Introduction to Animals
CH 26:
Introduction to Animals
Sec 1 and Sec 2
Section 2
Introduction to Animals
Section 2
General Features of Animals
• Animals are multicellular, heterotrophic organisms with
cells that lack cell walls.
• Humans depend on other animals for food,
companionship, and to pollinate crops.
• Most animals move to get food. But filter eaters, such as
sponges and corals, catch particles of food that drift by in
the water.
Introduction to Animals
Section 2
Kinds of Animals
• Animals are often grouped as invertebrates or
vertebrates.
• Vertebrates make up only a subgroup of one phylum—
Chordata.
• Most animals are invertebrates.
Introduction to Animals
Section 2
Kinds of Animals, continued
Vertebrates
• Vertebrates have a cranium and an internal skeleton
composed of bone or cartilage. Vertebrates are
chordates that have a backbone.
• The backbone supports and protects a dorsal nerve cord
and provides a site for muscle attachment.
• Pg 625
Introduction to Animals
Section 2
CH26 Sec 2: Animal Body Systems
Introduction to Animals
Section 2
Key Ideas
• Why is an animal's skeleton important?
• What are the functions of the digestive and excretory
systems?
• What is the function of the nervous system?
• Why are the respiratory and circulatory systems
important?
• What are two reproductive strategies of animals?
Introduction to Animals
Section 2
Support
• An animal's skeleton provides a framework that supports
the animal's body and is vital to an animal's movement.
• Many soft-bodied invertebrates, such as jellyfish, have a
hydrostatic skeleton, which is a water-filled cavity that
is under pressure.
• An exoskeleton is a rigid external skeleton that
encases the body of an animal.
• Insects, clams, and crabs have exoskeletons.
Introduction to Animals
Section 2
Support, continued
• An endoskeleton is an internal skeleton made of bone
and cartilage.
• Humans and other vertebrates have endoskeletons.
Introduction to Animals
Section 2
Digestive and Excretory Systems
• The digestive system is responsible for extracting energy
and nutrients from an animal's food.
• The excretory system removes waste products from the
animal's body.
Introduction to Animals
Digestive and Excretory Systems,
continued
Digestive System
• A gastrovascular cavity
is a digestive cavity with
only one cavity. There
are no specialized
digestive cells.
• The hydra has a
gastrovascular cavity.
Section 2
Introduction to Animals
Section 2
Digestive and Excretory Systems,
continued
Digestive System, continued
• In a digestive tract, food moves from one opening, the
mouth, to a second, the anus.
• Digestive tracts allow for specialization and more
efficient digestion.
Introduction to Animals
Section 2
Digestive and Excretory Systems,
continued
Excretory System
• Excretion is the removal of wastes produced by cellular
metabolism.
• Simple aquatic invertebrates and some fishes excrete
ammonia through their skin or gills.
• Terrestrial animals need to minimize water loss. Some
convert ammonia to less toxic chemicals before passing
them out of the body.
Introduction to Animals
Section 2
Nervous System
• The nervous system carries information about the
environment through the body and coordinates responses
and behaviors.
• Not all animals have a complex nervous system, and
some do not have a brain to coordinate the nervous
system.
Introduction to Animals
Section 2
Nervous System, continued
Simple Nervous Systems
• All animals except sponges have nerve cells.
• In the simplest arrangement of nerves, called a nerve net,
nerve cells do not coordinate actions efficiently.
• Jellyfish and hydras have a nerve net.
Introduction to Animals
Hydra Nervous System
Section 2
Introduction to Animals
Section 2
Nervous System, continued
Simple Nervous Systems, continued
• Many animals have clusters of nerve cells called ganglia
that can coordinate responses.
• Flatworms have large more-complex ganglia, similar to a
brain.
Introduction to Animals
Flatworm Nervous System
Section 2
Introduction to Animals
Section 2
Nervous System, continued
Complex Nervous Systems
• More-complex invertebrates have a true brain with
sensory structures, such as eyes, associated with it.
• Vertebrates have a relatively large brain, and may species
have special sensory systems that make these animals
even better at catching food and avoiding predators than
other animals are.
Introduction to Animals
Grasshopper Nervous System
Section 2
Introduction to Animals
Section 2
Respiratory and Circulatory Systems
• The respiratory system is responsible for exchanging
oxygen and carbon dioxide between the body and the
environment.
• The circulatory system transports gases, nutrients, and
other substances within the body.
Introduction to Animals
Section 2
Respiratory and Circulatory Systems,
continued
Respiratory System
• Most animals have specialized respiratory systems.
• Aquatic animals respire by using thin projections of tissue
called gills.
• A variety of respiratory organs, including lungs, have
evolved in terrestrial animals.
Introduction to Animals
Section 2
Respiratory and Circulatory Systems,
continued
Circulatory System
• In an open circulatory system, a heart pumps fluid containing
oxygen and nutrients through vessels into the body cavity.
The fluid provides oxygen and nutrients as it washes across
the tissues.
• In a closed circulatory system, the blood is pumped through
the body within vessels and is never in direct contact with the
body's tissues.
Introduction to Animals
Section 2
Open and Closed Circulatory Systems
Introduction to Animals
Section 2
Reproduction
• Asexual reproduction occurs when an individual produces
exact copies of itself and does not mix its genes with
those of another.
• Sea stars and some salamanders and fishes reproduce
asexually.
Introduction to Animals
Section 2
Reproduction, continued
• In sexual reproduction, a new individual is formed by the
union of a male and female gamete.
• Some species can reproduce either asexually or sexually.
• Coral colonies grow larger though asexual reproduction,
but new colonies are formed through sexual reproduction.