Transcript Section 25.1 Summary – pages 673

Biology
2nd period
McFall
Chapter 25 What is an animal?
25.1: Typical Animal Characteristics
25.2: Body Plans and Adaptations
Section Objectives:
• Identify the characteristics of animals.
• Identify cell differentiation in the
development of a typical animal.
• Sequence the development of a typical
animal.
Characteristics of Animals
• Animals are eukaryotic, multicellular
organisms with ways of moving that help
them reproduce, obtain food, and protect
themselves.
Characteristics of Animals
• Most animals have specialized cells that form
tissues and organs—such as nerves and
muscles.
• Animals are composed of cells that do not
have cell walls.
Animals obtain food
• One characteristic common to all animals is
that they are heterotrophic, meaning they
must consume food to obtain energy and
nutrients.
• All animals depend
either directly or
indirectly on
autotrophs for food.
Animals obtain food
• Scientists hypothesize that animals first
evolved in water.
• In water, some animals, such as barnacles
and oysters, do not move from place to place
and have adaptations that allow them to
capture food from their water environment.
Animals obtain food
• Organisms that
are permanently
attached to a
surface are
called sessile.
Animals obtain food
• Some aquatic animals,
such as corals and
sponges move about
only during the early
stages of their lives.
• Most adults are
sessile and attach
themselves to rocks
or other objects.
Animals obtain food
• There is little suspended food in the air.
• Land animals use more oxygen and
expend more energy to find food.
Animals digest food
• In some animals, digestion is carried out
within individual cells; in other animals,
digestion takes place in an internal cavity.
• Some of the food that an animal
consumes and digests is stored as fat or
glycogen, a polysaccharide, and used
when other food is not available.
Animals digest food
• In animals such as planarians and earthworms,
food is digested in a digestive tract.
Mouth
Digestive
tract
Digestive
tract
Extended
pharynx
Anus
Animal cell adaptations
• Most animal cells are differentiated and
carry out different functions.
• Animals have specialized cells that enable
them to sense and seek out food and mates,
and allow them to identify and protect
themselves from predators.
Development of Animals
• Most animals develop from a fertilized egg
cell called a zygote.
• After fertilization, the zygote of different
animal species all have similar, genetically
determined stages of development.
Fertilization
• Most animals reproduce sexually.
• Male animals produce sperm cells and
female animals produce egg cells.
• Fertilization occurs when a sperm cell
penetrates the egg cell, forming a new cell
called a zygote.
• In animals, fertilization may be internal or
external.
Cell division
• The zygote
divides by
mitosis and cell
division to
form two cells
in a process
called cleavage.
cleavage
Cell division
• Once cell division has begun, the organism
is known as an embryo.
Cell division
• The two cells that result from cleavage then
divide to form four cells and so on, until a
cell-covered, fluid-filled ball called a blastula
is formed.
• The blastula is
formed early in
the development
of an animal
embryo.
Gastrulation
• After blastula formation, cell division
continues.
• The cells on one side
of the blastula then
move inward to form a
gastrula—a structure
made up of two layers
of cells with an
opening at one end.
Gastrulation
• The cells at one end of the blastula move
inward, forming a cavity lined with a second
layer of cells.
• The layer of cells on the outer surface of the
gastrula is called the ectoderm.
• The layer of cells lining the inner surface is
called the endoderm.
Gastrulation
• The ectoderm cells
of the gastrula
continue to grow
and divide, and
eventually they
develop into the
skin and nervous
tissue of the animal.
Ectoderm
Gastrulation
• The endoderm
cells develop into
the lining of the
animal’s digestive
tract and into
organs associated
with digestion.
Endoderm
Formation of mesoderm
• Mesoderm is found in the middle of the
embryo; the term meso means “middle.”
• The mesoderm is
the third cell layer
found in the
developing
embryo between
the ectoderm and
the endoderm.
Mesoderm
Formation of mesoderm
• The mesoderm cells develop into the
muscles, circulatory system, excretory
system, and, in some animals, the respiratory
system.
Formation of mesoderm
• When the opening in the gastrula develops
into the mouth, the animal is called a
protostome.
• Snails,
earthworms,
and insects are
examples of
protostomes.
Formation of mesoderm
• In other animals, such as sea stars, fishes,
toads, snakes, birds, and humans, the mouth
does not develop from the gastrula’s opening.
Formation of mesoderm
• An animal whose mouth developed not from
the opening, but from cells elsewhere on the
gastrula is called a deuterostome.
Formation of mesoderm
• Scientists hypothesize that protostome
animals were the first to appear in
evolutionary history, and that deuterostomes
followed at a later time.
• Determining whether an animal is a
protostome or deuterostome can help
biologists identify its group.
Cell differentiation in Animal
Development
• The fertilized eggs of most animals follow a
similar pattern of development. From one
fertilized egg cell, many divisions occur until
a fluid-filled ball of cells forms.
• The ball folds inward and continues to
develop.
Sperm cells
Cell
Differentiation
in Animal
Development
Fertilization
Egg cell
Formation of
mesoderm
Endoderm
First cell
division
Mesoderm
Ectoderm
Gastrulation
Additional cell
divisions
Formation of a blastula
Growth and development
• Most animal embryos continue to develop
over time, becoming juveniles that look like
smaller versions of the adult animal.
• In some animals, such as insects and
echinoderms, the embryo develops inside an
egg into an intermediate stage called a larva
(plural larvae).
Growth and development
Growth and development
• A larva often bears little resemblance to the
adult animal.
• Inside the egg, the larva is surrounded by a
membrane formed right after fertilization.
• When the egg hatches, the larva breaks
through this fertilization membrane.
Adult animals
• Once the juvenile or larval stage has passed,
most animals continue to grow and develop
into adults.
• This growth and development may take just a
few days in some insects, or up to fourteen
years in some mammals.
• Eventually the adult animals reach sexual
maturity, mate, and the cycle begins again.
Section Objectives:
• Compare and contrast radial and bilateral
symmetry with asymmetry.
• Trace the phylogeny of animal body plans.
• Distinguish among the body plans of
acoelomate, pseudocoelomate, and
coelomate animals.
What is symmetry
• Symmetry is a term that describes the
arrangement of body structures.
• Different kinds of symmetry enable animals
to move about in different ways.
Asymmetry
• An animal that is irregular in shape has no
symmetry or an asymmetrical body plan.
• Animals with no
symmetry often are
sessile organisms that
do not move from
place to place.
• Most adult sponges
do not move about.
Asymmetry
• The bodies of most sponges consist of two
layers of cells.
• Unlike all other animals, a sponge’s
embryonic development does not include
the formation of an endoderm and
mesoderm, or a gastrula stage.
Radial symmetry
• Animals with
radial symmetry
can be divided
along any plane,
through a central
axis, into roughly
equal halves.
Radial symmetry
• Radial symmetry is an adaptation that
enables an animal to detect and capture
prey coming toward it from any direction.
Radial symmetry
• The body plan of a hydra can be
compared to a sack within a sack.
• These sacks are cell layers organized
into tissues with distinct functions.
Radial symmetry
• A hydra develops
from just two
embryonic cell
layers—ectoderm
and endoderm.
Inner cell layer
Outer cell layer
Bilateral symmetry
• An organism
with bilateral
symmetry can
be divided
down its
length into
similar right
and left
halves.
Bilateral symmetry
• Bilaterally symmetrical animals can be
divided in half only along one plane.
• In bilateral animals, the anterior, or head end,
often has sensory organs.
• The posterior of these animals is the tail
end.
Bilateral symmetry
• The dorsal, or upper surface, also looks
different from the ventral, or lower
surface.
• Animals with bilateral symmetry can find
food and mates and avoid predators because
they have sensory organs and good muscular
control.
Bilateral Symmetry and Body Plans
• All bilaterally symmetrical animals developed
from three embryonic cell layers—ectoderm,
endoderm, and mesoderm.
• Some bilaterally symmetrical animals also
have fluid-filled spaces inside their bodies
called body cavities in which internal organs
are found.
Acoelomates
• Animals that develop from three cell
layers—ectoderm, endoderm, and
mesoderm—but have no body cavities are
called acoelomate animals.
• They have a digestive tract that extends
throughout the body.
Acoelomates
• Flatworms are
bilaterally
symmetrical animals
with solid, compact
bodies. Like other
acoelomate animals,
the organs of
flatworms are
embedded in the solid
tissues of their bodies.
Acoelomate Flatworm
Ectoderm
Mesoderm
Endoderm
Body
cavity
Digestive
tract
Acoelomates
• A flattened body
and branched
digestive tract
allow for the
diffusion of
nutrients, water,
and oxygen to
supply all body
cells and to
eliminate wastes.
Acoelomate Flatworm
Ectoderm
Mesoderm
Endoderm
Body
cavity
Digestive
tract
Pseudocoelomates
Pseudocoelomate Roundworm
Ectoderm
Mesoderm
Endoderm
Body
cavity
Digestive
tract
• A roundworm is an
animal with
bilateral symmetry.
• The body of a
roundworm has a
space that develops
between the
endoderm and
mesoderm.
Pseudocoelomates
Pseudocoelomate Roundworm
• It is called a
pseudocoelom
—a fluid-filled
body cavity
partly lined
with
mesoderm.
Ectoderm
Mesoderm
Endoderm
Body
cavity
Digestive
tract
Pseudocoelom
Pseudocoelomates
• Pseudocoelomates can move quickly.
• Although the roundworm has no bones, it
does have a rigid, fluid-filled space, the
pseudocoelom.
• Its muscles attach to the mesoderm and brace
against the pseudocoelom.
Pseudocoelomates
• Pseudocoelomates have a one-way digestive
tract that has regions with specific functions.
• The mouth takes in food, the breakdown and
absorption of food occurs in the middle
section, and the anus expels waste.
Mouth
Intestine
Round body shape
Anus
Coelomates
Coelomate Segmented Worm
• The body cavity of an
earthworm develops
from a coelom, a fluidfilled space that is
completely surrounded
by mesoderm.
• The greatest diversity
of animals is found
among the coelomates.
Ectoderm
Mesoderm
Endoderm
Body
cavity
Digestive
tract
Coelom
Coelomates
• In coelomate animals, the digestive tract and
other internal organs are attached by double
layers of mesoderm and are suspended within
the coelom.
• The coelom cushions and protects the internal
organs. It provides room for them to grow and
move independently within an animal’s body.
Animal Protection and Support
• Over time, the development of body cavities
resulted in a greater diversity of animal
species.
• Some animals, such as mollusks, evolved hard
shells that protected their soft bodies.
• Other animals, such as sponges, evolved
hardened spicules between their cells that
provided support.
Animal Protection and Support
• Some animals developed exoskeletons. An
exoskeleton is a hard covering on the outside
of the body that provides a framework for
support.
Animal Protection and Support
• Exoskeletons also protect soft body tissues,
prevent water loss, and provide protection
from predators.
Animal Protection and Support
• As an animal grows, it secretes a new
exoskeleton and sheds the old one.
• Exoskeletons are often found in
invertebrates. An invertebrate is an
animal that does not have a backbone.
Animal Protection and Support
• Invertebrates, such as sea urchins and sea stars,
have an internal skeleton called an
endoskeleton. It is covered by layers of cells
and provides support for an animal’s body.
Animal Protection and Support
• The endoskeleton protects internal organs and
provides an internal brace for muscles to pull
against.
Animal Protection and Support
• An endoskeleton may be made of calcium
carbonate, as in sea stars; cartilage, as in
sharks; or bone.
Calcium carbonate
cartilage
Animal Protection and Support
• Bony fishes, amphibians, reptiles, birds, and
mammals all have endoskeletons made of
bone.
bone
Animal Protection and Support
• A vertebrate is an animal with an endoskeleton
and a backbone. All vertebrates are bilaterally
symmetrical.
Origin of Animals
• Most biologists agree that animals probably
evolved from aquatic, colonial protists.
• Scientists trace this evolution back in time to
late in the Precambrian.
Origin
of
Animals
Origin of Animals
• Many scientists agree that all the major animal
body plans that exist today were already in
existence at the beginning of the Cambrian
Period, 543 million years ago.
• All known species have variations of the
animal body plans developed during the
Cambrian Period.