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Form and Function
– The comparative study of animals reveals that
form and function are closely correlated. What
an animals does (function) is closely related to
the structure of its body (form).
– By selecting, over many generations, what
works best among the available variations in a
population, natural selection adapts an
organisms’ anatomy and physiology to suit its
environment.
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Size and shape are constrained by physical laws
• How well an organism performs an action (e.g.
swims, flies, runs) depends on the animal’s shape
and size, which are strongly influenced by physical
laws.
• For example, a major challenge for swimming
animals is overcoming drag. As a result, a wide
variety of organisms have evolved similar
streamlined body shapes and control structures
(fins and flippers) that enable them to move
smoothly and powerfully through water.
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Convergent evolution
• Different species have converged on similar
solutions to the same evolutionary challenge.
(a) Tuna
(b) Shark
(c) Penguin
(d) Dolphin
Figure 40.2a–e
(e) Seal
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Size and shape are constrained by physical laws
• Physical laws and the need to exchange materials
with the environment place limits on the range of
animal forms.
• An animal’s size and shape have a direct effect on
how the animal exchanges energy and materials
with its surroundings.
• Organisms that depend on exchanging gases
directly across their surface must have a large
surface area relative to their volume (e.g. an
amoeba).
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Size and shape are constrained by physical laws
• A single-celled protist living in water has a
sufficient surface area of plasma membrane to
service its entire volume of cytoplasm
Diffusion
Figure 40.3a
(a) Single cell
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Size and shape are constrained by physical laws
• Surface to volume ratio is a critical limiting factor in
how large a single celled organism can grow.
• As a cell’s linear dimensions (e.g. length) are
increased,its volume increases as a cube function
of that linear dimension. However, the surface
area by which the cell is supplied with its
requirements increases only as a square function.
• Thus, the volume a cell can attain is limited by its
surface area.
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Size and shape are constrained by physical laws
• Multi-cellular organisms can also depend on
diffusion to supply them with their needs, but they
must have thin body walls for diffusion to work.
Mouth
Gastrovascular
cavity
Diffusion
Diffusion
Figure 40.3b
(b) Two cell layers
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Size and shape are constrained by physical laws
• Insects have an impermeable exoskeleton and do
not exchange gases across it.
• To get gases to the tissues they depend on a
dense network of tubes called the tracheal system
that connect to the outside via pores.
• The system still depends on passive diffusion and
tubes must reach to within a few cells to transfer
gases. As a result, the size insects can attain is
limited (despite what Hollywood movies show).
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Size and shape are constrained by physical laws
• Organisms with more complex body plans solve
the surface area problem by having highly folded
internal surfaces specialized for exchanging
materials (e.g. villi of gut).
• The folding greatly increases the surface area. In
addition, active transportation of materials to and
from sites far from the surface takes place by
means of a circulatory system.
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External environment
Mouth
Food
CO2
O2
Respiratory
system
0.5 cm
Cells
Heart
Nutrients
Circulatory
system
50 µm
Animal
body
A microscopic view of the lung reveals
that it is much more spongelike than
balloonlike. This construction provides
an expansive wet surface for gas
exchange with the environment (SEM).
10 µm
Interstitial
fluid
Digestive
system
Excretory
system
The lining of the small intestine, a digestive organ, is elaborated with fingerlike
projections that expand the surface area
for nutrient absorption (cross-section, SEM).
Anus
Unabsorbed
matter (feces)
Figure 40.4
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Metabolic waste
products (urine)
Inside a kidney is a mass of microscopic
tubules that exhange chemicals with
blood flowing through a web of tiny
vessels called capillaries (SEM).
Form and function are correlated at all levels of
organization
• Animals are composed of cells
• Groups of cells with a common structure and
function make up tissues
• Different tissues make up organs which together
make up organ systems.
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Tissue Structure and Function
• Different types of tissues have different structures
that are suited to their functions
• Tissues are classified into four main categories:
Epithelial, connective, muscle, and nervous.
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Epithelial Tissue
• Epithelial tissue
– Covers the outside of the body and lines
organs and cavities within the body
– Contains cells that are closely joined
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Connective Tissue
• Connective tissue
– Functions mainly to bind and support other
tissues
– Contains sparsely packed cells scattered
throughout an extracellular matrix
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Muscle Tissue
• Muscle tissue
– Is composed of long cells called muscle fibers
capable of contracting in response to nerve
signals
– Is divided in the vertebrate body into three
types: skeletal, cardiac, and smooth
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Nervous Tissue
• Nervous tissue
– Senses stimuli and transmits signals
throughout the animal
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Organs and Organ Systems
• In all but the simplest animals (i.e. sponges)
different tissues are organized into organs.
• Organs are made up of multiple tissues each of
which performs a function that contributes to the
overall functioning of the organ.
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Arrangement of tissues in an organ (the stomach)
Lumen of
stomach
Mucosa. The mucosa is an
epithelial layer that lines
the lumen.
Submucosa. The submucosa is
a matrix of connective tissue
that contains blood vessels
and nerves.
Muscularis. The muscularis consists
mainly of smooth muscle tissue.
Serosa. External to the muscularis is the serosa,
a thin layer of connective and epithelial tissue.
Figure 40.6
0.2 mm
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Organ systems
• Representing a level of organization higher than
organs, organ systems carry out the major body
functions of most animals.
• These include: respiratory, circulatory, digestive,
excretory, and immune systems among others.
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• Organ systems in mammals
Table 40.1
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Energetics
• Animals use the chemical energy in food to
sustain form and function
• All organisms require chemical energy for growth,
repair, physiological processes, regulation, and
reproduction.
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Energy Sources and Allocation
• Animals harvest chemical energy from the food
they eat
• Once food has been digested, the energycontaining molecules are usually used to make
ATP (adenosine triphosphate), which powers
cellular work.
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Energetics
• After the energetic needs of staying alive are met
any remaining molecules from food can be used in
biosynthesis
Organic molecules
in food
External
environment
Animal
body
Digestion and
absorption
Heat
Nutrient molecules
in body cells
Carbon
skeletons
Cellular
respiration
Energy
lost in
feces
Energy
lost in
urine
Heat
ATP
Biosynthesis:
growth,
storage, and
reproduction
Figure 40.7
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Heat
Cellular
work
Heat
Bioenergetic strategies
• Birds and mammals are mainly endothermic,
meaning that their bodies are warmed mostly by
heat generated by metabolism. They typically
have high metabolic rates.
• Invertebrates, fishes, amphibians, and reptiles
other than birds are ectothermic, meaning that
they gain their heat mostly from external sources
and have lower metabolic rates.
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Thermoregulation
• Thermoregulation is the process by which animals
maintain an internal temperature within a tolerable
range.
• In general, ectotherms tolerate greater variation in
internal temperature than endotherms
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40
River otter (endotherm)
Body temperature (°C)
30
20
Largemouth bass (ectotherm)
10
0
Figure 40.12
10
20
30
Ambient (environmental) temperature (°C)
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40
• Endothermy is more energetically expensive than
ectothermy because energy must be expended to
maintain a higher body temperature than the
surrounding environment.
• However, endothermic animals can remain active
under a wider range of conditions than
ectothermic ones.
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Modes of Heat Exchange
• Organisms exchange heat by four physical
processes
– Radiation: the emission of electromagnetic
energy.
– Evaporation: loss of energy by loss of liquid
molecules as gas.
– Conduction: direct transfer of heat energy
between objects in contact.
– Convection: transfer of energy by movement
of air or liquid past an object.
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Modes of Heat Exchange
Radiation is the emission of electromagnetic
waves by all objects warmer than absolute
zero. Radiation can transfer heat between
objects that are not in direct contact, as when
a lizard absorbs heat radiating from the sun.
Figure 40.13
Convection is the transfer of heat by the
movement of air or liquid past a surface,
as when a breeze contributes to heat loss
from a lizard’s dry skin, or blood moves
heat from the body core to the extremities.
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Evaporation is the removal of heat from the surface of a
liquid that is losing some of its molecules as gas.
Evaporation of water from a lizard’s moist surfaces that
are exposed to the environment has a strong cooling effect.
Conduction is the direct transfer of thermal motion (heat)
between molecules of objects in direct contact with each
other, as when a lizard sits on a hot rock.
Balancing Heat Loss and Gain
• Thermoregulation involves physiological and
behavioral adjustments that balance heat gain and
loss.
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Insulation
• Insulation, which is a major thermoregulatory
adaptation in mammals and birds, reduces the
flow of heat between an animal and its
environment.
• Insulating materials include hair, feathers and
blubber.
• Hair and feathers trap air which is an excellent
insulator.
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Circulatory Adaptations
• Many endotherms and some ectotherms can alter
the amount of blood flowing between the body
core and the skin.
• In vasodilation: blood flow in the skin increases,
facilitating heat loss.
• In vasoconstriction: blood flow in the skin
decreases, lowering heat loss.
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Countercurrent heat exchangers
• Because heat can be lost rapidly in water by
convection many marine mammals and birds have
arrangements of blood vessels called
countercurrent heat exchangers in their
extremities that help limit heat loss.
• In these heat exchangers arteries and veins run
very close to each other. As a result, heat can
flow from one to the other.
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Countercurrent heat exchangers
• Blood in the core of the body is warm and flows
through the arteries out to the extremities.
• In the counter current heat exchanger the warm
arterial blood flows next to cooler venous blood
returning from the extremity and as a result heat is
transferred from the warm arterial blood to the
cooler venous blood.
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Countercurrent heat exchangers
• Even though the arterial blood is cooling as it
flows towards the extremity it remains warmer
than the venous blood it is flowing next to.
• As a result, heat continues to flow from the arterial
to the venous blood, and by the time the arterial
blood reaches the extremity most of the heat in the
arterial blood has been transferred to the venous
blood and the heat retained in the core of the
animal.
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• Countercurrent heat exchangers are found in the
legs of birds and flippers of dolphins and whales.
• They also are found in some ectotherms such as
tuna and moths, which maintain a core
temperature warmer than the rest of their body.
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1
Arteries carrying warm blood down the
legs of a goose or the flippers of a dolphin
are in close contact with veins conveying
cool blood in the opposite direction, back
toward the trunk of the body. This
arrangement facilitates heat transfer
from arteries to veins (black
arrows) along the entire length
of the blood vessels.
Canada
goose
Pacific
bottlenose
dolphin
Blood flow
2
1
Artery
Vein
35°C
33°
30º
27º
20º
18º
10º
9º
2
Near the end of the leg or flipper, where
arterial blood has been cooled to far below
the animal’s core temperature, the artery
can still transfer heat to the even colder
blood of an adjacent vein. The venous blood
continues to absorb heat as it passes warmer
and warmer arterial blood traveling in the
opposite direction.
1
Vein
Artery
3
3
3
2
3
As the venous blood approaches the
center of the body, it is almost as warm
as the body core, minimizing the heat lost
as a result of supplying blood to body parts
immersed in cold water.
Figure 40.15
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In the flippers of a dolphin, each artery is
surrounded by several veins in a
countercurrent arrangement, allowing
efficient heat exchange between arterial
and venous blood.
Cooling by Evaporative Heat Loss
• Many types of animals lose heat through the
evaporation of water in sweat or use panting to
cool their bodies.
• Bathing in water or mud also helps to cool animals
down.
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Behavioral Responses
• Both endotherms and ectotherms use a variety of
behavioral responses to control body temperature.
For example, they move into the sun or shade to
gain heat or cool down.
• They may also adopt certain body postures (e.g.
birds and insects spread their wings) to warm up
or cool down.
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Adjusting Metabolic Heat Production
• Some animals can regulate body temperature by
adjusting their rate of metabolic heat production.
• For example, many species of flying insects use
shivering to warm up before taking flight.
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PREFLIGHT
PREFLIGHT
WARMUP
Temperature (°C)
40
FLIGHT
Thorax
35
30
Abdomen
25
0
2
Time from onset of warmup (min)
Figure 40.20
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4
Feedback Mechanisms in Thermoregulation
• Mammals regulate their body temperature by a
complex negative feedback system that involves
several organ systems.
• In humans, a specific part of the brain, the
hypothalamus contains a group of nerve cells that
function as a thermostat.
• If the hypothalamus detects an increase in
temperature, for example, it signals sweat glands
to become more active and increase evaporative
cooling and blood vessels in the skin to vasodilate
facilitating heat loss.
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