1. 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.

3. 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.

4. 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

5. 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).

6. 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
(a) Single cell
Figure 40.3a

7. 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.

8. 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

9. 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).

10. 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.

11. Figure 40.4 External environment Mouth Food CO2 O2 Animal body
Respiratory
system
Blood
50 µm
0.5 cm
Cells
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).
Heart
Nutrients
Circulatory
system
10 µm
Interstitial
fluid
Digestive
system
The lining of the small intestine, a diges-
tive organ, is elaborated with fingerlike
projections that expand the surface area
for nutrient absorption (cross-section, SEM).
Excretory
system
Anus
Inside a kidney is a mass of microscopic
tubules that exhange chemicals with
blood flowing through a web of tiny
vessels called capillaries (SEM).
Unabsorbed
matter (feces)
Metabolic waste
products (urine)
Figure 40.4

12. 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.

13. 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.

14. Epithelial Tissue Epithelial tissue
Covers the outside of the body and lines organs and cavities within the body
Contains cells that are closely joined

15. Connective Tissue Connective tissue
Functions mainly to bind and support other tissues
Contains sparsely packed cells scattered throughout an extracellular matrix

16. 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

17. Nervous Tissue Nervous tissue
Senses stimuli and transmits signals throughout the animal

18. 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.

19. 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.
0.2 mm
Serosa. External to the muscularis is the serosa, a thin layer of connective and epithelial tissue.
Figure 40.6

20. 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.

21. Organ systems in mammals
Table 40.1

22. 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.

23. Energy Sources and Allocation
Animals harvest chemical energy from the food they eat
Once food has been digested, the energy-containing molecules are usually used to make ATP (adenosine triphosphate), which powers cellular work.

24. 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
Energy
lost in
feces
Nutrient molecules
in body cells
Energy
lost in
urine
Carbon
skeletons
Cellular
respiration
Heat
ATP
Biosynthesis:
growth,
storage, and
reproduction
Cellular
work
Heat
Figure 40.7
Heat

25. 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.

26. 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

27. Figure 40.12 40 River otter (endotherm) 30 Body temperature (°C) 20
Largemouth bass (ectotherm)
Ambient (environmental) temperature (°C)
Body temperature (°C) 40 30 20 10
Figure 40.12

28. 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.

29. Organisms exchange heat by four physical processes
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.

30. Modes of Heat Exchange Figure 40.13
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.
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.
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.
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.
Figure 40.13

31. Balancing Heat Loss and Gain
Thermoregulation involves physiological and behavioral adjustments that balance heat gain and loss.

32. 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.

33. 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.

34. 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.

35. 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.

36. 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.

37. 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.

38. Figure 40.15 Pacific bottlenose dolphin Canada goose Blood flow Artery
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.
Canada
goose
Artery
Vein
35°C
Blood flow
30º
20º
10º
33°
27º
18º 9º
Pacific
bottlenose
dolphin 2 1 3
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.
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.
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. 1 3
Figure 40.15

39. 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.

40. 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.

41. 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.

42. Time from onset of warmup (min)
PREFLIGHT
WARMUP
FLIGHT
Thorax
Abdomen
Temperature (°C)
Time from onset of warmup (min) 40 35 30 25 2 4
Figure 40.20

43. 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.