Transcript Document

Living
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The Three Domains of Life
The newest system recognizes two distinctive
groups or domains of prokaryotes:
• The domain Bacteria
• The domain Archaea
The third domain, the
Eukarya, includes all
kingdoms of eukaryotes
BACTERIA
ARCHAEA
EUKARYA
Earliest
organisms
Figure 15.14B
• Prokaryotes are
classified into
two domains,
based on
nucleotide
sequences and
other features
Table 16.8
In Zoology, we study the Kingdom
Animalia in the Domain Eukarya
WHAT IS AN ANIMAL?
(1) Animals are multicellular, heterotrophic Eukarya.
– They must take in preformed organic molecules through
ingestion, eating other organisms or organic material
that is decomposing. Animals oxidize glucose,
converting it to carbon dioxide, water plus energy.
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(2) Animal cells lack cell walls that provide
structural supports for plants and fungi.
– The multicellular bodies of animals are held
together with extracellular proteins (ie.Collagen).
– In addition, other structural proteins create several
types of intercellular junctions, including tight
junctions, desmosomes, and gap junctions, that hold
tissues together. Desmosomes use protein cables
that span the cell membrane of two adjacent cells
and bind them together.
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• (3) Animals sometimes have two unique
types of tissues: nervous tissue for
impulse conduction and muscle tissue for
movement.
(4) Most animals reproduce sexually, with the
diploid stage usually dominating the life cycle.
– In most species, a small flagellated sperm fertilizes a
larger, nonmotile eggs.
– The zygote undergoes cleavage  more mitotic cell
divisions  blastula  gastrula: gastrulation –
invagination producing two tissue layers, ectoderm
and endoderm.
Fig. 32.1
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Single cell through blastula in sea urchin
gastrulation
(5) The transformation of a zygote to an animal of
specific form depends on the controlled
expression in the developing embryo of special
regulatory genes called Hox genes.
– These genes regulate the expression of other genes.
– Many of these Hox genes contain common
“modules” of DNA sequences, called homeoboxes.
– Only animals possess genes that are both
homeobox-containing in structure and homeotic in
function.
• All animals, from sponges to the most complex insects
and vertebrates have Hox genes, with the number of Hox
genes correlated with complexity of the animal’s
anatomy.
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The Phylogenetic Classification of Animalia
Shows a Flagellated Protist Ancestor
PHYLUM
The various phylum of animals
can be organized into a
Phylogenetic Tree of Animals
The major divisions are distinguished by
structural changes at four deep branches.
(1) The first branch point 1 splits:
the Parazoa - lack true tissues, from the
the Eumetazoa - have true tissues.
– The parazoans, phylum Porifera or sponges,
represent an early branch of the animal
kingdom.
– Sponges have unique development and a
structural simplicity.
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(2) Second branch point 2 -- The eumetazoans
are divided into two major branches, partly based
on body symmetry.
– Radiata - radial symmetry. Cnidaria (hydras, jellies,
sea anemones etc), Ctenophora (comb jellies).
-- Bilateria – bilateral symmetry with a dorsal - ventral
side, an anterior and posterior end, and a left and
right side.
•Linked with bilateral symmetry is cephalization, an evolutionary
trend  anterior CNS, extending to the tail end as a longitudinal nerve
chord.
• Radiata and bilateria differ in the basic
organization of germ layers (embryonic tissues),
differs between.
• The Radiata are diploblastic - 2 germ layers.
– The ectoderm,outer layer  integument, and in some
phyla, the CNS.
– The endoderm, the innermost layer  lines the
developing digestive tube, or archenteron, and gives
rise to the lining of the digestive tract and the organs
derived from it, eg. liver and lungs of vertebrates.
• The Bilateria are triploblastic – 3 germ layers
– The third germ layer, the mesoderm lies between the
endoderm and ectoderm.
– The mesoderm  the muscles and most other organs
between the digestive tube and the outer covering of the
animal.
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(3) Third branch point 3 -- Bilateria divided by
the presence or absence of a body cavity (a
fluid-filled space separating the digestive tract
from the outer body wall) and by the structure the
body cavity.
Acoelomates (the phylum Platyhelminthes) have a
solid body and lack a body cavity.
Fig. 32.6a
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Pseudocoelomate - there is a body cavity,
but it is not completely lined by mesoderm.
– Pseudocoelomates include the rotifers
(phylum Rotifera) and the roundworms (phylum
Nematoda).
Fig. 32.6b
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Coelomates -- true coelom, a fluid-filled
body cavity completely lined by
mesoderm.
–
The inner and outer layers of tissue that surround the cavity connect
dorsally and ventrally to form mesenteries, which suspend the internal
organs for support.
•
Allows for space for organs to grow
•
Provides a cushion for internal organs
•
Prevents twisting of organs from their position
Fig. 32.6b
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(4) Fourth branch point 4 -- Coelomates are
divided into two groups based on
differences in their development.
– Protostomes - Mollusks, annelids, arthropods,
and several other phyla.
– Deuterostomes - Echinoderms, chordates and
several other phyla.
– These differences center on cleavage pattern,
coelom formation, and blastopore fate.
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Developmental
Difference
between
Protostomes
and
Deuterostomes
Fig. 32.7
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• Many protostomes undergo spiral cleavage, in which
planes of cell division are diagonal to the vertical axis of
the embryo.
– Some protostomes also show determinate cleavage
where the fate of each embryonic cell is determined
early in development. Thus, no identicle twins can
occur!!!!!
• The zygotes of many deuterostomes undergo radial
cleavage in which the cleavage planes are parallel or
perpendicular to the vertical egg axis.
– Most deuterostomes show indeterminate cleavage
whereby each cell in the early embryo retains the
capacity to develop into a complete embryo. This is
the etiology of identical twins
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• Coelom formation begins in the gastrula
stage.
– Prostostome: As the archenteron forms in a
protostome, solid masses of mesoderm split to
form the coelomic cavities, called
schizocoelous development.
– Deuterostomes: mesoderm buds off from the
wall of the archenteron and hollows to become
the coelomic cavities, called enterocoelous
development.
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• The fate of the blastopore, the opening of
the archenteron is different in protostomes
and deuterostomes.
– In many protostomes, the blastopore develops
into the mouth and a second opening at the
opposite end of the gastrula develops into the
anus.
– In deuterostomes, the blastopore usually
develops into the anus and the mouth is
derived from the secondary opening.
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Kingdom Animalia
• General Characteristics
• More than a million extant species of animals
are known, and at least as many more will
probably be identified by future biologists.
– Animals are grouped into about 35 phyla.
• Animals inhabit nearly all environments on
Earth, but most phyla consist mainly of
aquatic species.
– Most live in the seas, where the first animals
probably arose.
• Terrestrial habitats pose special problems for
animals.
– Only the vertebrates and arthropods have great
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diversity on land.
• Our sense of animal diversity is biased in
favor of vertebrates, the animals with
backbones, which are well represented in
terrestrial environments.
– But vertebrates are just one subphylum within
the phylum Chordata, less than 5% of all
animal species.
• Most of the animals inhabiting a tidepool, a
coral reef, or the rocks on a stream bottom
are invertebrates, the animals without
backbones.
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Parazoa
1. Phylum Porifera:
Sponges are sessile
with porous bodies
and choanocytes
. Phylum Porifera: Sponges are sessile
with porous bodies and choanocytes
• Choanocytes resemble the
choanoflagellates.
• Germ layers are loose federations of cells,
relatively unspecialized, but 12 different
types.
• No real tissues.
• Sessile animals that lack nerves or
muscles.
– But individual cells can sense and react to
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changes in the environment.
• The 9,000 or so species of sponges (1 cm
to 2 m in height). Mostly marine.
– Only ~ 100 species live in fresh water.
Fig. 33.2
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Giant sponges can provide sanctuary for other organisms
Sponge Anatomy
(structural fibers)
Choanocyte
suspension feeding
Fig. 33.3
Sponge Life Cycle
• Most sponges are hermaphrodites.
– Gametes arise from choanocytes or
amoebocytes.
– The eggs stay in mesohyl; sperms are
carried out the osculum by water current.
– Sperms drawn into neighboring individuals
and fertilize eggs.
– Zygotes develop into flagellated, swimming
larvae that disperse from the parent.
– Larva finds a suitable substratum, and
develops into a sessile adult.
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Sponge aggregation Expt.
• If a sponge is forced through a small
screen so that the cells are separated from
each other and then put in a glass beaker,
within two weeks the sponge will have
reassembled itself into its native form.
• What does this experiment tell us?
• That cells communicate with each other and
know their position relative to each other.
The animal kingdom probably
evolved from a colonial,
flagellated protist
• Most systematists now agree that the
animal kingdom is monophyletic.
• If we could trace all the animals lineages
back to their origin, they would converge
on a common ancestor.
• That ancestor was most likely a colonial
flagellated protist that lived over 700
million years ago in the Precambrian
era.
This protist was
probably related to
choanoflagellates, a
group that arose
about a billion years
ago.
Modern
choanoflagellates
are tiny, stalked
organisms
inhabiting shallow
ponds,
lakes, and marine
environments.
• One hypothesis for origin of animals from a
flagellated protist suggests that a colony of
identical cells evolved into a hollow sphere.
• The cells of this sphere then specialized,
creating two or more layers of cells.
Fig. 32.3
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