Chapter 40:Basic Principles of Animal
Form and Function
• Animals inhabit almost every part of the biosphere
• Despite their amazing diversity all animals face a similar set of problems, including how to nourish themselves
• The comparative study of animals reveals that form and function are closely correlated
• Natural selection can fit structure, anatomy, to function, physiology by selecting, over many generations, what works best among the available variations in a population
Concept 40.1: Physical laws and the environment constrain animal size and shape
• Physical laws and the need to exchange materials with the environment place certain limits on the range of animal forms
Physical Laws and Animal Form• The ability to perform certain actions depends
on an animal’s shape and size
• Evolutionary convergence reflects different species’ independent adaptation to a similar environmental challenge
Tuna
Shark
Penguin
Dolphin
Seal
Exchange with the Environment• An animal’s size and shape have a direct effect
on how the animal exchanges energy and materials with its surroundings
• Exchange with the environment occurs as substances dissolved in the aqueous medium diffuse and are transported across the cells’ plasma membranes
• 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
• Multicellular organisms with a sac body plan have body walls that are only two cells thick, facilitating diffusion of materials
Mouth
Gastrovascularcavity
Diffusion
Diffusion
(b) Two cell layers
• Organisms with more complex body plans have highly folded internal surfaces specialized for exchanging materials
Respiratorysystem
Digestivesystem
Excretorysystem
Circulatorysystem
Concept 40.2: Animal 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
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
Epithelial Tissue
• Epithelial tissue– Covers the outside of the body and lines organs and
cavities within the body– Contains cells that are closely joined
Connective Tissue– Functions mainly to bind and support other tissues– Contains sparsely packed cells scattered throughout
an extracellular matrix
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
Organs and Organ Systems• In all but the simplest animals different tissues
are organized into organs
Lumen ofstomach
Mucosa. The mucosa is anepithelial layer that linesthe lumen.
Submucosa. The submucosa isa matrix of connective tissuethat contains blood vesselsand nerves.
Muscularis. The muscularis consistsmainly of smooth muscle tissue.
0.2 mm
Serosa. External to the muscularis is the serosa,a thin layer of connective and epithelial tissue.
• In some organs the tissues are arranged in layers
Organ systems represent a level of organization higher than organs– Organ systems carry out the major body functions of
most animals
Organ systems in mammals:
Concept 40.3: 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
Bioenergetics--The flow of energy through an animal
– Ultimately limits the animal’s behavior, growth, and reproduction
– Determines how much food it needs
• Studying an animal’s bioenergetics– Tells us a great deal about the animal’s adaptations
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, which powers cellular work
• After the energetic needs of staying alive are met by remaining molecules from food can be used in biosynthesis
Organic moleculesin food
Digestion andabsorption
Nutrient moleculesin body cells
Cellularrespiration
Biosynthesis:growth,
storage, andreproduction
Cellularwork
Heat
Energylost infeces
Energylost inurine
Heat
Heat
Externalenvironment
Animalbody
Heat
Carbonskeletons
ATP
Quantifying Energy Use• An animal’s metabolic rate is the amount of
energy an animal uses in a unit of time– Can be measured in a variety of ways
• One way to measure metabolic rate is to determine the amount of oxygen consumed or carbon dioxide produced by an organism
This photograph shows a ghost crab in arespirometer. Temperature is held constant in thechamber, with air of known O2 concentration flow-ing through. The crab’s metabolic rate is calculatedfrom the difference between the amount of O2
entering and the amount of O2 leaving therespirometer. This crab is on a treadmill, runningat a constant speed as measurements are made.
(a)
(b) Similarly, the metabolic rate of a manfitted with a breathing apparatus isbeing monitored while he works outon a stationary bike.
Bioenergetic Strategies• An animal’s metabolic rate is closely related to
its bioenergetic strategy
• Birds and mammals are mainly endothermic, meaning that their bodies are warmed mostly by heat generated by metabolism– They typically have higher metabolic rates
• Amphibians and reptiles other than birds are ectothermic, meaning that:– They gain their heat mostly from external sources– They have lower metabolic rates
Influences on Metabolic Rate• The metabolic rates of animals are affected by
many factors
Size and Metabolic Rate• Metabolic rate per gram is inversely related to
body size among similar animals
Activity and Metabolic Rate• The basal metabolic rate (BMR)
– Is the metabolic rate of an endotherm at rest
• The standard metabolic rate (SMR)– Is the metabolic rate of an ectotherm at rest
• For both endotherms and ectotherms– Activity has a large effect on metabolic rate
• In general, an animal’s maximum possible metabolic rate is inversely related to the duration of the activity
Max
imum
met
abol
ic r
ate
(kca
l/min
; log
sca
le)
500
100
50
10
5
1
0.5
0.1
A H
AH
A
AA
HH
H
A = 60-kg alligator
H = 60-kg human
1second
1minute
1hour
Time interval
1day
1week
Key
Existing intracellular ATP
ATP from glycolysis
ATP from aerobic respiration
Energy Budgets• Different species of animals use the energy and
materials in food in different ways, depending on their environment
• An animal’s use of energy is partitioned to BMR (or SMR), activity, homeostasis, growth, and reproduction
Endotherms Ectotherm
Ann
ual e
nerg
y ex
pend
iture
(kc
al/y
r) 800,000Basalmetabolicrate
ReproductionTemperatureregulation costs
Growth
Activitycosts
60-kg female humanfrom temperate climate
Total annual energy expenditures (a)
340,000
4-kg male Adélie penguinfrom Antarctica (brooding)
4,000
0.025-kg female deer mousefrom temperateNorth America
8,000
4-kg female pythonfrom Australia
Ene
rgy
expe
nditu
re p
er u
nit
mas
s (k
cal/k
g•da
y)
438
Deer mouse
233
Adélie penguin
36.5
Human
5.5
Python
Energy expenditures per unit mass (kcal/kg•day)(b)
Concept 40.4: Animals regulate their internal environment within relatively narrow limits
• The internal environment of vertebrates is called the interstitial fluid, and is very different from the external environment
• Homeostasis is a balance between external changes and the animal’s internal control mechanisms that oppose the changes
Regulating and Conforming• Regulating and conforming are two extremes in
how animals cope with environmental fluctuations
• An animal is said to be a regulator if it uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation (endotherms)
• An animal is said to be a conformer if it allows its internal condition to vary with certain external changes (ectotherms)
Mechanisms of Homeostasis• Mechanisms of homeostasis moderate changes
in the internal environment
• A homeostatic control system has three functional components– A receptor, a control center, and an effector
Response
No heatproduced
Roomtemperaturedecreases
Heaterturnedoff
Set point
Toohot
Setpoint
Control center:thermostat
Roomtemperatureincreases
Heaterturnedon
Toocold
Response
Heatproduced
Setpoint
• Most homeostatic control systems function by negative feedback where buildup of the end product of the system shuts the system off
• A second type of homeostatic control system is positive feedback, which involves a change in some variable that triggers mechanisms that amplify the change
Positive Feedback and Global Warming
Concept 40.5: Thermoregulation contributes to homeostasis and involves anatomy, physiology, and behavior
• Thermoregulation– Is the process by which animals maintain an internal
temperature within a tolerable range
Ectotherms and Endotherms• Ectotherms
– Include most invertebrates, fishes, amphibians, and non-bird reptiles
• Endotherms– Include birds and mammals
• In general, ectotherms tolerate greater variation in internal temperature than endotherms
River otter (endotherm)
Largemouth bass (ectotherm)
Ambient (environmental) temperature (°C)
Bod
y te
mpe
ratu
re (
°C)
40
30
20
10
10 20 30 400
• Endothermy is more energetically expensive than ectothermy– But buffers animals’ internal temperatures against
external fluctuations– And enables the animals to maintain a high level
of aerobic metabolism
Modes of Heat Exchange• Organisms exchange heat by four physical
processesRadiation 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 aliquid 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
Balancing Heat Loss and Gain• Thermoregulation involves physiological and
behavioral adjustments that balance heat gain and loss
Insulation• Insulation, which is a major thermoregulatory
adaptation in mammals and birds– Reduces the flow of heat between an animal and its
environment– May include feathers, fur, or blubber
• In mammals, the integumentary system acts as insulating material
Hair
Sweatpore
Muscle
Nerve
Sweatgland
Oil glandHair follicle
Blood vessels
Adipose tissue
Hypodermis
Dermis
Epidermis
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
• Many marine mammals and birds have arrangements of blood vessels called countercurrent heat exchangers that are important for reducing heat loss
In the flippers of a dolphin, each artery issurrounded by several veins in acountercurrent arrangement, allowingefficient heat exchange between arterialand venous blood.
Canadagoose
Artery Vein
35°C
Blood flow
VeinArtery
30º
20º
10º
33°
27º
18º
9º
Pacific bottlenose dolphin
2
1
3
2
3
Arteries carrying warm blood down thelegs of a goose or the flippers of a dolphinare in close contact with veins conveyingcool blood in the opposite direction, backtoward the trunk of the body. Thisarrangement facilitates heat transferfrom arteries to veins (blackarrows) along the entire lengthof the blood vessels.
1
Near the end of the leg or flipper, wherearterial blood has been cooled to far below the animal’s core temperature, the artery can still transfer heat to the even colderblood of an adjacent vein. The venous bloodcontinues to absorb heat as it passes warmer and warmer arterial blood traveling in the opposite direction.
2
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 partsimmersed in cold water.
3
1 3
• Some specialized bony fishes and sharks also possess countercurrent heat exchangers
21º25º 23º
27º
29º31º
Body cavity
SkinArtery
Vein
Capillarynetwork withinmuscle
Dorsal aortaArtery andvein underthe skin
Heart
Bloodvesselsin gills
• Many endothermic insects have countercurrent heat exchangers that help maintain a high temperature in the thorax
Cooling by Evaporative Heat Loss• Many types of animals:
– Lose heat through the evaporation of water in sweat– Use panting to cool their bodies
• Bathing moistens the skin, which helps to cool an animal down
Behavioral Responses• Both endotherms and ectotherms use a variety
of behavioral responses to control body temperature
• Some terrestrial invertebrates have certain postures that enable them to minimize or maximize their absorption of heat from the sun
Adjusting Metabolic Heat Production
• Some animals can regulate body temperature by adjusting their rate of metabolic heat production
• Many species of flying insects use shivering to warm up before taking flight
PREFLIGHT PREFLIGHTWARMUP
FLIGHT
Thorax
Abdomen
Tem
per
atur
e (°
C)
Time from onset of warmup (min)
40
35
30
25
0 2 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
Thermostat inhypothalamusactivates coolingmechanisms.
Sweat glands secrete sweat that evaporates, cooling the body.
Blood vesselsin skin dilate:capillaries fillwith warm blood;heat radiates fromskin surface.
Body temperaturedecreases;thermostat
shuts off coolingmechanisms.
Increased bodytemperature (suchas when exercising
or in hotsurroundings)
Homeostasis:Internal body temperatureof approximately 36–38C
Body temperatureincreases;thermostat
shuts off warmingmechanisms.
Decreased bodytemperature
(such as whenin cold
surroundings)
Blood vessels in skinconstrict, diverting bloodfrom skin to deeper tissuesand reducing heat lossfrom skin surface.
Skeletal muscles rapidlycontract, causing shivering,which generates heat.
Thermostat inhypothalamusactivateswarmingmechanisms.
Adjustment to Changing Temperatures
• In a process known as acclimatization, many animals can adjust to a new range of environmental temperatures over a period of days or weeks
• Acclimatization may involve cellular adjustments– Or in the case of birds and mammals, adjustments of
insulation and metabolic heat production
Torpor and Energy Conservation• Torpor is an adaptation that enables animals to
save energy while avoiding difficult and dangerous conditions– Is a physiological state in which activity is low and
metabolism decreases
• Hibernation is long-term torpor that is an adaptation to winter cold and food scarcity during which the animal’s body temperature declines
Additional metabolism that would benecessary to stay active in winter
Actualmetabolism
Bodytemperature
Arousals
Outsidetemperature Burrow
temperature
June August October December February April
Tem
pera
ture
(°C
)M
etab
olic
rat
e(k
cal p
er d
ay)
200
100
0
35
30
25
20
15
10
5
0
-5
-10
-15
• Estivation, or summer torpor– Enables animals to survive long periods of high
temperatures and scarce water supplies
• Daily torpor– Is exhibited by many small mammals and birds and
seems to be adapted to their feeding patterns