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Living Animals, Continuity &
Design
Estimated earth formed about 4.5 billion
ANIMALS
years ago; life is thought to have begun a few
hundred million years later.
“Life is thought to have begun when a sequence of
chemical reactions in a defined environment occurred
which resulted in the formation of a product that could
replicate itself.”
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Oldest known fossils of
living organisms date to
about 3.5 billions years
ago
 Are thought to be
photosynthetic
organisms, perhaps
oxygen producers
 What does this
suggest???

One of the oldest fossils of multicelluar
oganisms is Dickinsonia. Estimated at 560
million years old, Dickinsonia may have
evolved after the end of the last
Neoproterozoic global glaciation
http://earthobservatory.nasa.gov/Study/wardhunt/
From “simple beginnings”, wide variety of living organisms which
inhabit a very diverse range of environments; each own role
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Fundamental Properties of Life

What is life? Can we define it?
◦ YES, but many possible definitions
 easiest way to describe is as a collection of fixed characteristics
that separate living from non-living

We should note that the properties that life
exhibits today is very different from those of
earliest life forms
Article

History of life shows extensive & ongoing
change
◦ evolution
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Chemical Uniqueness

Based on organic molecules
unique & complex organization
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Complex & Hierarchical
Organization

Each level builds from the level below
◦ level influenced & restricted by properties of previous level

Emergence
◦ appearance of new characteristic at a given level of
organization

emergent properties
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Reproduction

At each level of biological hierarchy, living forms reproduce
◦ molecular
◦ cellular
◦ organismal
 asexual or sexual
◦ species
 speciation

Observe complementary, yet contradictory, phenomena
◦ heredity
 transmission of traits from parents to offspring
◦ variation
 production of differences among the traits of different individuals
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Possession of Genetic Program

DNA
◦ stores genetic information

Genetic code
◦ correspondence between sequence of bases in DNA to sequence of amino acids in
proteins

Interestingly
◦ observe constancy of code among living organisms

suggest
 single origin of life
 genetic code undergone little evolutionary change since origin
Metabolism
Essential chemical processes
 Acquire nutrients from environment

◦ provide:



energy
construction components for building & maintaining living systems
Results from interaction of catabolic & anabolic reactions
◦ include digestive processes, cellular respiration and synthesis of molecules &
structures

Physiology
◦ study of metabolic fxn’s from biochemical to organismal level
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Development

Life cycle
◦ all living organisms flow through characteristic
changes that begin from its origin to its adult form
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Environmental Interaction

Ecology
◦ study of organismal interaction with their environment

Irritability
◦ organism responds to environmental stimuli
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Movement

energy derived from environment permits
living organism to initiate controlled
movement
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DOMAINS
Eukarya-all life
forms with
eukaryotic cells
Bacteria-more
advanced prokaryotic
microbes
comparison of DNA
sequences, rRNA, other
RNA along with protein
sequences---evolutionary
time clock
Archaea –very
ancient prokaryotic
microbes; extremists
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What is an “animal”?

Characteristics:
◦ multicellular, heterotrophic eukaryotes
◦ have cell boundaries but lack a cell wall
 use structural proteins to hold themselves together along with
intercellular junctions
◦ consume preformed organic molecules
 most ingest food and digest it in an internal cavity
◦ bodies of most animals (all except sponges) are made up of
cells organized into tissues, each tissue specialized to some
degree to perform specific functions
◦ capable of complex and relatively rapid movement
◦ development of most animals is characterized by
distinctive stages
◦ reproduce sexually/asexually, with diploid adult
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Nature of Reproductive Process

Modes of reproduction
◦ asexual
 production of individuals without gametes
◦ sexual
 production of individuals with gametes
mechanism for gene exchange between individuals more limited in
organisms with only asexual reproduction
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Asexual
Reproduction

•all offspring have same genotype, are clones of parent
unless mutations occur
•ensures rapid increase in numbers
Basic forms
◦ binary fission
 parent divides by mitosis
 can occur lengthwise or transverse
 multiple fission
 schizogony, nucleus divides repeatedly
 cytoplasm division produces many daughter cells
 sporogony, spore formation
 form of multiple fission in parasitic protozoa
◦ budding
 bud, an outgrowth of parent, develops organs & then
detaches
◦ gemmulation
 formation of new individual by form an aggregation of cells
from parent, surrounded by a resistant capsule – gemmule
 enclosed cells become active in good conditions, emerge and
grow a new sponge
◦ fragmentation
 multicellular organism breaks into many fragments that
become a new animal
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Sexual Reproduction

Bisexual/Biparental reproduction
◦
produces offspring from union of gametes from 2 genetically
different parents

◦
separate sexes – dioecious

◦

most vertebrates & many invertebrates
both male & female organs –
monoecious, or
Hermaphroditism
◦
◦
both male & female in same individual
most avoid self-fertilization


offspring have genotype different from either parent
exchange gametes with another individual of same species
Parthenogenesis
◦
◦
development of an embryo from an unfertilized egg
avoids energy & danger of bringing 2 sexes together, but
narrows diversity available for adaptations to new conditions
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Sexual vs Asexual

Due to prevalence, sexual
reproduction considered
advantageous
◦ yet
 complex, requires time,
uses a lot of energy
 cost of meiosis?
 producing males?
 breakup favorable gene combinations

So why?
◦ enriches gene pool by producing novel genotypes in
times of environmental change
◦ sexual recombination provides means to spread
beneficial mutations without a population being held
back by deleterious ones
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
Despite COST
◦ in colonizing new environments
 asexual reproduction most successful
◦ environment/habitat become more “crowded”/populated
 competition between species for resources increases
 selection more intense
 genetic variability provides diversity
 assists population in resisting extinction
◦ therefore,
 on a geologic timescale, asexual lineages more prone to
extinction
 lack genetic flexibility
 sexual reproduction more favored by species selection

Note - many invertebrates use both sexual & asexual
reproduction
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Reproductive
Patterns

Oviparous
◦ animals that lay eggs, with little or no other embryonic
development within the mother
◦ fertilization

internal or external
◦ found in many invertebrates and fish, amphibians, reptiles,
birds & monotremes

Ovoviparous
◦ animals produce eggs, but instead of laying the eggs, the
eggs develop within the mother's body and are birthed
live

embryos derive nutrition from yolk sac
◦ found in invertebrates and fish, lizards & snakes

Viviparous
◦ retention and growth of the fertilized egg within the
maternal body until the young animal, as a larva or
newborn, is capable of independent existence

nutrition derived from a placenta or similar structure
◦ found in lizards, snakes, mammals, elasmobranch fishes and
a few invertebrates & amphibians
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Structures of Reproductive Systems

Basic components of a sexual system
◦ primary organs
 gonads that produce gametes & sex hormones
◦ accessory organs
 assist gonads in function, delivery of gametes & may support embryo
Invertebrate
Endocrine system events orchestrate reproduction
seasonal, or cyclic activity
Vertebrate
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Development

Early concepts:
◦ preformation
 sperm or egg contains a preformed miniature adult
 young animals simply unfold structures that are already there & becomes
larger during development
◦ epigenesis
 development of a plant or animal from an egg or spore is a series of
progressive changes in which unorganized cell masses differentiate
into organs and organ systems
 fertilized egg contains building materials that are assembled by an unknown
directing force
KF Wolff in 1759 demonstrated
that there were no preformed
individual when investigating
the developmental stages of the
chicken, process began with
undifferentiated material
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
Development, cont’d
◦ describes progressive changes
in an individual form from
beginning to maturity
 process begins when fertilized egg
divides mitotically
 specialization occurs as a hierarchy
of developmental decisions
 cell types do not unfold but arise
from conditions created in preceding
stages
 structures arise from interaction
of less committed materials
 interactions become increasingly
restrictive, each stage limits
developmental fate
 with each new stage, cells lose
option to become something
different
 determined
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Fertilization
union of male & female gametes
to form a zygote
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What can we learn from
development?


study how a zygote, a single cell, produce a
multitude of body parts in an organism
provides us with a means to search for
commonalities among organisms
◦ all multicellular animals begin as a zygote, go
through cleavage & some subsequent
developmental stages
 observe developmental variation among animals
 developmental variation begins with zygotic cleavage patterns
 types of cleavage characterize particular groups of animals,
along with other developmental features to form a “suite of
characters”
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Cleavage & Early Development

Cleavage stage
◦ embryo divides, forming smaller
cells called blastomeres
 increasing cell numbers
 an orderly process
◦ polarity - animal-vegetal axis
 polarity develops due to
yolk/nutrition for developing
embryo
 amt of yolk at vegetal pole varies among
taxa
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Direct vs Indirect
Development
No larval form
Metamorphosis
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Development Following Cleavage

Blastulation
◦ mass of zygote partitioned among cells
 results in a single, spherical layer of cells, blastula, enclosing a hollow, central
fluid-filled cavity, the blastocoel
 stage thought to be end of cleavage and initiates gastrulation

Gastrulation
◦ reorganization of single-layered blastula into a 2(bilaminar/diploblastic) or 3-layered (trilaminar/triploblastic) embryo,
called a gastrula
 layers referred to as germ layers
 produce all structures of adult body
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Generalized Developmental
Sequence
coelom, a body cavity surrounded
by mesoderm, develops via
schizocoely or enterocoely
Blastocyst
coelom formation is an inheritable
trait, impt in grouping organisms
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Developmental Patterns in Animals


presence of blastula stage in development is a fundamental animal
homology
triploblastic, bilaterally symmetrical animals are divided into 2 major
clades, protostomes & deuterostomes
NOTE: cells that form coelom during enterocoely come from a different
region of the endoderm than those that make the coelom during schizocoely
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Development of
Systems and Organs
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Evolutionary Developmental Biology
Evo-Devo

use of embryology by zoologists for clues to evolutionary
history, or phylogeny, of animals
◦ developmental features suggest evolutionary relationships among
different phyla
◦ evolution is a process in which organisms become different as a
result in changes in genetic control of development
 observe that genes which control development are similar in diverse animals
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Hierarchical Organization of Animal
Complexity

observe a basic uniformity of
biological organization
◦ animals share structural
complexities that reflect common
ancestry

recognize 5 major grades of
organization
◦
◦
◦
◦
◦

protoplasmic
cellular
cell-tissue
tissue-organ
organ-system
each grade is more complex
than the preceding & builds in
a hierarchical manner
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Animal Body Plans
Animal
Symmetry
grade of organization
body symmetry
number of embryonic germ layers
number of body cavities
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Developmental Origins
of Body Plans
Segmentation
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Complexity & Body Size
more complexity of organization permit
& promote larger body size
benefit of larger size:
surface area-to-volume ratios
have impact consequences on
animal physiology
•larger size buffers against environmental fluctuations
•protection against predators/offensive tactics
•cost-body temperature, movement
ecological opportunities differ between
large & small animals
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Components of Animal Bodies

Learn about
Extracellular
Components &
Primary Tissue Types
◦ read pp188-193

Be able to:
◦ list major morphological
characteristics &
functions
◦ answer Review
Questions #4-9, pp 194
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