Transcript Document

Living
Things
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• A newer system recognizes two basically
distinctive groups of prokaryotes
– The domain Bacteria
– The domain Archaea
• A 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
– Bacteria and
Archaea
Table 16.8
WHAT IS AN ANIMAL?
Structure, nutrition and life history
define animals
• 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(ATP).
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Most animals reproduce sexually, with the
diploid stage usually dominating the life cycle.
– In most species, a small flagellated sperm fertilizes a
larger, nonmotile egg.
– The zygote undergoes cleavage  more mitotic cell
divisions  blastula  gastrula: gastrulation –
invagination producing two tissue layers, ectoderm
and endoderm and most mesoderm.
Fig. 32.1
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Single cell through blastula in sea urchin
Development of Mesoderm in Most Animals
PHYLUM
Traditional phylogenetic
tree of animals - based
mainly on grades in body
“plans”, and
characteristics of
embryonic development
unresolved
•Each major branch
represents a grade,
defined by certain
body-plan features
shared by the animals
belonging to that
branch.
Fig. 32.4
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The major grades are distinguished by structural
changes at four deep branches.
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.
Multiple cells living together/specialized
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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  gives rise to the muscles and most other
organs between the digestive tube and the outer covering of
the animal.
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Third branch point 3 -- Bilateria divided by
the presence or absence of a body cavity (a
fluid-filled space) and by the structure of the
cavity.
• Acoelomates (Platyhelminthes) have a solid body and
lack a body cavity.
Fig. 32.6a
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Pseudocoelomate – presence of a body cavity,
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
membranes, which suspend the internal organs.
– Include Phylum Mollusca and up…..
Fig. 32.6b
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Fourth branch point 4 -- Coelomates are
divided into two grades 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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• This
phylogenetic
tree is based
on nucleotide
sequences
from the
small subunit
ribosomal
RNA.
Fig. 32.8
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Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 32.12
. Phylum Porifera: Sponges are sessile with
porous bodies and choanocytes
• Choanocytes resemble the choanoflagellates.
• No Germ layers. Alternatively, 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 changes in
the environment.
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• 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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