Biology
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26-1 Introduction to the
Animal Kingdom
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26-1 Introduction to the Animal
Kingdom
What Is an Animal?
What characteristics do all animals share?
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26-1 Introduction to the Animal
Kingdom
What Is an Animal?
What Is an Animal?
Animals are multicellular, eukaryotic
heterotrophs whose cells lack cell walls.
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26-1 Introduction to the Animal
Kingdom
What Is an Animal?
Animals have the following types of tissues:
•epithelial
•muscular
•connective
•nervous
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26-1 Introduction to the Animal
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What Is an Animal?
Epithelial tissues cover body surfaces.
Muscle tissue cells contain proteins that enable them
to contract, moving parts of animals’ bodies.
Connective tissues support an animal’s body and
connect its parts.
Nervous tissue contains nerve cells, which carry
information throughout the body.
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26-1 Introduction to the Animal
Kingdom
What Is an Animal?
Invertebrates make up 95% of all animal species.
Invertebrates do not have a backbone, or vertebral
column.
They include sea stars, worms, jellyfishes, and
insects.
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26-1 Introduction to the Animal
Kingdom
What Is an Animal?
The other 5% of animals are vertebrates.
Vertebrates have a backbone.
Vertebrates include fishes, amphibians, reptiles,
birds, and mammals.
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26-1 Introduction to the Animal
Kingdom
What Animals Do to Survive
What Animals Do to Survive
What essential functions do animals carry
out?
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26-1 Introduction to the Animal
Kingdom
What Animals Do to Survive
Animals carry out the following essential
functions:
• feeding
• respiration
• circulation
• excretion
• response
• movement
• reproduction
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26-1 Introduction to the Animal
Kingdom
What Animals Do to Survive
Many body functions help animals maintain
homeostasis, or a relatively stable internal
environment.
Homeostasis is often maintained by internal feedback
mechanisms called feedback loops.
Most feedback loops involve feedback inhibition, in
which the product or result of a process stops or
limits the process.
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26-1 Introduction to the Animal
Kingdom
What Animals Do to Survive
Feeding
Herbivores eat plants.
Carnivores eat other animals.
Omnivores feed on both plants and animals.
Detritivores feed on decaying plant and animal
material.
Filter feeders are aquatic animals that strain tiny
floating organisms from water.
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26-1 Introduction to the Animal
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What Animals Do to Survive
Animals can also form symbiotic relationships, in
which two species live in close association with each
other.
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26-1 Introduction to the Animal
Kingdom
What Animals Do to Survive
Respiration
Whether they live in water or on land, all animals
respire—they take in oxygen and give off carbon
dioxide.
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26-1 Introduction to the Animal
Kingdom
What Animals Do to Survive
Circulation
Animals transport oxygen, nutrient molecules, and
waste products among all their cells through either
simple diffusion or some kind of circulatory system
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26-1 Introduction to the Animal
Kingdom
What Animals Do to Survive
Excretion
Ammonia is a waste product of cells and a
poisonous substance.
Most animals have an excretory system that
eliminates ammonia quickly or converts it into a
less toxic substance that is removed from the
body.
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26-1 Introduction to the Animal
Kingdom
What Animals Do to Survive
Response
Animals respond to events in their environment
using specialized cells, called nerve cells. In most
animals, nerve cells form a nervous system.
Receptor cells respond to sound, light, and
external stimuli. Other nerve cells process
information and determine how the animal
responds.
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26-1 Introduction to the Animal
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What Animals Do to Survive
Movement
Some animals stay at a single spot, but most can
move. Most animals have muscles or musclelike
tissues.
Muscle contraction enables motile animals to move
around by working in combination with a support
structure called a skeleton.
Muscles also help even sedentary animals feed
and pump water and fluids through their bodies.
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26-1 Introduction to the Animal
Kingdom
What Animals Do to Survive
Reproduction
Most animals reproduce sexually. This helps to
create and maintain genetic diversity in
populations and improve species’ abilities to
evolve when the environment changes.
Many invertebrates can also reproduce asexually.
This produces offspring that are genetically
identical to the parent. It allows animals to increase
their numbers rapidly.
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26-1 Introduction to the Animal
Kingdom
Trends in Animal Evolution
Trends in Animal Evolution
What are the important trends in animal
evolution?
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Complex animals tend to have:
• high levels of cell specialization and
internal body organization
• bilateral body symmetry
• a front end or head with sense organs
• a body cavity
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Cell Specialization and Levels of Organization
As animals have evolved, their cells have become
specialized to carry out different functions.
In multicellular organisms, each cell type has a
structure and chemical composition that enable it
to perform a specialized function.
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Groups of specialized cells form tissues.
Tissues join together to form organs and organ
systems—all of which work together to carry out a
variety of complex functions.
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Early Development
Animals that reproduce sexually begin life as a
zygote, or fertilized egg.
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26-1 Introduction to the Animal
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Trends in Animal Evolution
The zygote undergoes a series of divisions to form
a blastula, a hollow ball of cells.
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26-1 Introduction to the Animal
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Trends in Animal Evolution
The blastula folds in on itself, forming a single
opening called a blastopore.
The blastopore leads into a central tube that runs the
length of the developing embryo. This tube becomes
the digestive tract and is formed in one of two ways.
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Ectoderm
A protostome is an
animal whose mouth is
formed from the
blastopore.
Mesoderm
Endoderm
Blastopore
Most invertebrate animals
are protostomes.
Anus
Blastopore becomes mouth
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Ectoderm
A deuterostome is an
animal whose anus is
formed from the
blastopore.
Mesoderm
Endoderm
Blastopore
The anus is the opening
through which wastes
leave the digestive tract.
Mouth
Blastopore becomes anus
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26-1 Introduction to the Animal
Kingdom
Trends in Animal Evolution
Echinoderms and
vertebrates are both
deuterostomes.
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26-1 Introduction to the Animal
Kingdom
Trends in Animal Evolution
This similarity in
embryology may
indicate that vertebrates
have a closer
evolutionary relationship
to echinoderms than to
other invertebrates.
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26-1 Introduction to the Animal
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Trends in Animal Evolution
During early development, the cells of most animal
embryos differentiate into three layers called germ
layers.
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26-1 Introduction to the Animal
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Trends in Animal Evolution
The cells of the endoderm, or innermost germ layer,
develop into the linings of the digestive tract and
much of the respiratory system.
Only the label “endoderm”
should appear on this slide.
Endoderm
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26-1 Introduction to the Animal
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Trends in Animal Evolution
The cells of the mesoderm, or middle layer, develop
into muscles and much of the circulatory,
reproductive, and excretory organ systems.
Mesoderm
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26-1 Introduction to the Animal
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Trends in Animal Evolution
The ectoderm, or outermost layer, develops into the
sense organs, nerves, and the outer layer of the skin.
Ectoderm
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Body Symmetry
Except for sponges, every animal exhibits some
body symmetry in its structure.
Many simple animals, like the sea anemone, have
body parts that repeat around the center of the
body.
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Radial symmetry
These animals exhibit
radial symmetry, in
which any number of
imaginary planes can be
drawn through the
center, each dividing the
body into equal halves.
Planes of
symmetry
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26-1 Introduction to the Animal
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Trends in Animal Evolution
In animals with
bilateral symmetry,
only one imaginary
plane can divide the
body into two equal
halves—left and
right.
Plane of
symmetry
Bilateral symmetry
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26-1 Introduction to the Animal
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Posterior end
The anterior is the front
end.
The posterior is the
back end.
Trends in Animal Evolution
Anterior end
Bilateral symmetry
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The dorsal is the upper
side.
Trends in Animal Evolution
Dorsal side
The ventral is the lower
side.
Ventral
side
Bilateral symmetry
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Bilateral symmetry allows for segmentation, in which
the body is constructed of many repeated and similar
parts, or segments.
The combination of bilateral symmetry and
segmentation is found in two successful animal
groups—arthropods and vertebrates.
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Cephalization
Animals with bilateral symmetry exhibit
cephalization, which is the concentration of sense
organs and nerve cells at the front end of the body.
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Animals with bilateral symmetry usually move with
the anterior end forward, so this end comes in
contact with new parts of the environment first.
As sense organs have evolved, they have tended to
gather at the anterior end, as have nerve cells that
process information and “decide” what the animal
should do.
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26-1 Introduction to the Animal
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Trends in Animal Evolution
Body Cavity Formation
Most animals have a body cavity, a fluid-filled
space between the digestive tract and body wall.
A body cavity provides a space in which internal
organs can be suspended so that they are not
pressed on by muscles or twisted out of shape by
body movements.
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Homeostasis is often maintained by feedback
loops that involve
a. gastrulation.
b. feedback inhibition.
c. spontaneous generation.
d. equilibrium.
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26-1
Animals respond to events in their environments
using specialized cells called
a. muscle cells.
b. nerve cells.
c. gametes.
d. blood cells.
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26-1
A characteristic that all animals share is being
a. heterotrophic.
b. autotrophic.
c. prokaryotic.
d. anaerobic.
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Excretion is a function of all animals that
involves
a. exchange of oxygen and carbon dioxide.
b. transport of material from one part of the
body to another.
c. digestion and absorption of food molecules.
d. removal of metabolic wastes.
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One major trend in animal evolution has been
a. the simplification of body organ systems.
b. an increase in the degree of cephalization.
c. a shift from bilateral symmetry to radial
symmetry.
d. disappearance of the blastula stage in early
development.
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