALATION • Abdominal muscles relax; the
abdomen expands increasing the
volume of the abdominal cavity
and lowering the pressure inside to
below that of the atmosphere
causing fresh air rich in oxygen to
rapidly enter into the tracheal
system through the spiracles.
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68. EXHPIRATION/EXHALATION
• The abdominal muscles of the insect
contract, causing flattening of the
abdomen and the body and decreasing
the volume of the abdominal cavity and
increasing the pressure of the abdominal
cavity to more than that of the
atmosphere which forces waste air rich in
carbon dioxide to the exterior via the
spiracles especially of the abdomen.
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70. Previously
• Originally it was thought that continuously oxygen simply
diffuses into the tissue fluid while carbon dioxide is
exhaled to the tracheoles through trachea due to muscle
contraction.
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71. RECENTLY
• More recently, however it has been observed that at rest,
while some insects demonstrate continuous respiration
and may lack muscular control of the spiracles, others
utilize muscular contraction of the abdomen along with
coordinated spiracle contraction and relaxation to
generate cyclical gas exchange patterns, one of which is
termed discontinuous ventilation.
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72. DISCONTINUOUS VENTILATION
(discontinuous gas exchange cycles)
• During oxygen (O2) uptake and carbon dioxide (CO2) release
from the whole insect follow a cyclical pattern characterized by
periods of little to no release of CO2 to the external
environment.
• It occurs in 3 phases: the closed phase, the flutter phase, and
the open phase.
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73. Closed phase
• During the closed phase, the spiracle muscles contract, causing the spiracles
to shut tight, which drastically reduces the capacity for the exchange of gases
with the external environment.
• As O2 is consumed, its partial pressure decreases within the tracheal system.
In contrast, as CO2 is produced by the cells, it is buffered in the
haemolymph rather than being exported to the tracheal system. This
mismatch between O2 consumption and CO2 production within the tracheal
system leads to a negative pressure inside the system relative to the external
environment.
• Once partial pressure of O2 in the tracheal system drops below a lower limit,
activity in the nervous system causes the initiation of the flutter phase
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74. Flutter phase
During the flutter phase, spiracles open slightly and close in rapid
succession. As a result of the negative pressure within the tracheal
system, created during the closed phase small amount of air from
the environment enters the respiratory system each time the
spiracles are opened.
However, the negative internal pressure also prevents the liberation
of CO2 from the haemolymph and its exportation through the
tracheal system. As a result, during the flutter phase, additional O2
from the environment is acquired to satisfy cellular O2 demand,
while little to no CO2 is released.
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75. Flutter phase
• The flutter phase may continue even after tracheal pressure is equal to
that of the environment, and the acquisition of O2 may be assisted in
some insects by active ventilatory movements such as contraction of
the abdomen.
The flutter phase continues until CO2 production surpasses the
buffering capacity of the haemolymph and begins to build up within the
tracheal system.
• CO2 within the tracheal system has both a direct (acting on the muscle
tissue) and indirect (through the nervous system) impact on the
spiracle muscles and they are opened widely, initiating the open phase.
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76. open phase
During the open phase,
spiracular muscles relax and the spiracles open completely.
The open phase may initiate a single, rapid release of CO2, or
several spikes declining in amplitude with time as a result of the
repeated opening and closing of the spiracles.
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78. AQUATIC INSECTS
• Even aquatic insects use a tracheal system for gas exchange.
• (1) Some, like mosquito larvae, get their air by poking a
breathing tube - connected to their tracheal system -
through the water surface
• (2) Some insects that can submerge for long periods and
carry a bubble of air with them from which they breathe
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81. AQUATIC INSECTS
• (3) Still others have spiracles mounted on the tips of spines.
With these they pierce the leaves of underwater plants and
obtain oxygen from the bubbles formed by photosynthesis
within the leaves
• (4) Even in aquatic insects that have gills, after oxygen
diffuses from the water into the gills, it then diffuses through
a gas-filled tracheal system for transport through the body.
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83. GAS EXCHANGE IN AMPHIBIANS e.g.
frogs and toads
• Gaseous exchange in the frogs and toads takes place in three main parts of
the body:
• ❖ The skin (cutaneous respiration) - especially during low activity when
hibernating
• ❖ The mouth /buccal cavity (buccal respiration)
• ❖ The lungs (pulmonary respiration)
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84. The Skin:
• Air from the atmosphere diffuses through the moist thin skin;
into the dense capillary below the skin.
• Due to low concentration of oxygen in the blood than in the skin
surface, oxygen is then taken to the tissues via the red blood
cells. Carbon dioxide moves from the blood into the skin surface
then to the atmosphere. This happens due to its high
concentration in the blood tissues than in the surface of the skin.
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85. The mouth (Buccal cavity respiration):
• During inhalation; the muscles of the mouth contract and then
lower the surface (floor) of the mouth hence reducing its pressure
than that of the atmosphere.
• Air rich in oxygen is inhaled through the nostrils into the mouth
cavity
• There exists dense capillary network in the mouth cavity and as
such, gaseous exchange takes place.
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86. Mouth
• Oxygen due to its high concentration diffuses into the blood
and is transported by the red blood cells. Carbon dioxide
diffuses from the blood tissues to the buccal cavity.
• During exhalation; the mouth floor is raised, volume
decreases and pressure increases to above that of the
atmosphere forcing air out through the nostrils.
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88. The lungs (pulmonary respiration):
• During inhalation the mouth muscles contract then lower the
floor of the mouth hence increasing its volume.
• Pressure reduces in the mouth cavity than the atmosphere’s,
causing air to move into the mouth through the nostrils.
• The nostril then closes and the mouth’s floor is raised.
• This forces the air into the lungs.
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90. The lungs (pulmonary respiration):
• Gaseous exchange takes place between the alveoli of the
lungs and the blood; oxygen due to its high concentration in
the alveoli than the blood diffuse into the blood while
Carbon dioxide diffuses out of the blood tissue to the alveoli
where it is exhaled out through the nostrils by the muscles of
the lungs which contract and relax rhythmically.
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91. pulmonary respiration
• During exhalation the floor of the mouth is lowered,
decreasing volume and decreasing pressure to below that
in the lungs, air is forced from the lungs into the mouth
and then expelled to the exterior when nostrils open,
glottis close and the floor of the buccal cavity is raised,
decreasing volume and increasing pressure which forces
air out through the nostril.
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94. GAS EXCHANGE FISH
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• Fish posses gill slits in the wall of
the pharyngeal region of the
gut(between esophagus and buccal
cavity)
• These connect with the outside
environment (water). The tissue
between the slits forms supports
known as brachial arches or gill
arches. In bony fish there are four
pairs of gill arches separating five
pairs of gill slits

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97. The Gills
• Each gill is made up of two rows
of gill filaments arranged in a V
shape
• The filaments possess lamellae, thin
plates which have a rich supply of
blood capillaries. Theses plates
greatly increase the surface area of
the respiratory surface. The barrier
between blood and water is only
several cells think so diffusion
between the two is rapid.
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101. Gill lamellae
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102. Blood flow through lamellae
• Blood flows through the lamellae in one direction
and water flows over in the opposite direction. This
is called a counter-current system.
• It maintains a large concentration gradient between
the water and the blood. The concentration of
oxygen in the water is always higher than that in the
blood, so as much oxygen as possible diffuses from
the water into the blood.
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106. MECHANISM OF VENTILATION IN
BONY FISH
• During inhalation
• The muscles of the buccal cavity contract
lowering the flow of the buccal cavity,
increasing volume of the cavity and decreasing
pressure inside the buccal cavity to below that
of the surrounding water, causing water to be
drawn into the buccal cavity.
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107. Inhalation…
• At the same time pressure of water outside presses the valve of
the posterior end of the operculum preventing entry and escape
of water through the operculum.
• The operculum then contracts, its volume increases and pressure
decreases to below that of the buccal cavity causing water to be
drawn from the buccal cavity over the gills into the opercular
cavity, where gaseous exchange occurs by counter current flow.
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109. Exhalation
• The muscles of the buccal cavity relax, the mouth and opening to the
esophagus close, flow of the buccal cavity is raised decreasing volume
and increasing pressure to above that of the operculum, forcing the
remaining water out of the buccal cavity over the gills, through gill
slits and then to the outside via the posterior end of the operculum.
• The higher pressure developed around the gill region lifts the flexible
edge of the operculum causing the operculum valve to open letting
water to flow out over the gills.
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112. Adaptations of bony fish for efficient
gaseous exchange
• The gill lamellae are numerous increasing the surface
area over which a large volume of oxygen diffuse at a
higher rate.
• ii) Gill lamellae are well supplied with a dense network
of blood vessels for efficient transport of respiratory
gases hence maintaining a steep diffusion gradient.
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113. ADAPTATIONS
• iii) Membranes of gill lamellae are very thin for decreasing
the diffusion distance of respiratory gases hence rapid
diffusion.
• iv) The pattern of arrangements of gill lamellae and gill
plates is such that all the water flows between the gill
lamellae and gill plates therefore maximizing diffusion of
respiratory gases.
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114. ADAPTATIONS
• v) All the water currents flow in opposite direction to
that of blood which maintains a high concentration
gradient of respiratory gases resulting into their rapid
diffusion.
• vi) Gill filaments overlap offering resistance to water
flow hence reducing speed of flow thereby maximizing
diffusion of respiratory gasses
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115. CARTILAGINOUS FISH
• Examples of cartilaginous fish include
• dog fish, shark and rays.
• The respiratory surfaces are gills.
• They have five gill pairs each situated in a gill pouch.
Each gill is supported by a vertical rod of cartilage
called the branchial arch which supports a series of gill
filaments.
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118. VENTILATION IN CARTILAGINOUS
FISH
During inhalation;
• The hypobranchial muscles contract, the floor of the buccal
cavity and pharynx is lowered, increasing the volume of the
bucco-pharyngeal cavity and reducing pressure to below
that of the surrounding environment causing water to enter
through the mouth and spiracles.
• At the same time the branchial valves/flap valves are tightly
closed to prevent water from entering through this region.
Water moves into the pharynx and over the gill filaments,
meanwhile the esophagus is closed.
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120. EXHALATION
Gaseous exchange occurs by parallel flow.
During exhalation;
• The hypobranchial muscles relax raising the floor of the
buccal cavity and pharynx, increasing pressure to above that
of the surrounding, the mouth and spiracles are closed,
branchial valves open, water is forced over the gill filaments
and out of the gill slits. Continuous alternation of the
buccal pressure pump and branchial suction pump ensures
a continuous flow of water over the gills.
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122. COMPARISION BETWEEN COUNTERFLOW
AND PARALLELFLOW SYSTEMS
Parallel flow system
Blood in the gill lamellae flows in the
same direction and at the same speed
as the water passing over them,
resulting in only half (50%) of the
available oxygen from the water
diffusing into blood. The blood and
water reach equilibrium in oxygen
content and diffusion no longer takes
place.
Co-current flow system
Water flows across the gill
lamellae in an opposite
direction to the blood flow,
enabling almost all of the
oxygen (80- 90%) from the
water diffusing into the
blood.
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123. Parallel flow system VS Co-current flow
system
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124. Parallel flow system VS Co-current flow
system
• If the blood in the gill
lamellae and water flow in the
same direction, initially large
amounts of oxygen diffuse
into blood but the efficiency
reduces when the fluids start
to reach equilibrium.
• Although dissolved oxygen
levels in water drop as the
water flows across the gill
lamellae, the blood has lower
levels; therefore a sustained
diffusion gradient is
maintained throughout.
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125. Parallel flow system VS Co-current flow
system
• The concentration of
oxygen gained from
this system does not
meet the physiological
needs of the fish.
• By having the blood flow in the
opposite direction, the gradient is
always high such that the water has
more available oxygen than the blood,
and oxygen diffusion continues to take
place after the blood has acquired more
than 50% of the water's oxygen content.
The countercurrent exchange system
gives fish an 80-90% efficiency in
acquiring oxygen
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126. Countercurrent exchange system
• Water flows across the gill lamellae in an opposite direction
to the blood flow, enabling almost all of the oxygen (80-
90%) from the water diffusing into the blood.
• Although dissolved oxygen levels in water drop as the water
flows across the gill lamellae, the blood has lower levels;
therefore a sustained diffusion gradient is maintained
throughout
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127. Countercurrent exchange system
• • By having the blood flow in the opposite direction,
the gradient is always such that the water has more
available oxygen than the blood, and oxygen
diffusion continues to take place after the blood has
acquired more than 50% of the water's oxygen
content. The countercurrent exchange system gives
fish an 80-90% efficiency in acquiring oxygen
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128. How an efficient counterflow system is
prevented in a dogfish:
1. The main flow of the water through the gill
pouches is parallel to the lamellae
2. The vertical septum deflects the water so that it
tends to pass over rather than between the gill plates.
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129. How to improve parallel flow
• The flow of water being very rapid compared with
that of the blood, to ensure a higher saturation of
the blood by the time it leaves the respiratory
surface.
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130. Advantages of counterflow
• Enables blood of the gill lamellae to extract oxygen from the
water maximally for the entire period the water flows across
the gill filaments than if blood moved in the same direction
as the passing water
• Under conditions permitting adequate oxygen uptake, the
counter-current fish expends less energy in respiration
compared to the identical hypothetical co-current fish
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131. CHANGES IN THE PRESSURES OF THE BUCCAL
CAVITY AND OPERCULUM DURING VENTILATION
IN A BONY
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132. OBSERVATIONS AND
EXPLANATIONS FROM THE GRAPH
• At 1, the buccal cavity is expanding, the pressure reduces
and falls below that of opercular cavity (acquires negative
pressure); mouth valve opens and water enters from outside.
• At 2, opercular cavity is expanding, pressure reduces
(acquires negative pressure); opercular valve closes. At 3,
pressure in opercular cavity falls below that of buccal cavity
which has began to contract, resulting in water being sucked
into opercular cavity from buccal cavity
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133. Observations
• At 4, buccal cavity pressure increases (acquires
positive pressure); mouth valve closes and water is
forced from buccal cavity to opercular cavity.
• At 5, opercular cavity is contracting, pressure
increases (acquires positive pressure); opercular
valve opens and water is expelled
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134. Note
• Negative pressure: It refers to a situation in which an enclosed area has
lower pressure than the area around it. Positive pressure: a situation in
which an enclosed an area has higher pressure than the surrounding
regions
• Water almost flows in one direction from the buccal cavity to the
opercular cavity. evidence: Throughout the ventilation cycle, except for
one short period when the buccal cavity expands the pressure in the
buccal cavity is higher than that in the opercular cavity forcing water to
flow from the buccal cavity to the opercular cavity along the pressure
gradient.
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135. Note
Expansion of buccal cavity lowers the pressure
below that of opercular cavity, causing the water to
enter the buccal cavity but at the same time the
opercular valves close to prevent entry of water.
The buccal cavity acts as a force pump while the
opercular cavity as a suction pump
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136. CHANGES IN THE PRESSURES OF THE BUCCAL CAVITY AND
OPERCULUM DURING VENTILATION IN A BONY
.
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137. Questions and answer.
• QUESTIONS 1. (a) Explain why when fish are taken out of the water, they
suffocate. ANSWER; This is because their gill arches collapse and there is not
enough surface area for diffusion to take place ; the gill lamellae surface dries and
oxygen in air fails to dissolve and diffuse into blood; NB; some fish can survive out
of the water, such as the walking catfish because they have modified lamellae,
allowing them to breathe air. b) Under what circumstances do fish suffocate in the
water? ANSWER; when the oxygen in the water has been used up by other aerobic
organisms such as bacteria during decomposition. 2. The graph below shows the
changes in pressure in the buccal cavity and in the opercular cavity during a
ventilation cycle.
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138. continued
• a) Calculate the rate of ventilation in cycles per minute Duration of one cycle = 0.6
seconds, ventilation rate = 1.0 0.6 = 1.67 cycles per second b) (i) With evidence
from the graph, explain why water almost flows in one direction over the gills. The
pressure in the buccal cavity is higher than that in the opercular cavity in the first 0.4
seconds, therefore water moves from buccal cavity over the gills to opercular cavity
along the pressure gradient. After 0.3 seconds, the buccal cavity expands and lowers
the pressure, causing the water to enter the mouth but at the same time the
opercular valves close to prevent entry of water. ii) How does the fish increase
buccal cavity pressure? The mouth closes, the floor of buccal cavity is raised and the
buccal cavity pressure increases
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