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