What Characteristic Define an Animal?
• Eukaryotic cells
• Multicellular
• Ingestive Heterotroph
How did the animal kingdom evolve?
Oldest fossils are 700 million years old
Animals probably evolved from an ancestor
of a colonial choanoflagellate
protist
One hypothesis for the origin of animals
Major Trends in Animal Evolution:
• Development
of Tissue Layers
• Patterns of Body Symmetry
• Development of a Body Cavity
• Body Segmentation
• Specialization
Development of Tissue Layers
Most animals have tissues that arise
from three embryologic tissues layers:
• Ectoderm – produce skin and
nervous system
• Endoderm – produces GI tract
• Mesoderm – produces muscle,
skeleton and most organs
Patterns of Body Symmetry
• Asymmetrical
• Bilateral symmetry
• Radial symmetry
Development of a
Body Cavity:
• Allows independent movement of body wall
• Cushions internal organs
• Provides a hydrostatic skeleton
• Increases flexibility and mobility
Protostomes:
mesoderm
forms from
mass of cells
between
endoderm and
ectoderm
Deuterostomes:
mesoderm forms as
outpocketing of
gastrulation cavity
Visualizing Protostome & Deuterostome Development
Body Segmentation
• Most animals have
segmented bodies
• Segmentation increases
body flexibility and mobility
Evolution of Systems for
Exchange with the Environment
The maintenance of constant conditions in the internal environment is
called homeostasis. Homeostasis is an essential feature of complex
animals.
Animals have evolved variable adaptations to maintain homeostasis,
that depend on their environment and level of sophistication…
Evolution of Systems
• Every organism must exchange materials & energy
with environment, which ultimately occurs at the
cellular level.
•Most animals have
organ systems
specialized for
exchanging materials,
and many have an
internal transport
system that conveys
fluid (blood/interstitial
fluid) throughout the
body.
Evolution of the Circulatory System
• The bulk transport of
fluids throughout the
body connects aqueous
environment of body
cells to organs that
exchange gases, absorb
nutrients, and dispose
of wastes.
• For animals with many
cell layers,
gastrovascular cavities
are insufficient, due to
the amount of
transports.
Open Circulatory System
Closed Circulatory System
• There is no distinction between
blood and interstitial fluid,
collectively called hemolymph.
•Blood is confined to vessels and is
distinct from the interstitial fluid.
• One or more hearts pump the
hemolymph into interconnected
sinuses surrounding the organs,
allowing exchange between
hemolymph and body cells.
•One or more hearts pump blood
into large vessels that branch into
smaller ones cursing through
organs.
•Materials are exchanged by
diffusion between the blood and
the interstitial fluid bathing the
cells.
Arteries carry Away
Veins Veturn
Blood Arrives at Atria
Blood Vacates Ventricles
Left = oxygenated
Right = deoxygenated
Fig. 42.4
Evolution of the Nervous System
3 evolutionary
trends in
nervous
system
development:
1-bilateral
2cephalization
3-increased
numbers of
neurons
Evolution of Nervous Systems
• The nervous
system monitors
and controls
almost every
organ system
through a series
of positive and
negative
feedback loops.
Evolution of Respiratory Systems
• Large animals cannot
maintain gas exchange by
diffusion across their
outer surface. They
developed a variety of
respiratory surfaces that
all increase the surface
area for exchange, thus
allowing for larger bodies.
• A respiratory surface is
covered with thin, moist
epithelial cells that allow
oxygen and carbon dioxide
to exchange. Those gases
can only cross cell
membranes when they are
dissolved in water or an
aqueous solution, thus
respiratory surfaces must
be moist.
Evolution of Respiratory Surfaces
•
•
•
•
•
Single-celled organisms exchange gases directly across cell membrane. However, the slow diffusion rate of
oxygen/carbon dioxide limits size. Simple animals lack specialized exchange surfaces have flattened, tubular, or thin
shaped body plans
Earthworms have a series of thin-walled blood vessels known as capillaries. Gas exchange occurs at capillaries located
throughout the body as well as those in the respiratory surface.
Many terrestrial animals have their respiratory surfaces inside the body and connected to the outside by a series of
tubes.
Tracheae = tubes carry air directly to cells for exchange. Spiracles = openings at surface that lead to tracheae that
branch into smaller tubes. Body movements or contractions speed up the rate of diffusion. Does not function well in
animals whose body > 5 cm.
Amphibians use skin as a respiratory surface. Frogs eliminate carbon dioxide 2.5 times as fast through their skin as they
do through their lungs. Eels (a fish) obtain 60% of their O2 through their skin. Humans exchange only 1% of CO2
through skin. Constraints of water loss dictate that terrestrial animals must develop more efficient gas exchange.
Gills
• Gills greatly increase the surface
area for gas exchange.
• Gills typically are convoluted
outgrowths containing blood vessels
covered by a thin epithelial layer.
• Gills are very efficient at removing
oxygen from water: there is only
1/20 the amount of oxygen present
in water as in the same volume of
air. Water flows over gills in one
direction while blood flows in the
opposite direction through gill
capillaries. This countercurrent
flow maximizes oxygen transfer.
Lungs
• Lungs are ingrowths of the body wall and connect to the
outside by as series of tubes and small openings. Lung
breathing probably evolved about 400 million years ago.
Lungs are not entirely the sole property of vertebrates,
some terrestrial snails have a gas exchange structures
similar to those in frogs.
Evolution of Excretory System
• Osmoregulation balances the uptake
and loss of water and solutes.
• An animal's nitrogenous wastes
reflect its phylogeny and habitat.
• Diverse excretory systems are
variations on tubular theme
• The nephron is organized for stepwise
processing of blood filtrate.
• Hormonal circuits link kidney function,
water balance, and blood pressure.
Evolution of Digestive System
• Diffusioningestiongastrovascular cavity1
way digestive system.
Evolution of Digestive System
• Diffusioningestiongastrovascular cavity1
opening digestive system.
Evolution of
Digestive System
Resources
• External Environment I